A microstructural study of acid-activated montmorillonite from Choushan, China

Abstract

Abstract Bentonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, 29 Si and 27 Al MAS NMR to investigate the microstructure of the activated montmorillonites. Two types of structural units were formed during the activation: (1) (SiO) 3 SiOH, in which up to 15% of Si is bound; (2) Q 4 (0Al), a major building unit when the acid concentration is >10%. A significant 27 Al signal at 55.0 ppm was recorded for both untreated montmorillonite and (to a much greater extent) in acid-treated montmorillonites. This was interpreted as arising from four-fold coordinated Al located in the ‘bulk’ octahedral sheet of montmorillonite. In the course of activation, the removal of one of a pair of octahedral Al ions from montmorillonite removes two hydroxyl groups and leaves the other Al of the pair in four-fold coordination.