Preparation and properties of some hydroxy-aluminium beidellites

Abstract

Hydroxy-aluminium beidellites are prepared by treating Na-saturated beidellites from Taiwan, with compositions intermediate between end-member beidellite and end-member montmorillonite, with hydroxy-aluminium solutions having OH/Al ratios mainly between 2·00 and 2·50. Chemical analyses show that hydroxy-aluminium ions have compositions near Al₆(OH,O)₁₆ and charges near 1·0 in two cases, and near 2·2 in a third case. The basal spacing of the prepared clays is near 17 Å and remains without collapse up to 500°C. Argon adsorption measurements at liquid nitrogen temperatures, after heat-treatment up to 325°C in vacuo overnight, give surface areas near 500 m²/g when the exchangeable Na ions are about one-third replaced by hydroxy-aluminium, but near 200 m²/g when wholly replaced by hydroxy-aluminium. In the latter case the hydroxy-aluminium covers the internal surfaces of the clay almost completely prior to the heat-treatment.