Compressibility behaviour of homoionized bentonites

Abstract

The Paper reports the mechanisms controlling the Atterberg limits and compressibility characteristics of bentonite, homoionized with a series of monovalent, divalent and trivalent cations. An increase in cationic valency reduces the liquid limit and the compressibility of the clay material, while an increase in the hydrated ionic radius (for a constant valency) increases the liquid limit and compressibility. The size effect is more pronounced for the monovalent bentonites than for the divalent and trivalent clays. The influence of ionic size is explained qualitatively by the Stern model. In the potassium and ammonium bentonites, besides the relatively higher adsorption of cations in the Stern layer, the partial fixation of the cations in the hexagonal oxygen holes of the surface silicate layer also contributes to the marked changes in the properties studied. The consolidation rate and permeability are also significantly affected by the valency and size of the adsorbed cations. An increase in the valency of the adsorbed cations leads to quicker rates of consolidation and higher permeabilities, while, for a constant valency, an increase in the hydrated radius of the adsorbed cation results in a slower rate of consolidation and a lower permeability. Once again the size effect is more pronounced for the monovalent bentonites and is relatively small in the divalent and trivalent bentonites. The variations in the coefficient of secondary compression with cationic valency and size are similar to that noted for the compression index.