**3. Investigation of ion-exchange properties of natural zeolite**

The intensive use of zeolites in various fields of science and practice is based largely on their ion exchange properties, which are one of the main parameters that characterize their sorption and technological properties. The use of zeolites as selective sorbents can solve a number of important problems of technology and environment (Table 3). In this regard, commercial development of deposits of natural zeolites, which due to low cost can be applied in various fields where the use of synthetic analogues is marginal, is required.


**Table 3.** Use of natural zeolites in ion-exchange process

Acid resistance is crucial to the technological application of clinoptilolite. The study of the conditions for maintaining its crystallinity allows creating a basis to obtain the samples intermediate in the degree of cations removal and dealumination which have acidic properties.

It is established [5] that two stages of acid activated cation removal - ion exchange and dealumination – are observed as a result of zeolite reaction with dilute solutions. The former may be connected with polycationicity of mineral. In the latter case, the divalent cations Ca2+ are harder replaced by hydrogen than monovalent ones. In processing zeolites with more concentrated acid solutions there is a shift to the solution of aluminum from tetrahedron with the formation of high-silicon core. The crystal structure thereof can be preserved up to a very high degree of cations removal and dealumination.

In practice, in most cases, clinoptilolite containing material is rarely used in its natural form and it is usually subjected to additional chemical pre-treatment to improve its sorption, mainly ion-exchange properties. The most common method of zeolite adsorbent targeted modification is a cation-exchange modification, consisting in the transfer of polycationic natural material into one of monocationic form (H-, Na, Ca, NH4-, etc.).

266 Ion Exchange Technologies

Method of application

Without regeneration

Regeneration with solutions

With the self refresh clinoptilolite

**3. Investigation of ion-exchange properties of natural zeolite** 

clinoptilolite mordenite

mordenite

clinoptilolite mordenite

clinoptilolite mordenite

**Table 3.** Use of natural zeolites in ion-exchange process

a very high degree of cations removal and dealumination.

The intensive use of zeolites in various fields of science and practice is based largely on their ion exchange properties, which are one of the main parameters that characterize their sorption and technological properties. The use of zeolites as selective sorbents can solve a number of important problems of technology and environment (Table 3). In this regard, commercial development of deposits of natural zeolites, which due to low cost can be applied in various fields where the use of synthetic analogues is marginal, is required.

Zeolite Fields of application

clinoptilolite Purification of wastewater from the nonferrous

clinoptilolite The introduction of zeolites in the soil to increase

clinoptilolite Concentration of Sr from the waste and natural

Acid resistance is crucial to the technological application of clinoptilolite. The study of the conditions for maintaining its crystallinity allows creating a basis to obtain the samples intermediate in the degree of cations removal and dealumination which have acidic properties. It is established [5] that two stages of acid activated cation removal - ion exchange and dealumination – are observed as a result of zeolite reaction with dilute solutions. The former may be connected with polycationicity of mineral. In the latter case, the divalent cations Ca2+ are harder replaced by hydrogen than monovalent ones. In processing zeolites with more concentrated acid solutions there is a shift to the solution of aluminum from tetrahedron with the formation of high-silicon core. The crystal structure thereof can be preserved up to

In practice, in most cases, clinoptilolite containing material is rarely used in its natural form and it is usually subjected to additional chemical pre-treatment to improve its sorption,

Cleaning of waste water from the radioactive ions 137Cs, 90Sr, followed by burial of the zeolites. Treatment of domestic wastewater from ammonium nitrogen with followed by the use of zeolite as ammonium fertilizer

metals using zeolites as a flux

The use of zeolites as filter material for water treatment

the duration of fertilizer

Concentration and separation of alkali metals from technological solutions and natural waters

waters

Concentration of non-ferrous metals from technological solutions, waste and natural waters When processing high-silicon zeolites with strong acids a sequential substitution of cations hydroxonium ions [6] occurs. Hydrogen forms of zeolites can be regarded as solid crystalline alumosilicic polyacids. Therefore, the method of potentiometric titration with alkaline solutions which allows evaluating the active groups' acidity usual for ion exchanger may be used for hydrogen forms of zeolites. For high-silicon natural zeolites (clinoptilolite, mordenite) with enhanced stability in acidic solutions in comparison with other zeolites, the hydrogen forms can be obtained directly by treatment of acid solutions. The high stability of clinoptilolite to heating and acids can be explained by an increase in the stability of skeleton associated with a decrease in the number of weaker bonds Al-O (1,66 Å) and an increase in the number of strong bonds Si-O (1,62 Å).

