Sorption effects on cation diffusion in compacted bentonite

摘要

Diffusion of Na+ , Cs+ , Co2+ and Sr2+ in bentonitecompacted to a dry density of 1800 kg m-3 and saturated withgroundwaters and aqueous solutions of differing ionic strengthhave been studied experimentally using the through diffusiontechnique. Sorption experiments have been carried out under awide range of pH and concentration of supporting electrolyte.The dependence of the apparent diffusivity of Na+, Co2+ andSr2+, mainly sorbed by ion exchange, on the sorption intensity isaccommodated by a model encompassing diffusion of the sorbedcations within the electrical double layer next to the mineralsurface in addition to diffusion in the pore water. The apparentdiffusivity of Co2+ , sorbed by surface complexation reactions,corresponds to complete immobilization on sorption.