Study of the surface condition of AC and MS sorbents after the elimination of anions from wastewater from coal mining enterprises

Introduction. Currently, there is intense global environmental pollution and degradation of soil cover and surface water bodies as a result of open-pit coal mining. The marker components of wastewater from coal mining enterprises include suspended impurities, sulfate, nitrite ions, manganese and iron ions. Siliceous rocks, including MS and AC sorbents, are promising materials for the elimination of contaminants from wastewater. The purpose of the research is to study the surface condition of the initial samples of sorbents of mineral origin AS, MS and samples after sorption of sulfate and nitrite ions, which are marker components of wastewater from coal enterprises. Objects of research. Sorbents of the AS and MS brand (manufacturer Alsis LLC, Yekaterinburg) are obtained on the basis of the Kuryinsky deposit. Methods. The adsorption of sulfate and nitrite ions on sorbents of mineral nature AC and MS under static conditions has been studied. To study the nature of sorption processes, methods of physical-chemical analysis were used: X-ray fluorescence analysis, infrared spectroscopy, thermo-gravimetric analysis, nitrogen porometry and scanning electron microscopy. Results. The adsorption isotherms of sulfate and nitrite ions on sorbents of mineral nature AC and MS under equilibrium conditions are characterized by the S-type form according to Brunauer classification, the calculated Gibbs energy values indicate the physical nature of the interaction of sorbet and sorbent due to the formation of hydrogen bonds with oxygen-containing functional groups on the surface of the sorbent. According to IR spectroscopy data, the predominant type of interaction between sorbet and sorbent in the studied systems is physical sorption. At the same time, sorption of anions by the type of ion exchange of groups on the surface of the sorbent, for example, Si–OH, into more stable sulfur- and nitrogencontaining groups is possible, which is confirmed by data from thermo-gravimetric analysis. The study of mineral materials using methods of nitrogen porometry and scanning electron microscopy allowed us to establish that the adsorption of anions contained in an aqueous medium occurs in the mezo-pores of the studied MS and AC sorbents. A decrease in the total pore volume and specific surface area of the sorbent AC after adsorption confirms the possibility of ion exchange of oxygen groups (Si–OH) on the surface of the sorbent and anions. An increase in the specific surface area of the MS sorbent and the proportion of mezo-pores after anion adsorption due to the formation of salt crystal deposits on the surface of the sorbent was noted. Conclusions. Based on the analysis of the results of the surface condition of the sorbents AC and MS before and after the elimination of anions from the wastewater of coal mining enterprises, it is possible to recommend the use of these sorbents not only for the extraction of cations, but also anions from the wastewater of coal enterprises engaged in open-pit coal mining.