Section 3 Salt in Technology

*Salt in the Earth*

15 March 2019]

10.1038/sj.ejcn.1601583

[70] Matheson D, Spranger K, Saxe A. Preschool children's perceptions of food and their food experiences. Journal of Nutrition Education. 2002;**34**:85-92.

sciencedirect.com/science/article/abs/ pii/S1499404606600730 [Accessed:

[71] Girgis S, Neal B, Prescott J, et al. A one-quarter reduction in the salt content of bread can be made without detection. European Journal of Clinical Nutrition. 2003;**57**:616-620. DOI:

Available from: https://www.

**60**

Chapter 4

Abstract

1. Introduction

63

1.1 Characteristics of membrane concentrate

Boopathy Ramasamy

Short Review of Salt Recovery

from Reverse Osmosis Rejects

The membrane treatment is a physical separation which also generates considerable amount of waste, called as reject/concentrate. The reject/concentrate is more than three times concentrated than the feed water in terms of feed water salts. Recovery of valuables from reverse osmosis (RO) reject for its reuse of inorganic salts would be most obvious solution to eliminate environmental damage. In this report what are the available methods for the recovery of valuables from waste saline stream by selective crystallization method, chemical precipitation and physico-thermal route discussed in details. Also, methods to treat organic contamination in the residual solution through advanced oxidation treatment methods.

Keywords: reverse osmosis, salt recovery, reactive precipitation, crystallization

The demand of potable water led to significant improvements in the membrane separation process in water and waste-water treatment. Especially for developing countries, the demand of water supply is increasing and no less provision to mitigate the challenges. The state and central governments agencies are formulating strategy through environmental policies to mitigate the water scarcity. During last three decades significant expansion and upgradation of membrane filtration have been happening around the globe to lower it production costs. In market, there are many custom made membrane technologies that are available for both domestic and industrial applications. Reverse osmosis is one of the important technologies among which has energy and cost effective membrane system for producing potable water from brackish and saline water sources [1–7]. RO process can generates 50–80% of water drinkable or dischargeable quality as permeate [7] and the balance 20–30% formed as RO reject or retentate or concentrate. Generally, concentrate is allowed to avoid membrane fouling, coagulation and flocculation process over membrane surfaces as it cannot be further purified due to high osmotic pressure. The common application of membrane separation processes comprising ultrafiltration and reverse osmosis for the disposal of reverse osmosis (RO) rejects through thermal evaporator or multiple effect evaporator.

Membrane separation is a physical process which involving the separation of particulate, and dissolved organic/inorganic compounds from a feed liquid using a semi-permeable membrane system. The feed stream is fractionated into two streams:

#### Chapter 4

### Short Review of Salt Recovery from Reverse Osmosis Rejects

Boopathy Ramasamy

#### Abstract

The membrane treatment is a physical separation which also generates considerable amount of waste, called as reject/concentrate. The reject/concentrate is more than three times concentrated than the feed water in terms of feed water salts. Recovery of valuables from reverse osmosis (RO) reject for its reuse of inorganic salts would be most obvious solution to eliminate environmental damage. In this report what are the available methods for the recovery of valuables from waste saline stream by selective crystallization method, chemical precipitation and physico-thermal route discussed in details. Also, methods to treat organic contamination in the residual solution through advanced oxidation treatment methods.

Keywords: reverse osmosis, salt recovery, reactive precipitation, crystallization

#### 1. Introduction

The demand of potable water led to significant improvements in the membrane separation process in water and waste-water treatment. Especially for developing countries, the demand of water supply is increasing and no less provision to mitigate the challenges. The state and central governments agencies are formulating strategy through environmental policies to mitigate the water scarcity. During last three decades significant expansion and upgradation of membrane filtration have been happening around the globe to lower it production costs. In market, there are many custom made membrane technologies that are available for both domestic and industrial applications. Reverse osmosis is one of the important technologies among which has energy and cost effective membrane system for producing potable water from brackish and saline water sources [1–7]. RO process can generates 50–80% of water drinkable or dischargeable quality as permeate [7] and the balance 20–30% formed as RO reject or retentate or concentrate. Generally, concentrate is allowed to avoid membrane fouling, coagulation and flocculation process over membrane surfaces as it cannot be further purified due to high osmotic pressure. The common application of membrane separation processes comprising ultrafiltration and reverse osmosis for the disposal of reverse osmosis (RO) rejects through thermal evaporator or multiple effect evaporator.

#### 1.1 Characteristics of membrane concentrate

Membrane separation is a physical process which involving the separation of particulate, and dissolved organic/inorganic compounds from a feed liquid using a semi-permeable membrane system. The feed stream is fractionated into two streams:


solar evaporation ponds, and thermal evaporators. The selection of technologies for the disposal of RO rejects is based on the prevailing environmental regulations, investment and maintenance costs, and site-specific conditions [10, 11].

The reduction of concentrate volume is being achieved by incorporating zero liquid discharge technologies. The concentrate streams after conventional RO are being evaporated in thermal evaporators to sufficiently dry inorganic salt. The most common way is vertical falling film brine concentrator followed forced-circulation crystallizer, where it is heated above its normal boiling temperature with steam through heat exchanger. It requires 65–80 kWh of power per 1000 l of crystallizer feed water. Crystallizers and spray dryers have been implemented at the commercial level to reduce RO reject stream into a solid product for landfill disposal. One or more evaporation steps could also be considered to recover small amounts of water from the most soluble salts in RO reject stream. The primary practical obstacle in implementing thermal evaporators is size and complexity of the equipment. In addition, evaporators and crystallizers are relatively complex to operate and high energy intensive process compared with other zero liquid discharge (ZLD)

The evaporators and crystallizers are used to reduce the reject volume up to 5%

1.4 Limitations on disposal of residue after evaporation generated from leather

The disposal of RAE onto secured landfill sites is banned by the pollution control

Recovery of salts from RO concentrate is increasing for its environmental safe way to reuse of waste volume of reject. The change of solution temperature either by evaporation and cooling used to extract salts from concentrate has been widely used worldwide. In which, electro-dialysis, ion-exchange, eutectic freezing, and chemical processing are being practiced to recover salts from concentrate. Further, in advance hybrid systems which consisting of combination of two or more separation process techniques, such as the nanofiltration—reverse osmosis—thermal processes, are being deployed actively to increase the amount of extracted salt and

Buckley et al. has proposed detailed routs for the management of RO reject [12]:

i. Use of engineering knowledge: incorporation of engineering unit operation/

process to reduce dissolved solids in the reject stream.

agencies because the constituent ions are suspected to be leached into aqueous solution, and the treatability of leachate would be more difficult for its high salinity. Hence, RAE is collected and being stored in the storage yard without further reusable options in many textile and leather industries. The high concentration of mixture of inorganic and organic salts present in RAE restrains it from disposal

of the feed volume and the rest 95% was reclaimed as distillate (water) after condensation. Generally, the reject stream generated from leather industry is evaporated in solar evaporation pans to reduce its volume (for small volume of discharge and making use of solar energy to reduce the cost of evaporation) or in a multiple effect evaporator (MEE) (for large volume of discharge) leaving behind a solid

residue known as residue after evaporation (RAE).

Short Review of Salt Recovery from Reverse Osmosis Rejects

DOI: http://dx.doi.org/10.5772/intechopen.88716

2. Desalting process for RO concentrate

reduce the final volume of reject.

methods.

industry

[13, 14].

65

#### Table 1.

Characteristics of untreated, treated, RO permeate and RO reject stream generated in leather industry.

(i) a permeate stream that contains the solvent (water) that passes through the membrane, and (ii) the reject stream known as concentrate, reject or brine contains the solute. The characteristics of this reject stream depend primarily on the membrane technology used, the quality of feed water, the percent recovery of water, the physico-chemical treatment methods followed for cleaning procedures. The volume of reject stream varies widely from 10 to 60% of the feed water volume [7]. However, the reject stream arises from industrial effluents such as textile, pharmaceutical and tanneries are turbid and opaque, may be due to the presence of micro and macro organic molecules and inorganic ions, such as chlorides, sulfates, phosphate, carbonate, bicarbonate, sodium, calcium, magnesium and other heavy metal ions [8]. The characteristics of RO stream generated in leather industry are presented in Table 1. The TDS of water is increased from 5.58 1.8 to 20 6.14 g/L in RO reject stream leaving product water with a TDS of 0.25 0.13 g/L during separation process. The TDS concentration of RO rejects four fold higher than the initial TDS concentration. Similarly, concentration of sodium, chloride and sulfates ions were found to be increased significantly after RO separation process in reject stream.

#### 1.2 Impacts of membrane concentrate discharge without treatment

Discharge of RO reject stream into sea/ocean is considered to cause the "sea desert" in vicinity to pipe outlet because of dissolved substance with high specific weight and thus sink in bottom of the sea/ocean, which severely affecting local marine biota. Marine species have been affected by the salinity of the brine discharged into the sea include grass prairies called such as Cymodocea nodosa and Caulerpa prolifera or red algae [9]. Direct land disposal of RO reject stream from effluent treatment plants caused soil and groundwater contamination by the diffusion of inorganic impurities from it, and thus soil and ground water are turned unsuitable for human consumption for their harmful or toxic substances. Hence, there has been constant exploration to manage the RO reject stream.

#### 1.3 Options for membrane concentrate disposal

Various options have been reported for the disposal of RO reject stream generated in membrane separation. This option is discharge to surface water, deep wells,

#### Short Review of Salt Recovery from Reverse Osmosis Rejects DOI: http://dx.doi.org/10.5772/intechopen.88716

solar evaporation ponds, and thermal evaporators. The selection of technologies for the disposal of RO rejects is based on the prevailing environmental regulations, investment and maintenance costs, and site-specific conditions [10, 11].

The reduction of concentrate volume is being achieved by incorporating zero liquid discharge technologies. The concentrate streams after conventional RO are being evaporated in thermal evaporators to sufficiently dry inorganic salt. The most common way is vertical falling film brine concentrator followed forced-circulation crystallizer, where it is heated above its normal boiling temperature with steam through heat exchanger. It requires 65–80 kWh of power per 1000 l of crystallizer feed water. Crystallizers and spray dryers have been implemented at the commercial level to reduce RO reject stream into a solid product for landfill disposal. One or more evaporation steps could also be considered to recover small amounts of water from the most soluble salts in RO reject stream. The primary practical obstacle in implementing thermal evaporators is size and complexity of the equipment. In addition, evaporators and crystallizers are relatively complex to operate and high energy intensive process compared with other zero liquid discharge (ZLD) methods.

The evaporators and crystallizers are used to reduce the reject volume up to 5% of the feed volume and the rest 95% was reclaimed as distillate (water) after condensation. Generally, the reject stream generated from leather industry is evaporated in solar evaporation pans to reduce its volume (for small volume of discharge and making use of solar energy to reduce the cost of evaporation) or in a multiple effect evaporator (MEE) (for large volume of discharge) leaving behind a solid residue known as residue after evaporation (RAE).

#### 1.4 Limitations on disposal of residue after evaporation generated from leather industry

The disposal of RAE onto secured landfill sites is banned by the pollution control agencies because the constituent ions are suspected to be leached into aqueous solution, and the treatability of leachate would be more difficult for its high salinity. Hence, RAE is collected and being stored in the storage yard without further reusable options in many textile and leather industries. The high concentration of mixture of inorganic and organic salts present in RAE restrains it from disposal [13, 14].

#### 2. Desalting process for RO concentrate

Recovery of salts from RO concentrate is increasing for its environmental safe way to reuse of waste volume of reject. The change of solution temperature either by evaporation and cooling used to extract salts from concentrate has been widely used worldwide. In which, electro-dialysis, ion-exchange, eutectic freezing, and chemical processing are being practiced to recover salts from concentrate. Further, in advance hybrid systems which consisting of combination of two or more separation process techniques, such as the nanofiltration—reverse osmosis—thermal processes, are being deployed actively to increase the amount of extracted salt and reduce the final volume of reject.

Buckley et al. has proposed detailed routs for the management of RO reject [12]:

i. Use of engineering knowledge: incorporation of engineering unit operation/ process to reduce dissolved solids in the reject stream.

(i) a permeate stream that contains the solvent (water) that passes through the membrane, and (ii) the reject stream known as concentrate, reject or brine contains the solute. The characteristics of this reject stream depend primarily on the membrane technology used, the quality of feed water, the percent recovery of water, the physico-chemical treatment methods followed for cleaning procedures. The volume of reject stream varies widely from 10 to 60% of the feed water volume [7]. However, the reject stream arises from industrial effluents such as textile, pharmaceutical and tanneries are turbid and opaque, may be due to the presence of micro and macro organic molecules and inorganic ions, such as chlorides, sulfates, phosphate, carbonate, bicarbonate, sodium, calcium, magnesium and other heavy metal ions [8]. The characteristics of RO stream generated in leather industry are presented in Table 1. The TDS of water is increased from 5.58 1.8 to 20 6.14 g/L in RO reject stream leaving product water with a TDS of 0.25 0.13 g/L during separation process. The TDS concentration of RO rejects four fold higher than the initial TDS concentration. Similarly, concentration of sodium, chloride and sulfates ions were found to be

Characteristics of untreated, treated, RO permeate and RO reject stream generated in leather industry.

Table 1.

Salt in the Earth

64

increased significantly after RO separation process in reject stream.

1.2 Impacts of membrane concentrate discharge without treatment

there has been constant exploration to manage the RO reject stream.

1.3 Options for membrane concentrate disposal

Discharge of RO reject stream into sea/ocean is considered to cause the "sea desert" in vicinity to pipe outlet because of dissolved substance with high specific weight and thus sink in bottom of the sea/ocean, which severely affecting local marine biota. Marine species have been affected by the salinity of the brine discharged into the sea include grass prairies called such as Cymodocea nodosa and Caulerpa prolifera or red algae [9]. Direct land disposal of RO reject stream from effluent treatment plants caused soil and groundwater contamination by the diffusion of inorganic impurities from it, and thus soil and ground water are turned unsuitable for human consumption for their harmful or toxic substances. Hence,

Various options have been reported for the disposal of RO reject stream generated in membrane separation. This option is discharge to surface water, deep wells, ii. Chemical conversion of reject to products: chemical conversion of rejects to other reusable salts from waste RO reject.

If the unsaturated concentrate is reaching its freezing point. At the specific eutectic point of crystallization, the brine salt is crystallized out as product. The energy required for the EFC process are found to be very less than the conventional method of evaporative and cooling crystallization process and its theoretically possible way to complete the conversion of concentrate water into water and solidified solutes. Through this route magnesium sulfate heptahydrate (MgSO47H2O) from a magnesium sulfate industrial stream is being recovered using EFC process [26, 27]. In which MgSO412H2O was formed in the crystallizer and after recrystallization MgSO47H2O is formed spontaneously. In addition to EFC, coupling of cooled disk column crystallizer (CDCC) helps to recover CuSO4 crystals from copper sulfate solution [28, 29]. The cost towards energy required for EFC can be reduced up to 70% than conventional evaporative crystallization processes, further 100% conver-

Short Review of Salt Recovery from Reverse Osmosis Rejects

DOI: http://dx.doi.org/10.5772/intechopen.88716

sion of concentrate into water and salt separation is achieved by this route.

furnace at a temperature range of 300 and 800°C [35].

2.5 Extraction of potentially profitable material from RO rejects

ling the pH of the mixture of anion and cation regeneration solution.

The recovery of calcium from RO reject is done to avoid secondary RO scaling [36–38]. Bond and Veerapaneni [36] have developed detailed methodology for the recovery of calcium carbonate by chemical precipitation, in particular to separate calcium during desalination. Several other researchers have evaluated fluidized bed crystallizers for the production of calcium carbonate pellets from RO reject [36, 39], further studies have been reported on influence of anti-scalants, impurities, metals, and ions on calcium carbonate precipitation [40–42]. The concentration of calcium ions in seawater and desalination reject is relatively high, through this calcium carbonate pellets has been prepared from brackish water in Southern California [39]. However, the extraction of calcium sulfate from RO reject has not received significant attention, due to low price of commercial grade gypsum. Also, the mechanisms of calcium sulfate precipitation have been observed to form scaling minimized equipment failure in separation process [43–46]. The ion-exchange resin is being used to selectively extract calcium sulfate salts from RO reject by control-

Recovery of CaCO3 from nanofiltration reject is being achieved by reactive precipitation on addition of NaHCO3/Na2CO3 aqueous solution [30]. Similarly, recovery of MgSO47H2O from the reject from seawater nanofiltration, Ca2+ ions were precipitated as carbonates by reaction with NaHCO3/Na2CO3 to get calcium sulfate by precipitation, Sodium-bi-carbonate solutions are being produced by reactive transfer of carbon dioxide into sodium hydroxide solutions. This technique has been used successfully to recover magnesium sulfate from sulfate rich brine, rock forming minerals, and salty lake water [31–33]. There are many sequential extraction of salts from rejected brine thus which high concentration of dissolved sulfate, potassium, and magnesium salts are being separated through multiple effect evaporator and cooling crystallization method, reactive precipitation methods [15, 28]. The use of lime favors selective separation of magnesium hydroxide from concentrate solution and thermal calcination of concentrate having sodium sulfate helps to recover Na2SO4 from wastewater [34]. The reject generated from textile dyeing industry contains large amount of Na2SO4 and thus being recovered through multiple effect evaporation and/or calcinating the concentrated reject in a muffle

2.4 Chemical process

2.5.1 Calcium

67


#### 2.1 Evaporation and cooling

Recovery of valuable salts or minerals can be obtained from RO concentrate or brackish water by altering solution temperature either by evaporation or cooling effect. There are reports on evaporators are being practiced in brine management, among which multiple effect evaporator (MEE) are most promising and cost effective. The MEE operate based on the principle of reducing the vapor pressure of solution within the system to permit boiling occurs at low temperature. The multiple effect evaporator feed water is boiled and pumped into tube side in the evaporator in series. The outcome of steam has been condensed over the tube wall of the evaporator and collected as water to reuse. The excess heat is further used for the boiling of inlet water.

In other way, vapor compression distillation (VCD) is used for the desalination process. In VCD inlet water is boiled through heater to vaporize and discharged through evaporative compressor. The generated vapor has been compressed and used as steam supply for boiling concentrate and the condensate product is obtained after compression process.

#### 2.2 Electro-dialysis (ED) and ion exchange

Electro-dialysis system consists of anion-exchange and cation-exchange membranes are being arranged alternately in a large cell of compartment between an anode and a cathode. The influence of applied electric field, the various ions could migrate towards the electrodes based on its ionic charge. The membranes are permeable only to cations or anions, through which the water between the membranes are alternately depleted and enriched with salt ions. The cation membranes allow only positively charged ions to diffuse through them. Similarly, anion exchange membrane allows only negatively charge ions. Electro-dialysis is being considered used as a pre-treatment or a pre-concentration method for brine management [15–17]. This method of application significantly reduces the concentration of calcium or sulfate ions from gypsum crystallization during further evaporation [15]. However, fouling by colloidal material, organics, and bio-growth should be taken care for the effective and sustainable use of the equipment.

The performance of ion exchange processes based on packed bed column resin, which are generally organic resins that contains hydrogen ions and is capable of exchanging positive ions present in the feed water. The ion exchange processes are being studied, investigated, and applied for many desalting process over several decades [18–25]. However, this method of treatment applies only to low concentrations of salts containing brine water and its cost of regeneration is also higher.

#### 2.3 Eutectic freezing crystallization (EFC)

In this process, the feed concentrate stream is frozen continuously until it reaches a eutectic temperature. The ice being forming.

Short Review of Salt Recovery from Reverse Osmosis Rejects DOI: http://dx.doi.org/10.5772/intechopen.88716

If the unsaturated concentrate is reaching its freezing point. At the specific eutectic point of crystallization, the brine salt is crystallized out as product. The energy required for the EFC process are found to be very less than the conventional method of evaporative and cooling crystallization process and its theoretically possible way to complete the conversion of concentrate water into water and solidified solutes.

Through this route magnesium sulfate heptahydrate (MgSO47H2O) from a magnesium sulfate industrial stream is being recovered using EFC process [26, 27]. In which MgSO412H2O was formed in the crystallizer and after recrystallization MgSO47H2O is formed spontaneously. In addition to EFC, coupling of cooled disk column crystallizer (CDCC) helps to recover CuSO4 crystals from copper sulfate solution [28, 29]. The cost towards energy required for EFC can be reduced up to 70% than conventional evaporative crystallization processes, further 100% conversion of concentrate into water and salt separation is achieved by this route.

#### 2.4 Chemical process

ii. Chemical conversion of reject to products: chemical conversion of rejects to

iv. Stabilization of concentrate to inert material: stabilizing the waste concentrate

Recovery of valuable salts or minerals can be obtained from RO concentrate or brackish water by altering solution temperature either by evaporation or cooling effect. There are reports on evaporators are being practiced in brine management, among which multiple effect evaporator (MEE) are most promising and cost effective. The MEE operate based on the principle of reducing the vapor pressure of solution within the system to permit boiling occurs at low temperature. The multiple effect evaporator feed water is boiled and pumped into tube side in the evaporator in series. The outcome of steam has been condensed over the tube wall of the evaporator and collected as water to reuse. The excess heat is further used for the

In other way, vapor compression distillation (VCD) is used for the desalination process. In VCD inlet water is boiled through heater to vaporize and discharged through evaporative compressor. The generated vapor has been compressed and used as steam supply for boiling concentrate and the condensate product is obtained

Electro-dialysis system consists of anion-exchange and cation-exchange membranes are being arranged alternately in a large cell of compartment between an anode and a cathode. The influence of applied electric field, the various ions could migrate towards the electrodes based on its ionic charge. The membranes are permeable only to cations or anions, through which the water between the membranes are alternately depleted and enriched with salt ions. The cation membranes allow only positively charged ions to diffuse through them. Similarly, anion exchange membrane allows only negatively charge ions. Electro-dialysis is being considered used as a pre-treatment or a pre-concentration method for brine management [15–17]. This method of application significantly reduces the concentration of calcium or sulfate ions from gypsum crystallization during further evaporation [15]. However, fouling by colloidal material, organics, and bio-growth should be taken

The performance of ion exchange processes based on packed bed column resin, which are generally organic resins that contains hydrogen ions and is capable of exchanging positive ions present in the feed water. The ion exchange processes are being studied, investigated, and applied for many desalting process over several decades [18–25]. However, this method of treatment applies only to low concentrations of salts containing brine water and its cost of regeneration is also higher.

In this process, the feed concentrate stream is frozen continuously until it

iii. Direct and indirect discharge of concentrated brine by dilution without

other reusable salts from waste RO reject.

affecting receiving environment.

into chemically stable material.

2.1 Evaporation and cooling

Salt in the Earth

boiling of inlet water.

after compression process.

2.2 Electro-dialysis (ED) and ion exchange

care for the effective and sustainable use of the equipment.

2.3 Eutectic freezing crystallization (EFC)

66

reaches a eutectic temperature. The ice being forming.

Recovery of CaCO3 from nanofiltration reject is being achieved by reactive precipitation on addition of NaHCO3/Na2CO3 aqueous solution [30]. Similarly, recovery of MgSO47H2O from the reject from seawater nanofiltration, Ca2+ ions were precipitated as carbonates by reaction with NaHCO3/Na2CO3 to get calcium sulfate by precipitation, Sodium-bi-carbonate solutions are being produced by reactive transfer of carbon dioxide into sodium hydroxide solutions. This technique has been used successfully to recover magnesium sulfate from sulfate rich brine, rock forming minerals, and salty lake water [31–33]. There are many sequential extraction of salts from rejected brine thus which high concentration of dissolved sulfate, potassium, and magnesium salts are being separated through multiple effect evaporator and cooling crystallization method, reactive precipitation methods [15, 28]. The use of lime favors selective separation of magnesium hydroxide from concentrate solution and thermal calcination of concentrate having sodium sulfate helps to recover Na2SO4 from wastewater [34]. The reject generated from textile dyeing industry contains large amount of Na2SO4 and thus being recovered through multiple effect evaporation and/or calcinating the concentrated reject in a muffle furnace at a temperature range of 300 and 800°C [35].

#### 2.5 Extraction of potentially profitable material from RO rejects

#### 2.5.1 Calcium

The recovery of calcium from RO reject is done to avoid secondary RO scaling [36–38]. Bond and Veerapaneni [36] have developed detailed methodology for the recovery of calcium carbonate by chemical precipitation, in particular to separate calcium during desalination. Several other researchers have evaluated fluidized bed crystallizers for the production of calcium carbonate pellets from RO reject [36, 39], further studies have been reported on influence of anti-scalants, impurities, metals, and ions on calcium carbonate precipitation [40–42]. The concentration of calcium ions in seawater and desalination reject is relatively high, through this calcium carbonate pellets has been prepared from brackish water in Southern California [39]. However, the extraction of calcium sulfate from RO reject has not received significant attention, due to low price of commercial grade gypsum. Also, the mechanisms of calcium sulfate precipitation have been observed to form scaling minimized equipment failure in separation process [43–46]. The ion-exchange resin is being used to selectively extract calcium sulfate salts from RO reject by controlling the pH of the mixture of anion and cation regeneration solution.

#### 2.5.2 Magnesium

The main unit processes used for the extraction of magnesium is evaporation cum crystallization, precipitation, and ion-exchange. Ohya et al. [47–49] proposed a series of integrated processes (crystallization, electro-dialysis, ion-exchange) to recover salts of calcium carbonate, sodium chloride and magnesium sulfate from RO reject. Drioli et al. identified a process of membrane crystallization/distillation to separate out various inorganic salts from reject streams from an integrated NF/ RO process [30, 50]. In Russia, a large scale extraction plant is also being operated for the recovery of magnesium from seawater using ion-exchange, and extraction of magnesium from RO reject from seawater desalination system.

product purity using this approach Tanaka et al. [17]. Electrolytic method of simultaneous separation of chlorine and sodium chloride has good market potential for the effective management of RO reject. Melian-Martel et al. [62] used membrane electrolytic cells to recover chlorine, hydrogen and sodium hydroxide from seawater RO reject. Boopathy et al. reported separation of sodium chloride from the RO reject generated in leather processing industries through reactive precipitation

The movement of ions during precipitation is expressed in the form of chemical

The residue of RO rejects has been dissolved in water to prepare saturated RAE solution as shown in Eq. (1). The increase in ionic concentration in the saturated solution shifts the reaction to backward direction by common ion effect. In this study, hydrogen chloride gas was prepared and purged to increase the concentration of Cl� ions in the RAE solution. The incremental increase in Cl� ion concentration shifted dynamic equilibrium by increasing the ionic product of Na<sup>+</sup> and Cl�. The ionic product of Na<sup>+</sup> and Cl� exceeded the solubility product of sodium chlo-

sodium chloride was achieved from the saturated solution of RAE as illustrated in Eq. (2). The schematic flow diagram of separation of sodium chloride from RAE solution generated in leather industry has been illustrated in Figure 1. First saturated RAE solution has been prepared by dissolving 60% (w/v) RAE in water and the insoluble grits are removed after gravitational settlement. The clear supernatant solution was taken in reactive precipitation reactor and HCl gas has been purged continuously for the reactive precipitation of sodium chloride. The required HCl is being prepared and used spontaneously. Since the prepared HCl gas cannot be stored, if we store which may condensate and turn into liquid form. After successful purging of HCl gas the sodium chloride salt is separated out from the solution by

2.5.6.2 Effect of HCl gas injection time and RAE concentration on NaCl recovery

The HCl gas purging time for the separation of sodium chloride from RAE solution was carried out by varying time from 0.5 to 3 min at its native pH, 8.0 and temperature, 40°C. The optimum condition for the recovery of NaCl is achieved within 3 min of contact time as shown in Figure 2a. The optimum time of 3 min of contact time yield 81% recovery of sodium chloride. This is explained that the equilibrium was established i.e. the rate of precipitation of NaCl becomes equal to the rate of dissolution of NaCl in the solution. The mass of precipitated NaCl at the optimum time was 26.7 g with 81% recovery with respect to the dissolved salt

The concentration of RAE [40–65% (w/v)] was varied to identify the effect on precipitation of NaCl. The results in Figure 2b, shows that the percentage of salt recovery increased with the increase in concentration of RAE. In general, precipitation depends on the concentration of dissolved ions in solution. As the initial

<sup>2</sup>�, Mg2þ, Org�=Orgþ, H2O (1)

<sup>2</sup>�, Mg<sup>2</sup>þ, Org�=Org<sup>þ</sup> (2)

] and thus the precipitation of

2.5.6.1 Precipitation of sodium chloride from evaporated residue of RO rejects

RAE <sup>þ</sup> H2O ! Naþ, Cl�, Ca2þ, SO4

Short Review of Salt Recovery from Reverse Osmosis Rejects

DOI: http://dx.doi.org/10.5772/intechopen.88716

ride [solubility product of NaCl, (Ksp) is 36 (mol/L)<sup>2</sup>

reactive precipitation as per the reaction given in Eq. (2).

concentration (solubility of NaCl is 35 g in 100 mL of water).

