STUDY OF THE EFFICIENCY OF SORPTION OF Cu2+ AND Pb2 + IONS BY NATURAL CLAYS OF THE TURKESTAN REGION

STUDY OF THE EFFICIENCY OF SORPTION OF Cu²⁺  AND Pb^{2 +} IONS BY NATURAL CLAYS OF THE TURKESTAN REGION

Zhaina Baimuratova

PhD doctoral student M.KH. Dulati Taraz Regional University,

Kazakhstan, Taraz

Zhunisbek Akaysha Orazhankyzy

student, South Kazakhstan State Pedagogical University,

 Kazakhstan, Shymkent

Kambar Akzhan Nurbakytkyzy

student, South Kazakhstan State Pedagogical University,

Kazakhstan, Shymkent

Introduction

At present, the anthropogenic contribution to the distribution and migration of many substances in the biosphere has become commensurate with the natural migration flows of these substances. Pollution has arisen, the individual components of which, until recently, were completely absent in nature (chlorine and organophosphorus poisons, artificial radionuclides, etc.).

Environmental pollution with heavy metals - one of the most intense pollutants - is always potentially dangerous due to the introduction of heavy metals from the hydrosphere and lithosphere through metabolic and trophic chains into living organisms, including humans. Therefore, the problems of pollution of natural waters, an increase in the volume of wastewater and the search for effective methods of their purification are becoming urgent.

One of the physicochemical methods of fine water purification is sorption, which can be physical sorption, chemisorption, and ion exchange between the sorbate and the sorbent.

In recent years, studies have been carried out aimed at purifying water from heavy metal compounds using mineral aluminosilicate adsorbents: various clays, zeolite-containing rocks, etc., which are characterized by high absorption capacity, resistance to environmental influences and can serve as excellent carriers for fixing on surfaces of various compounds during their modification.

It is effective to use clay minerals of the 2:1 structural type with varying basal interplanar spacings. In the interpacket cavities of these minerals, water molecules, as well as positive or negative ions, can be adsorbed. In them, ion exchange with the external environment can take place. These clay minerals can swell by increasing the space between the basal layers in which adsorbed ions or molecules are located. In clay minerals belonging to the class of montmorillonites, part of silicon ions (Si^{4 +}) in tetrahedral positions are replaced by aluminum ions (Al^{3 +}), and part of aluminum ions in octahedral positions are replaced by magnesium ions (Mg^{2 +}) and ferrous iron (Fe^{2 +}). Each elementary package of layered silicates of the 2:1 structural type has a thickness of 0.94 nm, and the specific surface area of ​​elementary packages reaches 660m²/g [1]. Elementary packages are interconnected by weak van der Waals forces. Therefore, it is possible to place large ions between the layers, forming columns, and thus create a system of voids where various small molecules can be located. The dimensions of the pores formed as a result of the separation process are in the range of a few tenths of a nanometer.

The use of unconventional, affordable and cheap sorbents is of great practical interest in the technology of purification of huge volumes of natural and waste waters. The presented work is a continuation of earlier studies of the sorption activity of clays [2-4].

The authors of this article have determined the ability of clays to absorb Cu²⁺ and Pb²⁺ from model solutions, as the most common heavy metals in the Turkestan region [5]. We used clays of the Zhetysay, Turkestan and Saryagash  deposits as adsorbents.

Experiment

The following procedure was used to determine the adsorption properties of clay. The sorption of copper and lead was carried out at a constant temperature (20°C) from model solutions of salts (respectively, copper (II) sulfate pentahydrate and lead (II) nitrate) with a metal ion concentration of 5 mg/L. The concentration of heavy metals was presented in mg/L, as is customary in the technology of purification of various types of water. The sorbent was taken in an amount of 1,3 and 5g per 50ml of solution. The ratio of  sorbate: sorbent  0.000250:1; 0.000083:1 and 0.000050:1. The sorption time ranged from 15 minutes to 1.5 hours. The concentration of metal ions was determined by the photocolorimetric method on a KFK-3-01 device according to the appropriate methods for each metal [6].

Discussion of the results

As a result of the experimental studies, it is shown (Fig.1a) that Turkestan clay within 1.5 hours reduces the concentration of copper ions in the solution: from 5 mg/L to 1.35 mg/L (with a mass ratio of sorbate: sorbent 0.000250:1), up to 0.97mg /L (at a mass ratio of 0.000083:1) and up to 0.75mg/L (at mass ratio 0.000050:1).

