**2. Raw materials from natural brines**

The Tunisian territory contains a great number of sebkhas and chotts, especially in the South. The more important ones are Chott El Jerid, Sebkha El Melah of Zarzis, Sebkha Oum el Khialate, Sebkha El Briga and Sebkha El Adhibate (**Figure 1**) [13]. Previous geological, hydrogeological and geochemical studies proved that these deposits contain considerable reserves of natural brines (**Table 1**).

The meteorological conditions in the South of Tunisia and particularly at Sebkha El Melah of Zarzis (**Figure 2**) are favorable for the recovery of the existing salts by solar evaporation. The raw material is taken from Aïn Serab, located at the Northern border of Sebkha El Melah of Zarzis. This choice is justified by the advantages present in this mineral resource and the influence on the economic sector for possible industrial exploitation [14].

These salt lakes which are considered as important material resources useful for industry and agriculture. They are called sebkha or chott, and they cover a large part of Tunisian land. The liquid raw material enclosed in these deposits is named brine and always assimilated to the quinary system: Na<sup>+</sup> , K+ , Mg2+/Cl<sup>−</sup> , SO4 2−/H2 O. These solutions are valuable and expected to play an important role in the economic sector. To take advantage of this raw material, several works

were developed. Besides the study of geological aspects and phase diagrams of the system representing the brines, investigations were extended to the modeling of phase diagrams and

Sorel Cements from Tunisian Natural Brines http://dx.doi.org/10.5772/intechopen.74315 175

extraction of interesting salts.

**Figure 1.** Location of Tunisian sebkhas and chotts.

**Figure 1.** Location of Tunisian sebkhas and chotts.

MgCl2

take place:

.8H2

174 Cement Based Materials

ing chemical reactions [7]:

The presence of Mg(OH)2

of natural brines (**Table 1**).

quinary system: Na<sup>+</sup>

, K+

, Mg2+/Cl<sup>−</sup>

O (phase5) and 3Mg(OH)2

5MgO + MgCl2 + 13H2

3MgO + MgCl2 + 11H2

MgO + H2

**2. Raw materials from natural brines**

They are the only stable phases in the system MgO-MgCl<sup>2</sup>

.MgCl2

.8H2

O = 5Mg (OH)

O = 3Mg (OH)

O = Mg (OH)

indicates the low quality of magnesium oxychloride cement.

water, a parallel or competitive reaction, corresponding to magnesium oxide hydration, can

Furthermore, the widespread use of magnesium oxychloride cement has been limited because of loss of strength on prolonged excessive exposure to water [8]. Much research has long been processed to improve the water resistance of magnesium oxychloride based on the ability to

ring speed) on compressive strength and setting time of MOC was carried out. The application of the experimental design methodology was used in order to maximize synthesis yield

The Tunisian territory contains a great number of sebkhas and chotts, especially in the South. The more important ones are Chott El Jerid, Sebkha El Melah of Zarzis, Sebkha Oum el Khialate, Sebkha El Briga and Sebkha El Adhibate (**Figure 1**) [13]. Previous geological, hydrogeological and geochemical studies proved that these deposits contain considerable reserves

The meteorological conditions in the South of Tunisia and particularly at Sebkha El Melah of Zarzis (**Figure 2**) are favorable for the recovery of the existing salts by solar evaporation. The raw material is taken from Aïn Serab, located at the Northern border of Sebkha El Melah of Zarzis. This choice is justified by the advantages present in this mineral resource and the

These salt lakes which are considered as important material resources useful for industry and agriculture. They are called sebkha or chott, and they cover a large part of Tunisian land. The liquid raw material enclosed in these deposits is named brine and always assimilated to the

an important role in the economic sector. To take advantage of this raw material, several works

O. These solutions are valuable and expected to play

influence on the economic sector for possible industrial exploitation [14].

, SO4 2−/H2

by searching for optimum experimental conditions in a less number of experiments.

it binding to various organic and inorganic aggregates such as high active SiO<sup>2</sup>

aluminates [11] sulfates and phosphoric acid or phosphate [12].

In this chapter, the influence of three factors (mass ratio of MgCl<sup>2</sup>

2

2


.MgCl2 + 8H2

.MgCl2 + 8H2

O (phase 3) which are obtained by the follow-

O (1)

O (2)

[9, 10], active

O. Due to the presence of excess

<sup>2</sup> (3)

/MgO, mixing time and stir-

were developed. Besides the study of geological aspects and phase diagrams of the system representing the brines, investigations were extended to the modeling of phase diagrams and extraction of interesting salts.


