**2. Investigation of physico-chemical properties of natural zeolite**

Natural zeolites fields explored in Kazakhstan determine the intensive development of studies in different application areas. In spite of the numerous publications, the physicochemical properties of natural zeolites are still not sufficiently studied.

A quick diagnosis of natural zeolites can be significantly enhanced through a combination of such methods of analysis as X-ray phase and thermographic study. Recording the diffraction pattern makes it possible to state a presence of zeolites isostructural to heulandite even in the mixtures [4]. Analysis of thermogram allows determining the species within this group qualitatively. To that effect you can use the low-temperature area up to 4000 С. According to XRF data, the main phase of zeolite tuff studied is clinoptilolite-heulandite (Figure 1). The distinct peaks 9,58; 8,68; 7,42; 5,69; 5,07; 4,58; 4,37; 3,69; 3,62; 3,45; 3,23 ; 3,03 Å typical for clinoptilolite appear on natural zeolite's diffraction pattern. There are montmorillonite, plagioclase and quartz among other phase components. Comparison of the results with literature data obtained for monophasic clinoptilolite shows that the material in question is close to clinoptilolite according to the composition but it has higher sodium, calcium and iron contents (Table 1)**.** The study thereof showed that it was characterized by Si/Al ratio equal to 3,83.

As a result of the studies held it was stated that zeolite tuff of Shankhanai field of Kazakhstan contained up to 70% of the plate-like shape main product with high ratio between silica and aluminum oxides (heulandite – clinoptilolite). Brown-red colouring thereof specifies to the presence of fine iron oxides.

**Figure 1.** Derivatogram of natural zeolite. 1 – TG; 2 – DTA.


**Table 1.** Changing the chemical composition of clinoptilolite.

The results of thermographic studies are given in the Figure 2. Differential thermal analysis (DTA) data show that the dehydration of clinoptilolite-containing tuff begins from the lowest temperatures, approximately from 60°C, and proceeds continuously over a broad temperature range up to 400°C. The mass loss at this temperature reaches 3,3%. The total mass loss while heating zeolite up to 700°C is 6,7%. Water release in zeolite proceeds continuously and smoothly, as evidenced by the mass loss (TG) curve. The DTA curve of the raw zeolite exhibits several endothermic effects with minimums at 100; 180; 280; 550 and 660°C. The character of DTA and TG curves over the entire temperature range of 50–700°C is indicative of several forms of bound water in minerals [4]. The presence of two endothermic effects due to the release of adsorbed water indicates that active sites in clinoptilolite microcavities are inhomogeneous in energy. The natural zeolite heating curve shows the loss of weakly bound adsorption water and capillary-condensation water at 100°C. The energy of interaction of water molecules with potassium ions is lower, and the endothermic effect at 170°C is due to the desorption of water molecules bound as K+, as well as due to zeolite oxygen framework. Weakly expressed endothermic effects displayed by zeolitic rock thermograms are caused by foreign impurities. At 550°C it is stipulated by the detachment of hydroxyl groups. As follows from the given experimental data, the initial natural zeolite exhibits a fairly high thermal stability (above 700°C).

1 –natural zeolite (№1); after treatment: 2 – 3 N HCl solution, 22-250С (№2); 3 – 12 N HCl solution, 22-250С (№3); 4 – 1,5 N HCl solution, 96-980С (№4); 5 – concentrated solution of HCl, 96-980С (№5)

**Figure 2.** The diffractograms of the zeolite samples

262 Ion Exchange Technologies

A quick diagnosis of natural zeolites can be significantly enhanced through a combination of such methods of analysis as X-ray phase and thermographic study. Recording the diffraction pattern makes it possible to state a presence of zeolites isostructural to heulandite even in the mixtures [4]. Analysis of thermogram allows determining the species within this group qualitatively. To that effect you can use the low-temperature area up to 4000С. According to XRF data, the main phase of zeolite tuff studied is clinoptilolite-heulandite (Figure 1). The distinct peaks 9,58; 8,68; 7,42; 5,69; 5,07; 4,58; 4,37; 3,69; 3,62; 3,45; 3,23 ; 3,03 Å typical for clinoptilolite appear on natural zeolite's diffraction pattern. There are montmorillonite, plagioclase and quartz among other phase components. Comparison of the results with literature data obtained for monophasic clinoptilolite shows that the material in question is close to clinoptilolite according to the composition but it has higher sodium, calcium and iron contents (Table 1)**.**

