Impact of the solution ionic strength on strontium diffusion through the Callovo-Oxfordian clayrocks: An experimental and modeling study

The results showed that there was a good agreement of the distribution ratios (RD) determined on crushed and intact rocks by batch and through-diffusion methods with a RD decrease related to the increase of the sodium concentration, a sorption competitor. Such a trend was also well reproduced by means of a geochemical modeling based on the multi-site ion exchange (MSIE) theory. Moreover, the “enhanced” diffusion for strontium was clearly observed in this study: the Sr diffusive flux was almost five times higher than that for HTO in the cell with the lowest ionic strength, and diminished to less than 1.5 times in the cell with the highest ionic strength. The evolution of the Sr diffusive flux with the ionic strength was qualitatively reproduced by a surface diffusion model, based on the concept of relative diffusive mobility or mobile fraction.