69

<sup>2</sup>�; Mg<sup>2</sup>þ; Org�=Orgþ; H2O <sup>þ</sup> HClð Þ<sup>g</sup> ! NaClð Þ<sup>S</sup> <sup>þ</sup> ½ � H3O <sup>þ</sup> <sup>þ</sup> Na<sup>þ</sup> <sup>þ</sup> Cl� <sup>þ</sup> Ca2þ, SO4

techniques [63].

equations as given below:

Naþ;Cl�;Ca2þ; SO4

#### 2.5.3 Potassium

Worldwide potash consumption is increasing every year approximately at a rate of 3% due to population growth and other increased demand for fertilizers [51]. The main source of potash production is done by conventional shaft mining or deep-well solution mining process techniques. Currently, potassium is being produced from seawater as a byproduct from solar salt evaporation. As an alternative to solar evaporation/precipitation, several researchers have suggested that, potassium could be produced from RO reject using an evaporation/crystallization process [52, 53]. The extraction of potassium is done using natural zeolite (clinoptilolites) ionexchange materials which has high exchange capacity for potassium through a twostep dual-temperature process.

#### 2.5.4 Sodium

The production of sodium compounds from desalination reject is obtained through evaporation technologies, followed by crystallization [54, 55], membrane crystallization [56, 57], electrodialysis followed by multiple effect distillation (ED/ MED) [54–58], and evaporation ponds [59, 60]. Membrane crystallization (MCr) is being practiced to produce relatively pure salt crystals from a synthetic NF reject solution having calcium and magnesium [66]. Tanaka et al. [17] developed an electro dialysis process for the production of salt from seawater reverse osmosis (SWRO) reject with less than 80% energy than conventional process. A similar process developed by Davis [47] on electrodialysis metathesis which has integrated evaporator unit to separate out sodium sulfate and sodium chloride [61]. The SAL-PROC process (Geo-Processors USA Inc) is being used to produce sodium chloride, calcium sulfate, calcium chloride, and magnesium hydroxide from concentrated solutions including brackish water reverse osmosis (BWRO) and seawater reverse osmosis (SWRO) concentrate.

#### 2.5.5 Nitrogen

In general, RO reject stream was found to be more than 40 mg of nitrogen per liter. The available method to recover ammonia-nitrogen by struvite precipitation, since extraction of ammonia is economically poor.

#### 2.5.6 Sodium chloride

The SWRO reject through either electro-dialysis (ED) or electro-dialysis reversal (EDR) step is sufficient to separate out impurities and that the salt produced is fit for human consumption; however, there is little information available on final

2.5.2 Magnesium

Salt in the Earth

2.5.3 Potassium

2.5.4 Sodium

step dual-temperature process.

osmosis (SWRO) concentrate.

since extraction of ammonia is economically poor.

2.5.5 Nitrogen

68

2.5.6 Sodium chloride

The main unit processes used for the extraction of magnesium is evaporation cum crystallization, precipitation, and ion-exchange. Ohya et al. [47–49] proposed a series of integrated processes (crystallization, electro-dialysis, ion-exchange) to recover salts of calcium carbonate, sodium chloride and magnesium sulfate from RO reject. Drioli et al. identified a process of membrane crystallization/distillation to separate out various inorganic salts from reject streams from an integrated NF/ RO process [30, 50]. In Russia, a large scale extraction plant is also being operated for the recovery of magnesium from seawater using ion-exchange, and extraction of

Worldwide potash consumption is increasing every year approximately at a rate of 3% due to population growth and other increased demand for fertilizers [51]. The main source of potash production is done by conventional shaft mining or deep-well solution mining process techniques. Currently, potassium is being produced from seawater as a byproduct from solar salt evaporation. As an alternative to solar evaporation/precipitation, several researchers have suggested that, potassium could be produced from RO reject using an evaporation/crystallization process [52, 53]. The extraction of potassium is done using natural zeolite (clinoptilolites) ionexchange materials which has high exchange capacity for potassium through a two-

The production of sodium compounds from desalination reject is obtained through evaporation technologies, followed by crystallization [54, 55], membrane crystallization [56, 57], electrodialysis followed by multiple effect distillation (ED/ MED) [54–58], and evaporation ponds [59, 60]. Membrane crystallization (MCr) is being practiced to produce relatively pure salt crystals from a synthetic NF reject solution having calcium and magnesium [66]. Tanaka et al. [17] developed an electro dialysis process for the production of salt from seawater reverse osmosis (SWRO) reject with less than 80% energy than conventional process. A similar process developed by Davis [47] on electrodialysis metathesis which has integrated evaporator unit to separate out sodium sulfate and sodium chloride [61]. The SAL-PROC process (Geo-Processors USA Inc) is being used to produce sodium chloride, calcium sulfate, calcium chloride, and magnesium hydroxide from concentrated solutions including brackish water reverse osmosis (BWRO) and seawater reverse

In general, RO reject stream was found to be more than 40 mg of nitrogen per liter. The available method to recover ammonia-nitrogen by struvite precipitation,

The SWRO reject through either electro-dialysis (ED) or electro-dialysis reversal (EDR) step is sufficient to separate out impurities and that the salt produced is fit for human consumption; however, there is little information available on final

magnesium from RO reject from seawater desalination system.

product purity using this approach Tanaka et al. [17]. Electrolytic method of simultaneous separation of chlorine and sodium chloride has good market potential for the effective management of RO reject. Melian-Martel et al. [62] used membrane electrolytic cells to recover chlorine, hydrogen and sodium hydroxide from seawater RO reject. Boopathy et al. reported separation of sodium chloride from the RO reject generated in leather processing industries through reactive precipitation techniques [63].

#### 2.5.6.1 Precipitation of sodium chloride from evaporated residue of RO rejects

The movement of ions during precipitation is expressed in the form of chemical equations as given below:

$$\text{RAE} + \text{H}\_2\text{O} \rightarrow \text{Na}^+, \text{Cl}^-, \text{Ca}^{2+}, \text{SO}\_4{}^{2-}, \text{Mg}^{2+}, \text{Org}^-/\text{Org}^+, \text{H}\_2\text{O} \tag{1}$$

$$\begin{aligned} \text{(}\text{Na}^+,\text{Cl}^-,\text{Ca}^{2+},\text{SO}\_4^{2-},\text{Mg}^{2+},\text{Org}^-/\text{Org}^+,\text{H}\_2\text{O}\text{)}+\text{HCl}\_{(\text{g})}\\ \rightarrow \text{NaCl}\_{(\text{S})}+[\text{H}\_3\text{O}]^++\text{Na}^++\text{Cl}^-+\text{Ca}^{2+},\text{SO}\_4{}^{2-},\text{Mg}^{2+},\text{Org}^-/\text{Org}^+\end{aligned} \tag{2}$$

The residue of RO rejects has been dissolved in water to prepare saturated RAE solution as shown in Eq. (1). The increase in ionic concentration in the saturated solution shifts the reaction to backward direction by common ion effect. In this study, hydrogen chloride gas was prepared and purged to increase the concentration of Cl� ions in the RAE solution. The incremental increase in Cl� ion concentration shifted dynamic equilibrium by increasing the ionic product of Na<sup>+</sup> and Cl�. The ionic product of Na<sup>+</sup> and Cl� exceeded the solubility product of sodium chloride [solubility product of NaCl, (Ksp) is 36 (mol/L)<sup>2</sup> ] and thus the precipitation of sodium chloride was achieved from the saturated solution of RAE as illustrated in Eq. (2). The schematic flow diagram of separation of sodium chloride from RAE solution generated in leather industry has been illustrated in Figure 1. First saturated RAE solution has been prepared by dissolving 60% (w/v) RAE in water and the insoluble grits are removed after gravitational settlement. The clear supernatant solution was taken in reactive precipitation reactor and HCl gas has been purged continuously for the reactive precipitation of sodium chloride. The required HCl is being prepared and used spontaneously. Since the prepared HCl gas cannot be stored, if we store which may condensate and turn into liquid form. After successful purging of HCl gas the sodium chloride salt is separated out from the solution by reactive precipitation as per the reaction given in Eq. (2).

#### 2.5.6.2 Effect of HCl gas injection time and RAE concentration on NaCl recovery

The HCl gas purging time for the separation of sodium chloride from RAE solution was carried out by varying time from 0.5 to 3 min at its native pH, 8.0 and temperature, 40°C. The optimum condition for the recovery of NaCl is achieved within 3 min of contact time as shown in Figure 2a. The optimum time of 3 min of contact time yield 81% recovery of sodium chloride. This is explained that the equilibrium was established i.e. the rate of precipitation of NaCl becomes equal to the rate of dissolution of NaCl in the solution. The mass of precipitated NaCl at the optimum time was 26.7 g with 81% recovery with respect to the dissolved salt concentration (solubility of NaCl is 35 g in 100 mL of water).

The concentration of RAE [40–65% (w/v)] was varied to identify the effect on precipitation of NaCl. The results in Figure 2b, shows that the percentage of salt recovery increased with the increase in concentration of RAE. In general, precipitation depends on the concentration of dissolved ions in solution. As the initial

#### Figure 1.

Schematic flow diagram for the selective precipitation of sodium chloride from RAE generated in leather industry.

concentration of RAE increased, the dissolved ions concentration was also increased in the solution and reached the saturation limit at concentration 60% (w/v). The maximum amount of NaCl precipitation was achieved with 82% recovery for 60% (w/v) RAE solution. Further to evidence that the recovered salt is NaCl, SEM and EDAX analyses were carried for the recovered NaCl as shown in Figure 3. The surface morphology of RO reject looks aggregated mass like structure and thus may be due to mixture of many inorganic and organic salts. This is confirmed by EDAX spectrum shows presence of inorganic salts. However the recovered salt has a cubical structure, which is a characteristic morphology of sodium chloride and thus it claim that the recovered salt is sodium chloride. Further EDAX spectrum peak observed only for Na and Cl and thus confirmed that the recovered salt is NaCl.

#### 2.5.6.3 Mass balance on preparation of saturated RAE solution

$$\begin{aligned} \text{mass of RAE} + \text{deionised water} &\rightarrow \text{saturated RAE solution} + \text{grt} \\ 0.6 \text{ kg} + 1 \text{ kg} &\rightarrow 1.32 \text{ kg} + 0.28 \text{ kg} \end{aligned} \tag{3}$$

The mass of saturated solution of RAE was 1.32 kg, obtained by dissolving 0.6 kg of RAE in 1 l of deionized water. The undissolved grit (0.28 kg) mainly consists of sand, lime and clay being non-hazardous in nature, which can be disposed off onto secure landfill.

#### 2.5.6.4 Mass balance on precipitation of sodium chloride

$$\begin{aligned} \text{saturated RAE solution} + \text{HCl gas} &\rightarrow \text{ precipitated sodium chloride} \\ &+ \text{residual solution1.32 kg} + 0.105 \text{ kg} \rightarrow 0.268 \text{ kg} + 1.157 \text{ kg} \end{aligned} \tag{4}$$

The proposed process for the management of RAE was relatively lower in cost than the other disposal methods, and also the process has the scope to recover sodium chloride. The proposed process recovered 0.203 kg of NaCl from 1 kg of RAE. The resulted acidified supernatant solution (RAS) was considered for separation of sulfate ions as calcium sulfate. The sulfate ion in the RAS solution and synthetic RAS solutions were separated by the addition of various neutralizing

Precipitation of sodium chloride (a) effect of time (conditions: pH, 8.0; temperature, 40°C; mass of RAE, 60%

(w/v)), (b) effect of concentration of RAE (conditions: time, 3 min; pH, 8.0; temperature, 40°C).

Short Review of Salt Recovery from Reverse Osmosis Rejects

DOI: http://dx.doi.org/10.5772/intechopen.88716

Figure 2.

71

The maximum precipitation of sodium chloride of 0.268 kg was resulted from 1 l of saturated RAE solution under the optimized conditions.

Figure 2.

concentration of RAE increased, the dissolved ions concentration was also increased in the solution and reached the saturation limit at concentration 60% (w/v). The maximum amount of NaCl precipitation was achieved with 82% recovery for 60% (w/v) RAE solution. Further to evidence that the recovered salt is NaCl, SEM and EDAX analyses were carried for the recovered NaCl as shown in Figure 3. The surface morphology of RO reject looks aggregated mass like structure and thus may be due to mixture of many inorganic and organic salts. This is confirmed by EDAX spectrum shows presence of inorganic salts. However the recovered salt has a cubical structure, which is a characteristic morphology of sodium chloride and thus it claim that the recovered salt is sodium chloride. Further EDAX spectrum peak observed only for Na and Cl and thus confirmed that the recovered salt is NaCl.

Schematic flow diagram for the selective precipitation of sodium chloride from RAE generated in leather

2.5.6.3 Mass balance on preparation of saturated RAE solution

2.5.6.4 Mass balance on precipitation of sodium chloride

saturated RAE solution þ HCl gas ! precipitated sodium chloride

of saturated RAE solution under the optimized conditions.

secure landfill.

70

Figure 1.

Salt in the Earth

industry.

mass of RAE þ deionised water ! saturated RAE solution þ grit

The mass of saturated solution of RAE was 1.32 kg, obtained by dissolving 0.6 kg of RAE in 1 l of deionized water. The undissolved grit (0.28 kg) mainly consists of sand, lime and clay being non-hazardous in nature, which can be disposed off onto

The maximum precipitation of sodium chloride of 0.268 kg was resulted from 1 l

<sup>0</sup>:6 kg <sup>þ</sup> 1 kg ! <sup>1</sup>:32 kg <sup>þ</sup> <sup>0</sup>:28 kg (3)

þ residual solution1:32 kg þ 0:105 kg ! 0:268 kg þ 1:157 kg

(4)

Precipitation of sodium chloride (a) effect of time (conditions: pH, 8.0; temperature, 40°C; mass of RAE, 60% (w/v)), (b) effect of concentration of RAE (conditions: time, 3 min; pH, 8.0; temperature, 40°C).

The proposed process for the management of RAE was relatively lower in cost than the other disposal methods, and also the process has the scope to recover sodium chloride. The proposed process recovered 0.203 kg of NaCl from 1 kg of RAE. The resulted acidified supernatant solution (RAS) was considered for separation of sulfate ions as calcium sulfate. The sulfate ion in the RAS solution and synthetic RAS solutions were separated by the addition of various neutralizing

3. Conclusions

Table 2.

Acknowledgements

Conflict of interest

Nomenclature

RO reverse osmosis kWh kilowatt hour ZLD zero liquid discharge MEE multiple effect evaporator RAE residue after evaporation VC vapor compression ED electro-dialysis

NF nano filtration

73

EFC eutectic freezing crystallization

MED multiple effect distillation

CDCC coupling of cooled disk column crystallizer

laboratory and funding to carryout research activity.

Recovery of valuables from RO reject through integrated approach.

Short Review of Salt Recovery from Reverse Osmosis Rejects

DOI: http://dx.doi.org/10.5772/intechopen.88716

There is no conflict of interest with any funding agencies.

The thermal routes of evaporation are the most studied process techniques for the recovery of inorganic salt from RO reject; however, membrane separation techniques are cheaper for the recovery of product quality. The membrane separation process has generates reject volume which need further treatment. The ion-exchange, electro dialysis, eutectic freezing, and chemical reaction are also being explored more in recent times for its cost and efficiency on recovery of valuables from the reject stream. The integrated systems are being studied by combining one or more unit operation or process techniques to increase the recovery percentage of valuables. The selection of process or techniques may be selected based on the salt to be recovered, geological, hydrological, climatic, and economic conditions for its local specific.

The author is thankful to the Council of Scientific and Industrial Research for the

Figure 3. Scanning electron microscopy images of: (a) RAE, (b) recovered NaCl from RAE and energy dispersive X-ray spectra of (c) RAE, (d) recovered NaCl from RAE.

agents. Among the selected neutralizing agents, Ca(OH)2 was effective for the separation of sulfate ions from the RAS solution and synthetic RAS solutions. The total cost for the management of 1 kg of RAE by the proposed process was 0.155 USD while the cost on landfill disposal was 0.11 USD. The recovered salts proposed to be reused for the hide/skin presentation in slaughter house [63].

#### 2.6 Integrated process

Salt recovery or recovery of valuables from concentrate are being effectively done through an integrated approach by combining one or more separation process which serve as a pretreatment or post treatment step [64]. In electro-dialysis for concentrating reject brine solution, multi-stage flash being employed for desalting water, and crystallization for recovering salts, or with RO may be used instead of the multistage flash evaporator [65]. In another approach, RO reject are being supplied to an ion-exchange membrane electrodialyzer as post treatment, and then concentrated brine from the electrodialyzer is sent to a multi-effect vacuum evaporator to crystallize the salts present in water stream [58]. Variety of inorganic salts is also sequential extracted from rejected brine for the high concentration levels of dissolved sulfate, potassium, and magnesium salts through multiple effect evaporation and cooling of saline wastewater, chemical reactions, crystallization, washing, and dewatering. The processes developed by researchers to recover various valuables from RO reject are presented in Table 2. The combined process helps to recover both salts and water from textile rejects [66–68].

Short Review of Salt Recovery from Reverse Osmosis Rejects DOI: http://dx.doi.org/10.5772/intechopen.88716


Table 2.

Recovery of valuables from RO reject through integrated approach.

#### 3. Conclusions

The thermal routes of evaporation are the most studied process techniques for the recovery of inorganic salt from RO reject; however, membrane separation techniques are cheaper for the recovery of product quality. The membrane separation process has generates reject volume which need further treatment. The ion-exchange, electro dialysis, eutectic freezing, and chemical reaction are also being explored more in recent times for its cost and efficiency on recovery of valuables from the reject stream. The integrated systems are being studied by combining one or more unit operation or process techniques to increase the recovery percentage of valuables. The selection of process or techniques may be selected based on the salt to be recovered, geological, hydrological, climatic, and economic conditions for its local specific.

#### Acknowledgements

agents. Among the selected neutralizing agents, Ca(OH)2 was effective for the separation of sulfate ions from the RAS solution and synthetic RAS solutions. The total cost for the management of 1 kg of RAE by the proposed process was 0.155 USD while the cost on landfill disposal was 0.11 USD. The recovered salts proposed to be reused for the hide/skin presentation in slaughter house [63].

Scanning electron microscopy images of: (a) RAE, (b) recovered NaCl from RAE and energy dispersive X-ray

Salt recovery or recovery of valuables from concentrate are being effectively done through an integrated approach by combining one or more separation process which serve as a pretreatment or post treatment step [64]. In electro-dialysis for concentrating reject brine solution, multi-stage flash being employed for desalting water, and crystallization for recovering salts, or with RO may be used instead of the multistage flash evaporator [65]. In another approach, RO reject are being supplied to an ion-exchange membrane electrodialyzer as post treatment, and then concentrated brine from the electrodialyzer is sent to a multi-effect vacuum evaporator to crystallize the salts present in water stream [58]. Variety of inorganic salts is also sequential extracted from rejected brine for the high concentration levels of dissolved sulfate, potassium, and magnesium salts through multiple effect evaporation and cooling of saline wastewater, chemical reactions, crystallization, washing, and dewatering. The processes developed by researchers to recover various valuables from RO reject are presented in Table 2. The combined process helps to

recover both salts and water from textile rejects [66–68].

2.6 Integrated process

spectra of (c) RAE, (d) recovered NaCl from RAE.

Figure 3.

Salt in the Earth

72

The author is thankful to the Council of Scientific and Industrial Research for the laboratory and funding to carryout research activity.

#### Conflict of interest

There is no conflict of interest with any funding agencies.

#### Nomenclature



References

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Short Review of Salt Recovery from Reverse Osmosis Rejects

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### Author details

Boopathy Ramasamy CSIR-Institute of Minerals and Materials Technology, Bhubaneswar, Odisha, India

\*Address all correspondence to: boopathy@immt.res.in

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Short Review of Salt Recovery from Reverse Osmosis Rejects DOI: http://dx.doi.org/10.5772/intechopen.88716

#### References

MCr membrane crystallization EDM electrodialysis metathesis BWRO brackish water reverse osmosis SWRO seawater reverse osmosis EDR electro-dialysis reversal RAS resulted acidified solution

USD US dollar

Salt in the Earth

Author details

74

Boopathy Ramasamy

CSIR-Institute of Minerals and Materials Technology, Bhubaneswar, Odisha, India

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: boopathy@immt.res.in

provided the original work is properly cited.

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[49] Ohya H, Suzuki T, Nakao S. Integrated system for complete usage of components in seawater: A proposal of inorganic chemical combination seawater. Desalination. 2001;134:29-36. DOI: 10.1016/S0011-9164(01)00112-6

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[53] Khamizov RK, Ivanovand NA, Tikhonov NA. In: SenGupta AK, editor. Ion Exchange and Solvent Extraction Dual Temperature Methods of Separation and Concentration of Elements in Ion Exchange Columns. CRC Press; 2011. pp. 17-31

[54] Turek M, Dydo P, Klimek R. Salt production from coal-mine brine in ED evaporation crystallization system. Desalination. 2005;184:439-446. DOI: 10.1016/j.desal.2005.03.047

[62] Melian-Martel N, Sadhwani JJ, Ovidio Perez Baez S. Saline waste disposal reuse for desalination plants for the chlor-alkali industry: The particular

DOI: http://dx.doi.org/10.5772/intechopen.88716

Short Review of Salt Recovery from Reverse Osmosis Rejects

desalination plant. Desalination. 2011; 281:35-41. DOI: 10.1016/j.desal.2011.

[63] Boopathy R, Sekaran G. Studies on process development for the separation of sodium chloride from residue after evaporation of reverse osmosis reject solution. Separation and Purification Technology. 2017;183:127-135. DOI: 10.1016/j.seppur.2017.04.008

[64] Turek M. Seawater desalination and salt product ion in a hybrid membrane thermal process. Desalination. 2003;153: 173-177. DOI: 10.1016/S0011-9164(02)

[65] Seigworth A, Ludlum R, Reahl E. Case study: Integrating membrane processes with evaporation to achieve economical zero liquid discharge at the Doswell combined cycle facility. Desalination. 1995;102:81-86. DOI: 10.1016/0011-9164(95)00044-3

[66] Allegre C, Moulin P, Maisseu M, Charbit F. Savings and re-use of salts and water present in dye house effluents. Desalination. 2004;62:13-22. DOI: 10.1016/S0011-9164(04)00022-0

[67] Davis TA. Zero discharge seawater desalination: Integrating the Production of freshwater, salt, magnesium, and bromine report. In: USBR Research Report e 111. U.S. Reclamation; 2006

[68] Kim DH. A review of desalting process techniques and economic analysis of the recovery of salts from retentates. Desalination. 2011;270:1-8

case of pozo izquierdo SWRO

07.040

01123-2

79

[55] Turek M, Dydo P, Klimek R. Salt production from coal-mine brine in NF evaporation crystallization system. Desalination. 2008;221:238-243. DOI: 10.1016/j.desal.2007.01.080

[56] Drioli E, Curcio E, Di Profio G, Macedonio F, Criscuoli A. Integrating membrane contactors technology and pressure-driven membrane operations for seawater desalination. Energy, exergy and costs analysis. Chemical Engineering Research and Design. 2006; 82:209-220. DOI: 10.1205/cherd.05171

[57] Drioli E, Di Profio G, Curcio E. Progress in membrane crystallization. Current Opinion in Chemical Engineering. 2012;1:178-182. DOI: 10.1016/j.coche.2012.03.005

[58] Tanaka Y, Ehara R, Itoi S, Goto T. Ion-exchange membrane electrodialytic salt production using brine discharged from a reverse osmosis seawater desalination plant. Journal of Membrane Science. 2003;222:71-86. DOI: 10.1016/ S0376-7388(03)00217-5

[59] Ahmed M, Arakel A, Hoey D, Thumarukudy MR, Goosen MFA, Al-Haddabi M, et al. Feasibility of salt production from inland RO desalination plant reject brine: A case study. Desalination. 2003;158: 109-117. DOI: 10.1016/S0011-9164(03) 00441-7

[60] Ravizky A, Nadav N. Salt production by the evaporation of SWRO brine in Eilat: A success story. Desalination. 2007;205:374-379. DOI: 10.1016/j.desal.2006.03.559

[61] Veerapaneni V, Bond R, Dachille F, Hays B. Emerging desalination technologies e an overview. In: WateReuse Symposium. Phoenix, AZ; 2011. p. 34

Short Review of Salt Recovery from Reverse Osmosis Rejects DOI: http://dx.doi.org/10.5772/intechopen.88716

[62] Melian-Martel N, Sadhwani JJ, Ovidio Perez Baez S. Saline waste disposal reuse for desalination plants for the chlor-alkali industry: The particular case of pozo izquierdo SWRO desalination plant. Desalination. 2011; 281:35-41. DOI: 10.1016/j.desal.2011. 07.040

reverse osmosis concentrate. In: Report.

evaporation crystallization system. Desalination. 2005;184:439-446. DOI:

[55] Turek M, Dydo P, Klimek R. Salt production from coal-mine brine in NF evaporation crystallization system. Desalination. 2008;221:238-243. DOI:

[56] Drioli E, Curcio E, Di Profio G, Macedonio F, Criscuoli A. Integrating membrane contactors technology and pressure-driven membrane operations for seawater desalination. Energy, exergy and costs analysis. Chemical Engineering Research and Design. 2006; 82:209-220. DOI: 10.1205/cherd.05171

[57] Drioli E, Di Profio G, Curcio E. Progress in membrane crystallization.

