Acid activation of clay minerals

Abstract

Acid activation is a common chemical modification of clays, usually bentonites, with a hot solution of a mineral acid (typically HCl or H 2SO4), and it is used for both scientific and industrial purposes. The aim is to obtain partly dissolved material of increased specific surface area, porosity and surface acidity. The product consists partly of the remains of the starting mineral and partly of an amorphous, porous, protonated and hydrated silica phase with a three-dimensional cross-linked framework. Illites containing non-swelling interlayer spaces dissolve more slowly than smectites but the chemical composition of the layers has a greater effect on the process than swellability. The dissolution rate of organoclays decreases with the size of organic cations. Acid activation modifies principal clay properties and thus also their industrial applications. The extent of clay mineral dissolution is derived by many methods, such as chemical analysis, IR or NMR spectroscopy, X-ray diffraction, thermal analysis and microscopic investigation. © 2013 Elsevier Ltd.