STUDY OF MECHANICAL STRENGTH AND SORPTION PROPERTIES OF SYNTHESIZED ORGANOMINERAL SORBENTS

ABSTRACT

In the article, it was studied that the synthesized organomineral sorbent has the necessary strength during the sorption process and does not lose its sorption properties even in stable conditions. Organic sorbents have low consistency. If inorganic minerals are added to it, the degree of consistency will be partially increased. This can be explained by the decrease in the radius of the sorbent pores, the formation of a geometric barrier to the diffusion of ions, and the decrease in their permeability.

AННОТAЦИЯ

В статье исследовано, что синтезированный органоминеральный сорбент обладает необходимой прочностью в процессе сорбции и не теряет своих сорбционных свойств даже в стабильных условиях. Органические сорбенты имеют низкую консистенцию. Если к нему добавить неорганические минералы, степень консистенции частично увеличится. Это можно объяснить уменьшением радиуса пор сорбента, образованием геометрического барьера для диффузии ионов и снижением их проницаемости.

Keywords: organomineral sorbent, mechanical strength, bentonite, sorption, phase composition, wastewater treatment, sorbent.

Ключевые словa: органоминерал сорбент, механической прочности,  бентонит, соpбция, фaзовый состaв, очисткa сточных вод, соpбент.

Introduction. During the sorption process, sorbets are exposed to various external influences and lose their sorption capacity. In addition, sorbents with a polymer structure are affected by temperature, strongly acidic and alkaline environments, causing their disintegration and loss of functional groups. Compared to organic sorbents, inorganic mineral sorbents have relatively strong mechanical strength. These studies were analyzed by a number of scientists on the basis of special GOST requirements, and scientific research was carried out [1-3].

Experimental part. Organomineral sorbents are prepared using inorganic and organic raw materials in different proportions. Enriched forms of bentonites are used for synthesis. For this, bentonite mineral samples were cleaned of water-soluble salts and sand by washing with distilled water. The enriched mass of bentonite was separated from the liquid by centrifugation, and then the bentonite was dried at 105ºC. Modification technology and cation exchange processes are as follows: enriched bentonite with a particle size of not less than 0.5 mm is filled with 0.1 M cation exchange solution in a ratio of 1:22 (volume) and stirred at 55°C for 2 hours. After this time, the bentonite is filtered and washed from Cl- (checked by adding AgNO₃ solution), then placed in a drying cabinet and dried at 100-105ºC for 2 hours. NaCl solution was used as cation exchange solutions.

Dried bentonite is mixed with an aqueous solution of GIPAN (hydrolyzed polyacrylonitrile) and DGK (diglycidylcarbamide) with a concentration of 0.3 mol/l (at high concentrations, the surfactant forms a thick gel-like liquid, which makes it difficult to work with the solution) and 600 speed/ at min from 20-60ºC for 1-6 hours with constant stirring, the amount of modifier varied from 5 to 30%. The sorption properties of these organic modifiers have been studied by a number of scientists [4-6].

As a result of the experiments, the optimal amount of organic matter was determined to be no more than 15% of the weight of sodium montmorillonite in suspension for DGK, and no more than 10% for GIPAN. Perhaps, this amount of organic modifiers is primarily related to the cation exchange capacity (KAH) of bentonite and the molecular weights of these organic substances (Mr (GIPAN) = 394 g/mol and Mr (DGK) = 280 g/mol) . Accordingly, the amount of consumption for the DGK modifier with a molecular weight of 160 g / mol should be approximately the same as in the case of GIPAN. However, since this low molecular weight surfactant cannot form a stable foam, it is not possible to quantify it using the above method. Therefore, the quantitative characteristics of the modification process were evaluated by analyzing the results of thermogravimetric analysis. The synthesized organomineral sorbent is tentatively named GIPAN+DGK:Bentonite (hydrolyzed polyacrylonitrile and diglycidylurea modifier).

Analysis of the obtained results. The main structural-mechanical property of sorbents is strength, which is characterized by grinding and friction properties. The strength of the organomineral sorbent was studied in accordance with the requirements of GOST R 51641-2000 granular granule materials. General specifications [7]. Accordingly, the level of grinding and friction should not exceed 4 and 0.5%, respectively. To determine these properties, several different samples of organomineral sorbents, differing in fraction sizes, were used. The results of the study are presented in Table 1.

Table 1.

