Diffusion of sodium and copper in compacted sodium bentonite at room temperature

Diffusion studies were carried out with sodium and copper in sodium bentonite. The experiments were performed at room temperature and densities of the samples varied from 0.8 to 1.8 g/cm3. This paper describes the experimental methods used for the diffusion tests and gives the obtained measurement results. The evaluation of the diffusion mechanisms is at this stage preliminary, however. Diffusion of sodium seems to follow similar mechanisms as has been observed for cesium and strontium in several previous studies. The phenomena could be explained by some kind of diffusion of sorbed ions. The measured apparent diffusivities of sodium varied from 50×10−12 to 300×10−12 m2/s and the effective diffusivities from 80×10−12 to 1.6×10−9 m2/s depending on the density of bentonite and the salt concentration of water solution. Low solubility of copper caused precipitation thus interfering the diffusion experiments. However, the part of copper which did diffuse into bentonite seemed to follow the same type of mechanism as sodium. The measured apparent diffusivities of copper varied from 5×10−12 m2/s. The interaction between the cations in the circulating solutions and the sodium ion in bentonite were essential in this study.