To study the acid-base properties of the investigated zeolite air-dried sample, previously modified with 3 N hydrochloric acid was being treated with 0,1 N alkali solutions within one day at room temperature. Analysis of the potentiometric titration curve (Figure 4) shows that the hydrogen forms of zeolite obtained by treatment with acid are titrated with KOH solution. At alkali charge 0,5 mg-eq / g there is a clear inflection point.

Consequently, the hydrogen forms of zeolites obtained by treatment with HCl have a more acidic hydroxyl grouping. The other exchange centers are subacid and uniformly distributed in the mineral structure. The static exchange capacity of the activated zeolite is 2,7 mg-eq /g.

**Figure 4.** Potentiometric titration curve of the H + form of zeolite.

The capacity for chemical modification of natural zeolites gives the possibility of obtaining a large variety of adsorbents, catalysts and other fine general-purpose bodies. The results of these studies contribute to the establishment of limits of clinoptilolite in the presence of acidic reagents, and in addition, the identification of opportunities for obtaining the modified forms with novel properties. The successful implementation of technology of sorption metal extraction is realized by a comprehensive study of the processes occurring in a complex system ion exchanger-solution. The study of adsorption on decationated and dealuminated clinoptilolite samples revealed their ability to selective adsorption of large cations [7,8]. This is apparently due to the proximity of the ions sizes and the kinetic diameters of clinoptilolite channels, which defines a strong Coulomb interaction with structure of the zeolite. In addition, it may be due to the presence of stronger acid sites and stabilizing role of the major cations in conditions of a significant reduction in their number in the internal space stipulated by a decrease in tetrahedral aluminum content.

Analysis of the kinetic curves of lead ions sorption in zeolite under study showed that the time to reach equilibrium decreased as the concentration of original solution increased and the grain size [8] decreased. The obtained results indicate that the rate of exchange of lead ions on the H-form of clinoptilolite is controlled by internal diffusion mechanism of the process. The effective diffusion coefficient depends linearly on the radius of the incoming ion and does not depend on the concentration of external solution.

The problem of waste water treatment is largely due to the lack of low-cost multifunctional sorbents stable during operation. Existing industrial sorbents with high sorption capacity are economically unfeasible due to their high cost. The results of experiments with investigated zeolite show that sorption of phenol on the natural sample and aminated form thereof happens with high degree of extraction from dilute solutions [9]. Modification of the PAV sorbent allows adsorbing phenol from aqueous solutions to the level of MPC and increasing the efficiency of the process in the presence of organic impurity compounds.

The presence of commercial deposits of clinoptilolite and experience of its application in various sorption processes make it possible to use it in the process flow sheets designated to extract a number of metal cations from solutions and wastewater. Significant amounts of the latter require the methods of treatment to have low cost and high efficiency. Addressing these issues is also associated with an additional yield of these metals which are being irretrievably lost currently.

One of the criteria of the waste water condition is nonferrous and heavy metal ions content in it. The latter are contained in waste water of nonferrous and ferrous metallurgy enterprises, concentration plants, galvanizing rooms of plants. There are different methods either physical or chemical which enable to retrieve ions of metals from solutions and industrial waste. The treatment of this sewage by ions isolation in the form of hydroxides cannot provide the required drop of concentration of the latter in sewage. Metals deposition in a form of sulphides is connected with the use of toxic reagents such as Na2S and H2S. The effective sewage treatment can be obtained by the sorption process which is easy to control and allows reducing relative detection limits.

The sorption of copper ions (II) under static conditions at different concentrations of mother solution, pH medium and in presence of various metals ions was conducted on investigated natural zeolite.

The effectiveness of sorption in many respects is determined by kinetics of the process. The curves of copper ions sorption are presented in the Figure 5. The equilibrium in distribution of metal ions among the sorbent and solution at room temperature is established within short period of time (30 min). Short time of process is determined by the presence of chemically active groups in surface layers and high selectivity of sorbent toward metal ions. The results of conducted studies showed that natural zeolite has high activity at sorption of Cu2+ even in lower concentrations (0,125 g/l). Within 30 minutes the degree of recovery/extraction is 92% and it reaches 95% with increase of content of metal ions up to 0,5 g/l. At sorption of Cu2+ in areas of ions metal concentrations in natural waters 0,001-0,0005 mg/l high degree of recovery/extraction (90%) for 30 minutes is also reached, that shows the effectiveness of used sorbent. Hyperactivity of the latter at low contents stipulates for the suitability of use of metal ions for extraction of trace contaminants.

