**5. Investigation of mechanochemical modification of natural zeolite with various substances**

Diversity of centers formed in zeolites explains the fact that zeolites can be used in a wide range of chemical and technological processes. One of the effective ways of intensification of processing different types of mineral raw materials is mechanical activation, which determines the formation of a significant number of defects in the structure of minerals, which should lead to a change in surface properties of the constituent particles [13, 14].

Mechanochemical modification allows, first of all, intensifying the process of solids dispersing. As a result, the chemisorbed polymer layer passivates the surface of dispersed particles and lyophilized highly dispersed filler is formed. At the same time, the conditions for emergence of chemical interaction at the interface of filler-polymer are created, that leads to a deeper change in the surface.

Environmental cleanness and the possibility of simplifying the process flow sheet determine the prospects for such studies. In this regard, we conducted mechanochemical modification of natural zeolite with aminoacetic acid and epoxy resin for the first time ever.

### **5.1. Solid-phase interaction of natural zeolite with aminoacetic acid**

Layered silicates and zeolites are characterized by the presence of both basic and acid active sites on their surface [4,15]. The solid-phase interaction of these sites with amino acids is of interest [16]. In the sorption on solid supports, amino acids containing two functional groups can form different surface complexes. The structure and chemical properties of the surface and also theoretical and practical aspects of adsorption and catalysis on zeolites are studied by various methods. Widely used spectral methods provide valuable information on the structure and properties of supports [16].

The aim of this work was to study the interaction of α-aminoacetic acid (α-glycine) with natural zeolite during their mechanochemical activation. Natural aluminosilicate, zeolite from Shankhanai deposit (Kazakhstan), was used. To remove nonstructural impurities readily washed out with acids, zeolite was preliminarily activated with a 10% HCl solution for a day. Aluminosilicate samples were dried at 130°C for 2 h; α-glycine was used without additional purication. The mechanochemical activation of initial compounds (the amount of glycine was 30% of that of the zeolite) was performed in an agate mortar for 30 min. The IR absorption spectra of powders pressed into pellets with optically pure KBr were recorded on a UR-20 spectrophotometer.

α-Glycine has a layered crystal structure [14]. Glycine molecules are present in crystals as zwitterions, which are bound with each other by relatively short (therefore strong) N–H···O hydrogen bonds and form antiparallel layers,

#### **Scheme 1.** Scheme 1

The spectra of the samples are presented in the Figure 12. Carboxylic acids form very strong hydrogen bonds; therefore, OH group stretching vibration frequencies are characteristic frequencies. A broad absorption band and several weaker peaks are observed over the range 3000–2500 cm–1. In the spectra of aminoacetic acid and its activated mixture with zeolite, the main peak is observed at 3000 cm–1, and weaker peaks, at 2720, 2616 and 2700, 2600 cm–1, respectively; these peaks can be assigned as combination tones corresponding to C–O (1420 cm–1) and O–H (1300 cm–1) vibrations [17]. The band of stretching vibrations shifts toward lower frequencies, 3488; 3424 cm–1. A pronounced secondary band at 2175 cm–1 in the spectrum of α-glycine is evidence of the presence of a bipolar ionic structure; in the modied sample, this band is observed at 2170 cm–1.

Both samples exhibit absorption in the range 1420–1340 cm–1, which is assigned to C–O vibrations closely related to planar bending vibrations of OH groups. In the spectrum of the modied sample, νë=é and antisymmetric stretching vibrations in α-glycine(1720–1540 cm–1) and Si–O stretching vibrations in zeolite (1060 cm–1) are shifted toward longer wavelengths (1700–1500 and 1040 cm–1, respectively). Absorption in the range 1700–1500 cm–1 can also be assigned to hydrogen bonds of aminoacetic acid with OH surface groups. This assignment is based on the results obtained for the intra- and intermolecular association of carboxylic acids [18].

