Sorption effects on cation diffusion in compacted bentonite

Diffusion of Na+. Cs+, Co2+ and Sr2+ in bentonite compacted to a dry densit y of 1800 kg m(-3) and saturated with groundwaters and aqueous solutions of differing ionic strength have been studied experimentally using the throug h diffusion technique. Sorption experiments have been carried out under a w ide range of pH and concentration of supporting electrolyte. The dependence of the apparent diffusivity of Na+, Cs+ and Sr2+, mainly sor bed by ion exchange, on the sorption intensity is accommodated by a model e ncompassing diffusion of the sorbed cations within the electrical double la yer 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. (C) 1999 Elsevier Sci ence B.V. All rights reserved.