The effect of compaction on the surface characteristics of activated bentonite

Abstract

Nitrogen adsorption-desorption isotherms at 77 K were determined on powder and compacted samples (2 and 4 tons in −2) of bentonite clay and three acid-activated preparations of different normalities. Analysis of the adsorption isotherms using the α s method of Sing revealed that micropores were present in the original bentonite clay and that the microporosity developed progressively with acid activation. The presence of mesopores in addition to micropores in the samples studied was demonstrated by the occurrence of high pressure hysteresis loops. Observed changes in various surface parameters of bentonite on acid treatment were correlated with corresponding chemical changes. Compaction of the four unactivated and acid-activated powder samples at 2 tons in −2 invariably resulted in depression of the adsorption isotherm in the monolayer and multilayer regions, indicating the elimination of a fraction of the available surface in interparticulate contacts. However, for all the acid-activated clays, compaction at 4 tons in −2 invariably produced a marked upward shift in the adsorption isotherm over that for the samples compacted at 2 tons in −2 and even over that for the original powder samples; this effect is indicative of the occurrence of plastic deformation of the clay involving an increase in the surface area and void volume parameters. The response to plastic deformation is greater in acid-activated clay than in unactivated clay.