Thus, the NH3+ stretching vibration and СOO antisymmetric vibration frequencies shift toward lower frequencies. Similar results were obtained in the mechanochemical activation of caolinite and the amino acid with the formation of a salt with the NH2CH2COO- [14].

It is known [16] that, along with the absorption band of the ionized carboxyl group (1600– 1550 cm–1), all amino acids containing the group exhibit two characteristic bands at 1600– 1500 cm–1. One of these is observed at 1640–1610 cm–1. For the amino acid under study, bending vibrations occur at 1640 and 1608 cm–1. These bands are also present in the spectrum of the modied zeolite sample; the band at ~1640 cm–1 is, however, broadened. This band is a superposition of antisymmetric stretching vibrations of COO– groups and bending vibrations of water molecules and NH2 groups. The other characteristic band of Structural and Ion-Exchange Properties of Natural Zeolite 277

**Figure 12.** IR spectra of (1) natural zeolite, (2) activated mixture, and (3) aminoacetic acid.

276 Ion Exchange Technologies

**Scheme 1.** Scheme 1

acids [18].

on a UR-20 spectrophotometer.

hydrogen bonds and form antiparallel layers,

modied sample, this band is observed at 2170 cm–1.

Thus, the NH3+ stretching vibration and СOO-

additional purication. The mechanochemical activation of initial compounds (the amount of glycine was 30% of that of the zeolite) was performed in an agate mortar for 30 min. The IR absorption spectra of powders pressed into pellets with optically pure KBr were recorded

α-Glycine has a layered crystal structure [14]. Glycine molecules are present in crystals as zwitterions, which are bound with each other by relatively short (therefore strong) N–H···O

The spectra of the samples are presented in the Figure 12. Carboxylic acids form very strong hydrogen bonds; therefore, OH group stretching vibration frequencies are characteristic frequencies. A broad absorption band and several weaker peaks are observed over the range 3000–2500 cm–1. In the spectra of aminoacetic acid and its activated mixture with zeolite, the main peak is observed at 3000 cm–1, and weaker peaks, at 2720, 2616 and 2700, 2600 cm–1, respectively; these peaks can be assigned as combination tones corresponding to C–O (1420 cm–1) and O–H (1300 cm–1) vibrations [17]. The band of stretching vibrations shifts toward lower frequencies, 3488; 3424 cm–1. A pronounced secondary band at 2175 cm–1 in the spectrum of α-glycine is evidence of the presence of a bipolar ionic structure; in the

Both samples exhibit absorption in the range 1420–1340 cm–1, which is assigned to C–O vibrations closely related to planar bending vibrations of OH groups. In the spectrum of the modied sample, νë=é and antisymmetric stretching vibrations in α-glycine(1720–1540 cm–1) and Si–O stretching vibrations in zeolite (1060 cm–1) are shifted toward longer wavelengths (1700–1500 and 1040 cm–1, respectively). Absorption in the range 1700–1500 cm–1 can also be assigned to hydrogen bonds of aminoacetic acid with OH surface groups. This assignment is based on the results obtained for the intra- and intermolecular association of carboxylic

toward lower frequencies. Similar results were obtained in the mechanochemical activation

It is known [16] that, along with the absorption band of the ionized carboxyl group (1600– 1550 cm–1), all amino acids containing the group exhibit two characteristic bands at 1600– 1500 cm–1. One of these is observed at 1640–1610 cm–1. For the amino acid under study, bending vibrations occur at 1640 and 1608 cm–1. These bands are also present in the spectrum of the modied zeolite sample; the band at ~1640 cm–1 is, however, broadened. This band is a superposition of antisymmetric stretching vibrations of COO– groups and bending vibrations of water molecules and NH2 groups. The other characteristic band of

of caolinite and the amino acid with the formation of a salt with the NH2CH2COO-

antisymmetric vibration frequencies shift

[14].

amino acids (1540–1420 cm–1) is, as a rule, more intense than the rst characteristic band. In the zeolite activated with the amino acid, this band is shifted toward lower frequencies (1500–1400 cm–1). A similar result was obtained in [14]; however, in the spectra of activated caolinite samples, the absorption band of NH2 groups was observed at 1550–1450 cm–1 and had a low intensity or even disappeared against the background of the maximum at 1640 cm–1.

