Sorption effects on cation diffusion in compacted bentonite

Diffusion of Na +, Cs +, Co 2+ and Sr 2+ in bentonite compacted to a dry density of 1800 kg m −3 and saturated with groundwaters and aqueous solutions of differing ionic strength have been studied experimentally using the through diffusion technique. Sorption experiments have been carried out under a wide range of pH and concentration of supporting electrolyte. The dependence of the apparent diffusivity of Na +, Cs + and Sr 2+, mainly sorbed by ion exchange, on the sorption intensity is accommodated by a model encompassing diffusion of the sorbed cations within the electrical double layer next to the mineral surface in addition to diffusion in the pore water. The apparent diffusivity of Co 2+, sorbed by surface complexation reactions, corresponds to complete immobilization on sorption.