Diffusion and sorption of U(VI) in compacted bentonite studied by a capillary method

Diffusion and sorption of U(VI) in compacted bentonite were studied using a capillary method. The experiments were carried out at room temperature in 0.1 M NaClO4 solutions at pH 7.0±0.1. Effects of contact time, solution concentration and bentonite bulk density on diffusion were also investigated. The results fit the Fick's second law very well and are in good agreement with the literature data for similar bentonite dry densities. The Kd values from capillary method are in most cases lower than those from batch experiments. The interlaminary space of the compacted bentonite contributes significantly to the sorption of uranium. The apparent diffusion coefficient Da of diffusion derived from the experiments are used to simulate its diffusion in compacted bentonite and the results indicate that several meters of compacted bentonite is enough to prevent the diffusion of from the repository to the environment. (orig.)