The absorption band in the frequency range 960–900 cm–1 is assigned to OH group bending vibrations. In the spectrum of the modied zeolite sample, this band is narrowed and is observed at 940–900 cm–1.

To summarize, the solid-phase neutralization reaction in the mechanochemical activation of zeolite and the amino acid results in the formation of chemical bonds between carboxyl groups of the acid and basic sites of the aluminosilicate and also coordination bonds between aluminum atoms in the zeolite lattice and nitrogen atoms of amino acid molecules.

### **5.2. Mechanochemical modification of natural zeolite with epoxy resin**

The joint dispersion of fillers with polymers of different nature leads to the breakdown of macromolecules with formation of free radicals, which react with the active centers of minerals to form surface chemical compounds [19].

The specific features of zeolite structure, its high affinity to polar groups, the developed surface area, adsorption capacity determine the possibility of combining the filler with highmolecular compounds. Herewith, the additional intermolecular bonds form and the ability to structure the macromolecule as a result of adsorption at the interface appear. In this regard, the results of the study of the joint dispersion of natural aluminosilicate with an industrial epoxy resin ED-20 [20] were considered.

The results of the study of dependence of the value of epoxy resin weight gain on the surface of zeolite on its concentration showed that epoxy cycles open and the chemisorption of free radicals (Figure 13) takes place. Resin content change from 1 to 20 mass % in the process of dispersion system for 0,5 h leads to an increase in the value of the polymer grafting from 3,2 to 5,7%.

Modification of zeolite for 1 h contributes to a sharp increase in polymer weight gain on the surface, which reaches 7,5% at 1:10 mass parts components ratio (Figure 11). The maximum for these conditions dispersion of zeolite in the presence of ED-20 occurs within the first hour of grinding (Figure 14).

**Figure 13.** Degree of the grafting of polymer (Q) on the surаce of zeolite ) as a function of the content of epoxy resin (dispersion for 0,5 h)

**Figure 14.** Degree of the grafting of epoxy resin (Q) and the specific surface area (S) minerals (2) as a function of the process duration t. (Resin: Zeolite = 1:10 mass part by weight)

The data obtained shows that at mechanochemical interaction of natural aluminosilicate with an epoxy resin a number of transformations with the components of the system take place. Spectroscopic studies found the significant changes in the chemical structure of polymer as a result of the modification. It is observed that with the increase of process duration a decrease in the intensity of absorption band at 832 cm-1 and disappearance of frequency at 916 cm-1 are observed, characterizing the epoxy groups' vibrations (Figure 15). This indicates the mechanochemical activation of the latter. Free radicals formed as a result of disclosure thereof contribute to the dispersion and intensify the process of grafting, which affects certain increase in polymer weight gain. Thus, with increasing of grinding time up to 1 h, zeolite specific surface increases and the grafting of polymer (Figure 14) takes place. The process is intensified due to the interaction of freshly formed surface with products of mechanodestruction of macromolecules and its modification as a result of epoxy resin free radical grafting. A further increase in the duration of system dispersion up to 2 h leads to a decrease in the specific surface of modified aluminum silicate stipulated by the grafted layer of polymer the amount of which at this time is the maximum.

**Figure 15.** IR spectra of epoxy resin. 1 - in the absence of dispersion; 2 - dispersion for 0,5 h; 3 dispersion for 1 h.

Extraction data of polymer-zeolite system showed the physical and chemical nature of the adsorption bonds between molecules of resin and aluminum silicate surface. Herewith, the contribution of chemisorption bonds varies depending on the ratio of the components and process duration.