Zhetysay clay to a greater extent reduces the concentration of copper ions: from 5 mg/L to 0.56 mg/L, 0.54 mg/L and 0.46 mg /L, with a mass ratio of sorbate: sorbent, respectively, 0.000250: 1; 0.000083: 1 and 0.000050:1. The Saryagash clay has the highest sorption capacity with respect to copper ions: the concentration of ions in the experiments, respectively, changed to 0.20; 0.18 and 0.14 mg/L, that is, under these conditions, there was a decrease in the concentration of copper ions by 25-35 times.

a)                                                b)

 - Turkestan clay,  - Zhetysay clay,  - Saryagash clay,

 - wood charcoal,  - Activated carbon

Figure 1. Change in the concentration of copper (II) ions (a) and lead (II) ions (b) depending on the type of sorbent and the sorbate: sorbent ratio (sorption duration 1.5 hours)

The study of the sorption of lead ions by the indicated clays showed the following (Fig. 1 (b)). With a sorbate: sorbent ratio of 0.000083: 1, the Turkestan and Saryagash clays can reduce the concentration of lead ions to approximately the same values ​​(0.74 and 0.76 mg /L, respectively). With a sorbate: sorbent ratio of 0.000250:1 and 0.000050:1 Saryagash clay, in comparison with Turkestan clay, gives a slightly greater sorption effect. The best sorbent for lead ions is Zhetysay clay: in 1.5 hours, the concentration decreased by 9-11 times.

In general, it was found that the sorption capacity of Zhetysay clay is practically the same for copper and lead ions; Turkestan clay shows slight differences. Saryagash clay is a more effective sorbent for copper than for lead.

When using Saryagash and Zhetysay clays, the highest rate of solution purification from copper ions is observed in the first 15 minutes. With Turkestan clay, a more uniform process is observed during the entire sorption time. Saryagash clay allows for a more complete cleaning of solutions from copper ions: after 1.5 hours, the efficiency of cleaning the model solution with Saryagash clay was 97.2%, Zhetysay - 92%, and Turkestan - 85%.

The highest rate of cleaning solutions from lead ions with all the clays we used is also noted in the first 15 minutes, and then the process slows down. Unlike copper ions, the greatest cleaning efficiency of solutions is achieved when using Zhetysay clay as a sorbent (after 1.5 hours, the cleaning efficiency was 90.8%). The cleaning efficiency when using Saryagash clay was 88.6%, and Turkestan clay- 83%.

Comparative purification of model solutions from the ions of the indicated heavy metals was carried out using traditional, widely used sorbents - charcoal and activated carbon. The experiments were carried out at a sorbate: sorbent ratio of 0.000083:1.

The diagrams shown in Fig. 1(a) show that Saryagash clay reduces the concentration of copper ions in solution more significantly than other sorbents and is superior in this respect to both charcoal and activated charcoal.

Rice. 1 (b) shows that with the sorbate: sorbent ratio we used and the sorption duration of 1.5 hours, the clays of these deposits are inferior to activated carbon in terms of the absorption of lead ions. Zhetysay clay is superior to charcoal. Saryagash clay allows to achieve a more complete purification of solutions from copper ions, in comparison with other clays and charcoal, both wood and activated. Already in the first 15 minutes, the efficiency of cleaning using Saryagash clay is 94%, which corresponds to 0.234 mg of sorbed  ions with a sorbate: sorbent ratio of 0.000083: 1. After 1.5 hours, sorption practically reaches equilibrium and the efficiency of solution purification using the indicated sorbents was 80-98%. Zhetysay clay under the conditions of our experiment is also inferior to activated carbon, but surpasses woody in its ability to absorb lead ions. The highest cleaning speed, as with copper, is observed in the first 15 minutes.

To explain the mechanism of sorption of Cu^{2 +} and Pb^{2 +}  ions by the studied clays, a comparative determination was carried out, first, the pH of the initial solutions of salts and the pH of the filtrates after the sorption of the corresponding ions; secondly, the concentration of Ca^{2 +} ions in the filtrates of aqueous suspensions of clay after 1.5-hour dispersion in distilled water and in the filtrates after the sorption of the corresponding ions under similar conditions. Studies have shown that the concentration of Ca^{2 +} ions in experiments with copper is higher than in experiments with lead. This is noted in experiments with both native and enriched clays. Based on the results obtained, it can be assumed that there is a cation exchange of Ca^{2 +} ions for Cu^{2 +} ions. If there was only leaching of Ca^{2 +} ions from clay in acidic solutions of these salts, then in a more acidic solution of the Pb(NO₃) ₂ salt (pH = 4, 16) the concentration of Ca^{2 +} ions should be higher than in a CuSO₄ solution, pH = 4.76). Leaching of Ca^{2 +} ions, as well as  K, Na from clay, actually occurs to a greater extent in experiments with Pb salt (pH values ​​are 5.51 and 6.00 after sorption of  Cu^{2 +} ions and 6.30 and 6.81 after sorption of Pb^{2 +} ions, respectively native and enriched with clays).

Conclusion

The use of montmorillonite clays from various deposits of the Turkestan region as sorbents of heavy metals shows that Saryagash clay provides a higher cleaning efficiency from copper ions (97.2%), and Zhetysay clay - from lead ions (90.8%).

Comparison of the tested clays with traditional sorbents - charcoal and activated charcoal, shows that under the conditions of our experiments, with a mass ratio of sorbate: sorbent = 0.000083: 1 and a sorption duration of 1.5 hours, the most effective sorbent of copper ions is clay from the Saryagash deposit (efficiency purification is 96%).

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