Effect of pH and concentration on the diffusion of radiostrontium in compacted bentonite--a capillary experimental study.

The effects of pH and Sr2+ solution concentration on diffusion and sorption of Sr2+ in compacted bentonite (rhob = 1000+/-30 kg/m3) were studied using an "in-diffusion" method at an ionic strength of 0.1M NaClO4. The results (distribution coefficients, Kd, apparent and effective diffusion coefficients, Da and De) derived from the capillary method are in good agreement with the literature data obtained for similar bentonite dry densities and fit Fick's second law very well. The results suggest that the diffusion of Sr2+ in compacted bentonite decreases slightly with increasing pH values and also increases slightly with increasing Sr2+ solution concentration. The distribution coefficients are weakly dependent on the solution concentrations and show a slight increase with increasing pH values. The average effective diffusion coefficient of Sr2+ in compacted bentonite is (1.2+/-0.2) x 10(-9) m2/s, surface diffusion effects are found for the diffusion of Sr2+ in compacted bentonite.