Strength properties of organomineral sorbent particles of different sizes*

*(Sample 1 - fractions of organomineral sorbents with a particle size of up to 1 mm; Sample 2 - fractions with mixed particles in the range of 1-3 nm; Sample 3 - with a size of more than 3 mm fractions (larger than sample 1)).

GIPAN:Bentonite-3 sample has the highest values of crushing index. It is known that particles up to 3 mm in size differ from larger ones in their resistance to crushing and abrasion.

Studies have shown that GIPAN:Bentonite-2 is characterized by the following optimal high parameters: the average crushing value is 1.4 ± 0.1% (not more than 4% according to GOST) and friction It was determined in the research results that the value is equal to 0.23 ± 0.1% (not more than 0.5% according to GOST).

Table 2.

The main physical properties of organomineral sorbents

The main physical properties that determine the quality characteristics are represented by porosity, plasticity and density. These features were also implemented in accordance with the requirements of GOST R 51641-2000. The obtained results are presented in Table 2. As indicated, the density of organomineral sorbents is 2.3 ± 0.1 g/cm³.

The porosity of the organomineral sorbent as an adsorbent is of great practical importance. In the process of making granules from small adsorbent particles, the porosity index is one of the defining characteristics. It should also be noted that porosity is an important indicator for determining the antibacterial ability of an adsorbent in the process of wastewater treatment. According to laboratory studies, the average porosity of the organomineral sorbent used in the research is 43.6 ± 0.1% (Table 3).

Table 3.

Porosity of organomineral sorbent, %

In the process of mixing the organogyl suspension and as a result of the adsorption effect, it was found that amine molecules are absorbed on the interface surface, as a result of which the bentonite aggregates are further distributed, as well as the penetration of amines causes a decrease in the hardness of bentonite. newly formed surfaces. Water is the most surfactant for bentonite, which facilitates the process of reducing the strength and dispersion of bentonite by adsorption [8].

The main method of studying the crystal structure of organomineral sorbents is X-ray diffraction analysis and electron microdiffraction [9]. The values of the "b" parameter of the silicate layers of montmorillonite were measured with an accuracy of 0.002 Å. In each preparation, the "b" parameter was determined for all microparticles with sufficiently clear diffraction patterns. Electron microscopic images of orgomineral sorbents based on bentonite samples are shown in Figure 2.8.

Figure 1. Electron microscopic image of organomineral sorbents based on GIPAN+DGK:Bentonite

Electron microscopic analysis of GIPAN:Bentonite shows that this sample is mainly represented by individual aggregates of bentonite particles having the shape of elongated polygons. It was found that an increase in molecular weight increases the degree of formation of associations of modifying cations with a double thickness sufficient to cover both basalt surfaces. Instead of the hydrate-ion layers of the outer surfaces of diglycidylurea montmorillonite crystals, which is a polymer modifier, associations of modifier cations are observed in one layer thickness. At the same time, an increase in the size of the modifier molecules contributes to an increase in the degree of three-dimensional order in packing silicate layers. Under the electron microscope, it can be seen that the large GIPAN, DGK, and Bentonite particles are mostly rectangular in size and about 1 µm in size. These assumptions are fully consistent with the results of X-ray phase analysis. As can be seen from the X-ray diffraction pattern, the interplanar distance from the d001 plane of the montmorillonite layers increased from 12.4 Å to 25.9 and 21 Å for GIPAN+DGK:Bentonite (Figure 1).

In addition, the sorption properties of these synthesized organomineral sorbets with respect to various metal ions were also studied. The degree of sorption was carried out in standard solutions containing metal ions. The results were determined according to the concentration of the solution before and after sorption. The concentration of metal ions in the solution was determined using the method of complexonometric titration and potentiometric titration.

Table 4.

The main physicochemical properties of sorbents synthesized in different mole ratios of diglycidylurea and GIPAN

The data in Table 4 show that the exchange capacity gradually increases with the increase in the amount of organic modifier. This can be explained by the decrease in the radius of the sorbent pores, the formation of a geometric barrier to the diffusion of ions, as well as the decrease in their permeability.

Summary. In conclusion, it can be said that the synthesized organomineral sorbent has the required strength during the sorption process and does not lose its sorption properties even in stable conditions. Organic sorbents have a low level of consistency. If inorganic minerals are added to it, the degree of consistency will be partially increased.

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