[58] Tanaka Y, Ehara R, Itoi S, Goto T. Ion-exchange membrane electrodialytic salt production using brine discharged from a reverse osmosis seawater

desalination plant. Journal of Membrane Science. 2003;222:71-86. DOI: 10.1016/

[59] Ahmed M, Arakel A, Hoey D, Thumarukudy MR, Goosen MFA, Al-Haddabi M, et al. Feasibility of salt production from inland RO desalination plant reject brine: A case study. Desalination. 2003;158: 109-117. DOI: 10.1016/S0011-9164(03)

[60] Ravizky A, Nadav N. Salt

brine in Eilat: A success story. Desalination. 2007;205:374-379. DOI:

Hays B. Emerging desalination technologies e an overview. In: WateReuse Symposium. Phoenix, AZ;

10.1016/j.desal.2006.03.559

production by the evaporation of SWRO

[61] Veerapaneni V, Bond R, Dachille F,

Current Opinion in Chemical Engineering. 2012;1:178-182. DOI: 10.1016/j.coche.2012.03.005

S0376-7388(03)00217-5

00441-7

2011. p. 34

10.1016/j.desal.2005.03.047

10.1016/j.desal.2007.01.080

[47] Davis TA. Zero discharge seawater desalination: Integrating the production of freshwater, salt, magnesium, and bromine. Report USBR Research Report 111. U.S. Bureau of Reclamation.

[48] Le Dirach J, Nisan S, Poletiko C. Extraction of strategic materials from the concentrated brine rejected by integrated nuclear desalination systems. Desalination. 2005;182:449-460. DOI:

10.1016/j.desal.2005.02.037

[49] Ohya H, Suzuki T, Nakao S.

Integrated system for complete usage of components in seawater: A proposal of inorganic chemical combination

seawater. Desalination. 2001;134:29-36. DOI: 10.1016/S0011-9164(01)00112-6

[50] Drioli E, Curcio E, Di Profio G, Macedonio F, Criscuoli A. Integrating membrane contactors techology and pressure-driven membrane operations for seawater desalination. Energy, exergy and costs analysis. Chemical Engineering Research and Design. 2006; 82:209-220. DOI: 10.1205/cherd.05171

[51] In JSMP. United States Geological Survey Mineral Commodity Summaries.

[52] Jeppesen T, Shu L, Keir G, Jegatheesan V. Metal recovery from reverse osmosis concentrate. Journal of Cleaner Production. 2009;17:703-707. DOI: 10.1016/j.jclepro.2008.11.013

[53] Khamizov RK, Ivanovand NA, Tikhonov NA. In: SenGupta AK, editor. Ion Exchange and Solvent Extraction Dual Temperature Methods of Separation and Concentration of Elements in Ion Exchange Columns.

[54] Turek M, Dydo P, Klimek R. Salt production from coal-mine brine in ED

CRC Press; 2011. pp. 17-31

78

2013. pp. 122-123

W.R. Foundation; 2013

Salt in the Earth

2006

[63] Boopathy R, Sekaran G. Studies on process development for the separation of sodium chloride from residue after evaporation of reverse osmosis reject solution. Separation and Purification Technology. 2017;183:127-135. DOI: 10.1016/j.seppur.2017.04.008

[64] Turek M. Seawater desalination and salt product ion in a hybrid membrane thermal process. Desalination. 2003;153: 173-177. DOI: 10.1016/S0011-9164(02) 01123-2

[65] Seigworth A, Ludlum R, Reahl E. Case study: Integrating membrane processes with evaporation to achieve economical zero liquid discharge at the Doswell combined cycle facility. Desalination. 1995;102:81-86. DOI: 10.1016/0011-9164(95)00044-3

[66] Allegre C, Moulin P, Maisseu M, Charbit F. Savings and re-use of salts and water present in dye house effluents. Desalination. 2004;62:13-22. DOI: 10.1016/S0011-9164(04)00022-0

[67] Davis TA. Zero discharge seawater desalination: Integrating the Production of freshwater, salt, magnesium, and bromine report. In: USBR Research Report e 111. U.S. Reclamation; 2006

[68] Kim DH. A review of desalting process techniques and economic analysis of the recovery of salts from retentates. Desalination. 2011;270:1-8

Chapter 5

Abstract

metals.

81

1. Introduction

Upward Capillary Mass Transfer

Margarita Yu Kharitonova and Margarita L. Sviridova

Keywords: upward mass transfer, geochemical barrier, soil capillaries, aeration zone, upward fluid, sedimentation, vapor barrier, leaching

Many natural minerals that form mineral deposits during oxidation become water-soluble like the conversion of metal sulfides to oxides. Mineral deposits

The natural process of circulation of ground and atmospheric water through evaporation from the surface and precipitation from the atmosphere to the surface leads to colonization of the surface soil layer. The main source of salts in the soil is groundwater. Groundwater reaches the surface soil layer and evaporates, and its constituent salts accumulate in the soil. The concentration of salts on the surface can reach to 100% (crust). This process is widespread. Vast areas of solonetzes are located in deserts and semideserts of Asia, Australia, South America, northern Africa, and the western United States. This natural process can be applied in the field of extraction of natural resources from the bowels. The process of salting the soil surface is low and gradual and is subject to study for possible use in technological solutions for the extraction of minerals. In this chapter, the authors intend to show the beneficial advantages of the phenomenon of surface salinization of the soil layer. Water-soluble salts due to their high mobility allow directional mass transfer along the capillary system of the soil and deposition in the aeration zone. However, the utility does not belong to plant biota. This phenomenon can be effective and safely used in the creation of near-surface concentration zones. The natural process of the filtration upward of salt solutions from the depths of the massif to the surface will purposefully carry out the transfer of valuable components with deposition in the area of the evaporation barrier. The speed of the process of ascending capillary mass transfer is technologically low but rather suitable as a preparatory operation at the place of storage of industrial wastes and burials and in the formation of zones of high concentration of small substandard natural mineral deposits. The chapter presents the results of experimental studies of ascending mass transfer of useful components from the waste material of the concentrating production of nonferrous

as a Process for Growing

Concentration Zones

Alexandr Mikhailov, Ivan I. Vashlaev,

#### Chapter 5

## Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

Alexandr Mikhailov, Ivan I. Vashlaev, Margarita Yu Kharitonova and Margarita L. Sviridova

#### Abstract

The natural process of circulation of ground and atmospheric water through evaporation from the surface and precipitation from the atmosphere to the surface leads to colonization of the surface soil layer. The main source of salts in the soil is groundwater. Groundwater reaches the surface soil layer and evaporates, and its constituent salts accumulate in the soil. The concentration of salts on the surface can reach to 100% (crust). This process is widespread. Vast areas of solonetzes are located in deserts and semideserts of Asia, Australia, South America, northern Africa, and the western United States. This natural process can be applied in the field of extraction of natural resources from the bowels. The process of salting the soil surface is low and gradual and is subject to study for possible use in technological solutions for the extraction of minerals. In this chapter, the authors intend to show the beneficial advantages of the phenomenon of surface salinization of the soil layer. Water-soluble salts due to their high mobility allow directional mass transfer along the capillary system of the soil and deposition in the aeration zone. However, the utility does not belong to plant biota. This phenomenon can be effective and safely used in the creation of near-surface concentration zones. The natural process of the filtration upward of salt solutions from the depths of the massif to the surface will purposefully carry out the transfer of valuable components with deposition in the area of the evaporation barrier. The speed of the process of ascending capillary mass transfer is technologically low but rather suitable as a preparatory operation at the place of storage of industrial wastes and burials and in the formation of zones of high concentration of small substandard natural mineral deposits. The chapter presents the results of experimental studies of ascending mass transfer of useful components from the waste material of the concentrating production of nonferrous metals.

Keywords: upward mass transfer, geochemical barrier, soil capillaries, aeration zone, upward fluid, sedimentation, vapor barrier, leaching

#### 1. Introduction

Many natural minerals that form mineral deposits during oxidation become water-soluble like the conversion of metal sulfides to oxides. Mineral deposits

located near the surface are exposed to oxygen from the atmosphere, and minerals oxidized (hypergenesis) become water-soluble and can be subjected to water leaching by filtration mass transfer. Hypergenesis is a strong geological process of chemical and physical transformation of minerals and rocks in the upper parts of the Earth's crust and on its surface under the influence of the atmosphere, hydrosphere, and living organisms at temperatures characteristic of the Earth's surface. Among them, hypergene transformation refers to the number of common and most productive geological processes. Hypergene transformations are very dynamic in the geological sense, but very slow in the technological sense. The process of geological formation of such deposits consists in the mass transfer and deposition of useful components on physical and geochemical barriers. The study of these processes and their application may be appropriate as a preparatory process before the extraction of minerals by common technological technologies. The directed application of geological processes in the technological foundations of the structural and material transformation of the array will lead to the achievement of standards to the existing capabilities of technology.

According to the laws of communication of groundwater with the atmosphere, the solutions of groundwater can move upward through the evaporation zone to the surface by capillary action mechanism. Along with this, a very powerful natural mechanism for solution flow through a massif enables upward vertical movement due to the pressure gradient between the surface and the fluid level in the water table. The reason for the formation of a pressure gradient consists in evaporation of water from the surface of the array. The upward fluid flow rate is controlled by all the forces in the capillary system and the humidity [1–3]. Water evaporation from the solution increases the concentrations of the useful mineral compounds along the direction of flow in the surface aeration zone. When these concentrations exceed the solubility limits, the useful compounds are deposited in the column. Different mineral compounds have different concentration limits in the solution; therefore, the compounds can be selectively precipitated at different heights in the aeration zone. Essentially, the aeration zone acts as a natural evaporation barrier. Selective enrichment can be achieved due to the physical nature of the capillary action in the upward direction and the deposition surface. Partial laws for the upward capillary rise of solutions were formulated in studies of agricultural soils [4–9]. The soil particle size and stratification structure were shown to influence the capillary action considerably [9–14]. To leach valuable compounds in a column, their velocity and the large contact surface area between the solution and solid material in the capillary system are important [15]. These parameters must be optimized to ensure that the extraction is complete and the upward capillary leaching process can be controlled. Upward capillary leaching was studied by investigating the upward capillary flow of solutions with access to the column surface and of the solutions that deposit salts in the near-surface aeration zone. The concentration of precipitated salts was estimated by samples at different levels of the evaporation barrier in the

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

DOI: http://dx.doi.org/10.5772/intechopen.90121

The leaching process is one of the main technological solutions for recovering useful components from poor ore [16, 17]. Leaching can sometimes be the only and therefore the most important method for recovering components from poor-quality ores. Now, underground leaching and heap leaching are well-known technological solutions that are widely used for metal ores [18–21] and nonmetallic minerals [20] (such as Chilean saltpeter). Very often the leaching is one of the only effective extraction technologies for removing valuable components from ores given that their contents have been decreasing recently. In fact, the United States and Australia are world leaders in the gold mining industry through the use of leaching technologies. Heap leaching technology is the most widely used. In heap leaching, gravity-driven fluid flow through the column is exploited. For each type of ore, the leaching technological process must be optimized. For example, Padilla et al. [20] analyzed two parameters of heap leaching, the leaching time and heap height, to determine the best performance indicators. Ghorbani [23] examined the effects of the surface characteristics and mineralogy of particles in the heap leaching process. The mineralogical composition of the ore and the leaching reagent properties control the transfer kinetics of useful species between the solid and liquid phases, demonstrating the applicability and efficacy of leaching under specific conditions. In addition to the dissolution of the column material in the fluid and precipitation of valuable compounds in the column, the fluid flow kinetics and direction are also important parameters in p leaching technology. Depending on the initial concentration of solutions and the size of a subsurface aeration zone, the precipitation distribution can be varied, and these very parameters can play a key role in monitoring of component

columns.

concentrations.

83

The water-based mass transfer occurs by dissolving salts with water from the capillary surface, moving as a salt solution and precipitating salt from the solution under the influence of physicochemical factors. Water-soluble forms of mineral compounds (salts) are involved in such mass transfer. The shape, content of nonferrous oxides, the location, and size of ore concentration zones depend on the conditions of the source and the potential of the subsoil (water content of the subsurface massif, pressure gradient, mass structure porosity, etc.), which causes the fluid to move. Natural geological ore concentration zones do not always correspond to the technological conditions of mining. Sometimes it is required to look for the presence of driving factors or, if it is possible, to create them.

The principle of filtration formation of concentrated zones is a kinetically dynamic geological process [1]. It involves three operations: transfer of watersoluble mineral compounds to the fluid, movement of the fluid in the capillary medium of the massif, and deposition on the physical or geochemical barrier. Due to the high kinetics (in geological sense) of this process, it can be applied in the field of mining as a preparatory stage—bringing the parameters of the subsoil section to effective technological conditions. The process due to the inconsistency of the speed by the technological processes should be brought to a separate—preparatory stage. The whole complex of leaching operations must be assessed in studies of the potential formation of artificial concentration zones.

The presence of water-soluble compounds, the minimum and maximum concentrations of the studied solutions, and the kinetics of the capillary motion of fluids are very important in the complex for the leaching process. If there are no such mineral compounds, they must be created.

The most suitable object for using such an approach is enrichment waste zones. The waste flotation enrichment of Norilsk mining was taken as the object of study in such objects in which there is always a useful component in a dispersed form. The whole object of tailing dump is located on the surface and is isolated from the natural environment by an engineering dam. The waste mass is flooded and finely dispersed; as a rule it has water-soluble metal oxides, and with the access of oxygen from the atmosphere, oxidation of sulfides is possible with the formation of watersoluble minerals. These conditions completely provide guaranteed controllability of mass transfer. In order to assess the feasibility of the filtration formation of oxidized ores of nonferrous metal concentration zones, expert studies were conducted on directional upward mass transfer for the conditions of the tailing dump of waste flotation enrichment of the Norilsk mining and smelting hub.

#### Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

According to the laws of communication of groundwater with the atmosphere, the solutions of groundwater can move upward through the evaporation zone to the surface by capillary action mechanism. Along with this, a very powerful natural mechanism for solution flow through a massif enables upward vertical movement due to the pressure gradient between the surface and the fluid level in the water table. The reason for the formation of a pressure gradient consists in evaporation of water from the surface of the array. The upward fluid flow rate is controlled by all the forces in the capillary system and the humidity [1–3]. Water evaporation from the solution increases the concentrations of the useful mineral compounds along the direction of flow in the surface aeration zone. When these concentrations exceed the solubility limits, the useful compounds are deposited in the column. Different mineral compounds have different concentration limits in the solution; therefore, the compounds can be selectively precipitated at different heights in the aeration zone. Essentially, the aeration zone acts as a natural evaporation barrier. Selective enrichment can be achieved due to the physical nature of the capillary action in the upward direction and the deposition surface. Partial laws for the upward capillary rise of solutions were formulated in studies of agricultural soils [4–9]. The soil particle size and stratification structure were shown to influence the capillary action considerably [9–14]. To leach valuable compounds in a column, their velocity and the large contact surface area between the solution and solid material in the capillary system are important [15]. These parameters must be optimized to ensure that the extraction is complete and the upward capillary leaching process can be controlled. Upward capillary leaching was studied by investigating the upward capillary flow of solutions with access to the column surface and of the solutions that deposit salts in the near-surface aeration zone. The concentration of precipitated salts was estimated by samples at different levels of the evaporation barrier in the columns.

The leaching process is one of the main technological solutions for recovering useful components from poor ore [16, 17]. Leaching can sometimes be the only and therefore the most important method for recovering components from poor-quality ores. Now, underground leaching and heap leaching are well-known technological solutions that are widely used for metal ores [18–21] and nonmetallic minerals [20] (such as Chilean saltpeter). Very often the leaching is one of the only effective extraction technologies for removing valuable components from ores given that their contents have been decreasing recently. In fact, the United States and Australia are world leaders in the gold mining industry through the use of leaching technologies. Heap leaching technology is the most widely used. In heap leaching, gravity-driven fluid flow through the column is exploited. For each type of ore, the leaching technological process must be optimized. For example, Padilla et al. [20] analyzed two parameters of heap leaching, the leaching time and heap height, to determine the best performance indicators. Ghorbani [23] examined the effects of the surface characteristics and mineralogy of particles in the heap leaching process. The mineralogical composition of the ore and the leaching reagent properties control the transfer kinetics of useful species between the solid and liquid phases, demonstrating the applicability and efficacy of leaching under specific conditions. In addition to the dissolution of the column material in the fluid and precipitation of valuable compounds in the column, the fluid flow kinetics and direction are also important parameters in p leaching technology. Depending on the initial concentration of solutions and the size of a subsurface aeration zone, the precipitation distribution can be varied, and these very parameters can play a key role in monitoring of component concentrations.

located near the surface are exposed to oxygen from the atmosphere, and minerals oxidized (hypergenesis) become water-soluble and can be subjected to water leaching by filtration mass transfer. Hypergenesis is a strong geological process of chemical and physical transformation of minerals and rocks in the upper parts of the Earth's crust and on its surface under the influence of the atmosphere, hydrosphere, and living organisms at temperatures characteristic of the Earth's surface. Among them, hypergene transformation refers to the number of common and most productive geological processes. Hypergene transformations are very dynamic in the geological sense, but very slow in the technological sense. The process of geological formation of such deposits consists in the mass transfer and deposition of useful components on physical and geochemical barriers. The study of these processes and their application may be appropriate as a preparatory process before the extraction of minerals by common technological technologies. The directed application of geological processes in the technological foundations of the structural and material transformation of the array will lead to the achievement of standards to the

The water-based mass transfer occurs by dissolving salts with water from the capillary surface, moving as a salt solution and precipitating salt from the solution under the influence of physicochemical factors. Water-soluble forms of mineral compounds (salts) are involved in such mass transfer. The shape, content of nonferrous oxides, the location, and size of ore concentration zones depend on the conditions of the source and the potential of the subsoil (water content of the subsurface massif, pressure gradient, mass structure porosity, etc.), which causes the fluid to move. Natural geological ore concentration zones do not always correspond to the technological conditions of mining. Sometimes it is required to look for

The principle of filtration formation of concentrated zones is a kinetically dynamic geological process [1]. It involves three operations: transfer of watersoluble mineral compounds to the fluid, movement of the fluid in the capillary medium of the massif, and deposition on the physical or geochemical barrier. Due to the high kinetics (in geological sense) of this process, it can be applied in the field of mining as a preparatory stage—bringing the parameters of the subsoil section to effective technological conditions. The process due to the inconsistency of the speed by the technological processes should be brought to a separate—preparatory stage. The whole complex of leaching operations must be assessed in studies of the

The presence of water-soluble compounds, the minimum and maximum concentrations of the studied solutions, and the kinetics of the capillary motion of fluids are very important in the complex for the leaching process. If there are no such

The most suitable object for using such an approach is enrichment waste zones. The waste flotation enrichment of Norilsk mining was taken as the object of study in such objects in which there is always a useful component in a dispersed form. The whole object of tailing dump is located on the surface and is isolated from the natural environment by an engineering dam. The waste mass is flooded and finely dispersed; as a rule it has water-soluble metal oxides, and with the access of oxygen from the atmosphere, oxidation of sulfides is possible with the formation of watersoluble minerals. These conditions completely provide guaranteed controllability of mass transfer. In order to assess the feasibility of the filtration formation of oxidized ores of nonferrous metal concentration zones, expert studies were conducted on directional upward mass transfer for the conditions of the tailing dump of waste

the presence of driving factors or, if it is possible, to create them.

potential formation of artificial concentration zones.

flotation enrichment of the Norilsk mining and smelting hub.

mineral compounds, they must be created.

82

existing capabilities of technology.

Salt in the Earth

As for technogenic formations, the evaporation barriers can be helpful for purposeful concentration of components in tailing dumps to mitigate the environmental load. The presence of salts with different solubility in solutions at evaporation barriers makes it possible their selective extraction. The filtration type of natural deposits plays an important role as a mineral source of minerals. Geological processes of filtration mass transfer formed quite a few deposits with a rich content of useful components [24].

In geological filtration processes, the main solvent and main carrier is water and aqueous solutions of salts. The possibilities of water mass transfer of useful components for low concentrations in the field of mining and hydrometallurgy in the process of upward capillary movement were carried out in the conditions of an array of separate wastes from the enrichment of nonferrous and noble metal ores. Low content of nonferrous and noble metals in tailings can identify the diffuse distribution of components in the bowels of the Earth. In addition, the mining industry has created a huge amount of waste enrichment. All of them are located on the surface of the Earth and have an area many times larger than the area of the deposits themselves. The overwhelming part of the man-made mining waste has a high degree of danger. The total reserves of useful components in industrial waste are several times higher than the proven reserves in the bowels of the Earth. Carrying out extraction is currently unprofitable due to its low content. There is a great temptation to find and launch the natural process of structural and material transformation of the array, which forms the concentration zones of useful components from the diffuse state that will be profitable for the existing technological level. This approach will make a profit and eliminate toxic environmental pollution. With the application of this solution, experimental studies of the ascending capillary movement of aqueous solutions of the soil layer near the surface were carried out. Nature uses this process extensively and suggests a variety of technological solutions.

a flexible pipe. The solution tank, which was a Mariotte bottle, was mounted on a platform that could be moved along the entire column height. The material to be tested was charged in the column. The solution was fed to the column at a constant feed rate through a bottom opening. The feed rate was controlled by the solution level in the Mariotte bottle, which was set to the height of the material surface in the column. In the first pilot version of the continuous upward flow system, the column was loaded with flotation tailings from the Norilsk industrial hub. These flotation tailings consisted of finely crushed ore with a predominant fraction particle size of 0.05–1.2 mm. The main minerals in the ore were rock-forming minerals, i.e., aluminum silicates (muscovite, illite, serpentine) and quartz. The ore also contained pyrrhotite, chromite, and minor amounts of chalcopyrite, calcite, brucite, and pentlandite. The sulfide mineral content was as high as 10%. The flotation tailings looked like a gray sand. The nonferrous and platinum group metal contents of the tailings were 0, 34% Cu, 0.39% Ni, 0.019% Co, 1.3 g/t Pt, 3.1 g/m Pd, and 0.23 g/t Au (atomic absorption spectroscopy). The content of useful components in the materials of the experiment was obtained by chemical analysis of its own chemical laboratory and was compared with the values of the chemical laboratory of the Norilsk mining and smelting hub. The initial working solution had a mineral content similar to that of mineralized drinking water at pH7.0 and flowed through the capillaries in the material to the surface. The solution that reached the surface was removed for extraction. The useful component content of the flotation tailings in the column was monitored by serial geochemical analysis during the experiment by the method [14], which showed that the exchangeable fraction consisted of readily water-soluble compounds and accounted for the largest percent of the noble metal species (31–46%). Crystalline Fe and Mn oxides constituted the second largest fraction of the tailings (20–30%). The copper, nickel, and cobalt sulfide mineral contents were in the range of 13–27% and, together with the oxide phases,

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

Installation of the upward movement of water-soluble solutions.

DOI: http://dx.doi.org/10.5772/intechopen.90121

Figure 1.

85

accounted for 43–61% of their total contents. The nonferrous metal content of the exchangeable fraction ranged from 4 to 10% (Figure 2). During the entire experiment, which was conducted for 15 months, the level of water was at the same level using a Mariotte vessel to evaluate fluid kinetics over time. The water solution at the surface was periodically analyzed for Cu, Ni, Co, Pt, Pd, and Au. In addition to these experiments, experiments in which an absorbent layer was placed on the surface were performed. This layer was designed to collect the product solution. A

The mineralogical composition of the ore and the leaching reagent properties control the transfer kinetics of useful species between the solid and liquid phases, demonstrating the applicability and efficacy of leaching under specific conditions. In addition to the dissolution of mineral materials and its movement in the column and precipitation of valuable compounds in the column, the kinetics and mass transfer direction are also important parameters in p leaching technology. To assess the applicability of the natural mechanism, only water and aqueous solutions of salts were used in technological solutions. The upward velocity of the fluid flow depends on the pressure gradient, which is the driving force of in situ leaching.

#### 2. Materials and methods

#### 2.1 Capillary rise with fluid release of the column surface

Drinking mineralization water was used in mass exchange experimental studies. The results of studies have been obtained on the directional upward mass transfer of water-soluble salts of nonferrous and noble metals in the conditions of the tailing dump of mineral processing. The speed and variability over time of the directed capillary ascending rise of aqueous solutions were obtained for dispersed materials of enrichment waste. The kinetics of formation of water-soluble salts of nonferrous and noble metals was evaluated for the tailing dump. This process is basic of the water leaching for enrichment waste. The experiments were performed using the setup shown in Figure 1. The core polycarbonate column had a height of 1.5 m and a diameter of 110 mm. The bottom of the column was connected to a solution tank by Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

Figure 1. Installation of the upward movement of water-soluble solutions.

a flexible pipe. The solution tank, which was a Mariotte bottle, was mounted on a platform that could be moved along the entire column height. The material to be tested was charged in the column. The solution was fed to the column at a constant feed rate through a bottom opening. The feed rate was controlled by the solution level in the Mariotte bottle, which was set to the height of the material surface in the column. In the first pilot version of the continuous upward flow system, the column was loaded with flotation tailings from the Norilsk industrial hub. These flotation tailings consisted of finely crushed ore with a predominant fraction particle size of 0.05–1.2 mm. The main minerals in the ore were rock-forming minerals, i.e., aluminum silicates (muscovite, illite, serpentine) and quartz. The ore also contained pyrrhotite, chromite, and minor amounts of chalcopyrite, calcite, brucite, and pentlandite. The sulfide mineral content was as high as 10%. The flotation tailings looked like a gray sand. The nonferrous and platinum group metal contents of the tailings were 0, 34% Cu, 0.39% Ni, 0.019% Co, 1.3 g/t Pt, 3.1 g/m Pd, and 0.23 g/t Au (atomic absorption spectroscopy). The content of useful components in the materials of the experiment was obtained by chemical analysis of its own chemical laboratory and was compared with the values of the chemical laboratory of the Norilsk mining and smelting hub. The initial working solution had a mineral content similar to that of mineralized drinking water at pH7.0 and flowed through the capillaries in the material to the surface. The solution that reached the surface was removed for extraction. The useful component content of the flotation tailings in the column was monitored by serial geochemical analysis during the experiment by the method [14], which showed that the exchangeable fraction consisted of readily water-soluble compounds and accounted for the largest percent of the noble metal species (31–46%). Crystalline Fe and Mn oxides constituted the second largest fraction of the tailings (20–30%). The copper, nickel, and cobalt sulfide mineral contents were in the range of 13–27% and, together with the oxide phases, accounted for 43–61% of their total contents. The nonferrous metal content of the exchangeable fraction ranged from 4 to 10% (Figure 2). During the entire experiment, which was conducted for 15 months, the level of water was at the same level using a Mariotte vessel to evaluate fluid kinetics over time. The water solution at the surface was periodically analyzed for Cu, Ni, Co, Pt, Pd, and Au. In addition to these experiments, experiments in which an absorbent layer was placed on the surface were performed. This layer was designed to collect the product solution. A

As for technogenic formations, the evaporation barriers can be helpful for purposeful concentration of components in tailing dumps to mitigate the environmental load. The presence of salts with different solubility in solutions at evaporation barriers makes it possible their selective extraction. The filtration type of natural deposits plays an important role as a mineral source of minerals. Geological processes of filtration mass transfer formed quite a few deposits with a rich content of

In geological filtration processes, the main solvent and main carrier is water and aqueous solutions of salts. The possibilities of water mass transfer of useful components for low concentrations in the field of mining and hydrometallurgy in the process of upward capillary movement were carried out in the conditions of an array of separate wastes from the enrichment of nonferrous and noble metal ores. Low content of nonferrous and noble metals in tailings can identify the diffuse distribution of components in the bowels of the Earth. In addition, the mining industry has created a huge amount of waste enrichment. All of them are located on the surface of the Earth and have an area many times larger than the area of the deposits themselves. The overwhelming part of the man-made mining waste has a high degree of danger. The total reserves of useful components in industrial waste are several times higher than the proven reserves in the bowels of the Earth. Carrying out extraction is currently unprofitable due to its low content. There is a great temptation to find and launch the natural process of structural and material transformation of the array, which forms the concentration zones of useful components from the diffuse state that will be profitable for the existing technological level. This approach will make a profit and eliminate toxic environmental pollution. With the application of this solution, experimental studies of the ascending capillary movement of aqueous solutions of the soil layer near the surface were carried out. Nature uses this process extensively and suggests a variety of technological

The mineralogical composition of the ore and the leaching reagent properties control the transfer kinetics of useful species between the solid and liquid phases, demonstrating the applicability and efficacy of leaching under specific conditions. In addition to the dissolution of mineral materials and its movement in the column and precipitation of valuable compounds in the column, the kinetics and mass transfer direction are also important parameters in p leaching technology. To assess the applicability of the natural mechanism, only water and aqueous solutions of salts were used in technological solutions. The upward velocity of the fluid flow depends on the pressure gradient, which is the driving force of in situ leaching.

