INFLUENCE OF ACID-BASE ACTIVATION ON CHANGES IN THE SURFACE PROPERTIES OF ALUMINOSILICATES

Abstract

The effect of activation with weak acids and weakly alkaline solutions on the change in the surface properties of natural materials, which are aluminosilicates, has been investigated. The use of natural sorbents has a wide range of practical applications, which actualizes the study of their physicochemical and adsorption properties. A comparative study of the native material - the flask of the Astrakhan region, as well as the material activated with a 6% solution of oxalic acid, and then activated with a solution of sodium bicarbonate of the same concentration was carried out. The study of the morphology of the obtained samples indicates a more developed surface of the native material. The presence of isometric open pores in the native material confirms the clay component. Moreover, activation with a weak acid leads to a decrease in the pore size and specific surface area by a factor of 1.3, and further exposure to a weakly alkaline solution causes the surface to become uniform (it decreases by a factor of 1.5 from the initial value). The results obtained are confirmed by the BET method. The specific surface of the material and porosity decrease by 23% upon activation with a weak acid and by 31% upon further activation with a weak alkaline solution, which also confirms the destruction of the structure. The data obtained on the change in the chemical composition during the activation process make it possible to classify the natural material as belonging to the class of montmorillonite (SiO2: 30 – 33%), and the presence of a clay component (Al2O3: 2 – 3%) indicates the destruction of the material upon activation not only with strong acids, but also with weak ones. A change in the Si/Al ratio, extraction of metal ions in the exchange region does not lead to the expected increase in the specific surface area and pore volume, which can be explained by surface recrystallization. The study of the acid-base characteristics of the surface by the pKa method indicates a wide variety of active centers on the surface and is inhomogeneous in nature, with the advantage of the cationic function. Upon activation, an increase in the anionic function of the surface is observed.