The effect of acid and alkaline activation of complex natural aluminosilicate sorbent on its chemical composition, surface properties, and adsorption capacity towards ammonium ions was studied. An increase in specific surface area of the sorbent by 1.3 times after acid treatment and by 1.5 times after alkaline activation was shown. The change of ion-exchange complex of sorbent as a result of activation was observed. Sorption isotherms of ammonium ions on natural and activated samples were obtained and were satisfactorily described by the Langmuir equation. The evaluation and comparison of desorbed cations of alkali and alkaline earth metals were carried out. It was confirmed that ion-exchange processes primarily contributed to sorption of ammonium ions by natural and acid-activated silica-alumina, in contrast to alkali-activated one, for which absorption of nonexchangeable ammonium ions increased adsorption capacity of ammonium ions by 1.5 times. 1. Introduction Use of natural aluminosilicates in sorption purification processes [1, 2] and catalytic conversion of various substances [3] is currently receiving increasing interest due to their unique properties already available in their natural state, as well as new properties acquired during modifying and activation of aluminosilicates [4]. Natural aluminosilicates have good adsorption and ion-exchange properties; they widely occur in nature and have low cost. The structure of these materials can be represented by a variety of components, for example, a layered clayey (montmorillonite), a framework zeolite structure (clinoptilolite), and so forth. Usually montmorillonite and clinoptilolite containing clays are activated by various methods of treatment, such as thermal treatment [5], ion exchange [6, 7], and treatment with acids [8, 9] and alkali [10, 11]. By activation the chemical composition of minerals is selectively modified that results in an increase in specific surface area, specific pore surface and thermostability, changes in the surface pH, and so forth. Currently, montmorillonite minerals are often modified in such processes as grafting [12], silylation [13], and intercalation [14, 15] due to inclined swelling capacity. At the same time, the materials based on natural zeolites are valuable as catalysts and supports owing to their rigid frame structure. Due to specificity of crystal structure and chemical composition, montmorillonite and clinoptilolite reveal high ability to ion-exchange reactions of movable cations of Ca2+, Mg2+, Na+, and K+, which mostly equivalently contribute to adsorption
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