Drinking mineralization water was used in mass exchange experimental studies. The results of studies have been obtained on the directional upward mass transfer of water-soluble salts of nonferrous and noble metals in the conditions of the tailing dump of mineral processing. The speed and variability over time of the directed capillary ascending rise of aqueous solutions were obtained for dispersed materials of enrichment waste. The kinetics of formation of water-soluble salts of nonferrous and noble metals was evaluated for the tailing dump. This process is basic of the water leaching for enrichment waste. The experiments were performed using the setup shown in Figure 1. The core polycarbonate column had a height of 1.5 m and a diameter of 110 mm. The bottom of the column was connected to a solution tank by

useful components [24].

Salt in the Earth

solutions.

84

2. Materials and methods

2.1 Capillary rise with fluid release of the column surface

the array, the temperature of the atmosphere, and humidity, taking into account the atmospheric pressure. The correlation between speed and temperature (from 18 to 30°С) and atmospheric humidity is proportional, and the coefficient is 0.70–0.85 (linear with varying atmospheric pressure). Experiment imitates condition migration and evaporation in summer in moderate climate regions of Russia. In other test conditions, the capillary motion of the solutions was intensified by heating of massif material up to 50°С in the upper zone and by subsurface blowing with a directed warm air jet at 5–7 m/sec to imitate speedy evaporation in hot climate conditions. The massif structure and variations of mineral content of material in experimental columns were comprehensively analyzed in terms of structure to evaluate salt precipitate distribution in the porous aeration zone. The theory of the salt precipitation phenomenon with crystallization from the capillary mouth is developed in [12]. Condition for

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

where a is evaporation rate, cm/s; D is coefficient of salt diffusion in a solution,

. Formula (1) determines the evaporation rate, which excess of concentration can cause crystallization in the capillary mouth. At the high evaporation rate, the solution concentration on the capillary surface due to size changes can exceed Csat limit and result in the formation of precipitate and salt crystals. As for solutions and low evaporation rates, the solution concentration nearby retreating meniscus Cm should

/s. The direct experimental verification

/s; L is capillary length, cm; Csat is concentration of saturated solution, g/cm<sup>3</sup>

In the course of long-term experiments on rising capillary filtration, the kinetic regularities of lifting solutions in the aeration zone were obtained (Figure 2). In the initial period of long-term experiments of ascending filtration of solutions, periods with a high rate of rise were recorded. The real velocity of the solution in the array repeatedly (up to 7 times) exceeded the calculated value (Darcy's law) [21, 22]. It is difficult to unambiguously explain this effect; most likely this may be due to the unsteady capillary flow of solutions due to a change in viscosity when external

The experiment showed us that at low evaporation rates (t ≤ 22°), the salt crystallization at surface was visually observed since 43 days from the start of the experiment. Figure 3a shows a dependence obtained for a solution motion rate at capillary hoist of concentrated nickel nitrate solution at the initial stage of the test. It is obvious that when the solution concentration does not exceed the saturated solution concentration and no crystallization is observed, the evaporation rate varies rather intensively, and evaporation mode can be estimated as unstable. Since the crystallization starts, the evaporation rate reduces in regular linear fashion. It is a long-lasting process at rather slow crystal growth, perhaps, due to the fact that a precipitate narrows capillary section, reduces actual evaporation surface, and diminishes the evaporation rate. Under the theory (2) the salt concentration nearby meniscus should be constant with probable partial dissolving of fresh-formed crystals. This, in its turn, increases evaporation rate and growth of concentration.

ð1Þ

;

ð2Þ

salting out can be approximately written as:

DOI: http://dx.doi.org/10.5772/intechopen.90121

and С<sup>0</sup> is initial solution concentration, g/cm<sup>3</sup>

remain constant and equal by theory [15]:

where β is an evaporation factor, cm2

factors are superimposed.

87

confirmed the correctness in terms of the theory [11].

cm2

Figure 2. Geochemical phase analysis of the metal distribution in the feedstock.

series of experiments (Figure 1) in which the starting feed solution level was decreased relative to the material surface height in the column were performed with the hygroscopic layer.

#### 2.2 Сapillary selective precipitation in the vapor barrier

To assess the distribution of sediment in the aeration zone in the quartz sand massif, nickel and cobalt nitrates of different concentrations were used. Experimental studies in which the feed solution level was either variable (level varied from bottom to surface) or fixed based on the calculated capillary rise height were performed in a pilot plant (Figure 1). The experiments were carried out with the supply of aqueous solutions of cobalt and nickel nitrates of different initial concentrations. The Co and Ni nitrate concentrations of the feed solution were varied to assess the distribution of salts on a surface of the aeration zone. The column was filled with quartz sand with a narrow particle size range, and the capillary radius of the material, which was chemically neutral for the Ni and Co nitrate solution, was calculated. The experiment was conducted over a 15-month period. During the entire experiment, the solution filtration speed and nitrate concentration distribution along the column height were estimated. The concentration distribution in the column material was determined by periodic testing. The effect of the column surface (atmospheric pressure, temperature, and humidity) on the upward fluid flow rate was also evaluated, which correlates with [13].

#### 3. Kinetic of filtration capillary moving

A series of experiments to study the kinetics of the ascending capillary rise of the solutions were studied on a laboratory bench. The zone of the capillary hoist of solution works as an aeration zone with variable humidity in height. The upward capillary mechanism of fluid and pressure gradient forces stimulates the solution hoist through pores to subsurface areas of the massif. When the solution passing through the aeration zone, the salt concentration grows due to water evaporation with followup. Precipitation solid phase in the porous mass medium [8]. The mass humidity varies from complete inside to atmospheric levels in the aeration zone. For this experiment the aqueous solutions nickel nitrate and cobalt have been used. Nitrates have different initial concentrations: from 0.34 Mol/l (unconcentrated) to 2.75 Mol/l, (close to extremely saturated concentration). Evaporation proceeded at different capillary hoist velocities. The rate of evaporation was controlled by the temperature of Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

the array, the temperature of the atmosphere, and humidity, taking into account the atmospheric pressure. The correlation between speed and temperature (from 18 to 30°С) and atmospheric humidity is proportional, and the coefficient is 0.70–0.85 (linear with varying atmospheric pressure). Experiment imitates condition migration and evaporation in summer in moderate climate regions of Russia. In other test conditions, the capillary motion of the solutions was intensified by heating of massif material up to 50°С in the upper zone and by subsurface blowing with a directed warm air jet at 5–7 m/sec to imitate speedy evaporation in hot climate conditions. The massif structure and variations of mineral content of material in experimental columns were comprehensively analyzed in terms of structure to evaluate salt precipitate distribution in the porous aeration zone. The theory of the salt precipitation phenomenon with crystallization from the capillary mouth is developed in [12]. Condition for salting out can be approximately written as:

$$a \le \frac{D}{L} \ln\left(\frac{c\_{\text{out}}}{c\_{\text{0}}}\right) \tag{1}$$

where a is evaporation rate, cm/s; D is coefficient of salt diffusion in a solution, cm2 /s; L is capillary length, cm; Csat is concentration of saturated solution, g/cm<sup>3</sup> ; and С<sup>0</sup> is initial solution concentration, g/cm<sup>3</sup> .

Formula (1) determines the evaporation rate, which excess of concentration can cause crystallization in the capillary mouth. At the high evaporation rate, the solution concentration on the capillary surface due to size changes can exceed Csat limit and result in the formation of precipitate and salt crystals. As for solutions and low evaporation rates, the solution concentration nearby retreating meniscus Cm should remain constant and equal by theory [15]:

$$\frac{\mathcal{L}\_m}{\mathcal{L}\_0} = 1 + \left(\frac{\pi \mathcal{P}}{D}\right)^{1/2} \tag{2}$$

where β is an evaporation factor, cm2 /s. The direct experimental verification confirmed the correctness in terms of the theory [11].

In the course of long-term experiments on rising capillary filtration, the kinetic regularities of lifting solutions in the aeration zone were obtained (Figure 2). In the initial period of long-term experiments of ascending filtration of solutions, periods with a high rate of rise were recorded. The real velocity of the solution in the array repeatedly (up to 7 times) exceeded the calculated value (Darcy's law) [21, 22]. It is difficult to unambiguously explain this effect; most likely this may be due to the unsteady capillary flow of solutions due to a change in viscosity when external factors are superimposed.

The experiment showed us that at low evaporation rates (t ≤ 22°), the salt crystallization at surface was visually observed since 43 days from the start of the experiment. Figure 3a shows a dependence obtained for a solution motion rate at capillary hoist of concentrated nickel nitrate solution at the initial stage of the test. It is obvious that when the solution concentration does not exceed the saturated solution concentration and no crystallization is observed, the evaporation rate varies rather intensively, and evaporation mode can be estimated as unstable. Since the crystallization starts, the evaporation rate reduces in regular linear fashion. It is a long-lasting process at rather slow crystal growth, perhaps, due to the fact that a precipitate narrows capillary section, reduces actual evaporation surface, and diminishes the evaporation rate. Under the theory (2) the salt concentration nearby meniscus should be constant with probable partial dissolving of fresh-formed crystals. This, in its turn, increases evaporation rate and growth of concentration.

series of experiments (Figure 1) in which the starting feed solution level was decreased relative to the material surface height in the column were performed with

To assess the distribution of sediment in the aeration zone in the quartz sand massif, nickel and cobalt nitrates of different concentrations were used. Experimental studies in which the feed solution level was either variable (level varied from bottom to surface) or fixed based on the calculated capillary rise height were performed in a pilot plant (Figure 1). The experiments were carried out with the supply of aqueous solutions of cobalt and nickel nitrates of different initial concentrations. The Co and Ni nitrate concentrations of the feed solution were varied to assess the distribution of salts on a surface of the aeration zone. The column was filled with quartz sand with a narrow particle size range, and the capillary radius of the material, which was chemically neutral for the Ni and Co nitrate solution, was calculated. The experiment was conducted over a 15-month period. During the entire experiment, the solution filtration speed and nitrate concentration distribution along the column height were estimated. The concentration distribution in the column material was determined by periodic testing. The effect of the column surface (atmospheric pressure, temperature, and humidity) on the upward fluid

A series of experiments to study the kinetics of the ascending capillary rise of the

solutions were studied on a laboratory bench. The zone of the capillary hoist of solution works as an aeration zone with variable humidity in height. The upward capillary mechanism of fluid and pressure gradient forces stimulates the solution hoist through pores to subsurface areas of the massif. When the solution passing through the aeration zone, the salt concentration grows due to water evaporation with followup. Precipitation solid phase in the porous mass medium [8]. The mass humidity varies from complete inside to atmospheric levels in the aeration zone. For this experiment the aqueous solutions nickel nitrate and cobalt have been used. Nitrates have different initial concentrations: from 0.34 Mol/l (unconcentrated) to 2.75 Mol/l, (close to extremely saturated concentration). Evaporation proceeded at different capillary hoist velocities. The rate of evaporation was controlled by the temperature of

2.2 Сapillary selective precipitation in the vapor barrier

Geochemical phase analysis of the metal distribution in the feedstock.

flow rate was also evaluated, which correlates with [13].

3. Kinetic of filtration capillary moving

the hygroscopic layer.

Figure 2.

Salt in the Earth

86

Figure 3.

The evaporation rate for aqueous Ni(NO3)2 solutions from porous material under different evaporation conditions: (a) t = 22°; (b) t = 52°, blowing velocity 5–7 m/s.

are blind pores with no outcrop to the surface. There are also through pores, providing prompt passage for the solution to the surface. Crystallization proceeds primarily nearby such pores. It is also found that in all the cases, including the intensified evaporation tests, salt used to crystallize in the mass periphery closer to the column walls (Figure 3b). Under the present test conditions, a threefold higher salt content is recorded in the periphery along the column walls as compared to the central experimental mass section. One of the reasons for this effect can be higher evaporation rate nearby column walls than that in the central section, thanks to higher solution motion velocity along the smooth column surface, confining the test mass. The established effect is in compliance with experimental data reported in [16]. A series of tests on measurement of intensity of the evaporation stream at the porous body surface revealed that at a rather small distance (about 2.5 mm) between porous material surface and an outlet of a hollow cylinder (that is correct for our tests), the evaporation stream is much higher in the periphery. In the tests with no heating, the evaporation stream is more homogenous at the surface with relatively uniform salt deposits (Figure 3a). The evaporation barrier in the aeration zone of mineral processing tailings serves as an integrated zone of valuable component accumulation under sustaining of "water mirror" at tailing mass and a directed ascending motion of solutions to the surface. The water evaporation from the surface contributes to the preliminary concentration of valuable components in the subsurface aeration zone of the tailing mass. The precipitation nature of watersoluble nickel and cobalt nitrates depends on how solutions pass the evaporation barrier. Distribution of nitrate concentration in the aeration zone depends on a solution motion velocity (evaporation rate). At low motion velocity, the evaporation zone develops in the depth of the mass displacing to the central section of the mass thanks to the decreasing diffusion of solution because the reduced humidity in the middle section of the mass height is compensated with inflow from more watersaturated lower section. This process results in the growth of solution concentration in lower and central sections of the mass aeration zone. The low solution motion velocity at indoor temperature and average humidity level does not provide the sharp zoning of salt crystallization. The salt crystallizes throughout the aeration zone with reduction in content from lower layers to the surface. This distribution is specific for both initial high- and low-concentrated solutions. As the moisturetransition rate increases, the evaporation area forms closer to the surface of the mass aeration zone, perhaps, due to the appearance of extra thermo-moistureconductivity phenomena. With the increase in evaporation intensity by heating or surface blowing, 61% of salt fed to the column tend to crystallize inside the mass pores starting from 7 to 10% from the surface, thus indicating the local higher nitrate concentration zone. It is established experimentally that it is possible to

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

The rate of the filtration upward flow of the aqueous solution.

DOI: http://dx.doi.org/10.5772/intechopen.90121

Figure 4.

89

Crystals increase in volume and the evaporation surface reduces again. This mode of variability in crystal volume lasts for a long term. For 2 years of the experimental work, the solution motion rate stabilizes at 0.4–0.7 mm/h level with possible linear reduction within 3–5% per year. The test results confirmed theoretical conclusions made in [14], viz., in the course of evaporation, the growth of solution concentration is compensated with diffusive diversion of electrolyte in the depth of a capillary, where the evaporation rate tends to lower on the regular basis. The reduction in evaporation intensity due to transfer of salt to surface layers is proven by experimental data on different solutions and materials [15]. To intensify subsurface crystallization requires increasing evaporation rate, therefore, the velocity of solution motion in capillaries of the mass according to Formula (1). In the tests this effect was gained by raising the temperature of a mass material up to 50–52°С with blowing of a warm air jet toward the mass surface. These parameters contribute to the growth up to 3–4 mm/h of the solution transition velocity to the surface; this is 5–10 times higher than the solution motion velocity under conventional test conditions. After a precipitate is formed and crystallized in the capillaries, the evaporation rate used to lower negligibly (Figure 3b). The crystals appear at the mass surface in 7 days, and their further growth remains intensive even after the feeding of the solution is canceled. In 10 days from the test launch, the most portion (80%) of salt fed to the column is found in a crystallized state.

It is apparent in Figure 3a that salt, crystallized from unconcentrated solution with no heating, distributes practically uniformly throughout the height of sand column. The effect of local concentrated salt cluster on subsurface aeration zone is not really detected. The growth of initial solution concentration conditions the precipitation of most portion of salt in the middle section of mass height. This effect may relate to the diffusion of solution in rock pores. Under the present experimental conditions at incomplete moisture saturation in pores in the middle section of column height, the diffusion of the solution declines, thus resulting in the growth of solution concentration in this section of the test mass. In tests with intensified evaporation distribution of precipitated nickel nitrate, salt appreciably differs by the zoning of precipitation. The highest concentration with high content of nickel and cobalt nitrates is detected at the surface of the test mass. Figure 3b presents the plot of zoning of nickel nitrate (2.75 Mol/l) distribution. The identical relationship is established for other solutions. It is established experimentally that the covering formed at the surface of the test mass is not regular, but with discrete crystal clusters (Figure 4). We suppose that it is mainly due to irregularities in the structure of a porous material. Pores distribute in a random manner, intercrossed; there

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

Figure 4. The rate of the filtration upward flow of the aqueous solution.

are blind pores with no outcrop to the surface. There are also through pores, providing prompt passage for the solution to the surface. Crystallization proceeds primarily nearby such pores. It is also found that in all the cases, including the intensified evaporation tests, salt used to crystallize in the mass periphery closer to the column walls (Figure 3b). Under the present test conditions, a threefold higher salt content is recorded in the periphery along the column walls as compared to the central experimental mass section. One of the reasons for this effect can be higher evaporation rate nearby column walls than that in the central section, thanks to higher solution motion velocity along the smooth column surface, confining the test mass. The established effect is in compliance with experimental data reported in [16]. A series of tests on measurement of intensity of the evaporation stream at the porous body surface revealed that at a rather small distance (about 2.5 mm) between porous material surface and an outlet of a hollow cylinder (that is correct for our tests), the evaporation stream is much higher in the periphery. In the tests with no heating, the evaporation stream is more homogenous at the surface with relatively uniform salt deposits (Figure 3a). The evaporation barrier in the aeration zone of mineral processing tailings serves as an integrated zone of valuable component accumulation under sustaining of "water mirror" at tailing mass and a directed ascending motion of solutions to the surface. The water evaporation from the surface contributes to the preliminary concentration of valuable components in the subsurface aeration zone of the tailing mass. The precipitation nature of watersoluble nickel and cobalt nitrates depends on how solutions pass the evaporation barrier. Distribution of nitrate concentration in the aeration zone depends on a solution motion velocity (evaporation rate). At low motion velocity, the evaporation zone develops in the depth of the mass displacing to the central section of the mass thanks to the decreasing diffusion of solution because the reduced humidity in the middle section of the mass height is compensated with inflow from more watersaturated lower section. This process results in the growth of solution concentration in lower and central sections of the mass aeration zone. The low solution motion velocity at indoor temperature and average humidity level does not provide the sharp zoning of salt crystallization. The salt crystallizes throughout the aeration zone with reduction in content from lower layers to the surface. This distribution is specific for both initial high- and low-concentrated solutions. As the moisturetransition rate increases, the evaporation area forms closer to the surface of the mass aeration zone, perhaps, due to the appearance of extra thermo-moistureconductivity phenomena. With the increase in evaporation intensity by heating or surface blowing, 61% of salt fed to the column tend to crystallize inside the mass pores starting from 7 to 10% from the surface, thus indicating the local higher nitrate concentration zone. It is established experimentally that it is possible to

Crystals increase in volume and the evaporation surface reduces again. This mode of variability in crystal volume lasts for a long term. For 2 years of the experimental work, the solution motion rate stabilizes at 0.4–0.7 mm/h level with possible linear reduction within 3–5% per year. The test results confirmed theoretical conclusions made in [14], viz., in the course of evaporation, the growth of solution concentration is compensated with diffusive diversion of electrolyte in the depth of a capillary, where the evaporation rate tends to lower on the regular basis. The reduction in evaporation intensity due to transfer of salt to surface layers is proven by experimental data on different solutions and materials [15]. To intensify subsurface crystallization requires increasing evaporation rate, therefore, the velocity of solution motion in capillaries of the mass according to Formula (1). In the tests this effect was gained by raising the temperature of a mass material up to 50–52°С with blowing of a warm air jet toward the mass surface. These parameters contribute to the growth up to 3–4 mm/h of the solution transition velocity to the surface; this is 5–10 times higher than the solution motion velocity under conventional test conditions. After a precipitate is formed and crystallized in the capillaries, the evaporation rate used to lower negligibly (Figure 3b). The crystals appear at the mass surface in 7 days, and their further growth remains intensive even after the feeding of the solution is canceled. In 10 days from the test launch, the most portion (80%)

The evaporation rate for aqueous Ni(NO3)2 solutions from porous material under different evaporation

It is apparent in Figure 3a that salt, crystallized from unconcentrated solution with no heating, distributes practically uniformly throughout the height of sand column. The effect of local concentrated salt cluster on subsurface aeration zone is not really detected. The growth of initial solution concentration conditions the precipitation of most portion of salt in the middle section of mass height. This effect may relate to the diffusion of solution in rock pores. Under the present experimental conditions at incomplete moisture saturation in pores in the middle section of column height, the diffusion of the solution declines, thus resulting in the growth of solution concentration in this section of the test mass. In tests with intensified evaporation distribution of precipitated nickel nitrate, salt appreciably differs by the zoning of precipitation. The highest concentration with high content of nickel and cobalt nitrates is detected at the surface of the test mass. Figure 3b presents the plot of zoning of nickel nitrate (2.75 Mol/l) distribution. The identical relationship is established for other solutions. It is established experimentally that the covering formed at the surface of the test mass is not regular, but with discrete crystal clusters (Figure 4). We suppose that it is mainly due to irregularities in the structure of a porous material. Pores distribute in a random manner, intercrossed; there

of salt fed to the column is found in a crystallized state.

conditions: (a) t = 22°; (b) t = 52°, blowing velocity 5–7 m/s.

Figure 3.

Salt in the Earth

88

control the processes of precipitation and crystallization of salts and to localize delivery of soluble salts to the mass surface with their respective lower concentration in the inner mass layers by regulating the intensity of solution motion in porous masses.

The capillary structure of massif has areas of "high-speed" pathways that allowed more rapid fluid flow and thus developed crystals more rapidly at their exit points on the surface. But instead of blocking evaporation at the pore, these crystals would boost the rate of evaporation by providing more surface area from which the fluid could evaporate. The increased evaporation would draw up fluid even faster along these high-speed pathways. In response, the flow through neighboring pathways would become slow, and the corresponding pores would be starved of salt. The salt crystallization in the salt mass on the surface forms capillaries commensurate with the capillaries of the soil. The height of the "salt mass" layer corresponds to the maximum height of the capillary rise of salt solutions with its own viscosity.

We have conducted experiments on the study of moisture transfer using media with different filtration characteristics: a layer of quartz sand and a layer of sand with a surface layer of hygroscopic material (microfiber). Investigated the suction effect of the material of the array above the boundary of the groundwater level. We studied the parameter of water capacity of a gyroscopic material with the aim of its possible use in calculations for production geotechnology. The influence of the hygroscopic layer on the surface of the changes in the kinetics of filtration and the groundwater level is established. The surface layer of a hygroscopic microfiber material increases the suction pressure by 100–250 mm and raises the water table by 40–45 mm.

whole peat layer. Humic acids are supposed to perform chemisorption concentration and provoke immobilization of cobalt nitrates in the form of complex compounds. Close-in-character cobalt nitrate distributions were obtained in the test with a geochemical barrier made of foamed vermiculite originated from Severny site of Low Angara area (Figure 5b, curve 4). A threefold increase in cobalt nitrate content was recorded in the sorption layer. In the background of neutral properties of vermiculite, the well-developed micro-, meso-, and macro-porosity of the interlayer material promotes concentration of cobalt nitrate in the layer. Velocities of solution motion in the aeration zone are closely related to atmosphere humidity (pair correlation factor r ≈ 0.8–0.9). The tendency to lower solution velocity 1 month later in a long-term test is traced. Variation in velocity of capillary ascend-

Distribution of salt throughout the column height under different evaporation conditions: (a) t = 22°; (1)

0.34 Mol/l; (2) 1.7 Mol/l; (3) 2.75 Mol/l; (b) t = 52°, blowing rate 5–7 m/s.

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

DOI: http://dx.doi.org/10.5772/intechopen.90121

ing of the solution in the test with lignite interlayer is shown in Figure 6.

Figure 6.

91

Figure 5.

(b) (3) peat; (4) vermiculite.

Investigation into the filtration of solutions through sorption collector being a component of the evaporating barrier in the aeration zone of the massif enabled to establish that in the course of ascending capillary lifting of the solution, the components redistributed with 1.5–3-fold concentration of cobalt nitrates in the neutral sorbent layer. The concentration in the sorption barrier does not depend on the sorption layer location in the aeration zone in the massif. In the tests with peat, the interlayers revealed feasibility to accumulate cobalt nitrate (nickel nitrate) from a solution with presumptive formation of a partially complex compound (approximately 10–12%). The sorption barrier made of marble with permeability, identical to permeability of the massif layer, does not actually generate the concentrating zone. Regularities of distribution in this case are similar to general regularities, specific for the evaporating barrier in the aeration zone. Sorption of cobalt and nickel nitrates in sorption barriers made of lignite and foamed vermiculite is not the

Distribution of Co(NO3)2 content in aeration zone in the column with an interlayer: (a) (1) marble; (2) coal;

Experimental evaluation is given for mineral preconcentration in a bed of a sorption collector in aeration zones from aqueous solutions of salts of low concentration useful components. Sorption collectors represented by interior layers of lignite, peat, marble, and vermiculite are included in an evaporation barrier installed in the subsurface zone of rock mass aeration in medium distance aeration zone in column (Figure 1). Migrating solution was aqueous solutions of salts of cobaltous and nickelous nitrates. The character of cobalt nitrate and nickel nitrate distribution is identical in all the tests. In view of this, the regularities of solely cobalt nitrate distribution are reported. Under conditions of bottom-up ascending of the test solution and its filtration through a marble sand layer, the distribution of cobalt nitrate content over the aeration zone height is close to linear and uniformly fading toward the surface (Figure 3a, curve 1).

