Alteration of non-swelling clay minerals and magadiite by acid activation

The bulk material of three kaolins, a sepiolite, art illite and one magadiite were treated with 1, 5 and 10 M H2SO4 at 80 degrees C for several hours. The alteration of the non-swelling clay mineral structures was controlled by the individual character of each mineral (chemical composition and initial particle size). The reaction resulted in a successive dissolution of the octahedral sheets by edge attack. The number of substitutions by Mg or Fe in the octahedral sheet promoted the dissolution of these layers and the formation of a silica phase. High amounts of Al in the tetrahedral sheet of the clay minerals caused partial dissolution of these sheets. The dissolution of the octahedral cations occurred in the following order: Mg>Fe>Al. Thus, dioctahedral clay minerals were more stable against acid attack than trioctahedral clay minerals. The release of the octahedral cations caused the lightening of the material together with a development of micropores and an increasing specific surface. Dissolution and splitting of the particles required longer reaction times compared to swellable smectites and vermiculites. Acid activation of non-swelling clay minerals can be used to produce layered materials with simple chemical composition and high specific surface area. (C) 2009 Elsevier B.V. All rights reserved.