Properties of Reduced Charge Montmorillonite: Tetra-Alkylammonium Ion Exchange Forms

Abstract

Surface properties of reduced charge montmorillonites (RCM) whose exchange capacities were saturated with tetra-alkylammonium cations, were studied with X-ray diffraction, nitrogen, and water adsorption. Methods were utilized for preparing montmorillonite of varying charge and of swelling reduced-charge clay with ethanol. As charge reduction proceeds, all layers retain some exchangeable cations until about half the original charge is reached at which point collapsed layers begin to appear and increase to about 60 per cent at maximum charge reduction. Charge reduction thus appears to proceed in a non-homogeneous fashion. When saturating exchange sites with tetra-alkylammonium ions in ethanol solvent, intercalation of salt in uncharged layers was noted if the samples were not completely washed. Nitrogen adsorption isotherms at liquid nitrogen temperatures showed considerable interlamellar penetration of tetramethylammonium (TMA₊) clays, resulting in high calculated surface areas. Much less adsorption on the tetra-n-propylammonium (TPA₊) clays was observed. Surface areas were increased upon reduction of charge up to the point where collapsed layers began to be appreciable, whereupon measured areas decreased. Water adsorption isotherms reflected the hydration properties of the exchangeable cation as well as the surface available for adsorption.