Selective estimates of the influence of geochemical and sorption barriers on the kinetics and nature of the deposition of useful components in the indicated concentration zones were carried out experimentally. Layers of marble, vermiculite, brown coal, and peat were used in the aeration zone. The geochemical barrier made of a marble interlayer does not actually exhibit sorption properties and does not influence the character of cobalt nitrate distribution over the aeration zone height. In tests with bottom-up ascending of the solution through the aeration zone with the geochemical barrier made of lignite, the distribution of cobalt nitrate and nickel nitrate content is characterized with the increasing concentration of nitrates before the interlayer and nearby the upper boundary of lignite layer (Figure 5a, curve 2). The nitrate content linearly diminishes on the zone from the interlayer up to the surface. Cobalt nitrate content was not high at the surface of the column through the entire test. Lignite layer contributes to a partial reduction in cobalt content thanks to cobalt transition upward with ascending solution from lower layers. More than twofold rise of cobalt nitrate content was detected when the cobalt nitrate solution ascended through geochemical barrier made of Seibinsky peat (Figure 5b, curve 3). The higher cobalt nitrate content was recorded practically through the

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

Figure 5.

control the processes of precipitation and crystallization of salts and to localize delivery of soluble salts to the mass surface with their respective lower concentration in the inner mass layers by regulating the intensity of solution motion in porous

The capillary structure of massif has areas of "high-speed" pathways that allowed more rapid fluid flow and thus developed crystals more rapidly at their exit points on the surface. But instead of blocking evaporation at the pore, these crystals would boost the rate of evaporation by providing more surface area from which the fluid could evaporate. The increased evaporation would draw up fluid even faster along these high-speed pathways. In response, the flow through neighboring pathways would become slow, and the corresponding pores would be starved of salt. The salt crystallization in the salt mass on the surface forms capillaries commensurate with the capillaries of the soil. The height of the "salt mass" layer corresponds to the maximum height of the capillary rise of salt solutions with its own viscosity. We have conducted experiments on the study of moisture transfer using media with different filtration characteristics: a layer of quartz sand and a layer of sand with a surface layer of hygroscopic material (microfiber). Investigated the suction effect of the material of the array above the boundary of the groundwater level. We studied the parameter of water capacity of a gyroscopic material with the aim of its possible use in calculations for production geotechnology. The influence of the hygroscopic layer on the surface of the changes in the kinetics of filtration and the groundwater level is established. The surface layer of a hygroscopic microfiber material increases the suction pressure by 100–250 mm and raises the water table

Experimental evaluation is given for mineral preconcentration in a bed of a sorption collector in aeration zones from aqueous solutions of salts of low concentration useful components. Sorption collectors represented by interior layers of lignite, peat, marble, and vermiculite are included in an evaporation barrier installed in the subsurface zone of rock mass aeration in medium distance aeration zone in column (Figure 1). Migrating solution was aqueous solutions of salts of cobaltous and nickelous nitrates. The character of cobalt nitrate and nickel nitrate distribution is identical in all the tests. In view of this, the regularities of solely cobalt nitrate distribution are reported. Under conditions of bottom-up ascending of the test solution and its filtration through a marble sand layer, the distribution of cobalt nitrate content over the aeration zone height is close to linear and uniformly

Selective estimates of the influence of geochemical and sorption barriers on the kinetics and nature of the deposition of useful components in the indicated concentration zones were carried out experimentally. Layers of marble, vermiculite, brown coal, and peat were used in the aeration zone. The geochemical barrier made of a marble interlayer does not actually exhibit sorption properties and does not influence the character of cobalt nitrate distribution over the aeration zone height. In tests with bottom-up ascending of the solution through the aeration zone with the geochemical barrier made of lignite, the distribution of cobalt nitrate and nickel nitrate content is characterized with the increasing concentration of nitrates before the interlayer and nearby the upper boundary of lignite layer (Figure 5a, curve 2). The nitrate content linearly diminishes on the zone from the interlayer up to the surface. Cobalt nitrate content was not high at the surface of the column through the entire test. Lignite layer contributes to a partial reduction in cobalt content thanks to cobalt transition upward with ascending solution from lower layers. More than twofold rise of cobalt nitrate content was detected when the cobalt nitrate solution ascended through geochemical barrier made of Seibinsky peat (Figure 5b, curve 3). The higher cobalt nitrate content was recorded practically through the

masses.

Salt in the Earth

by 40–45 mm.

90

fading toward the surface (Figure 3a, curve 1).

Distribution of salt throughout the column height under different evaporation conditions: (a) t = 22°; (1) 0.34 Mol/l; (2) 1.7 Mol/l; (3) 2.75 Mol/l; (b) t = 52°, blowing rate 5–7 m/s.

whole peat layer. Humic acids are supposed to perform chemisorption concentration and provoke immobilization of cobalt nitrates in the form of complex compounds. Close-in-character cobalt nitrate distributions were obtained in the test with a geochemical barrier made of foamed vermiculite originated from Severny site of Low Angara area (Figure 5b, curve 4). A threefold increase in cobalt nitrate content was recorded in the sorption layer. In the background of neutral properties of vermiculite, the well-developed micro-, meso-, and macro-porosity of the interlayer material promotes concentration of cobalt nitrate in the layer. Velocities of solution motion in the aeration zone are closely related to atmosphere humidity (pair correlation factor r ≈ 0.8–0.9). The tendency to lower solution velocity 1 month later in a long-term test is traced. Variation in velocity of capillary ascending of the solution in the test with lignite interlayer is shown in Figure 6.

Investigation into the filtration of solutions through sorption collector being a component of the evaporating barrier in the aeration zone of the massif enabled to establish that in the course of ascending capillary lifting of the solution, the components redistributed with 1.5–3-fold concentration of cobalt nitrates in the neutral sorbent layer. The concentration in the sorption barrier does not depend on the sorption layer location in the aeration zone in the massif. In the tests with peat, the interlayers revealed feasibility to accumulate cobalt nitrate (nickel nitrate) from a solution with presumptive formation of a partially complex compound (approximately 10–12%). The sorption barrier made of marble with permeability, identical to permeability of the massif layer, does not actually generate the concentrating zone. Regularities of distribution in this case are similar to general regularities, specific for the evaporating barrier in the aeration zone. Sorption of cobalt and nickel nitrates in sorption barriers made of lignite and foamed vermiculite is not the

#### Figure 6.

Distribution of Co(NO3)2 content in aeration zone in the column with an interlayer: (a) (1) marble; (2) coal; (b) (3) peat; (4) vermiculite.

same. Nevertheless, their content in sorption layers exceeds two to three times nitrate content in the aeration zone free from sorption interlayers. The technological potential of sorption interlayers being a component of evaporating barriers of the aeration zone proves the reasonability to apply them as a preconcentration stage. Artificial sorption and evaporating barriers mounted in the way of solution motion make it possible to enrich the material of the sorption barrier with a valuable component with its feasible recovery in follow-up processing circuits. Application of sorption and geochemical barriers for the rising flow of fluids warranted performance deposition and accumulation of salts in the barriers.

upward capillary leaching process can be controlled. For estimation of some

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

(17, 40, 63 cm). The experiment was ran in two stages: water washing for 2.5 months and weak acid solution washing for same months. Daily, the contact solution was sampled, and chemical composition of the samples was analyzed using mass-spectrometer Agilent 7500 IGPMS. The content of Cu, Ni, Co, Fe, Mg, Pt, Pd, and Au was under control. Phase compositions of mineral forms were determined by geochemical analysis [10] of samples from the top, middle, and bottom layers of the process column. The initial geochemical analysis is presented in Figure 2. Mineralogical analysis of original material showed that the water-soluble forms made up the major part of the precious metals (31–46%), and the next largest was the part of crystal iron and manganese oxides (20–30%). Copper, nickel, and cobalt were in the form of sulfide minerals (43–61%); oxide phases were 13–27%. Exchange phases

The tailing sample 5500 cm3 was placed in the cylindrical process column. The process solution was fed from below of the column; the solution was drinking water with рH 7.0 and acid water with рН 3.0 The column was equipped with branch tubes to sample the solution after filtration through different layers of solid phase

The test with drinking water for 2.5 months revealed that nonferrous and precious metals are prone to transit to a water-soluble exchangeable phase from the old tailing material. The transition of precious metals to the exchangeable phase runs no more intensively as compared to copper, nickel, and cobalt. Very weak partial dissolution of precious metals and their transition to the solution were established: gold and platinum up to 0.0006 mg/l and palladium up to 0.018 mg/l. The maximum content in the production solution was recorded for Au on the 5–7th days of activation, for Pt and Pd on the 2nd–3rd days with the further concentration decrease of the said components in the production solution. Redeposited mineral forms of precious metals contained water-soluble forms (9–17% gold and platinum, 5–8% palladium), iron oxide forms (26–53% platinum and 16–55% palladium), and organic matter forms (to 50% gold, to 17% platinum and palladium) as shown in Figure 1. Transfer of precious metals in the exchange form causes secondary geochemical processes when precious metals can go to amorphous oxides. That was observed experimentally: to 39% palladium and to 16% gold and platinum passed into amorphous oxides. Distribution of precious metals in the phase forms is different at different check levels heightwise the column of the tailings. For Pt in the top and middle layers, 50% are oxide forms, and the bottom layer is mainly carbonated. Pd oxide forms prevail in any layer. Gold from 31 to 50% is bound to organic matter forms and from 14 to 32%—to oxides. The water-washed nonferrous metal distribution in mineral forms is nearly identical in the tailings' column layers. There are almost no soluble forms, except for a few in the top layer (to 3%). In the middle and bottom layers, 54–71% nonferrous metals occur in sulfide and metal forms; in the top layer, there are few sulfides and more carbonates and sulfates (29–36%) and oxide phases (20–30%). There is low transfer of nonferrous metals to the exchange phase because these metals occur in the original material in weak-soluble forms of sulfide and oxides, which prevents from the redistribution. A low content of copper, cobalt, and nickel ions in the solution, mg/l: Cu up to 1.8, Сo up to 0.11, and Ni up to 4.1, is explained by the fact that they are present in the initial material in the hardly soluble form as sulfides and oxides, thus hampering their redistribution. Migration capabilities of copper, nickel, and cobalt species are extremely low in an actually neutral aqueous medium. It is found that with the increase in time of percolation through a tailing layer, the content of copper, cobalt, and nickel tends to grow in the solution with the respective correlation versus iron content in the solution. This fact justifies the statement that nonferrous metals (copper and cobalt

main parameters, the laboratory experiments were made.

DOI: http://dx.doi.org/10.5772/intechopen.90121

contained 4–10% of precious metals.

93

#### 4. Upward capillary leaching

The evaporation from the surface forms a capillary ascending rise of groundwater from the bowels. The groundwater contains water-soluble salts and passes by capillary flow through the aeration zone of the massif. When water evaporates into the atmosphere, all mineralization is retained and accumulates in the aeration zone and on the surface. This very powerful natural mechanism for solution flow through a column enables upward vertical movement due to the pressure gradient between the surface and the fluid level in the column. We see this mechanism as the main one for the formation of concentration zones on the surface of such man-made objects as tailing dumps. The water that evaporates from the solid surface into the atmosphere leads to the formation of this pressure gradient. The upward fluid flow rate is controlled by all the forces in the capillary system and the humidity. Water evaporation from the solution increases the concentrations of the useful mineral compounds along the direction of flow in the surface aeration zone. Here is a powerful natural method for the upward movement of solutions from the groundwater horizon to the surface. This very powerful natural mechanism for solution flow through a massif enables upward vertical movement due to the pressure gradient between the surface and the fluid level in this distance. Water evaporates from the solid surface into the atmosphere leads to the formation of this pressure gradient. The upward fluid flow rate is controlled by all the forces in the capillary system and the humidity. In agricultural areas, this phenomenon leads to harmful soil salinization. The lifting of salts in the solution to the surface and their deposition can be used in technological leaching solutions. This phenomenon has not yet been used in the leaching process and is just getting ready to become one. Solutions with a low concentration of salts are very mobile, have high fluidity, and are able to quickly move a useful component to the surface. They can move upward through the evaporation zone to the surface by capillary action. Water evaporation from the solution increases the concentrations of the useful mineral compounds along the direction of flow in the surface aeration zone. When these concentrations exceed the solubility limits, the useful compounds are deposited in the column. Different mineral compounds have different concentration limits in the solution; therefore, the compounds can be selectively precipitated at different heights in the aeration zone. Essentially, the aeration zone acts as a natural evaporation barrier. Selective enrichment can be achieved due to the physical nature of the capillary action in the upward direction and the deposition surface. Partial laws for the upward capillary rise of solutions were formulated in studies of agricultural soils. The soil particle size and stratification structure were shown to influence the capillary action considerably. To leach valuable compounds in situ, their velocity and the large contact surface area between the solution and solid material in the capillary system are important. These parameters must be optimized to ensure that the extraction is complete and the

#### Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

upward capillary leaching process can be controlled. For estimation of some main parameters, the laboratory experiments were made.

The tailing sample 5500 cm3 was placed in the cylindrical process column. The process solution was fed from below of the column; the solution was drinking water with рH 7.0 and acid water with рН 3.0 The column was equipped with branch tubes to sample the solution after filtration through different layers of solid phase (17, 40, 63 cm). The experiment was ran in two stages: water washing for 2.5 months and weak acid solution washing for same months. Daily, the contact solution was sampled, and chemical composition of the samples was analyzed using mass-spectrometer Agilent 7500 IGPMS. The content of Cu, Ni, Co, Fe, Mg, Pt, Pd, and Au was under control. Phase compositions of mineral forms were determined by geochemical analysis [10] of samples from the top, middle, and bottom layers of the process column. The initial geochemical analysis is presented in Figure 2. Mineralogical analysis of original material showed that the water-soluble forms made up the major part of the precious metals (31–46%), and the next largest was the part of crystal iron and manganese oxides (20–30%). Copper, nickel, and cobalt were in the form of sulfide minerals (43–61%); oxide phases were 13–27%. Exchange phases contained 4–10% of precious metals.

The test with drinking water for 2.5 months revealed that nonferrous and precious metals are prone to transit to a water-soluble exchangeable phase from the old tailing material. The transition of precious metals to the exchangeable phase runs no more intensively as compared to copper, nickel, and cobalt. Very weak partial dissolution of precious metals and their transition to the solution were established: gold and platinum up to 0.0006 mg/l and palladium up to 0.018 mg/l. The maximum content in the production solution was recorded for Au on the 5–7th days of activation, for Pt and Pd on the 2nd–3rd days with the further concentration decrease of the said components in the production solution. Redeposited mineral forms of precious metals contained water-soluble forms (9–17% gold and platinum, 5–8% palladium), iron oxide forms (26–53% platinum and 16–55% palladium), and organic matter forms (to 50% gold, to 17% platinum and palladium) as shown in Figure 1. Transfer of precious metals in the exchange form causes secondary geochemical processes when precious metals can go to amorphous oxides. That was observed experimentally: to 39% palladium and to 16% gold and platinum passed into amorphous oxides. Distribution of precious metals in the phase forms is different at different check levels heightwise the column of the tailings. For Pt in the top and middle layers, 50% are oxide forms, and the bottom layer is mainly carbonated. Pd oxide forms prevail in any layer. Gold from 31 to 50% is bound to organic matter forms and from 14 to 32%—to oxides. The water-washed nonferrous metal distribution in mineral forms is nearly identical in the tailings' column layers. There are almost no soluble forms, except for a few in the top layer (to 3%). In the middle and bottom layers, 54–71% nonferrous metals occur in sulfide and metal forms; in the top layer, there are few sulfides and more carbonates and sulfates (29–36%) and oxide phases (20–30%). There is low transfer of nonferrous metals to the exchange phase because these metals occur in the original material in weak-soluble forms of sulfide and oxides, which prevents from the redistribution. A low content of copper, cobalt, and nickel ions in the solution, mg/l: Cu up to 1.8, Сo up to 0.11, and Ni up to 4.1, is explained by the fact that they are present in the initial material in the hardly soluble form as sulfides and oxides, thus hampering their redistribution. Migration capabilities of copper, nickel, and cobalt species are extremely low in an actually neutral aqueous medium. It is found that with the increase in time of percolation through a tailing layer, the content of copper, cobalt, and nickel tends to grow in the solution with the respective correlation versus iron content in the solution. This fact justifies the statement that nonferrous metals (copper and cobalt

same. Nevertheless, their content in sorption layers exceeds two to three times nitrate content in the aeration zone free from sorption interlayers. The technological potential of sorption interlayers being a component of evaporating barriers of the aeration zone proves the reasonability to apply them as a preconcentration stage. Artificial sorption and evaporating barriers mounted in the way of solution motion make it possible to enrich the material of the sorption barrier with a valuable component with its feasible recovery in follow-up processing circuits. Application of sorption and geochemical barriers for the rising flow of fluids warranted perfor-

The evaporation from the surface forms a capillary ascending rise of groundwater from the bowels. The groundwater contains water-soluble salts and passes by capillary flow through the aeration zone of the massif. When water evaporates into the atmosphere, all mineralization is retained and accumulates in the aeration zone and on the surface. This very powerful natural mechanism for solution flow through a column enables upward vertical movement due to the pressure gradient between the surface and the fluid level in the column. We see this mechanism as the main one for the formation of concentration zones on the surface of such man-made objects as tailing dumps. The water that evaporates from the solid surface into the atmosphere leads to the formation of this pressure gradient. The upward fluid flow rate is controlled by all the forces in the capillary system and the humidity. Water evaporation from the solution increases the concentrations of the useful mineral compounds along the direction of flow in the surface aeration zone. Here is a powerful natural method for the upward movement of solutions from the groundwater horizon to the surface. This very powerful natural mechanism for solution flow through a massif enables upward vertical movement due to the pressure gradient between the surface and the fluid level in this distance. Water evaporates from the solid surface into the atmosphere leads to the formation of this pressure gradient. The upward fluid flow rate is controlled by all the forces in the capillary system and the humidity. In agricultural areas, this phenomenon leads to harmful soil salinization. The lifting of salts in the solution to the surface and their deposition can be used in technological leaching solutions. This phenomenon has not yet been used in the leaching process and is just getting ready to become one. Solutions with a low concentration of salts are very mobile, have high fluidity, and are able to quickly move a useful component to the surface. They can move upward through the evaporation zone to the surface by capillary action. Water evaporation from the solution increases the concentrations of the useful mineral compounds along the direction of flow in the surface aeration zone. When these concentrations exceed the solubility limits, the useful compounds are deposited in the column. Different mineral compounds have different concentration limits in the solution; therefore, the compounds can be selectively precipitated at different heights in the aeration zone. Essentially, the aeration zone acts as a natural evaporation barrier. Selective enrichment can be achieved due to the physical nature of the capillary action in the upward direction and the deposition surface. Partial laws for the upward capillary rise of solutions were formulated in studies of agricultural soils. The soil particle size and stratification structure were shown to influence the capillary action considerably. To leach valuable compounds in situ, their velocity and the large contact surface area between the solution and solid material in the capillary system are important. These parameters must be optimized to ensure that the extraction is complete and the

mance deposition and accumulation of salts in the barriers.

4. Upward capillary leaching

Salt in the Earth

92

in a greater degree and nickel in a less degree) are prone to adsorb onto iron compounds, for example, on its hydroxides (III), and to transit to the solution with decomposition of iron-containing minerals: pyrrhotite and chalcopyrite with the release of iron species into the solution. The acidity of the solution in the middle part of the column increased to pH 3.0 after 2.5 weeks of filtration. At the top of the column, the acidity was close to normal (pH 6.0) until the end of the third week. Geochemical phase analysis shows significant changes in the massif structure (Figure 7). This effect is due to water filtration. Phase transformations of mineral compounds in the bowels of the Earth are due to the occurrence of geological processes of hypergenesis. The geological natural process of hypergenesis in the presence of filtration does not stop, and even more than that, it proceeds more intensively than when there is no access of oxygen to the massif.

in the presence of crystalline and sulfide phase states in the original massif. Redistribution intensity of metal in mineral phases is different with different thickness of filtering layers and with different treatment solutions. After the water washing, epigenetic minerals contain precious metals in the form of organic compounds and iron oxide phases and a few soluble and ion exchange forms (9–17% gold and platinum, 5–8% palladium). After filtration of the weak acid solution, the amount of soluble forms remains the same, but metal passing into solution is higher. Passing of metals into solution correlates with the thickness of the filtering layer: under the water treatment, the thicker is the filtering layer, the less is the metal passing into the solution; under the weak acid solution treatment, the metal passing into solution is higher in the thicker filtering layer. The occurrence of soluble forms of precious metals inspires further research toward the creation of brand-new methods of commercial mineral recovery from processing waste. One of the methods may be the method of leaching by ecological nonaggressive solutions. The test experiments have shown recoverability of 28.4% gold and 3.9% platinum using the weak acid treatment solution. The water leaching approach requires smaller investment and is

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

DOI: http://dx.doi.org/10.5772/intechopen.90121

Experimental studies with the upward movement of solutions in the array, at the water base, are aimed at carrying out a fundamental assessment of the technological applicability of direct concentration formation in the near-surface place of the massifs. The development option for the natural part of the field can be formed along the directions of concentration of mineralization on the surface of the massif, in the near-surface zone of the evaporation barrier, hygroscopic accumulation, and collection of the production solution from the surface area of the massif. In addition, there may be new approaches with geochemical and physical barriers to the upward capillary movement of solutions. The basis of such technological options for the extraction of useful components lies in the use of the hydrogeological natural

Figure 8 shows the scheme of surface collection of the production solution with rising capillary filtration for an enrichment waste massif as a probable technological

The content of useful components in the places of storage of the wastes is very low, and it is unprofitable to extract them by existing technology. The natural effect of the ascending capillary movement of fluids in the near-surface layer of the Earth's subsoil array allows preliminary selective concentration of useful and harmful components. When the zones of accumulated concentration of the useful component are created, the technology allows extracting profitably

ecologically friendly. This research direction seems advisable.

variant of the upward capillary lifting of the solution.

Geochemical phase analysis of the metals at the end of the experiment.

resource of the Earth's interior.

(Figure 9).

Figure 8.

95

With an increase in the acidity of the medium, a more intense transition of nonferrous metals into the solution should be associated. Due to the effect of changing the acidity of the fluids during the supply of neutral water, experimental studies were carried out with the supply of initially weakly acidic water.

Pretreatment of the sampled material by acid solution to рН = 3 also changes the composition of nonferrous and precious metals subject to the thickness of the filtering layer. In this case, the correlation is direct unlike the first stage of the experiments. For thicker filtering layers, it is typical that the solutions have higher average values of the commercial mineral contents. The solutions sampled from layer 85.5 cm thick have nickel and cobalt contents 1.5 times higher than the solutions sampled from layer 40.5 cm in thickness. The platinum and gold contents change three times, while the copper and palladium contents are scarcely changed. The metal recovery in solution results obtained on the samples after the water washing and acid solution washing for 90 days is significantly different. The major portion (75%) of the soluble ion exchange forms of precious metals has gone to solution or redeposited in the epigenetic mineral forms. This share for nonferrous metals is 50–75%. Thus, water-soluble forms of nonferrous and precious metals are mobile, and their water leaching is quite feasible. The higher recovery is observed for gold (24%) and platinum (3.9%) in the filtering layer of tailings 85.5 cm thick, with the acid water pretreatment. Dissolution of the components with the weak acid solution is more intensive than with the water drink solution. The weak acid solution pretreatment improves copper, nickel, cobalt, and palladium recovery 4–9 times and platinum and gold recovery 500–4000 times. The analysis of redistribution of nonferrous and platinum group metals and gold in different mineral phases has confirmed the assumption on soluble forms of nonferrous and precious metals to appear in weathered aged tailings; some of the water-soluble forms go to solution and some redeposit as epigenetic minerals. Passing into solution intensifies in a weak acid solution with pH = 3. A weak acid solution forms independently in massif

#### Figure 7.

Variations in velocity of Co(NO3)2 solution filtration with geochemical lignite barrier in terms of variations in atmosphere humidity during the test: (1) percolation velocity; (2) humidity.

#### Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

in the presence of crystalline and sulfide phase states in the original massif. Redistribution intensity of metal in mineral phases is different with different thickness of filtering layers and with different treatment solutions. After the water washing, epigenetic minerals contain precious metals in the form of organic compounds and iron oxide phases and a few soluble and ion exchange forms (9–17% gold and platinum, 5–8% palladium). After filtration of the weak acid solution, the amount of soluble forms remains the same, but metal passing into solution is higher. Passing of metals into solution correlates with the thickness of the filtering layer: under the water treatment, the thicker is the filtering layer, the less is the metal passing into the solution; under the weak acid solution treatment, the metal passing into solution is higher in the thicker filtering layer. The occurrence of soluble forms of precious metals inspires further research toward the creation of brand-new methods of commercial mineral recovery from processing waste. One of the methods may be the method of leaching by ecological nonaggressive solutions. The test experiments have shown recoverability of 28.4% gold and 3.9% platinum using the weak acid treatment solution. The water leaching approach requires smaller investment and is ecologically friendly. This research direction seems advisable.

Experimental studies with the upward movement of solutions in the array, at the water base, are aimed at carrying out a fundamental assessment of the technological applicability of direct concentration formation in the near-surface place of the massifs. The development option for the natural part of the field can be formed along the directions of concentration of mineralization on the surface of the massif, in the near-surface zone of the evaporation barrier, hygroscopic accumulation, and collection of the production solution from the surface area of the massif. In addition, there may be new approaches with geochemical and physical barriers to the upward capillary movement of solutions. The basis of such technological options for the extraction of useful components lies in the use of the hydrogeological natural resource of the Earth's interior.

Figure 8 shows the scheme of surface collection of the production solution with rising capillary filtration for an enrichment waste massif as a probable technological variant of the upward capillary lifting of the solution.

The content of useful components in the places of storage of the wastes is very low, and it is unprofitable to extract them by existing technology. The natural effect of the ascending capillary movement of fluids in the near-surface layer of the Earth's subsoil array allows preliminary selective concentration of useful and harmful components. When the zones of accumulated concentration of the useful component are created, the technology allows extracting profitably (Figure 9).

Figure 8. Geochemical phase analysis of the metals at the end of the experiment.

in a greater degree and nickel in a less degree) are prone to adsorb onto iron compounds, for example, on its hydroxides (III), and to transit to the solution with decomposition of iron-containing minerals: pyrrhotite and chalcopyrite with the release of iron species into the solution. The acidity of the solution in the middle part of the column increased to pH 3.0 after 2.5 weeks of filtration. At the top of the column, the acidity was close to normal (pH 6.0) until the end of the third week. Geochemical phase analysis shows significant changes in the massif structure (Figure 7). This effect is due to water filtration. Phase transformations of mineral compounds in the bowels of the Earth are due to the occurrence of geological processes of hypergenesis. The geological natural process of hypergenesis in the presence of filtration does not stop, and even more than that, it proceeds more

Salt in the Earth

intensively than when there is no access of oxygen to the massif.

Figure 7.

