Influence of Heat Treatment of Clays on Their Adsorption of Methylene Blue Dye
The adsorption activity of soils largely depends on their composition and properties and, first of all, on the specific surface area and energy potential of clay particles. For the formation of "specified" properties, including adsorption, various methods of clay activation have been developed: thermal, ultraviolet, ultrasonic, mechanical, acidic, alkaline. However, despite the published data, the issues of the influence of heat treatment on the formation of the clays properties, including adsorption ones, have not been sufficiently studied. In this regard, an assessment was made of the of clays thermal activation effect on their adsorption activity for the methylene blue dye. Experimental and theoretical studies have shown that the change in the adsorption activity of clays is associated with the degree of their heat treatment. When clays are treated with temperatures up to 200° C, energy centers on the surface of structural elements are activated, which leads to an increase in the clays adsorption in terms of methylene blue by 12-24%; with an increase in the processing temperature of clays to 450-960° С, the processes of their (clays) structural transformation change, which reduces the adsorption activity of clays by 11-16 times. In addition, the influence of the clays saturation degree with water vapor on their adsorption activity has been established. During the heat treatment of clays and their partial saturation with water vapor, water molecules occupy part of the energy centers on the surface of the particles; therefore, the particles have a sufficient energy potential, which is realized in the form of high values of their adsorption to methylene blue. During the clays thermal treatment and their complete saturation with water vapor, the charges on the surface of the particles are mostly compensated by water molecules. Water molecules, entering the inter-package space, compensate charges on the surface of the packages and minerals, which are realized in the form of clay swelling processes. Swelling processes lead to an increase in the size of structural elements, which manifests itself in the form of a decrease in the specific surface of clays. Therefore, clays completely saturated with water vapor are less active adsorption than clays partially saturated with water vapor.