As a result of the studies held it was stated that zeolite tuff of Shankhanai field of Kazakhstan contained up to 70% of the plate-like shape main product with high ratio between silica and aluminum oxides (heulandite – clinoptilolite). Brown-red colouring

№ НСl, N *The composition of clinoptilolite, %* SiO2/

1 --- 58,08 15,16 2,30 1,42 4,92 2,53 5,95 3,83 2 3 (20-220С, 24 h) 58,19 15,09 1,75 1,27 4,02 2,28 5,60 3,86 3 12 (20-220С, 24h) 58,86 15,05 1,77 1,25 4,05 2,34 5,54 3,91 4 1,5 (96-980С, 6h) 69,16 15,43 1,67 1,18 2,24 1,41 4,95 4,48

The results of thermographic studies are given in the Figure 2. Differential thermal analysis (DTA) data show that the dehydration of clinoptilolite-containing tuff begins from the

SiO2 Al2O3 Na2O К2О CaO MgO Fe2O3 Al2O3

79,10 6,20 1,24 1,01 0,58 0,29 0,70 12,80

The study thereof showed that it was characterized by Si/Al ratio equal to 3,83.

thereof specifies to the presence of fine iron oxides.

**Figure 1.** Derivatogram of natural zeolite. 1 – TG; 2 – DTA.

**Table 1.** Changing the chemical composition of clinoptilolite.

5 Concentration (96-980С, 6h)

It is known that in the process of natural mineral sorbents treatment with acids their pore structure develops. Therefore, we tested different ways of acid processing of natural zeolite with hydrochloric acid. From the standpoint of environmental friendliness of the process (simplicity of purication and regeneration of spent solutions), HCl was used as a modifying acid for sorbent treatment, since the wastes of dilute hydrochloric acid are much easier to purify of leaching products and to neutralize.

In the experiments, we varied the acid concentration, temperature and duration of processing. The effectiveness of activation was evaluated in terms of the total porosity of a sorbent and specific surface area thereof.

Activation typically involves three stages: removal of exchangeable cations, framework dealumination and formation of an amorphous silicon-oxygen phase. The sequence and intensity of the stages are determined by processing conditions and the specific features of zeolites. Acid modification of the investigated zeolite with 3 and 12 N HCl solution within the day (№ 2 and №3) at room temperature showed that the value of silica modulus (Table 1) was not changing essentially. More stringent processing conditions lead to a sharp increase in the silica modulus (Si / Al). At modification by 1,5 N HCl solution by heating (№ 4) clinoptilolite is subject to dealumination and removal of cations without significant destruction of the crystal lattice in comparison with the treatment thereof under the same conditions with a concentrated acid (№ 5). In the latter case the amorphous phase of zeolite forms. These results confirm the XRF data (Figure 1). Comparison of natural and modified samples radiographs indicates to a decrease in the intensity of main reflection characteristics of the mineral up to complete disappearance due to the amorphization of the structure and changes in zeolite cation composition after mineral acid treatment.

The obtained results show that removal of cations and dealumination are insignificant under milder conditions of acid processing. More severe activation conditions result in intensication of these processes. The removal of exchangeable zeolite cations and occupation of the free sites by protons have an effect on the cationic density of the framework and can change the sizes of channel windows. The removal of aluminum from mineral framework also results in partial degradation of zeolite crystal structure.

Location and exploration of large deposits of natural zeolites in different regions of Kazakhstan creates significant scientific-technical prospects for the complex use of natural sorbents, especially for the creation of nanomaterials on their basis.

For the study of morphology of the porous structure of natural zeolites and those ones, activated by acidic treatment, adsorption-desorption measurements have been carried out (Table 2). Natural zeolite (sample №1) is characterized, by the isotherm data, by mesoporosity. It also contains some micropores, because nitrogen vapors are absorbed to some degree at low pressures (p/pS less than 0,1). Its treatment with a 3 N НСl solution (№2) pracically does not change the surface characteristics of the sorbent, and the treatment by a 12 N НСl solution (№3) results in an increase in the total pore volume by a factor of about 2. Porocity increases considerably with the activation with a 1,5 N НСl upon heating (№4). For the initial sample the total pore volume constitutes 0,019574, whereas for the activated ones – 0,19611 (№2); 0,031348 (№3); 0,064101 (№4); 0,122297 (№5) сm3/g. Chemical treatment increases porosity of zeolite by a factor of 6. Differential curves of the pore size distribution have shown that the studied samples possess mainly mono- and bi-dispersion structures. Natural zeolite possesses the mono-dispersion structure with a large maximum in the area of mesopores d ~ 30 Å. For the sample №3, besides, an increase in the field of d~ 20 Å is observed, i.е. the activation of the mineral with 12 N acid in the usual conditions results in the development of micropores, the volume of which increases more than 5 times (Table 2). Differential dimensional spectra of such samples are characterized by the narrow distribution. The sample №4 is characterized by bioporosity, the volume of mesopores increases by a factor of 1,5 and microporosity – by a factor of 217. The further activation of zeolite also leads to an increase in the micro- and mesoporous structure with an extension of the range of the mesopores (№5).