94

studies were carried out with the supply of initially weakly acidic water.

composition of nonferrous and precious metals subject to the thickness of the filtering layer. In this case, the correlation is direct unlike the first stage of the experiments. For thicker filtering layers, it is typical that the solutions have higher average values of the commercial mineral contents. The solutions sampled from layer 85.5 cm thick have nickel and cobalt contents 1.5 times higher than the solutions sampled from layer 40.5 cm in thickness. The platinum and gold contents change three times, while the copper and palladium contents are scarcely changed. The metal recovery in solution results obtained on the samples after the water washing and acid solution washing for 90 days is significantly different. The major portion (75%) of the soluble ion exchange forms of precious metals has gone to solution or redeposited in the epigenetic mineral forms. This share for nonferrous metals is 50–75%. Thus, water-soluble forms of nonferrous and precious metals are mobile, and their water leaching is quite feasible. The higher recovery is observed for gold (24%) and platinum (3.9%) in the filtering layer of tailings 85.5 cm thick, with the acid water pretreatment. Dissolution of the components with the weak acid solution is more intensive than with the water drink solution. The weak acid solution pretreatment improves copper, nickel, cobalt, and palladium recovery 4–9 times and platinum and gold recovery 500–4000 times. The analysis of redistribution of nonferrous and platinum group metals and gold in different mineral phases has confirmed the assumption on soluble forms of nonferrous and precious metals to appear in weathered aged tailings; some of the water-soluble forms go to solution and some redeposit as epigenetic minerals. Passing into solution intensifies in a weak acid solution with pH = 3. A weak acid solution forms independently in massif

With an increase in the acidity of the medium, a more intense transition of nonferrous metals into the solution should be associated. Due to the effect of changing the acidity of the fluids during the supply of neutral water, experimental

Pretreatment of the sampled material by acid solution to рН = 3 also changes the

Variations in velocity of Co(NO3)2 solution filtration with geochemical lignite barrier in terms of variations in

atmosphere humidity during the test: (1) percolation velocity; (2) humidity.

metals from the bottom up to the direction of movement of aqueous solutions. In such a way, the carried out experiment with water as a leaching agent for moving water-soluble compounds of nonferrous metals in the massif of flotation tailings shows that the geological processes of hypergenesis allow the leaching by water to conduct a directed preliminary concentration of nonferrous metals near the surface. The conducted simple experiments with enrichment waste materials for the entire test period allowed more than 70% of water-soluble nonferrous metal salts to rise to the surface. The concentration of nonferrous metals in the surface layer rose and exceeded the values of the existing conditions. So the content of Ni, Co, and Cu in the aeration layer amounted to 0.11, 0.09, and 0.07%, respectively. This way allows the subsequent intensive extraction of useful components. To accumulate useful components in close proximity to the surface of the array, both physical barriers

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

DOI: http://dx.doi.org/10.5772/intechopen.90121

The nonferrous metals are constantly present in the aqueous solution throughout the entire experiment. The concentration of the salts of nonferrous metals in the solution is not the same at different levels of the massif. In the initial period of the experiment, the trend of decreases of all elements of nonferrous metals in the solution from the bottom-up takes place. In the final period of the experimental cycle, the concentration of nonferrous metals in the upper zone exceeds the concentration of the lower zone by a factor of 2–4. The mass exchange process of hypergenesis carries out a gradual redeposition of the salts of nonferrous metals from the bottom-up in the direction of movement of aqueous solutions. The concentration of the zone of nonferrous metals shifts in the direction of movement of aqueous solutions in the array. After 1.5 years of experiment, the concentration of water-soluble compounds of nonferrous metals moved to the surface. Such results allow us to propose technological schemes for preparing the deposit for development. This approach to the development of deposits is suitable for natural deposits with a low subgrade content of useful components in the massif. Also, this approach is applicable to technogenic objects, such as wastes of enrichment and warehouses of substandard ores. The basic schemes are given in the materials of this article. The such experiment with water as a leaching agent for moving water-soluble compounds of nonferrous metals in the massif of flotation tailings shows that the geological processes of hypergenesis allow the leaching by water to conduct a directed preliminary concentration of nonferrous metals near the surface. This way allows the subsequent intensive extraction of useful components. To accumulate useful components in close proximity to the surface of the array, both physical barriers (evaporation) and geochemical (sorption) barriers can be used.

The geochemical analysis of the material composition showed that the capillary water flow intensifies the process of hypergenesis and changes the ratio of the phase composition of nonferrous and noble metals. To the end of the experiment, the content of the sulfide phase is reduced by 80%, the carbonate phase is increased by 24%, and the oxide phase is increased by 41%. Such hypergene transformations increase the proportion of water-soluble salts and increase recovery by capillary

A more complete extraction of useful components from enrichment wastes will significantly reduce pollution of the groundwater and increase the natural attrac-

The presented studies, which are quite simple, made the first step toward the development of a new technology for the cultivation of mineral deposits with the

maximum use of natural processes for the transformation of the material

leaching.

97

composition in situ.

tiveness of the development territory.

(evaporation) and geochemical (sorption) barriers can be used.

Figure 9.

Technological scheme for extracting useful components by water leaching and filtration lifting with surface collection of the production solution. (1) waste massif; (2) aquifer; (3) catchment surface channels (hygroscopic material).

#### 5. Conclusion

The capillary leaching method is considered to be subsequently intensive and nontoxic to biota extraction of useful components. This way allows the subsequent intensive extraction of useful components. The mass exchange process in the capillary rise of hypergenesis carries out a gradual redeposition of the salts of nonferrous

#### Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

metals from the bottom up to the direction of movement of aqueous solutions. In such a way, the carried out experiment with water as a leaching agent for moving water-soluble compounds of nonferrous metals in the massif of flotation tailings shows that the geological processes of hypergenesis allow the leaching by water to conduct a directed preliminary concentration of nonferrous metals near the surface. The conducted simple experiments with enrichment waste materials for the entire test period allowed more than 70% of water-soluble nonferrous metal salts to rise to the surface. The concentration of nonferrous metals in the surface layer rose and exceeded the values of the existing conditions. So the content of Ni, Co, and Cu in the aeration layer amounted to 0.11, 0.09, and 0.07%, respectively. This way allows the subsequent intensive extraction of useful components. To accumulate useful components in close proximity to the surface of the array, both physical barriers (evaporation) and geochemical (sorption) barriers can be used.

The nonferrous metals are constantly present in the aqueous solution throughout the entire experiment. The concentration of the salts of nonferrous metals in the solution is not the same at different levels of the massif. In the initial period of the experiment, the trend of decreases of all elements of nonferrous metals in the solution from the bottom-up takes place. In the final period of the experimental cycle, the concentration of nonferrous metals in the upper zone exceeds the concentration of the lower zone by a factor of 2–4. The mass exchange process of hypergenesis carries out a gradual redeposition of the salts of nonferrous metals from the bottom-up in the direction of movement of aqueous solutions. The concentration of the zone of nonferrous metals shifts in the direction of movement of aqueous solutions in the array. After 1.5 years of experiment, the concentration of water-soluble compounds of nonferrous metals moved to the surface. Such results allow us to propose technological schemes for preparing the deposit for development. This approach to the development of deposits is suitable for natural deposits with a low subgrade content of useful components in the massif. Also, this approach is applicable to technogenic objects, such as wastes of enrichment and warehouses of substandard ores. The basic schemes are given in the materials of this article.

The such experiment with water as a leaching agent for moving water-soluble compounds of nonferrous metals in the massif of flotation tailings shows that the geological processes of hypergenesis allow the leaching by water to conduct a directed preliminary concentration of nonferrous metals near the surface. This way allows the subsequent intensive extraction of useful components. To accumulate useful components in close proximity to the surface of the array, both physical barriers (evaporation) and geochemical (sorption) barriers can be used.

The geochemical analysis of the material composition showed that the capillary water flow intensifies the process of hypergenesis and changes the ratio of the phase composition of nonferrous and noble metals. To the end of the experiment, the content of the sulfide phase is reduced by 80%, the carbonate phase is increased by 24%, and the oxide phase is increased by 41%. Such hypergene transformations increase the proportion of water-soluble salts and increase recovery by capillary leaching.

A more complete extraction of useful components from enrichment wastes will significantly reduce pollution of the groundwater and increase the natural attractiveness of the development territory.

The presented studies, which are quite simple, made the first step toward the development of a new technology for the cultivation of mineral deposits with the maximum use of natural processes for the transformation of the material composition in situ.

5. Conclusion

Figure 9.

Salt in the Earth

material).

96

The capillary leaching method is considered to be subsequently intensive and nontoxic to biota extraction of useful components. This way allows the subsequent intensive extraction of useful components. The mass exchange process in the capillary rise of hypergenesis carries out a gradual redeposition of the salts of nonferrous

Technological scheme for extracting useful components by water leaching and filtration lifting with surface collection of the production solution. (1) waste massif; (2) aquifer; (3) catchment surface channels (hygroscopic Salt in the Earth

### Author details

Alexandr Mikhailov\*, Ivan I. Vashlaev, Margarita Yu Kharitonova and Margarita L. Sviridova Russian Academy of Sciences, Institute of Chemistry and Chemical Technology, Siberian Branch, Krasnoyarsk, Russia

References

17(4):623-627

[1] Bartlett RW. Simulation of ore heap leaching using deterministic models. Hydrometallurgy. 1992;29(1–3):231-243

DOI: http://dx.doi.org/10.5772/intechopen.90121

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones

recharge in semiarid and arid regions. Hydrological Processes. 2006;20(15):

Evaporation from layered porous media. Journal of Geophysical Research: Solid Earth Journal of Geophysical Research:

[11] Ma Y, Feng S, Zhan H, Liu X, Su D, Kang S, et al. Water infiltration in layered soils with air entrapment: Modified green– Ampt. Model and experimental validation. Journal of Hydrologic Engineering. 2011;

Qualizza CV, Dobchuk BS. Evolution of

[13] Piatak NM, Seal RRII, Sanzolone RF, Lamothe PJ, Brown ZA. Preliminary results of sequential extraction

experiments for selenium on mine waste and stream sediments from Vermont, Maine, and New Zealand: U.S.

Geological Survey Report. 2006;1184:21

[14] Zolotarev PP. Evaporation of liquid from plane solution surface. Doklady

Akademii Nauk. 1966;168:21

Zhurnal. 1979;5(37):12

Mironov VA. Osmoticheskii

Tver: TGTU. 2007;4(78):15-21

[17] Veran-Tissoires S, Marcoux M, Prat M. Why salt clusters form on basement walls. Physics. 2012;5(15):13-20

[15] Tishkova PA, Churaev NV, Ershov AP. Evaporation rates for concentrated electrolyte solutions from thin capillaries. Inzhenerno-Fizicheskii

[16] Gamayunov NI, Gamayunov SN,

massoperenos (osmotic mass transport).

[10] Shokri N, Lehmann P, Or D.

Solid Earth. 2010;B06204:115

[12] Meiers GP, Barbour SL,

the hydraulic conductivity of reclamation covers over sodic/saline mining overburden. Journal of Geotechnical and Geoenvironmental Engineering. 2011;137(10):968-976

3335-3370

16(8):628-638

[2] Oddie TA, Bailey AW. Subsoil thickness effects on yield and soil water when reclaiming sodic minespoil. Journal of Environmental Quality. 1988;

[3] Purdy BG, MacDonald SE, Lieffers VJ. Naturally saline boreal communities as models for reclamation of saline oil sand tailings. Restoration

Ecology. 2005;13(4):667-677

2009;23(2):127-136

Reviews. 2013;1:21

1978;3(2):181-196

158(1):23-34

10(4):1309-1318

99

[4] Sadegh-Zadeh F, Seh-Bardan BJ, Samsuri AW, Mohammadi A, Chorom M, Yazdani GA. Saline soil reclamation by means of layered mulch. Arid Land Research and Management.

[5] Li X, Chang SX, Salifu KF. Soil texture and layering effects on water and salt dynamics in the presence of a water table: A review. Environmental

[6] Apostolidis CI, Distin PA. The kinetics of the sulphuric acid leaching of nickel and magnesium from reduction roasted serpentine. Hydrometallurgy.

[7] Antonijević MM, Dimitrijević MD,

Bogdanovic GD. Investigation of the possibility of copper recovery from the flotation tailings by acid leaching. Journal of Hazardous Materials. 2008;

[8] Shokri N, Salvucci GD. Evaporation from porous media in the presence of a water table. Vadose Zone Journal. 2011;

[9] Scanlon BR, Keese KE, Flint AL, Flint LE, Gaye CB, Edmunds WM, et al.

Global synthesis of groundwater

Stevanović ZO, Serbula SM,

\*Address all correspondence to: mag@icct.ru

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Upward Capillary Mass Transfer as a Process for Growing Concentration Zones DOI: http://dx.doi.org/10.5772/intechopen.90121

#### References

[1] Bartlett RW. Simulation of ore heap leaching using deterministic models. Hydrometallurgy. 1992;29(1–3):231-243

[2] Oddie TA, Bailey AW. Subsoil thickness effects on yield and soil water when reclaiming sodic minespoil. Journal of Environmental Quality. 1988; 17(4):623-627

[3] Purdy BG, MacDonald SE, Lieffers VJ. Naturally saline boreal communities as models for reclamation of saline oil sand tailings. Restoration Ecology. 2005;13(4):667-677

[4] Sadegh-Zadeh F, Seh-Bardan BJ, Samsuri AW, Mohammadi A, Chorom M, Yazdani GA. Saline soil reclamation by means of layered mulch. Arid Land Research and Management. 2009;23(2):127-136

[5] Li X, Chang SX, Salifu KF. Soil texture and layering effects on water and salt dynamics in the presence of a water table: A review. Environmental Reviews. 2013;1:21

[6] Apostolidis CI, Distin PA. The kinetics of the sulphuric acid leaching of nickel and magnesium from reduction roasted serpentine. Hydrometallurgy. 1978;3(2):181-196

[7] Antonijević MM, Dimitrijević MD, Stevanović ZO, Serbula SM, Bogdanovic GD. Investigation of the possibility of copper recovery from the flotation tailings by acid leaching. Journal of Hazardous Materials. 2008; 158(1):23-34

[8] Shokri N, Salvucci GD. Evaporation from porous media in the presence of a water table. Vadose Zone Journal. 2011; 10(4):1309-1318

[9] Scanlon BR, Keese KE, Flint AL, Flint LE, Gaye CB, Edmunds WM, et al. Global synthesis of groundwater

recharge in semiarid and arid regions. Hydrological Processes. 2006;20(15): 3335-3370

[10] Shokri N, Lehmann P, Or D. Evaporation from layered porous media. Journal of Geophysical Research: Solid Earth Journal of Geophysical Research: Solid Earth. 2010;B06204:115

[11] Ma Y, Feng S, Zhan H, Liu X, Su D, Kang S, et al. Water infiltration in layered soils with air entrapment: Modified green– Ampt. Model and experimental validation. Journal of Hydrologic Engineering. 2011; 16(8):628-638

[12] Meiers GP, Barbour SL, Qualizza CV, Dobchuk BS. Evolution of the hydraulic conductivity of reclamation covers over sodic/saline mining overburden. Journal of Geotechnical and Geoenvironmental Engineering. 2011;137(10):968-976

[13] Piatak NM, Seal RRII, Sanzolone RF, Lamothe PJ, Brown ZA. Preliminary results of sequential extraction experiments for selenium on mine waste and stream sediments from Vermont, Maine, and New Zealand: U.S. Geological Survey Report. 2006;1184:21

[14] Zolotarev PP. Evaporation of liquid from plane solution surface. Doklady Akademii Nauk. 1966;168:21

[15] Tishkova PA, Churaev NV, Ershov AP. Evaporation rates for concentrated electrolyte solutions from thin capillaries. Inzhenerno-Fizicheskii Zhurnal. 1979;5(37):12

[16] Gamayunov NI, Gamayunov SN, Mironov VA. Osmoticheskii massoperenos (osmotic mass transport). Tver: TGTU. 2007;4(78):15-21

[17] Veran-Tissoires S, Marcoux M, Prat M. Why salt clusters form on basement walls. Physics. 2012;5(15):13-20

Author details

Salt in the Earth

98

and Margarita L. Sviridova

Siberian Branch, Krasnoyarsk, Russia

\*Address all correspondence to: mag@icct.ru

provided the original work is properly cited.

Alexandr Mikhailov\*, Ivan I. Vashlaev, Margarita Yu Kharitonova

Russian Academy of Sciences, Institute of Chemistry and Chemical Technology,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

[18] Dixon DG. Heap leach modelling— Current state of the art. In: Proceedings of the Fifth International Conference in Honor of Professor Ian Ritchie. TMS, the Minerals, Metals & Materials Society. 2003. pp. 289-314

[19] Padilla GA, Cisternas LA, Cueto JY. On the optimization of heap leaching. Minerals Engineering. 2008;21(9): 673-683

[20] Brierley JA, Brierley CL. Present and future commercial applications in biohydrometallurgy. Hydrometallurgy. 2001;59:233-239

[21] Valencia JA, Méndez DA, Cueto JY, Cisternas LA. Saltpeter extraction and modelling of caliche mineral heap leaching. Hydrometallurgy. 2007;90: 103-114

[22] Ghorbani Y, Becker M, Mainza A, Franzidis J-P, Petersen J. Large particle effects in chemical/biochemical heap leach processes. Minerals Engineering. 2011;24(11):1172-1184

[23] Smirnov VI. Geologiya poleznykh iskopayemykh. Moskva: Nedra; 1969. 688p

[24] Leontyev NE. Fundamentals of the theory of filtration. Moscow State University: Publishing house of the Center for Computer Science at the Faculty of Mechanics and Mathematics; 2009. 88p

**101**

Section 4

The Importance of Salt in

Road Safety

Section 4

## The Importance of Salt in Road Safety

[18] Dixon DG. Heap leach modelling— Current state of the art. In: Proceedings of the Fifth International Conference in Honor of Professor Ian Ritchie. TMS, the Minerals, Metals & Materials Society. 2003. pp. 289-314

[19] Padilla GA, Cisternas LA, Cueto JY. On the optimization of heap leaching. Minerals Engineering. 2008;21(9):

[20] Brierley JA, Brierley CL. Present and future commercial applications in biohydrometallurgy. Hydrometallurgy.

[21] Valencia JA, Méndez DA, Cueto JY, Cisternas LA. Saltpeter extraction and modelling of caliche mineral heap leaching. Hydrometallurgy. 2007;90:

[22] Ghorbani Y, Becker M, Mainza A, Franzidis J-P, Petersen J. Large particle effects in chemical/biochemical heap leach processes. Minerals Engineering.

[23] Smirnov VI. Geologiya poleznykh iskopayemykh. Moskva: Nedra; 1969.

[24] Leontyev NE. Fundamentals of the theory of filtration. Moscow State University: Publishing house of the Center for Computer Science at the Faculty of Mechanics and Mathematics;

673-683

Salt in the Earth

103-114

688p

2009. 88p

100

2001;59:233-239

2011;24(11):1172-1184

**103**

**Chapter 6**

**Abstract**

*Ivana Durickovic*

environmental impacts, road runoff

**1. Introduction**

NaCl Material for Winter

All over the world, winter maintenance is based on the application of the NaCl salt on roads, a product necessary for the elimination of slippery conditions. The quantities used for the salting operations are increasing with the development of the road network (in France, up to 2 million tons are applied each winter). This chapter will present the salt used as a deicer (its origin and chemical composition) and its chemical properties that are exploited for that purpose. Furthermore, an overview of the means of its transfer from the roads to the environment (soils and waters) as well as its impacts on these media will be presented, a special attention being devoted to the soil. The interactions of salt with other road pollutants and the

treatment possibilities in the road pollution context will be discussed.

accidents by 88% and human injuries due to icy conditions by 85% [7].

According to various climatic characteristics, urban environments, economy, and life requirements, people in different regions have different requirements for the consumptions of chlorine deicing salt [8, 9]. Improved management practices and regulations have resulted in reduced road salt application in some regions [4, 10]. However, the amount of deicing salt spread during cold periods increased since the 1940s [5, 11], but more particularly during the 1960s with the increasing road and highway network [12–14] and when its usage became widespread for highway maintenance [2]. For instance, the quantities applied in the USA increased from 149,000 tons in 1940 to over 18 million tons in 2005 [11]. Hence, this led the transportation

**Keywords:** NaCl, winter maintenance, road salt, pollution, environmental media,

In order to ensure the road safety and accessibility during winter in cold regions, winter road maintenance operations need to be performed. These operations are mainly based on the application of chemicals on roads with specialized vehicles. Large quantities of the so-called road salts, or deicing salts, are thus applied in order to clear the pavement and allow the normal traffic flow and economic activity [1]. Road salt was first introduced for snow melting operations in the 1930s [2], in order to improve vehicle traction [3] and thus reduce automobile collisions [4]. Sodium chloride (NaCl) has been the most commonly used deicing agent since the late 1940s [5, 6]. Application of road salts has been shown to reduce automobile

Maintenance and Its

Environmental Effect

#### **Chapter 6**

## NaCl Material for Winter Maintenance and Its Environmental Effect

*Ivana Durickovic*

#### **Abstract**

All over the world, winter maintenance is based on the application of the NaCl salt on roads, a product necessary for the elimination of slippery conditions. The quantities used for the salting operations are increasing with the development of the road network (in France, up to 2 million tons are applied each winter). This chapter will present the salt used as a deicer (its origin and chemical composition) and its chemical properties that are exploited for that purpose. Furthermore, an overview of the means of its transfer from the roads to the environment (soils and waters) as well as its impacts on these media will be presented, a special attention being devoted to the soil. The interactions of salt with other road pollutants and the treatment possibilities in the road pollution context will be discussed.

**Keywords:** NaCl, winter maintenance, road salt, pollution, environmental media, environmental impacts, road runoff

#### **1. Introduction**

In order to ensure the road safety and accessibility during winter in cold regions, winter road maintenance operations need to be performed. These operations are mainly based on the application of chemicals on roads with specialized vehicles. Large quantities of the so-called road salts, or deicing salts, are thus applied in order to clear the pavement and allow the normal traffic flow and economic activity [1].

Road salt was first introduced for snow melting operations in the 1930s [2], in order to improve vehicle traction [3] and thus reduce automobile collisions [4]. Sodium chloride (NaCl) has been the most commonly used deicing agent since the late 1940s [5, 6]. Application of road salts has been shown to reduce automobile accidents by 88% and human injuries due to icy conditions by 85% [7].

According to various climatic characteristics, urban environments, economy, and life requirements, people in different regions have different requirements for the consumptions of chlorine deicing salt [8, 9]. Improved management practices and regulations have resulted in reduced road salt application in some regions [4, 10]. However, the amount of deicing salt spread during cold periods increased since the 1940s [5, 11], but more particularly during the 1960s with the increasing road and highway network [12–14] and when its usage became widespread for highway maintenance [2]. For instance, the quantities applied in the USA increased from 149,000 tons in 1940 to over 18 million tons in 2005 [11]. Hence, this led the transportation

officials to yearly apply approximately 17 million tons in the United States, 6 million tons in Canada [7], up to 2 million tons of NaCl in France [15], and 600,000 tons in China [16]. The precise amounts of road salt applied are difficult to quantify [17], especially when it comes to road salts applied by individual land owners and other private entities. Kelly et al. [4] estimated that up to 40% of deicing salt application in some areas may be from private users [8].

Once spread on roads, due to several meteorological conditions and traffic, the road salt is transported out of the roads into the surrounding environment [10]. Another part remains on the road surface until the humidity coming from the precipitations or from the ice/snow melting is sufficient for flows of a road runoff [12]. In order to diminish the direct transfers of road runoffs to the environment, treatment systems, such as retention ponds, are constructed alongside roads [13, 18]. However, these ponds treating the pollutants only by sedimentation, dissolved pollutants, such as sodium chloride, will only pass through the pond and be rejected into the environment at its output [5, 18].

Severe impacts related to road salt applications have been reported on water and soil, as well as on their vegetation and population. Significant increases in chloride and sodium concentrations in surface water, groundwater, roadside soils, and organisms have been reported and were correlated to deicing salt application [19–21]. Indeed, salt stress can reduce the utilization rate of water in soil, cause water shortage, and even cause plant death in severe cases [22]. Different soil types and plants suffered different degrees of deicing salt damage [23, 24]. In some cases, concentrations have even reached toxicity thresholds beginning to threaten biodiversity [25, 26]. Moreover, salt has indirect environmental impacts, as Na<sup>+</sup> and Cl<sup>−</sup> ions are known to remobilize heavy metals adsorbed on the particle surface (soils and sludge) [27].

Despite the increasing use and concerns about the environmental impacts of road salt, only a few countries regulated the quantities spread on roads or developed a specific treatment for wastewaters contaminated by sodium chloride [28]. Canada, on the other hand, has much more drastic regulation declaring deicing salts as toxic products and limiting their use [29].

#### **2. Salting operations**

During winter conditions, certain meteorological phenomena lead to slippery conditions that provoke a decrease of the friction between the vehicle tires and the road surface [30], thus representing a risk for traffic. Thus, the transportation officials have the responsibility to ensure the winter road maintenance, which encompasses all the actions and decisions aiming to fight the consequences of winter phenomena on the road network necessary in order to maintain the viability and safety of road users. Snow and ice control can be made with mechanical or chemical methods [31]. Mechanical methods for the removal of snow, ice, or frost from the road surface consist of scraping or pushing [1]. These methods are mainly used on the mountain roads, where the thickness of the accumulated snow on the roads is too large [32]. Chemical treatment, based on the use of road salts, is the method used in a large number of countries of Europe, Africa, Asia, and the USA. Numerous road salts exist: chlorides of sodium, magnesium, or calcium, alcohols (methanol, ethanol, and ethylene glycol), acetates of potassium or sodium, and formates of potassium or sodium [33]. The salt selection depends not only on the local climate and legislation [9] but also on the surface that needs to be treated. Hence, for more sensitive zones, less corrosive acetates and formates are employed [34].

**105**

**Figure 1.**

*NaCl Material for Winter Maintenance and Its Environmental Effect*

efficiency up to a temperature of approximately −8°C [2, 5, 31].

**2.1 Origin and composition of sodium chloride as a road salt**

For the road treatment, on the other hand, sodium chloride is the most preferred anti-icing compound, and is thus used in the largest quantities. It has been widely selected because of its low cost, high availability, easy use and storage, and high

Sodium chloride used as road salt can come from different sources. The main types are sea salt (produced by natural evaporation of sea water) and rock salt (salt mechanically extracted from underground deposits) (**Figure 1**), but the new European standard includes other possible origins: ignigenic salt (obtained by recrystallization of brine produced by injection of water into the salt layers), salt of second intention (coproduct or industrial waste revalued), and brine of natural sodium chloride or produced from the dissolution of salt

Besides the origin, road salt has to fulfill requirements stated in the European standard also in terms of granularity, humidity, pH, and composition (proportion of chlorides, soluble sulfates, heavy metals, insolubles, and anti-caking agents). Road salt is mainly composed of its so-called active compound (sodium chloride), but it also contains insolubles and impurities such as metallic trace elements, whose quantity and nature vary as a function of the salt origin [12, 36]. Furthermore, other substances may be added for better efficiencies, such as anti-

As an example, the composition of the rock salt extracted from the Varangéville

Deicing salt is a product whose physical and chemical characteristics permit to move the equilibrium of water phases in order to lower the freezing point. Under atmospheric pressure, pure water will have a freezing point at 0°C, and beneath that temperature, it will be in its solid form and will form ice on the road surface. It is possible to decrease the freezing point by the addition and dissolution of a solute, such as salt, in water (**Figure 2**). Thus, the formed aqueous solution is called brine

*Stocks of sea salt coming from the Aigues-Mortes in the Occitanie region of France (left) and of rock salt coming* 

*from the Varangéville mine in the Lorraine region of France (right).*

mine, the only mine extracting rock salt for winter maintenance in France, is

*DOI: http://dx.doi.org/10.5772/intechopen.86907*

in water [35].

caking agents [2].

presented in **Table 1**.

**2.2 Principles of operation of road salt**

when the solute is sodium chloride.

*Salt in the Earth*

(soils and sludge) [27].

