Physico-chemical and sorption properties of original and modified clay from the Levashinskoye deposit of the Republic of Dagestan

Abstract

The high sorption, ion exchange, and catalytic properties of natural clay minerals determine their widespread use in various technological processes. More than 30 deposits of various clays have been identified and explored within the territory of the Republic of Dagestan, one of which is the Levashinskoye deposit. Available data on the adsorption of ions of rare alkali (Rb+ and Cs+) and alkaline earth (Sr2+) metals on clay minerals make the task of study of the possibility of using clay from this deposit as a sorbent for extracting these ions from aqueous solutions even more relevant. This, in turn, is due to the need for effective sorbents for concentrating and extracting ions of alkali and alkaline earth metals when solving problems of complex processing of hydromineral raw materials. The purpose of this study was the investigation of the physicochemical and sorption properties of Rb+, Cs+, Sr2+ native and hydrochloric acid-modified clay from the Levashinskoye deposit of the Republic of Dagestan. Based on a comprehensive study, the mineralogical composition of native clay was established, the main clay minerals of which were: illite, nontronite, and montmorillonite. In addition, the sample contained calcite and quartz. In order to increase the content of clay minerals, with which the sorption activity of clay is mainly associated, the original clay was treated with a 1 M hydrochloric acid solution, which led to an increase in the content of clay minerals from 62% in the original clay to 75% in the clay treated with HCl. Sorption experiments for Rb+, Cs+, Sr2+ were carried out in model solutions, the concentration of the studied ions in solutions varied in the range of 20-700 mg/dm3. It was shown that the equilibrium of adsorption of these ions on the studied clay can be satisfactorily described both by equations for a non-uniform surface (Freundlich, Temkin, Dubinin-Radushkevich) and by the Langmuir isotherm for a homogeneous surface. It was found that the modification of the original clay with a solution of hydrochloric acid increases the sorption capacity of the clay for the studied ions. It has been established that the main mechanism of sorption of these ions on both the original and modified clay of the Levashinskoye deposit was ion exchange, while other mechanisms cannot be excluded. The study of the kinetics of Rb+, Cs+, Sr2+ sorption on modified clay showed that the sorption process of these ions can be described by a mixed-diffusion model and a pseudo-second-order model.