Formation, Compositions, and Properties of Hydroxy-Al- and Hydroxy-Mg-Montmorillonite

G. W. Brindley and Chih-Chun Kao
Mineral Sciences Building, The Pennsylvania State University University Park, Pennsylvania 16802

Abstract: Hydroxy-Al- and hydroxy-Mg-montmorillonite were prepared by treating dispersed Na-montmorillonite with aluminum and magnesium nitrate solutions and titrating with NaOH solutions so that the OH/Al ratio varied from zero to 3.0 and the OH/Mg ratio from zero to 2.0. External precipitation of Al and Mg hydroxides was observed when the OH/M ratios (M = metal) approached 3 and 2, respectively. From chemical analyses of the initial Na-montmorillonite and the hydroxy-metal montmorillonites, structural formulae were derived by assuming that the silicate layer compositions remained unchanged. Prior to the addition of NaOH, the average interlayer material approximated in composition to [Al(OH)2]+ and [Mg(OH)]+. With additions of NaOH the interlayer compositions moved progressively towards Al(OH)3 and Mg(OH)2. When the hydroxy interlayers approached completion, external precipitation was observed. X-ray powder diffraction data showed that the hydroxy-Mg products have less tendency to swell in ethylene glycol and water, and greater thermal stability than the hydroxy-Al products. Initially, when the average interlayer compositions were near Al(OH)2 and Mg(OH), swelling followed more nearly the normal behavior.

Key Words: Hydrolysis • Hydroxy interlayer • Montmorillonite • Swelling • Thermal stability

Clays and Clay Minerals; December 1980 v. 28; no. 6; p. 435-443; DOI: 10.1346/CCMN.1980.0280605
© 1980, The Clay Minerals Society
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