Diffusion and Sorption of Cesium, Strontium, and Iodine in Water-Saturated Cement

Diffusion and sorption in cementitious materials are important factors influencing radionuclide migration in radioactive waste disposal. Four different experimental techniques have been used to study these processes for Cs⁺, Sr²⁺, and I⁻ ions in Sulphate Resisting Portland Cement paste saturated with water. The results of different experimental methods are compared and their relative merits discussed. The observations can be rationalized only by taking into account departures from the usual simple description of transport in porous media. These are that the cement pore structure has fast and slow diffusivity networks, that all ions do not have the same diffusibility, and that some ions (in this case I⁻) have nonlinear sorption isotherms. When these factors are taken into account, the present observations are also found to be compatible with the results of other studies. The most appropriate values of characteristic parameters for diffusion and sorption in this system are deduced.