Thus, a modified aluminum silicate which can be used effectively to create a variety of organo-mineral systems with a complex of valuable properties was obtained by combined dispersion of natural zeolite and epoxy resin.

#### **6. Сonclusion**

278 Ion Exchange Technologies

grafting from 3,2 to 5,7%.

hour of grinding (Figure 14).

epoxy resin (dispersion for 0,5 h)

industrial epoxy resin ED-20 [20] were considered.

**Q ,%**

molecular compounds. Herewith, the additional intermolecular bonds form and the ability to structure the macromolecule as a result of adsorption at the interface appear. In this regard, the results of the study of the joint dispersion of natural aluminosilicate with an

The results of the study of dependence of the value of epoxy resin weight gain on the surface of zeolite on its concentration showed that epoxy cycles open and the chemisorption of free radicals (Figure 13) takes place. Resin content change from 1 to 20 mass % in the process of dispersion system for 0,5 h leads to an increase in the value of the polymer

Modification of zeolite for 1 h contributes to a sharp increase in polymer weight gain on the surface, which reaches 7,5% at 1:10 mass parts components ratio (Figure 11). The maximum for these conditions dispersion of zeolite in the presence of ED-20 occurs within the first

**Figure 13.** Degree of the grafting of polymer (Q) on the surаce of zeolite ) as a function of the content of

**0 0,05 0,1 0,15 0,2 Content of epoxy resin,g/g**

**Figure 14.** Degree of the grafting of epoxy resin (Q) and the specific surface area (S) minerals (2) as a

t, h

function of the process duration t. (Resin: Zeolite = 1:10 mass part by weight)

The study of sorption activity of natural and modified sorbents has made it possible to substantiate the decisive role of the nature of the acid-base properties of a mineral in the

process of extraction, as well as the influence of the porous structure upon sorption of organic compounds (acetone, toluene, acetic acid) and inorganic ions (the ions of nonferrous metals).

Physico-chemical study of the composition and thermal stability of natural zeolite allowed to determine the ratio of Si / Al as a 3,8, a high thermal stability, and to find optimal conditions for acid activation of the zeolite with the aim further modification of the samples with epoxy and amine reagents. It is shown that, depending on the nature of adsorbate and adsorbent type can be selected appropriate modes of activation of natural zeolite as a result of vapor sorption studies of various organic solvents, water and acetic acid.

It has been shown for the first time by the method of IR-spectroscopy that a chemical interaction takes place between the main centers of natural zeolite and carboxylic groups of aminoacetic acid in the process of their mechanic-chemical activation, as well as the formation of a coordination bond between the aluminum atoms of its lattice and nitrogen of aminoacid. Stereoscopic studies have established considerable changes in the chemical structure of the polymer as a result of mechanic-chemical modification of natural zeolite by epoxy resin. The extraction data of the system polymer-zeolite testify to the physical and chemical nature of adsorption bonds between the molecules of resin and the surface of alumosilicate. Incidentally, the contribution of chemosorption bonds is different in dependence of the ratio of the components and duration of the process.

Development of methods for modification of natural zeolite by various oligomers and functional materials opens up the possibility of synthesis of chemically modified materials for ion-exchange technology. Therefore, an interest is evoked by a profound research of the processes, proceeding on the surface of the modified natural sorbents, the state of engrafted compounds and creation of methods of purposeful alternation of the structure of the engrafted layer and the properties of the modified sorbents, connected with this structure, as well as establishing of a possibility to use them in the modern sorption processes, creation of new competitive technologies for the extraction of metal ions from technological solution.

The profound theoretical and practical studies of the methods of modification of natural sorbents will result in the development of available methods of obtaining of organomineral sorbents as the most problematic aspect of the development of the modern ion-exchange technology and related fields. And the achievements in this field should be connected, first of all, with the physical-chemical approach to the assessment and generalization of the existing vast experimental and theoretical material.