**2. Salting operations**

as toxic products and limiting their use [29].

in some areas may be from private users [8].

officials to yearly apply approximately 17 million tons in the United States, 6 million tons in Canada [7], up to 2 million tons of NaCl in France [15], and 600,000 tons in China [16]. The precise amounts of road salt applied are difficult to quantify [17], especially when it comes to road salts applied by individual land owners and other private entities. Kelly et al. [4] estimated that up to 40% of deicing salt application

Once spread on roads, due to several meteorological conditions and traffic, the road salt is transported out of the roads into the surrounding environment [10]. Another part remains on the road surface until the humidity coming from the precipitations or from the ice/snow melting is sufficient for flows of a road runoff [12]. In order to diminish the direct transfers of road runoffs to the environment, treatment systems, such as retention ponds, are constructed alongside roads [13, 18]. However, these ponds treating the pollutants only by sedimentation, dissolved pollutants, such as sodium chloride, will only pass through the

Severe impacts related to road salt applications have been reported on water and soil, as well as on their vegetation and population. Significant increases in chloride and sodium concentrations in surface water, groundwater, roadside soils, and organisms have been reported and were correlated to deicing salt application [19–21]. Indeed, salt stress can reduce the utilization rate of water in soil, cause water shortage, and even cause plant death in severe cases [22]. Different soil types and plants suffered different degrees of deicing salt damage [23, 24]. In some cases, concentrations have even reached toxicity thresholds beginning to threaten biodiversity [25, 26]. Moreover, salt has indirect environmental impacts, as Na<sup>+</sup> and Cl<sup>−</sup> ions are known to remobilize heavy metals adsorbed on the particle surface

Despite the increasing use and concerns about the environmental impacts of road salt, only a few countries regulated the quantities spread on roads or developed a specific treatment for wastewaters contaminated by sodium chloride [28]. Canada, on the other hand, has much more drastic regulation declaring deicing salts

During winter conditions, certain meteorological phenomena lead to slippery conditions that provoke a decrease of the friction between the vehicle tires and the road surface [30], thus representing a risk for traffic. Thus, the transportation officials have the responsibility to ensure the winter road maintenance, which encompasses all the actions and decisions aiming to fight the consequences of winter phenomena on the road network necessary in order to maintain the viability and safety of road users. Snow and ice control can be made with mechanical or chemical methods [31]. Mechanical methods for the removal of snow, ice, or frost from the road surface consist of scraping or pushing [1]. These methods are mainly used on the mountain roads, where the thickness of the accumulated snow on the roads is too large [32]. Chemical treatment, based on the use of road salts, is the method used in a large number of countries of Europe, Africa, Asia, and the USA. Numerous road salts exist: chlorides of sodium, magnesium, or calcium, alcohols (methanol, ethanol, and ethylene glycol), acetates of potassium or sodium, and formates of potassium or sodium [33]. The salt selection depends not only on the local climate and legislation [9] but also on the surface that needs to be treated. Hence, for more

sensitive zones, less corrosive acetates and formates are employed [34].

pond and be rejected into the environment at its output [5, 18].

**104**

For the road treatment, on the other hand, sodium chloride is the most preferred anti-icing compound, and is thus used in the largest quantities. It has been widely selected because of its low cost, high availability, easy use and storage, and high efficiency up to a temperature of approximately −8°C [2, 5, 31].

#### **2.1 Origin and composition of sodium chloride as a road salt**

Sodium chloride used as road salt can come from different sources. The main types are sea salt (produced by natural evaporation of sea water) and rock salt (salt mechanically extracted from underground deposits) (**Figure 1**), but the new European standard includes other possible origins: ignigenic salt (obtained by recrystallization of brine produced by injection of water into the salt layers), salt of second intention (coproduct or industrial waste revalued), and brine of natural sodium chloride or produced from the dissolution of salt in water [35].

Besides the origin, road salt has to fulfill requirements stated in the European standard also in terms of granularity, humidity, pH, and composition (proportion of chlorides, soluble sulfates, heavy metals, insolubles, and anti-caking agents).

Road salt is mainly composed of its so-called active compound (sodium chloride), but it also contains insolubles and impurities such as metallic trace elements, whose quantity and nature vary as a function of the salt origin [12, 36]. Furthermore, other substances may be added for better efficiencies, such as anticaking agents [2].

As an example, the composition of the rock salt extracted from the Varangéville mine, the only mine extracting rock salt for winter maintenance in France, is presented in **Table 1**.

#### **2.2 Principles of operation of road salt**

Deicing salt is a product whose physical and chemical characteristics permit to move the equilibrium of water phases in order to lower the freezing point. Under atmospheric pressure, pure water will have a freezing point at 0°C, and beneath that temperature, it will be in its solid form and will form ice on the road surface. It is possible to decrease the freezing point by the addition and dissolution of a solute, such as salt, in water (**Figure 2**). Thus, the formed aqueous solution is called brine when the solute is sodium chloride.

#### **Figure 1.**

*Stocks of sea salt coming from the Aigues-Mortes in the Occitanie region of France (left) and of rock salt coming from the Varangéville mine in the Lorraine region of France (right).*


#### **Table 1.**

*Composition of a sample of rock salt from the Varangéville mine [37].*

A brine can be characterized by its so-called weight percentage, that is, the ratio between the mass of the salt dissolved and the mass of the solution. As shown in the NaCl-H2O phase diagram presented in **Figure 2**, a brine's freezing point decreases with the concentration increase until the eutectic point, which corresponds to a weight percentage of 23.31 and a freezing point at −21°C. For temperatures lower than −21°C, a sodium chloride dihydrate, NaCl \* 2H2O, is formed.

The NaCl-H2O phase diagram permits to identify the role of the salt diluted in water. Indeed, if we concentrate on what happens at −5°C, we can see that for low concentrations, the solution will be composed of ice and liquid. A part of the solution being frozen, there is danger of appearance of slippery conditions. However, for higher concentrations (weight percentage above 10%), the solution will be entirely liquid.

In winter maintenance context, rock salt applied on ice will captivate free water, forming a brine. When the thus formed brine's freezing point becomes lower than the surrounding temperature, the fusion of ice or snow will start, diminishing the presence of the solid phase. The efficiency of the deicing salt to melt ice will depend on its concentration, the quantity of water present (from

**107**

biotope [45–48].

represented in **Figure 3**.

**3.1 Transfers**

*NaCl Material for Winter Maintenance and Its Environmental Effect*

• dry salt: method convenient for very wet periods,

the soil or infiltrate and percolate to groundwater [6, 31].

though the brine can be easily drained off,

precipitations, air humidity, or water on the road surface), as well as on the

Depending on the state of the road, deicing salt can be spread as [12, 31]:

• in solution as a brine: efficient at dry conditions as it adheres to the surface, even

• moistured/humidified salt (mixture of a 30 wt% brine and of rock salt): efficient in numerous situations, as the dry salt will be the salt stock and ensures a mechanical effect, whereas the brine will bring the humidity necessary for the fusion.

The application can be performed either before the appearance of slippery conditions (preventive salt spreading) or once they are present on the road surface (curative salt spreading). With its capacity to lower the freezing point of the liquid present at the road surface, road salt prevents the formation of ice or provokes its melting.

Numerous parameters and mechanisms lead the salt to be transported out of the roads into the environment. When deposited on soils, it can either be retained by

This represents a real environmental issue since NaCl is known to have adverse environmental impacts [5]. Indeed, besides increasing the salinity in soil and water, salt may induce a range of other effects [39]. First of all, it increases the hardness of water, provokes acidification of receiving waters [40], and strongly influences water geochemistry by the ion mobility, more specifically of metallic ions, *via* ionic exchanges and complexation with chlorides [20, 41–43]. Secondly, it can be retained onto soils and increase ionic strength and pH, thus modifying ion speciation [41, 44], but may also lead to alteration of the soil structure [31]. As a result, the disintegration of soil aggregates and increased mobilization of colloids can lead to a transport of heavy metals from soil to groundwater [27, 39]. And finally, in high concentrations, NaCl causes stress to ecosystems, decreasing biomass development and increasing mortality of species and therefore causing a modification of the

Any salt spread eventually ends up being in some part of the environment [2]. After their application on roads, road salt will be submitted to numerous parameters, such as meteorological conditions (precipitations and wind) and traffic [23, 49], which will influence its evolution. Most of this salt is removed through drainage (after precipitations or snow/ice melting) [3, 8] or traffic spray processes which will transfer it to the adjacent roadside environment [2]. The main transfer mechanisms, such as runoff, infiltration, airborne spreading, and plowing, are

The transfers to the different environmental compartments will take place in the first hours following the salting operations [31]. First of all, it is estimated that 20–40% of the totality of rock salt spread is directly projected out of the roads during the salting operation [15]. Blomqvist and Johansson [31] stated that 20–63% of

road salt is transported by air (projected by vehicles and wind).

**3. Transfers of salt to the environment and its environmental impacts**

*DOI: http://dx.doi.org/10.5772/intechopen.86907*

temperature [38].

**Figure 2.** *NaCl-H2O phase diagram [37].*

*NaCl Material for Winter Maintenance and Its Environmental Effect DOI: http://dx.doi.org/10.5772/intechopen.86907*

precipitations, air humidity, or water on the road surface), as well as on the temperature [38].

Depending on the state of the road, deicing salt can be spread as [12, 31]:


The application can be performed either before the appearance of slippery conditions (preventive salt spreading) or once they are present on the road surface (curative salt spreading). With its capacity to lower the freezing point of the liquid present at the road surface, road salt prevents the formation of ice or provokes its melting.

#### **3. Transfers of salt to the environment and its environmental impacts**

Numerous parameters and mechanisms lead the salt to be transported out of the roads into the environment. When deposited on soils, it can either be retained by the soil or infiltrate and percolate to groundwater [6, 31].

This represents a real environmental issue since NaCl is known to have adverse environmental impacts [5]. Indeed, besides increasing the salinity in soil and water, salt may induce a range of other effects [39]. First of all, it increases the hardness of water, provokes acidification of receiving waters [40], and strongly influences water geochemistry by the ion mobility, more specifically of metallic ions, *via* ionic exchanges and complexation with chlorides [20, 41–43]. Secondly, it can be retained onto soils and increase ionic strength and pH, thus modifying ion speciation [41, 44], but may also lead to alteration of the soil structure [31]. As a result, the disintegration of soil aggregates and increased mobilization of colloids can lead to a transport of heavy metals from soil to groundwater [27, 39]. And finally, in high concentrations, NaCl causes stress to ecosystems, decreasing biomass development and increasing mortality of species and therefore causing a modification of the biotope [45–48].

#### **3.1 Transfers**

*Salt in the Earth*

SO4

**Table 1.**

entirely liquid.

A brine can be characterized by its so-called weight percentage, that is, the ratio between the mass of the salt dissolved and the mass of the solution. As shown in the NaCl-H2O phase diagram presented in **Figure 2**, a brine's freezing point decreases with the concentration increase until the eutectic point, which corresponds to a weight percentage of 23.31 and a freezing point at −21°C. For temperatures lower

The NaCl-H2O phase diagram permits to identify the role of the salt diluted in water. Indeed, if we concentrate on what happens at −5°C, we can see that for low concentrations, the solution will be composed of ice and liquid. A part of the solution being frozen, there is danger of appearance of slippery conditions. However, for higher concentrations (weight percentage above 10%), the solution will be

In winter maintenance context, rock salt applied on ice will captivate free water, forming a brine. When the thus formed brine's freezing point becomes lower than the surrounding temperature, the fusion of ice or snow will start, diminishing the presence of the solid phase. The efficiency of the deicing salt to melt ice will depend on its concentration, the quantity of water present (from

than −21°C, a sodium chloride dihydrate, NaCl \* 2H2O, is formed.

**Solubles (mass % on dry) Insolubles (mass %)**

Na+ 36.6 Ca2+ 0.36 Mg2+ 0.02 K+ 0.09

*Composition of a sample of rock salt from the Varangéville mine [37].*

Fe(Cn6)Na4, 10H2O: 114 mg/kg

Cl<sup>−</sup> 56.4 Silicates 90

<sup>2</sup><sup>−</sup> 0.86 Carbonates 5 Br<sup>−</sup> 0.01 Sulfates 5

**106**

**Figure 2.**

*NaCl-H2O phase diagram [37].*

Any salt spread eventually ends up being in some part of the environment [2]. After their application on roads, road salt will be submitted to numerous parameters, such as meteorological conditions (precipitations and wind) and traffic [23, 49], which will influence its evolution. Most of this salt is removed through drainage (after precipitations or snow/ice melting) [3, 8] or traffic spray processes which will transfer it to the adjacent roadside environment [2]. The main transfer mechanisms, such as runoff, infiltration, airborne spreading, and plowing, are represented in **Figure 3**.

The transfers to the different environmental compartments will take place in the first hours following the salting operations [31]. First of all, it is estimated that 20–40% of the totality of rock salt spread is directly projected out of the roads during the salting operation [15]. Blomqvist and Johansson [31] stated that 20–63% of road salt is transported by air (projected by vehicles and wind).

**Figure 3.** *A conceptual model of the transport mechanisms and pathways from the road [10].*

The NaCl dissolved in storm water can be transferred in two ways. Firstly, it is projected out of the roads by nebulization. The distance to which road salt is transferred by nebulization can reach 400 m [50], even though more than 90% is found within 20 m from the road [31] and 98% within 50 m of the road edge [14]. Secondly, the runoff containing dissolved salt can be collected in retention ponds. These systems can collect between 40 and 80% of the totality of the road salt applied, depending on the meteorological conditions [12] and have the role of improving water quality and reducing flooding risks. Retention ponds allow the reduction of metallic pollution by decantation of suspended solids bearing trace elements, but in general, they are not designed to treat dissolved pollutants like NaCl [5]. Since sodium chloride is not removed by the retention ponds, after passing through those systems, road salt is rejected into the environment. There is thus a lack of appropriate storm water management practices [6].

It is found that up to 50% of the applied road salt reaches surface waters [6, 51, 52]. The remaining 50% enters the subsurface as aquifer recharge and migrates toward groundwater [6, 46, 53].

Further transfers will depend on the nature of the elements that are deposited, as the salt will be dissociated into sodium and chloride. On the one hand, chloride is considered to be a conservative element as it does not participate in chemical reactions. It will therefore follow the water and be transported down to the groundwater, from where it can be further transported to other groundwater aquifers or to various surface waters. Sodium, on the other hand, takes part in chemical processes, such as cation exchanges, with soil particles and is therefore retained in the soil [39, 54].

#### **3.2 Impacts on waters**

Concentrations of Na<sup>+</sup> and Cl<sup>−</sup> increase in superficial and underground waters during winter, following the salting operations [14, 20, 36, 42, 43, 55–61]. Due to long retention times of these ions by soils and waters, this increase can continue during the summer period [56] and high concentrations in lakes and underground waters can be observed during several years [36, 42, 57].

Increased chloride concentrations in groundwater or surface waters because of deicing salt application are the first observable change in water quality and indicate that there is a hydraulic connection between the road and the water [39].

**109**

*NaCl Material for Winter Maintenance and Its Environmental Effect*

Road runoff reaches underground waters by infiltration in soils [62]. Salt concentration of underground waters varies with the quality of soil or from 1 year to another. The increase of the salting operations leads to an increase in the salt concentration of shallow ground waters [53–55]. The concentrations of Na+

ions present in underground waters were also correlated with the permeable surface

Aquifers play a role of reservoir wells for NaCl during winter [62], and become a source during summer, rejecting salted waters in the streams, thus contaminating

Road runoff presents very high Cl<sup>−</sup> concentrations during winter, leading to salinity increase and water quality degradation [20, 36, 40, 58, 63]. In suburban and urban streams of Maryland, chloride concentrations can achieve 5 g/L [20] and the

The impacts of road salt on surface water can be physical, chemical, or biological: change of lake density stratification, eutrophication, mobilization of metals,

In France, the Luitel Lake (Isère) is a remarkable example of the road salt influence on surface waters. Indeed, the winter Olympic Games organized in 1968 at Grenoble led to the emergence of winter sport resorts and the development of the road network to access it. The Luitel bog, located upstream and below a department road leading to the Chamrousse resort, suffered the consequences of

1968: chloride concentration measured in 1955 was 3.7 mg/L, 34 mg/L in 1982, and 49 mg/L in 1999 [15]. A change in the lake's aquatic population was later observed [64]. Another example is the Saint-Augustin Lake in Québec where an unexpected presence of some brackish water and marine samples appeared in the second half of the twentieth century. This was identified as a result of the increasingly saline

tions. If the residence time is lower than a year, these concentrations will diminish before the next winter season, forming annual cycles [36, 65]. If the residence

and will still be present in waters next winter, leading to a gradual increase of these concentrations from 1 year to another [62]. Hence, Kelly et al. [42] observed

The salinity increase in waters was correlated to the increase of Mg2+, K+

Ca2+ cation concentrations coming from soil road runoff passed through [66, 67].

lake (Michigan) between 1981 and 2004, to cationic exchanges between those ions

Lakes present stratification with a temperature and density gradient, the superficial layer being warmer. In autumn, as the air temperature decreases, it induces convection streams leading to a homogenization of the water column permitting the brewing of nutrients and dissolved oxygen. In winter, the presence of ice on the lake surface leads to a stratification reversal, the surface layer becoming colder than the

and Cl<sup>−</sup> will not be flushed completely between salting seasons

concentration in rural streams of New York of 1.5 and

concentration increase in the Third Sister

<sup>2</sup><sup>−</sup> remained unchanged.

lakes of Minneapolis receiving waters charged in road salt have Na+

this development, with an important increase of Na<sup>+</sup>

conditions from road and highway saltings [21].

The residence time will determine the evolution of Na<sup>+</sup>

and Cl<sup>−</sup>

and Cl<sup>−</sup> concen-

and Cl<sup>−</sup> concentrations since

and Cl<sup>−</sup> concentra-

, and

*DOI: http://dx.doi.org/10.5772/intechopen.86907*

fraction which can receive road salt [46].

*3.2.1 Underground waters*

surface waters [42, 54].

trations 10–25 times greater [36].

reduced diversity, and so on [58].

*3.2.2 Surface waters*

time is longer, Na<sup>+</sup>

the increase of Cl<sup>−</sup> and Na<sup>+</sup>

Judd et al. [68] attributed the Ca2+ and K+

and sodium, whereas concentrations of Mg2+ and SO4

lower layer. At spring, air warming inverses the process [69].

0.9 mg/L, respectively.

#### *3.2.1 Underground waters*

*Salt in the Earth*

**Figure 3.**

The NaCl dissolved in storm water can be transferred in two ways. Firstly, it is projected out of the roads by nebulization. The distance to which road salt is transferred by nebulization can reach 400 m [50], even though more than 90% is found within 20 m from the road [31] and 98% within 50 m of the road edge [14]. Secondly, the runoff containing dissolved salt can be collected in retention ponds. These systems can collect between 40 and 80% of the totality of the road salt applied, depending on the meteorological conditions [12] and have the role of improving water quality and reducing flooding risks. Retention ponds allow the reduction of metallic pollution by decantation of suspended solids bearing trace elements, but in general, they are not designed to treat dissolved pollutants like NaCl [5]. Since sodium chloride is not removed by the retention ponds, after passing through those systems, road salt is rejected into the environment. There is thus a

It is found that up to 50% of the applied road salt reaches surface waters [6, 51, 52]. The remaining 50% enters the subsurface as aquifer recharge and migrates toward

Further transfers will depend on the nature of the elements that are deposited, as the salt will be dissociated into sodium and chloride. On the one hand, chloride is considered to be a conservative element as it does not participate in chemical reactions. It will therefore follow the water and be transported down to the groundwater, from where it can be further transported to other groundwater aquifers or to various surface waters. Sodium, on the other hand, takes part in chemical processes, such as cation exchanges, with soil particles and is therefore retained in

during winter, following the salting operations [14, 20, 36, 42, 43, 55–61]. Due to long retention times of these ions by soils and waters, this increase can continue during the summer period [56] and high concentrations in lakes and underground

Increased chloride concentrations in groundwater or surface waters because of deicing salt application are the first observable change in water quality and indicate

that there is a hydraulic connection between the road and the water [39].

and Cl<sup>−</sup> increase in superficial and underground waters

lack of appropriate storm water management practices [6].

*A conceptual model of the transport mechanisms and pathways from the road [10].*

waters can be observed during several years [36, 42, 57].

groundwater [6, 46, 53].

the soil [39, 54].

**3.2 Impacts on waters**

Concentrations of Na<sup>+</sup>

**108**

Road runoff reaches underground waters by infiltration in soils [62]. Salt concentration of underground waters varies with the quality of soil or from 1 year to another. The increase of the salting operations leads to an increase in the salt concentration of shallow ground waters [53–55]. The concentrations of Na+ and Cl<sup>−</sup> ions present in underground waters were also correlated with the permeable surface fraction which can receive road salt [46].

Aquifers play a role of reservoir wells for NaCl during winter [62], and become a source during summer, rejecting salted waters in the streams, thus contaminating surface waters [42, 54].

#### *3.2.2 Surface waters*

Road runoff presents very high Cl<sup>−</sup> concentrations during winter, leading to salinity increase and water quality degradation [20, 36, 40, 58, 63]. In suburban and urban streams of Maryland, chloride concentrations can achieve 5 g/L [20] and the lakes of Minneapolis receiving waters charged in road salt have Na+ and Cl<sup>−</sup> concentrations 10–25 times greater [36].

The impacts of road salt on surface water can be physical, chemical, or biological: change of lake density stratification, eutrophication, mobilization of metals, reduced diversity, and so on [58].

In France, the Luitel Lake (Isère) is a remarkable example of the road salt influence on surface waters. Indeed, the winter Olympic Games organized in 1968 at Grenoble led to the emergence of winter sport resorts and the development of the road network to access it. The Luitel bog, located upstream and below a department road leading to the Chamrousse resort, suffered the consequences of this development, with an important increase of Na<sup>+</sup> and Cl<sup>−</sup> concentrations since 1968: chloride concentration measured in 1955 was 3.7 mg/L, 34 mg/L in 1982, and 49 mg/L in 1999 [15]. A change in the lake's aquatic population was later observed [64]. Another example is the Saint-Augustin Lake in Québec where an unexpected presence of some brackish water and marine samples appeared in the second half of the twentieth century. This was identified as a result of the increasingly saline conditions from road and highway saltings [21].

The residence time will determine the evolution of Na<sup>+</sup> and Cl<sup>−</sup> concentrations. If the residence time is lower than a year, these concentrations will diminish before the next winter season, forming annual cycles [36, 65]. If the residence time is longer, Na<sup>+</sup> and Cl<sup>−</sup> will not be flushed completely between salting seasons and will still be present in waters next winter, leading to a gradual increase of these concentrations from 1 year to another [62]. Hence, Kelly et al. [42] observed the increase of Cl<sup>−</sup> and Na<sup>+</sup> concentration in rural streams of New York of 1.5 and 0.9 mg/L, respectively.

The salinity increase in waters was correlated to the increase of Mg2+, K+ , and Ca2+ cation concentrations coming from soil road runoff passed through [66, 67]. Judd et al. [68] attributed the Ca2+ and K+ concentration increase in the Third Sister lake (Michigan) between 1981 and 2004, to cationic exchanges between those ions and sodium, whereas concentrations of Mg2+ and SO4 <sup>2</sup><sup>−</sup> remained unchanged.

Lakes present stratification with a temperature and density gradient, the superficial layer being warmer. In autumn, as the air temperature decreases, it induces convection streams leading to a homogenization of the water column permitting the brewing of nutrients and dissolved oxygen. In winter, the presence of ice on the lake surface leads to a stratification reversal, the surface layer becoming colder than the lower layer. At spring, air warming inverses the process [69].

#### *Salt in the Earth*

The income of dissolved NaCl induces a modification of the thermal stratification in favor of a chemical stratification. Waters charged in NaCl, denser, are located in depths [70]. This chemical stratification prevents the brewing of water masses, with eutrophication risks [36].

#### **3.3 Impacts on soils**

After being deposited on the ground, road salt infiltrates the soil and is further transported down the soil profile to eventually reach the groundwater [39]. Despite the runoff and storm drains, one part of salt is accumulated in soil [23]. Hence, Howard and Haynes [51] estimated that only 45% of the chlorides were removed annually by surface runoff in Toronto (Canada), the rest of it remaining in soil water or ground water.

#### *3.3.1 Cation speciation*

It was observed that Ca and Mg are present in higher concentrations in soils in the vicinity of roads [23, 40, 41]. Indeed, after salting operations, Na+ concentration increases in the soil solution. Sodium enters in competition with other cations at the sites of ionic exchanges leading to an increase in Mg2+ and Ca2+ concentrations in the soil solution [19, 41, 56, 61, 63, 66, 71–75]. Because of its stronger attraction to negatively charged soil particles, Mg2+ may accelerate Na+ leaching by displacing it in soils [23]. Thus, faster movement of Na<sup>+</sup> through soils make Na+ less available to plants, but more available to aquatic systems [23].

Sodium can also enhance the release of metals from soils to groundwater [19, 23, 27, 76]. Hence, increased transport of heavy metals (Zn, Cd, Cu and Pb) coincident with road salt applications has been observed in roadside soils in Germany, Sweden, and the United States [36].

Due to their physicochemical properties, metallic trace elements have different speciations according to the pH and chemical environment. Metallic trace elements with weak solubilities fix on preferential phases that vary according to physicochemical conditions on the water-solid interface. Metals such as Cu and Cd have strong affinities for organic matter and are present in aqueous phases in the form of chloride complexes. Other metal, such as Pb, Cr, and Zn have a strong affinity for organic matter that influences their mobility in the presence of Na+ and Cl<sup>−</sup>. Li et al. [77] showed that in a soil of a nontreated road, Pb and Zn were present mainly in the phases of carbonates and oxides of Fe and Mn, whereas Cu was mainly associated to organic fractions and to sulfides. Durand et al. [78] observed in sediments of retention ponds that Cd, Pb, and Zn were linked to fulvic acids and were mobile, while Ni and Cr were mainly present in the humic fraction and were thus little mobile. Pb and Zn can also precipitate as oxides [76], while Cd forms chloride complexes in the presence of dissolved NaCl [74].

#### *3.3.2 Impacts on the soil quality*

Several anthropogenic factors disturb the state of urban soil by changing its natural features and internal processes [79]. Geomechanical transformations are often accompanied by chemical changes. The accumulation of different pollutants and their subsequent synergetic and antagonistic reactions lead to an increasing level of toxicity in urban soil [80]. One of the observed changes is the salinification of urban soils, a side effect of salting the roads in winter, which will lead to a physicochemical modification of the soil and influence the mobility of metallic trace elements.

**111**

*NaCl Material for Winter Maintenance and Its Environmental Effect*

Soils in the vicinity of roads present higher concentration of metals and road salts. As an example, the first 20 cm of depth next to main roads in Opole (Poland),

Road salt accumulation in soils depends on several parameters: the soil permeability and its density, and its mechanical properties influence the salt transport and

rural and urban roads in Missouri for 2–3 months after the end of the salting period, namely in soils containing organic matter, such as sandy soils [61]. According to Lundmark and Olofsson [81], soils with coarse particle size, which are more perme-

More conservative Cl<sup>−</sup> is less retained by soils [2], leading to concentrations in

ions interacting with the soil components [82, 84]. The ions are then leached

Numerous lixiviation tests showed the capacity of NaCl to remobilize metallic trace elements. The alternation of leaching with rainwater charged in Na+

Salinization is a threat for soils, mainly in arid countries where irrigation is performed with salted waters [12]. Clays can contain in their structure Ca2+ ions that permit to obtain structures presenting little swelling or dispersion. Conversely, the

organic matter) dispersions [66] and a swelling decreasing hydraulic conductivity by obstruction of pores [86, 87]. Structural stability of a soil, apparent density, and

evacuated during the leaching of soils by salty waters [72, 74]. The soils presenting

Once in the roadside environment, salt may percolate downward into the soil and become available to plant roots or the underlying water table or be deposited directly on roadside vegetation [79]. Many authors have shown a direct correlation

cations, which can result in nutrient deficiencies in certain soil types [24, 72]. The

The most significant symptoms of salts on roadside trees are growth limitation/reduction in biomass, necrosis, defoliation, and in extreme cases, the entire destruction of a plant [12, 49, 79]. These symptoms can be caused by several salt effects: photosynthesis reduction, decrease of soil moisture, decrease of water content in leaf tissues, alteration of nutrient availability, etc. [24]. It is estimated that the use of road salt is responsible for the death of 700,000 trees/year in Western

tion in plants and, consequently, the greater the damage to plants [79].

in clays induces the formation of a platelet structure, more mobile

Cl<sup>−</sup> and water with weak ionic force promotes the release of colloids formed of carbonates, clay, and organic matter [27, 72, 74, 85]. Moreover, the presence of Na<sup>+</sup> and Cl<sup>−</sup> leads to a competition for the sorption sites [63]. Metallic trace elements are easily leached in the presence of NaCl [19, 27, 72, 74, 76, 85] and can be transported

ies showed that chlorides can be retained in forest soils [82], as well as rural soils [83]. Indeed, the chloride ion can interact with the organic matter in order to form chlorinated organic complexes and be stocked in soil micropores [40, 56, 82, 84]. Besides acting like a well, soil is also a source by liberation mechanisms with Cl<sup>−</sup> and

and Cl<sup>−</sup> ions can be retained in soils next to

concentration [40]. However, several stud-

in the soil provokes particle (clay and

and Cl<sup>−</sup> ions in the soil and the degree of plant damage

concentration tend to leach out K, Ca, and Mg

and Cl<sup>−</sup> ions in the soil, the higher their accumula-

[86–89]. Colloids are

and

*DOI: http://dx.doi.org/10.5772/intechopen.86907*

the physicochemical processes. The Na+

water higher by 10–15% than the Na+

Na<sup>+</sup>

presence of Na<sup>+</sup>

chloride concentration can go up to 1.5 g/kg [79].

able, will have greater salt leaching down the soil profile.

toward underground waters or transported to surface waters.

by the soil solution toward surface or underground water.

soil permeability will then decrease in the presence of Na+

high salinities induce a release of Ca, Mg, and K.

in interstitial water. The presence of Na+

*3.3.3 Impacts on the vegetation*

between the content of Na<sup>+</sup>

Europe [91] (**Figure 4**).