268 Ion Exchange Technologies

irretrievably lost currently.

natural zeolite.

and allows reducing relative detection limits.

sorption metal extraction is realized by a comprehensive study of the processes occurring in a complex system ion exchanger-solution. The study of adsorption on decationated and dealuminated clinoptilolite samples revealed their ability to selective adsorption of large cations [7,8]. This is apparently due to the proximity of the ions sizes and the kinetic diameters of clinoptilolite channels, which defines a strong Coulomb interaction with structure of the zeolite. In addition, it may be due to the presence of stronger acid sites and stabilizing role of the major cations in conditions of a significant reduction in their number

Analysis of the kinetic curves of lead ions sorption in zeolite under study showed that the time to reach equilibrium decreased as the concentration of original solution increased and the grain size [8] decreased. The obtained results indicate that the rate of exchange of lead ions on the H-form of clinoptilolite is controlled by internal diffusion mechanism of the process. The effective diffusion coefficient depends linearly on the radius of the incoming

The problem of waste water treatment is largely due to the lack of low-cost multifunctional sorbents stable during operation. Existing industrial sorbents with high sorption capacity are economically unfeasible due to their high cost. The results of experiments with investigated zeolite show that sorption of phenol on the natural sample and aminated form thereof happens with high degree of extraction from dilute solutions [9]. Modification of the PAV sorbent allows adsorbing phenol from aqueous solutions to the level of MPC and increasing the efficiency of the process in the presence of organic impurity compounds.

The presence of commercial deposits of clinoptilolite and experience of its application in various sorption processes make it possible to use it in the process flow sheets designated to extract a number of metal cations from solutions and wastewater. Significant amounts of the latter require the methods of treatment to have low cost and high efficiency. Addressing these issues is also associated with an additional yield of these metals which are being

One of the criteria of the waste water condition is nonferrous and heavy metal ions content in it. The latter are contained in waste water of nonferrous and ferrous metallurgy enterprises, concentration plants, galvanizing rooms of plants. There are different methods either physical or chemical which enable to retrieve ions of metals from solutions and industrial waste. The treatment of this sewage by ions isolation in the form of hydroxides cannot provide the required drop of concentration of the latter in sewage. Metals deposition in a form of sulphides is connected with the use of toxic reagents such as Na2S and H2S. The effective sewage treatment can be obtained by the sorption process which is easy to control

The sorption of copper ions (II) under static conditions at different concentrations of mother solution, pH medium and in presence of various metals ions was conducted on investigated

The effectiveness of sorption in many respects is determined by kinetics of the process. The curves of copper ions sorption are presented in the Figure 5. The equilibrium in distribution

in the internal space stipulated by a decrease in tetrahedral aluminum content.

ion and does not depend on the concentration of external solution.

Due to the fact that waste outlet waters may contain both different composition and variable acidity, there is a need to study the influence of pH degree on sorption of copper ions. The curves of recovery degree dependence on acidity of solution under constancy of concentration Cu2+ (0,25 g/l) show (Figure 6) that the degree of metal ions recovery in studied conditions decreases with increase of acidity of solution due to competitive effect of hydrogen ions. Thus, in рН<4 area the extracting ability of zeolite falls to 10%. With increase of pH medium to more than 4-5 the sediments of basic salts and hydroxides delayed by ionite are generated and sorption occurs additionally due to adhesion of generated sediments (recovery is 90-91%). Under collective concentration of Cu2+, Pb2+, Co2+, Ni2+ with cumulative content of metals ions 0,5 g/l (concentration of each ion is 0,125 g/l) sorption of copper ions occurs with delayed kinetics (Figure 7). The maximum degree of recovery is 67% for 120 minutes. According to the obtained data under accepted conditions natural zeolite equally sorbs copper and lead ions.

It is determined that ratio of the solution volume to sorbent mass influences recovering ability thereof. Growth of zeolite content in the solution from 0,5 g to 2 g (V=50 ml) leads to increase of recovery effectiveness by 3%. Degree of sorption reaches 97% within 30 minutes.

**Figure 5.** Degree Cu2+ by natural zeolite as a function of the process duration t. Cs: 0,125 (1); 0,25 (2); 0,5 (3); CСu2+=0,5 g/l; V=50 ml; m=0,5 g.

**Figure 6.** Degree of Cu2 + by natural zeolite as a function of the pH. CСu2+=0,25 g/l; V = 50 ml; m = 0,25 g / l; = 30 min.

**Figure 7.** Degree Pb2+ (1); Cu2+ (2); Co2+ (3); Ni2+ (4) by natural zeolite as a function of the process duration t. CМе2+=0,5g/l; V=50 ml; m=0,5 g.

Thus, the suggested sorbent effectively recovers copper ions from model solutions within short periods of time. Cheap natural zeolites may be used in the processes which do not provide regeneration of ionites. The opportunity of its one-time use with subsequent burial provides application thereof in such spheres where synthetic zeolites or ion-exchange polymers cannot be used under economical reasons.
