Mechanism of Inversion of Montmorillonite Sorption Properties by Cationic Surfactant

Abstract

Organo-mineral derivatives of montmorillonite modified by salts of quaternary ammonium compounds are promising adsorbents for wastewater purification from heavy metal anions, as well as anionic dyes and pesticides. The understanding of the mechanism of anion adsorption by the example of montmorillonite modified by didecyldimethylammonium chloride cationic surfactant is expanded. The high rate of chromium anion adsorption, the appearance of adsorption capacity only during charge exchange of the surface, and the pH dependence of adsorption, including for pH-independent nitrate anions, indicate that a significant contribution to adsorption of anions is made by silanol and aluminol groups on the edge surface of the aluminosilicate layers of the mineral. The redistribution of access to various types of adsorption centers of the surface for adsorptive is the mechanism of inversion of the adsorption properties for montmorillonite. The inner negatively charged surface is screened by the double layer of the surfactant molecules that block the interlayer space. The surfactant molecules are not hydrated, which impedes delamination of the mineral in aqueous medium.