[22, 90]. Indeed, increases in Na+

higher the concentration of Na+

#### *NaCl Material for Winter Maintenance and Its Environmental Effect DOI: http://dx.doi.org/10.5772/intechopen.86907*

*Salt in the Earth*

**3.3 Impacts on soils**

water or ground water.

*3.3.1 Cation speciation*

masses, with eutrophication risks [36].

The income of dissolved NaCl induces a modification of the thermal stratification in favor of a chemical stratification. Waters charged in NaCl, denser, are located in depths [70]. This chemical stratification prevents the brewing of water

After being deposited on the ground, road salt infiltrates the soil and is further transported down the soil profile to eventually reach the groundwater [39]. Despite the runoff and storm drains, one part of salt is accumulated in soil [23]. Hence, Howard and Haynes [51] estimated that only 45% of the chlorides were removed annually by surface runoff in Toronto (Canada), the rest of it remaining in soil

It was observed that Ca and Mg are present in higher concentrations in soils in

tion increases in the soil solution. Sodium enters in competition with other cations at the sites of ionic exchanges leading to an increase in Mg2+ and Ca2+ concentrations in the soil solution [19, 41, 56, 61, 63, 66, 71–75]. Because of its stronger attraction

Sodium can also enhance the release of metals from soils to groundwater [19, 23, 27, 76]. Hence, increased transport of heavy metals (Zn, Cd, Cu and Pb) coincident with road salt applications has been observed in roadside soils in

Due to their physicochemical properties, metallic trace elements have different speciations according to the pH and chemical environment. Metallic trace elements with weak solubilities fix on preferential phases that vary according to physicochemical conditions on the water-solid interface. Metals such as Cu and Cd have strong affinities for organic matter and are present in aqueous phases in the form of chloride complexes. Other metal, such as Pb, Cr, and Zn have a strong affinity for

[77] showed that in a soil of a nontreated road, Pb and Zn were present mainly in the phases of carbonates and oxides of Fe and Mn, whereas Cu was mainly associated to organic fractions and to sulfides. Durand et al. [78] observed in sediments of retention ponds that Cd, Pb, and Zn were linked to fulvic acids and were mobile, while Ni and Cr were mainly present in the humic fraction and were thus little mobile. Pb and Zn can also precipitate as oxides [76], while Cd forms chloride

Several anthropogenic factors disturb the state of urban soil by changing its natural features and internal processes [79]. Geomechanical transformations are often accompanied by chemical changes. The accumulation of different pollutants and their subsequent synergetic and antagonistic reactions lead to an increasing level of toxicity in urban soil [80]. One of the observed changes is the salinification of urban soils, a side effect of salting the roads in winter, which will lead to a physicochemical modification of the soil and influence the mobility of metallic

concentra-

less available

and Cl<sup>−</sup>. Li et al.

leaching by displacing

through soils make Na+

the vicinity of roads [23, 40, 41]. Indeed, after salting operations, Na+

to negatively charged soil particles, Mg2+ may accelerate Na+

organic matter that influences their mobility in the presence of Na+

it in soils [23]. Thus, faster movement of Na<sup>+</sup>

Germany, Sweden, and the United States [36].

complexes in the presence of dissolved NaCl [74].

*3.3.2 Impacts on the soil quality*

to plants, but more available to aquatic systems [23].

**110**

trace elements.

Soils in the vicinity of roads present higher concentration of metals and road salts. As an example, the first 20 cm of depth next to main roads in Opole (Poland), chloride concentration can go up to 1.5 g/kg [79].

Road salt accumulation in soils depends on several parameters: the soil permeability and its density, and its mechanical properties influence the salt transport and the physicochemical processes. The Na+ and Cl<sup>−</sup> ions can be retained in soils next to rural and urban roads in Missouri for 2–3 months after the end of the salting period, namely in soils containing organic matter, such as sandy soils [61]. According to Lundmark and Olofsson [81], soils with coarse particle size, which are more permeable, will have greater salt leaching down the soil profile.

More conservative Cl<sup>−</sup> is less retained by soils [2], leading to concentrations in water higher by 10–15% than the Na+ concentration [40]. However, several studies showed that chlorides can be retained in forest soils [82], as well as rural soils [83]. Indeed, the chloride ion can interact with the organic matter in order to form chlorinated organic complexes and be stocked in soil micropores [40, 56, 82, 84]. Besides acting like a well, soil is also a source by liberation mechanisms with Cl<sup>−</sup> and Na<sup>+</sup> ions interacting with the soil components [82, 84]. The ions are then leached toward underground waters or transported to surface waters.

Numerous lixiviation tests showed the capacity of NaCl to remobilize metallic trace elements. The alternation of leaching with rainwater charged in Na+ and Cl<sup>−</sup> and water with weak ionic force promotes the release of colloids formed of carbonates, clay, and organic matter [27, 72, 74, 85]. Moreover, the presence of Na<sup>+</sup> and Cl<sup>−</sup> leads to a competition for the sorption sites [63]. Metallic trace elements are easily leached in the presence of NaCl [19, 27, 72, 74, 76, 85] and can be transported by the soil solution toward surface or underground water.

Salinization is a threat for soils, mainly in arid countries where irrigation is performed with salted waters [12]. Clays can contain in their structure Ca2+ ions that permit to obtain structures presenting little swelling or dispersion. Conversely, the presence of Na<sup>+</sup> in clays induces the formation of a platelet structure, more mobile in interstitial water. The presence of Na+ in the soil provokes particle (clay and organic matter) dispersions [66] and a swelling decreasing hydraulic conductivity by obstruction of pores [86, 87]. Structural stability of a soil, apparent density, and soil permeability will then decrease in the presence of Na+ [86–89]. Colloids are evacuated during the leaching of soils by salty waters [72, 74]. The soils presenting high salinities induce a release of Ca, Mg, and K.

#### *3.3.3 Impacts on the vegetation*

Once in the roadside environment, salt may percolate downward into the soil and become available to plant roots or the underlying water table or be deposited directly on roadside vegetation [79]. Many authors have shown a direct correlation between the content of Na<sup>+</sup> and Cl<sup>−</sup> ions in the soil and the degree of plant damage [22, 90]. Indeed, increases in Na+ concentration tend to leach out K, Ca, and Mg cations, which can result in nutrient deficiencies in certain soil types [24, 72]. The higher the concentration of Na+ and Cl<sup>−</sup> ions in the soil, the higher their accumulation in plants and, consequently, the greater the damage to plants [79].

The most significant symptoms of salts on roadside trees are growth limitation/reduction in biomass, necrosis, defoliation, and in extreme cases, the entire destruction of a plant [12, 49, 79]. These symptoms can be caused by several salt effects: photosynthesis reduction, decrease of soil moisture, decrease of water content in leaf tissues, alteration of nutrient availability, etc. [24]. It is estimated that the use of road salt is responsible for the death of 700,000 trees/year in Western Europe [91] (**Figure 4**).

**Figure 4.** *Roadside vegetation impacted by road salt [92].*

A good example of the impact of urban runoff on biota is the Frenchman's Bay lagoon, receiving direct runoff from Canada's busiest highway. Eyles et al. [53] underlined a marked reduction in the area of vegetation of a wetland corresponding to 30% since 1970 and 60% since 1939. Furthermore, reduced diversity and coverage of submergent plant species is reflected in changing fish populations in the lagoon. The authors showed that the largest contemporary impactor on environmental quality in Frenchman's Bay watershed derives from the salting operations.

#### **4. Treatment possibilities**

Contaminated soils and waters can be remediated by various methods which are not suitable for an *in situ* treatment. For the road runoff treatment, conventional desalination techniques (reverse osmosis and membrane processes) are too expensive.

Currently, preference is being given to *in situ* methods that are less environmentally disruptive and more economical. In this context, biotechnology offers phytoremediation techniques as a suitable alternative [93].

Phytoremediation is based on the use of plants and their associated microorganisms for the removal, degradation, or stabilization of toxic substances from the environment. Depending on the contaminant and on the plant characteristics, different phytoremediation techniques take place (**Figure 5**).

The first objective of the phytoremediation is to limit the impacts of some contaminants. This can be obtained by several ways. Firstly, by phytostabilization, that is, immobilization of the contaminant in the contaminated soils (after incorporation of contaminants into roots, metals are precipitated as insoluble forms and trapped in the soil matrix). This technique diminishes the mobility and bioavailability of contaminants by different mechanisms such as sorption, complexation, or precipitation [94]. Secondly, by phytodegradation of the contaminant (contaminants are degraded inside plant cells by specific enzymes) [93, 95]. And finally, by phytoextraction from the soil which involves the absorption of contaminants by roots and their accumulation in the aerial parts [96]. It is mainly applied to metals (Cd, Ni, Cu, Zn, and Pb) and preferentially uses hyperaccumulator plants that have the ability to store high concentrations of specific metals in their aerial parts (0.01–1% dry weight, depending on the metal). Phytoextraction is the most commonly used technique and probably the most economic and efficient one [94].

**113**

**Figure 5.**

*NaCl Material for Winter Maintenance and Its Environmental Effect*

In order to develop such a technique for the remediation of a contaminated soil, it is important to choose appropriate plants. Indeed, the choice of the plant will depend on the environmental conditions it will be submitted to, mainly soil composition and pollutant that is aimed for phytoremediation. In order for a plant to be considered as a good phytoremediator, it has to have high tolerance to the pollutants and has to be able to accumulate or degrade pollutants. For a good efficiency, it is necessary that the plant has fast growth and high biomass production, as well as a well-developed root system. Finally, it has to be well adapted on the climatic and

Phytodesalination, in particular, is a modality of phytoextraction based on the use of halophytes for removal of salts from saline soils. Several studies investigate the possibility of using phytodesalination for road runoff treatment [97–102]. Morteau et al. [100] investigated a possibility for the treatment of road runoff in Québec by *Atriplex patula*, *Salicornia europaea*, and *Spergularia canadensis*. The authors showed that all species accumulated important masses of salt, but that the mass of accumulated salt depends on the plant morphology (size and weight), species, and concentration of the salt exposure. Their study shows that, taking into account the chloride accumulation and plant weight, *Atriplex patula* is the most

Suaire et al. [102] and Durickovic et al. [97] showed that two Atriplex species (*Atriplex hortensis* and *Atriplex halimus*) seem to be well adapted for the road runoff remediation. Indeed, these species showed they both have salt and metal

environmental conditions it will be submitted to [18].

*Schematic representation of phytoremediation strategies [93].*

suitable for the accumulation of chlorides and of sodium.

*DOI: http://dx.doi.org/10.5772/intechopen.86907*

*NaCl Material for Winter Maintenance and Its Environmental Effect DOI: http://dx.doi.org/10.5772/intechopen.86907*

*Salt in the Earth*

**Figure 4.**

A good example of the impact of urban runoff on biota is the Frenchman's Bay lagoon, receiving direct runoff from Canada's busiest highway. Eyles et al. [53] underlined a marked reduction in the area of vegetation of a wetland corresponding to 30% since 1970 and 60% since 1939. Furthermore, reduced diversity and coverage of submergent plant species is reflected in changing fish populations in the lagoon. The authors showed that the largest contemporary impactor on environmental qual-

Contaminated soils and waters can be remediated by various methods which are not suitable for an *in situ* treatment. For the road runoff treatment, conventional desalination techniques (reverse osmosis and membrane processes) are

Currently, preference is being given to *in situ* methods that are less environmentally disruptive and more economical. In this context, biotechnology offers phytore-

Phytoremediation is based on the use of plants and their associated microorgan-

isms for the removal, degradation, or stabilization of toxic substances from the environment. Depending on the contaminant and on the plant characteristics,

The first objective of the phytoremediation is to limit the impacts of some contaminants. This can be obtained by several ways. Firstly, by phytostabilization, that is, immobilization of the contaminant in the contaminated soils (after incorporation of contaminants into roots, metals are precipitated as insoluble forms and trapped in the soil matrix). This technique diminishes the mobility and bioavailability of contaminants by different mechanisms such as sorption, complexation, or precipitation [94]. Secondly, by phytodegradation of the contaminant (contaminants are degraded inside plant cells by specific enzymes) [93, 95]. And finally, by phytoextraction from the soil which involves the absorption of contaminants by roots and their accumulation in the aerial parts [96]. It is mainly applied to metals (Cd, Ni, Cu, Zn, and Pb) and preferentially uses hyperaccumulator plants that have the ability to store high concentrations of specific metals in their aerial parts (0.01–1% dry weight, depending on the metal). Phytoextraction is the most commonly used technique and probably the most economic and

ity in Frenchman's Bay watershed derives from the salting operations.

**4. Treatment possibilities**

*Roadside vegetation impacted by road salt [92].*

mediation techniques as a suitable alternative [93].

different phytoremediation techniques take place (**Figure 5**).

too expensive.

**112**

efficient one [94].

**Figure 5.** *Schematic representation of phytoremediation strategies [93].*

In order to develop such a technique for the remediation of a contaminated soil, it is important to choose appropriate plants. Indeed, the choice of the plant will depend on the environmental conditions it will be submitted to, mainly soil composition and pollutant that is aimed for phytoremediation. In order for a plant to be considered as a good phytoremediator, it has to have high tolerance to the pollutants and has to be able to accumulate or degrade pollutants. For a good efficiency, it is necessary that the plant has fast growth and high biomass production, as well as a well-developed root system. Finally, it has to be well adapted on the climatic and environmental conditions it will be submitted to [18].

Phytodesalination, in particular, is a modality of phytoextraction based on the use of halophytes for removal of salts from saline soils. Several studies investigate the possibility of using phytodesalination for road runoff treatment [97–102].

Morteau et al. [100] investigated a possibility for the treatment of road runoff in Québec by *Atriplex patula*, *Salicornia europaea*, and *Spergularia canadensis*. The authors showed that all species accumulated important masses of salt, but that the mass of accumulated salt depends on the plant morphology (size and weight), species, and concentration of the salt exposure. Their study shows that, taking into account the chloride accumulation and plant weight, *Atriplex patula* is the most suitable for the accumulation of chlorides and of sodium.

Suaire et al. [102] and Durickovic et al. [97] showed that two Atriplex species (*Atriplex hortensis* and *Atriplex halimus*) seem to be well adapted for the road runoff remediation. Indeed, these species showed they both have salt and metal

accumulation abilities, but also have capacities suited for the implementation in the road runoff treatment systems. Indeed, *Atriplex hortensis* is particularly interesting because of its fast growth rate, attending 1 m of height in 1 year and *Atriplex halimus* because of its water stress tolerance and ability to accumulate metals, contaminants that are also present in road runoffs.

#### **5. Conclusion**

Significant increases in sodium and chloride concentrations in the different environmental compartments (water, soil, and biota) have been reported and correlated to deicing salt application. These increases lead to important environmental impacts such as the increase in soil pH and salinity, modification of the soil structure, reduction of the availability of nutriments for the vegetation, and loss of biodiversity. Hence, many European countries (Germany, Finland, Norway, Sweden, and Switzerland) and Canada are preoccupied with the environmental risks that the usage of deicing salt implies. They entered the usage of deicing salts in their code of the environment and prohibited their use in vulnerable areas. Canada also entered road salt in their list of toxic products of the Canadian law for the protection of the environment in 1999.

Despite of its well-known environmental impacts, it is not possible to overcome the need of usage of salt as road salt. Numerous studies are led in order to optimize its applications and diminish its rejections into the environment. However, even if the quantities applied on roads are diminished, the salt will nevertheless end in the environment.

The concentrations of sodium and chlorides rejected into the environment may only be regulated by controlling the water output flow of collection systems or retention ponds along roadside. Several studies investigate the possibility of using phytodesalination (i.e., extraction of salt from soil or water by plants which concentrate it in their biomass) for road runoff treatment. These studies show promising results, particularly with the *Atriplex* halophytes species, but are still in their research phase and are not yet operational. In the meantime, salt surveillance in environmental media is thus of great importance in order to identify the areas that are most vulnerable and where optimization of salting operations, as well as of retention systems are needed.

#### **Author details**

Ivana Durickovic Cerema, TEAM, Tomblaine, France

\*Address all correspondence to: ivana.durickovic@cerema.fr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**115**

*NaCl Material for Winter Maintenance and Its Environmental Effect*

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*NaCl Material for Winter Maintenance and Its Environmental Effect DOI: http://dx.doi.org/10.5772/intechopen.86907*

### **References**

*Salt in the Earth*

**5. Conclusion**

accumulation abilities, but also have capacities suited for the implementation in the road runoff treatment systems. Indeed, *Atriplex hortensis* is particularly interesting because of its fast growth rate, attending 1 m of height in 1 year and *Atriplex halimus* because of its water stress tolerance and ability to accumulate metals,

Significant increases in sodium and chloride concentrations in the different environmental compartments (water, soil, and biota) have been reported and correlated to deicing salt application. These increases lead to important environmental impacts such as the increase in soil pH and salinity, modification of the soil structure, reduction of the availability of nutriments for the vegetation, and loss of biodiversity. Hence, many European countries (Germany, Finland, Norway, Sweden, and Switzerland) and Canada are preoccupied with the environmental risks that the usage of deicing salt implies. They entered the usage of deicing salts in their code of the environment and prohibited their use in vulnerable areas. Canada also entered road salt in their list of toxic products of the Canadian law for the

Despite of its well-known environmental impacts, it is not possible to overcome the need of usage of salt as road salt. Numerous studies are led in order to optimize its applications and diminish its rejections into the environment. However, even if the quantities applied on roads are diminished, the salt will

The concentrations of sodium and chlorides rejected into the environment may only be regulated by controlling the water output flow of collection systems or retention ponds along roadside. Several studies investigate the possibility of using phytodesalination (i.e., extraction of salt from soil or water by plants which concentrate it in their biomass) for road runoff treatment. These studies show promising results, particularly with the *Atriplex* halophytes species, but are still in their research phase and are not yet operational. In the meantime, salt surveillance in environmental media is thus of great importance in order to identify the areas that are most vulnerable and where optimization of salting operations, as well as of

contaminants that are also present in road runoffs.

protection of the environment in 1999.

nevertheless end in the environment.

retention systems are needed.

Cerema, TEAM, Tomblaine, France

provided the original work is properly cited.

\*Address all correspondence to: ivana.durickovic@cerema.fr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

**Author details**

Ivana Durickovic

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*Salt in the Earth*

[16] Ke C, Li Z, Liang Y, Tao W, Du M. Impacts of chloride de-icing salt on bulk soils, fungi, and bacterial populations surrounding the plant rhizosphere. Applied Soil Ecology. 2013;**72**:69-78. DOI: 10.1016/j.apsoil.2013.06.003

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management facility: Evidence obtained by adapting an integrated sediment quality assessment approach. Water Research. 2012;**46**(20):6671-6682. DOI:

Research Branch; 2007. 264p

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10.1021/es00028a006

2011. 33p

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s11252-007-0031-x

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[18] Suaire R. Dynamique de transfert des fondants routiers dans un bassin de rétention des eaux de ruissellement

d'assainissement par phytoremédiation [thesis]. Nancy: Université de Lorraine;

[19] Backstrom M, Karlsson S, Baeckman L, Folkeson L, Lind B. Mobilisation of heavy metals by deicing salts in a roadside environment. Water Research. 2004;**38**:720-732. DOI: 10.1016/j.

[20] Kaushal SS, Groffman PM, Lineks GE, Belt KT, Stack WP, Kelly VR, et al. Increased salinization of freshwater in the northeastern United States. Proceedings of the National Academy of Sciences of the United States of America. 2005;**102**(38):13517-13520. DOI: 10.1073/pnas.0506414102

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[22] Munns R, Termaat A. Whole-plant responses to salinity. Functional Plant Biology. 1986;**13**(1):143-160. DOI:

[23] Cunningham MA, Snyder E, Yonkin D, Ross M, Elsen T. Accumulation

routières: Vers une solution

Cerema; 2016. 57p

watres.2003.11.006

2015. 56p

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B05-152

10.1071/PP9860143

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10.1016/j.scitotenv.2014.12.012

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*Salt in the Earth*

2004;**132**(3):375-384

2004;**19**(4):296-301

Ireland. 1981;**20**:161-207

using different methods of

measurement. Water, Air, and Soil Pollution. 2007;**182**(1-4):173-185

[82] Öberg G, Sandén P. Retention of chloride in soil and cycling of organic matter-bound chlorine. Hydrological Processes. 2005;**19**(11):2123-2136

[83] Kincaid DW, Findlay SEG. Sources of elevated chloride in local streams: Groundwater and soils as potential reservoirs. Water, Air, and Soil Pollution. 2009;**203**(1-4):335-342

[84] Svensson T, Sandén P, Bastviken D, Öberg G. Chlorine transport in a small catchment in Southeast Sweden during two years. Biogeochemistry.

[85] Acosta JA, Jansen B, Kalbitz K, Faz A, Martínez-Martínez S. Salinity increases mobility of heavy metals in soils. Chemosphere.

[86] Quirk JP, Schofield RK. The effect of electrolyte concentration on soil permeability. Journal of Soil Science.

[87] Frenkel H, Goertzen JO, Rhoades JD. Effects of clay type and content,

2007;**82**(2):181-199

2011;**85**(8):1318-1324

1955;**6**(2):163-178

road retention/infiltration ponds in France. Environmental Pollution.

exchangeable sodium percentage, and electrolyte concentration on clay dispersion and soil hydraulic conductivity. Soil Science Society of America Journal. 1978;**42**(1):32-39

[88] Quirk JP. Soil permeability in relation to sodicity and salinity.

Philosophical Transactions of the Royal Society A. 1986;**316**(1537):297-317

[89] Tejada M, Gonzalez J. Beet vinasse applied to wheat under dryland conditions affects soil properties and yield. European Journal of Agronomy.

[90] Flückinger W, Braun S. Perspectives of reducing the deleterious effect of de-icing salt upon vegetation. Plant and Soil. 1981;**63**(3):527-529. DOI: 10.1007/

2005;**23**(4):336-347

[91] Durickovic I. Impacts

[Accessed: 30 June 2019]

[93] Favas PJC, Pratas J, Varun M, D'Souza R, Paul MS. Phytoremediation of soils contaminated with metals and metalloids at mining areas: Potential of native flora. In: Hernandez Soriano MC, editor. Environmental Risk Assessment of Soil Contamination. Rijeka, Croatia: IntechOpen; 2014. pp. 485-517. DOI:

[94] Morel JL, Chaineau CH, Schiavon M, Lichtfouse E. The role of plants in the remediation of contaminated soils. In: Baveye P, Block J-C, Goncharuk V, editors. Bioavailability of Organic Xenobiotics in the Environment, Volume 64 of the NATO ASI Series. Netherlands:

Springer; 1999. pp. 429-449

environnementaux de l'exploitation hivernale des routes. Journées Techniques Routes (JTR 2013); 6-7 February 2013;

[92] Urban J. Minimizing the Effects of Salting on Urban Trees [Internet]. 2010. Available from: http://www.deeproot. com/blog/blog-entries/minimizingthe-effects-of-salting-on-urban-trees

BF02370056

Nantes (France)

10.5772/57469

[79] CzerniawskaKusza I, Kusza G, Dużyński M. Effect of deicing salts on urban soils and health status of roadside trees in the Opole region. Environmental Toxicology.

[80] Manning R. On the flow of water in open channels and pipes. Transactions of the Institution of Civil Engineers of

[81] Lundmark A, Olofsson B. Chloride deposition and distribution in soils along a deiced highway—Assessment

**120**

[96] Mench M, Schwitzguebel J-P, Schroeder P, Bert V, Gawronski S, Gupta S. Assessment of successful experiments and limitations of phytotechnologies: Contaminant uptake, detoxification and sequestration, and consequences for food safety. Environmental Science and Pollution Research. 2009;**16**(7):876-900

[97] Durickovic I, Suaire R, Colin C, Barbier L, Leblain JY, DeRouck AC. An investigation of the road salt phytoremediation possibilities in France. Routes/Roads. 2018;**377**:44-48

[98] Greipsson S. Phytoremediation. Nature Education Knowledge. 2011;**3**:7

[99] Manousaki E, Kalogerakis N. Halophytes present new opportunities in phytoremediation of heavy metals and saline soils. Industrial and Engineering Chemistry Research. 2011;**50**:656-660

[100] Morteau B, Galvez-Cloutier R, Leroueil S. Développement d'une chaine de traitement pour l'atténuation des contaminants provenant des sels de voiries de l'autoroute Félix-Leclerc: Lit filtrant et marais épurateur construit adapté. Technical Report, Université de Laval, Québec; 2006

[101] Shelef O, Gross A, Rachmilevitch R. The use of Bassia indica for salt phytoremediation. Water Research. 2012;**46**:3967-3976

[102] Suaire R, Durickovic I, Framont-Terrasse L, Leblain J-Y, De Rouck A-C, Simonnot M-O. Phytoextraction of Na<sup>+</sup> and Cl<sup>−</sup> by *Atriplex halimus* and *Atriplex hortensis* L.: A promising solution for remediation of road runoff contaminated with deicing salts. Ecological Engineering. 2016;**67**:182-189

### *Edited by Mualla Cengiz and Savas Karabulut*

Salt is a predominant compound for humankind and the earth preserves an important source of this element of life. This book reviews this multi-disciplinary issue in which geoscientists, historians, agriculturalists, medical doctors, and general scientists have been interested in its nature. The authors have provided contributions on the origin and history of salt, intrusion with freshwater effect, its usability as a material, and its role in life. The safety of groundwater resources should be a priority for humanity. Contribution on this important topic is provided by geophysical investigations to characterize saltwater intrusions in aquifers. This book also presents a general overview on salt intake and its role in food and human health. Methods of salt recovery and surface salination as well as its usage in the environment will provide new aspects in earth science.

Published in London, UK © 2020 IntechOpen © Anna Usova / iStock

Salt in the Earth

Salt in the Earth

*Edited by Mualla Cengiz* 

*and Savas Karabulut*