Sorption effects on cation diffusion in compacted bentonite

Diffusion of Na+, Cs+, Co2+ and Sr2+ 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. pendence of the apparent diffusivity of Na+, Cs+ and Sr2+, 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 Co2+, sorbed by surface complexation reactions, corresponds to complete immobilization on sorption.