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

Author： He Hongping Guo Jiugao Xie Xiande Lin Hongfu Li Liyun

ISSN： 1471-8030

Source： Clay Minerals, Vol.37, Iss.2, 2002-06, pp. : 337-344

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Abstract

Bentonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, ²⁹Si and ²⁷Al MAS NMR to investigate the microstructure of the activated montmorillonites. Two types of structural units were formed during the activation: (1) (SiO)₃SiOH, in which up to 15% of Si is bound; (2) Q⁴(0Al), a major building unit when the acid concentration is >10%. A significant ²⁷Al signal at 55.0 ppm was recorded for both untreated montmorillonite and (to amuch 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.