**Table 1.** Characteristics of south Tunisian sebkhas and chotts.

## **2.1. Magnesium oxide**

Exceptional proprieties of MgO as a catalytic material [15, 16] or as an additive in building supplies (Sorel cement, lightweight building panels) and superconductor products have attracted both fundamental and application studies [17–22].

Magnesium oxide (MgO or periclase) is one among the most industrially important magnesium compounds. Approximately 20% of worldwide production came from seawater, brines and desalination reject brine [15]. Magnesium oxide is used as an exceptionally important material in catalysis [15, 16], toxic waste remediation [18] or as additives in refractories, paints, in the manufacture of fertilizers, animal feedstuffs, building materials (Sorel cement, lightweight building panels) and superconductor products [19–21]. A panel of fundamental and applied studies is encountered in literature [21–25]. It shows particularly that magnesium hydroxide production from seawater or brine precipitates by adding a strong base and after separation is calcined to produce MgO. Furthermore, magnesia qualities may differ depending upon the physicochemical conditions of preparation and the precursor type.

In the literature, MgO was prepared mainly by calcination of Mg(OH)<sup>2</sup> obtained either by precipitation [21, 22] or by MgO hydration [21, 23–25]. In our case, magnesium oxide was produced from magnesium sulfate (MgSO4 .7H2 O) by precipitation into Mg(OH)<sup>2</sup> using a strong base (NH<sup>4</sup> OH) in the first step and then calcined in a programmable furnace under controllable conditions to produce MgO in the second step.

The sensitivity of the present reactions to several parameters was carried out. These considerations altogether led to applying the experimental design methodology in order to maximize synthesis yield by searching for the optimum experimental conditions in a smaller number of experiments.

#### **2.2. Magnesium chloride**

Magnesium chloride is industrially useful in some agricultural applications. It is mainly used for magnesium metal production and Sorel cement manufacturing (Büchel et al., 2000). Frequently, natural raw material is complex and must be treated to recover solid magnesium chloride. Various procedures (Boyum et al., 1973; Burke and Smith, 1949; Fezei et al., 2009; Smith, 1970) have been developed in order to produce this salt from natural brines. The

present work is devoted to magnesium chloride hexahydrate recovery from a mixed salt solution. 1.4-Dioxan was chosen to achieve this aim. The action of this organic solvent on magnesium chloride has been often studied in the case of pure magnesium chloride solu-

Sorel Cements from Tunisian Natural Brines http://dx.doi.org/10.5772/intechopen.74315 177

tions (Gaska, 1967; Weissenberg, 1969).

**Figure 2.** Sebkha El Melah of Zarzis [14].

**Figure 2.** Sebkha El Melah of Zarzis [14].

**2.1. Magnesium oxide**

176 Cement Based Materials

the precursor type.

**2.2. Magnesium chloride**

base (NH<sup>4</sup>

duced from magnesium sulfate (MgSO4

lable conditions to produce MgO in the second step.

Exceptional proprieties of MgO as a catalytic material [15, 16] or as an additive in building supplies (Sorel cement, lightweight building panels) and superconductor products have

Magnesium oxide (MgO or periclase) is one among the most industrially important magnesium compounds. Approximately 20% of worldwide production came from seawater, brines and desalination reject brine [15]. Magnesium oxide is used as an exceptionally important material in catalysis [15, 16], toxic waste remediation [18] or as additives in refractories, paints, in the manufacture of fertilizers, animal feedstuffs, building materials (Sorel cement, lightweight building panels) and superconductor products [19–21]. A panel of fundamental and applied studies is encountered in literature [21–25]. It shows particularly that magnesium hydroxide production from seawater or brine precipitates by adding a strong base and after separation is calcined to produce MgO. Furthermore, magnesia qualities may differ depending upon the physicochemical conditions of preparation and

precipitation [21, 22] or by MgO hydration [21, 23–25]. In our case, magnesium oxide was pro-

The sensitivity of the present reactions to several parameters was carried out. These considerations altogether led to applying the experimental design methodology in order to maximize synthesis yield by searching for the optimum experimental conditions in a smaller number of experiments.

Magnesium chloride is industrially useful in some agricultural applications. It is mainly used for magnesium metal production and Sorel cement manufacturing (Büchel et al., 2000). Frequently, natural raw material is complex and must be treated to recover solid magnesium chloride. Various procedures (Boyum et al., 1973; Burke and Smith, 1949; Fezei et al., 2009; Smith, 1970) have been developed in order to produce this salt from natural brines. The

OH) in the first step and then calcined in a programmable furnace under control-

O) by precipitation into Mg(OH)<sup>2</sup>

.7H2

obtained either by

using a strong

attracted both fundamental and application studies [17–22].

