The concentration and pH dependent diffusion of 137Cs in compacted bentonite by using capillary method

The ‘in-diffusion’ method was used to study the diffusion behavior of radionuclide 137Cs in compacted bentonite using a capillary. The results (distribution coefficient, Kd, apparent and effective diffusion coefficients, Da and De) derived from the capillary method are in good agreement with the literature data, and fit the Fick’s second law very well. The experiments were carried out at 3.3 × 10−3 and 3.3 × 10−5mol/l cesium, pH 3–12, ionic strength 0.1 M NaClO4, and at room temperature. The results suggest that the diffusion of cesium in compacted bentonite is dependent on solution concentrations and pH values. In agreement with the literatures, the Kd values derived from the capillary experiments are in most cases lower than those derived from batch experiments: the Kd values are about one-half to one-third the values of those from batch experiments. The interlaminary space plays a very important role to the sorption, diffusion and transport of Cs+ in compacted bentonite. The effective diffusion coefficient is higher than that of other nuclides in compacted bentonite, and the diffusion of cesium in compacted bentonite may be dominated by the surface diffusion.