**Table 2.** Surface area and porosity of the zeolite samples

264 Ion Exchange Technologies

It is known that in the process of natural mineral sorbents treatment with acids their pore structure develops. Therefore, we tested different ways of acid processing of natural zeolite with hydrochloric acid. From the standpoint of environmental friendliness of the process (simplicity of purication and regeneration of spent solutions), HCl was used as a modifying acid for sorbent treatment, since the wastes of dilute hydrochloric acid are much

In the experiments, we varied the acid concentration, temperature and duration of processing. The effectiveness of activation was evaluated in terms of the total porosity of a

Activation typically involves three stages: removal of exchangeable cations, framework dealumination and formation of an amorphous silicon-oxygen phase. The sequence and intensity of the stages are determined by processing conditions and the specific features of zeolites. Acid modification of the investigated zeolite with 3 and 12 N HCl solution within the day (№ 2 and №3) at room temperature showed that the value of silica modulus (Table 1) was not changing essentially. More stringent processing conditions lead to a sharp increase in the silica modulus (Si / Al). At modification by 1,5 N HCl solution by heating (№ 4) clinoptilolite is subject to dealumination and removal of cations without significant destruction of the crystal lattice in comparison with the treatment thereof under the same conditions with a concentrated acid (№ 5). In the latter case the amorphous phase of zeolite forms. These results confirm the XRF data (Figure 1). Comparison of natural and modified samples radiographs indicates to a decrease in the intensity of main reflection characteristics of the mineral up to complete disappearance due to the amorphization of the structure and

The obtained results show that removal of cations and dealumination are insignificant under milder conditions of acid processing. More severe activation conditions result in intensication of these processes. The removal of exchangeable zeolite cations and occupation of the free sites by protons have an effect on the cationic density of the framework and can change the sizes of channel windows. The removal of aluminum from

Location and exploration of large deposits of natural zeolites in different regions of Kazakhstan creates significant scientific-technical prospects for the complex use of natural

For the study of morphology of the porous structure of natural zeolites and those ones, activated by acidic treatment, adsorption-desorption measurements have been carried out (Table 2). Natural zeolite (sample №1) is characterized, by the isotherm data, by mesoporosity. It also contains some micropores, because nitrogen vapors are absorbed to some degree at low pressures (p/pS less than 0,1). Its treatment with a 3 N НСl solution (№2) pracically does not change the surface characteristics of the sorbent, and the treatment by a 12 N НСl solution (№3) results in an increase in the total pore volume by a factor of about 2. Porocity increases considerably with the activation with a 1,5 N НСl upon heating (№4). For the initial sample the total pore volume constitutes 0,019574, whereas for the activated ones – 0,19611 (№2);

mineral framework also results in partial degradation of zeolite crystal structure.

easier to purify of leaching products and to neutralize.

changes in zeolite cation composition after mineral acid treatment.

sorbents, especially for the creation of nanomaterials on their basis.

sorbent and specific surface area thereof.

In the NMR spectra of the zeolite samples № 4 and №5 alongside with the signals from aluminum atoms in the tetrahedral coordination (56 ppm), show the signals with the size of chemical shift of 3 and 11 ppm., characteristic for the atoms of aluminum in the octahedral medium by oxygen (Figure 3). With an increase in decationation their intensity increases. An increase in decationation of zeolite leads to an increase in the intensity of the signal from the atoms of alluminum in the octahedral coordination. On the whole the predominant part of aluminum atoms remains in the structure of the carcass also after removal of cations of zeolite.

**Figure 3.** 27Al NMR spectra of zeolite after acid treatment. 1 - sample №4 (1,5 N solution of HCl, 96- 980С); 2 - sample № 5 (conc. solution of HCl, 96-980С)