**Table 1.** Characteristics of south Tunisian sebkhas and chotts.

In the literature, MgO was prepared mainly by calcination of Mg(OH)<sup>2</sup>

present work is devoted to magnesium chloride hexahydrate recovery from a mixed salt solution. 1.4-Dioxan was chosen to achieve this aim. The action of this organic solvent on magnesium chloride has been often studied in the case of pure magnesium chloride solutions (Gaska, 1967; Weissenberg, 1969).

As shown in **Figure 3**, the investigated process is mainly composed of six stages. The adopted flow sheet is principally supported by the previous works on natural brines (Janecké, 1907; Berthon, 1962; Cohen-Adad et al., 2002; M'nif and Rokbani, 2004; Hammi, 2004) usually described using the oceanic quinary diagram Na<sup>+</sup> , K+ , Mg2+/Cl<sup>−</sup> , SO4 2−/H2 O. This useful graphic-tool is helpful in natural brines exploitation or valorization. In fact, it defines, during the system's evolution, the number, the nature, the composition and the relative quantity of different condensed phases that crystallize or disappear. The first treatment step consists in evaporating at 35°C the raw brine to precipitate the maximum of sodium chloride (halite).

In the second step, The precipitated salts consist of sodium chloride and small amounts of magnesium-potassium double salt. The third stage consists in maintaining the obtained magnesium salts saturated solution under stirring during four hours at 5°C and to recover the precipitated salt. The fourth step consists in precipitating the potassium- magnesium double

with the production of an end product having good quality. In the two last stages of the process the solution is desulphated by reaction with calcium chloride solution. After removing the calcium sulfate precipitate, the resulting brine; consisted of magnesium chloride together with residual potassium and sodium chloride; is concentrated by evaporation at 35°C to pre-

Magnesium oxide powder was mixed with magnesium chloride solution mechanically to form homogenous MOC pastes. The weight of MgO is fixed and the weight of MgCl<sup>2</sup>

has been varied. Mixtures were cast in cylindrical molds (26 mm in diameter, 50 mm high)

The X-ray diffraction (XRD) analysis was carried out on the powdered sample using X-ray

Differential thermograms were obtained using the Netzsch 449 STA F1 Jupiter thermal analy-

The microstructure of the samples was examined using scanning electron microscope, the

Measurement of thermal conductivity was performed in dry state using the photothermal

Porosity accessible to water of MOC is determined according to EN 12390-7 norm. The measurement of porosity in water under a vacuum of 0.1 bar quantifies the volume of open pores

Cement samples are placed in sealed desiccators and kept under vacuum of 0.1 bar for 12 h.

Previously degassed water is introduced progressively in desiccators to fill all the pores of

Once the samples are saturated, they are kept immersed in water for 24 h, and finally we

*imm* and saturated dry surface mass mss.

deflection technique. Setting time was determined by using the Vicat Apparatus.

O) to eliminate potassium ions; in order to avoid interference

Sorel Cements from Tunisian Natural Brines http://dx.doi.org/10.5772/intechopen.74315

> .6H2 O

179

salt, carnallite (KCl.MgCl2

cipitate the magnesium chloride salt.

**3. Results and discussion**

**3.1. Experimental procedure**

. 6H2

and stored for 24 h, then unmolded and air-cured for 28 days.

sis system. The rate of heating was 15°C/min.

(accessible to water) using the following protocol:

samples, without introducing air bubbles.

determined hydrostatic mass *msss*

The porosity is calculated by Eq. (4):

Carl ZEIIS LEICA S430i model.

powder diffractometer (XRD PHILIPS) with Cu K radiation (λ K = 1.54 Å).

**Figure 3.** Flow sheet of the process for the bischofite salt recovery from Sebkha El Melah natural brine.

In the second step, The precipitated salts consist of sodium chloride and small amounts of magnesium-potassium double salt. The third stage consists in maintaining the obtained magnesium salts saturated solution under stirring during four hours at 5°C and to recover the precipitated salt. The fourth step consists in precipitating the potassium- magnesium double salt, carnallite (KCl.MgCl2 . 6H2 O) to eliminate potassium ions; in order to avoid interference with the production of an end product having good quality. In the two last stages of the process the solution is desulphated by reaction with calcium chloride solution. After removing the calcium sulfate precipitate, the resulting brine; consisted of magnesium chloride together with residual potassium and sodium chloride; is concentrated by evaporation at 35°C to precipitate the magnesium chloride salt.
