Evaluation of sorption site capacity in colloidal montmorillonite

Ishidera, Takamitsu ; Hayashi, Masanori*; Sukegawa, Akihiro*

In the geological disposal of radioactive waste, montmorillonite, which is the major mineral component of bentonite, possibly forms colloidal particles due to the erosion of compacted bentonite. To evaluate the impact of colloid on radionuclide migration, distribution coefficient of radionuclides on colloidal montmorillonite is a key parameter. The distribution coefficient on colloidal montmorillonite is considered to be derived from the sorption behavior of radionuclides on non-colloidal montmorillonite (montmorillonite sediment). In this study, the sorption site capacity of colloidal montmorillonite was investigated by acid titration to evaluate the difference of sorption site capacity between colloidal montmorillonite and montmorillonite sediment. The experimental results suggested that the sorption site capacity in colloidal montmorillonite generated in low Na concentration was comparable to that of montmorillonite sediment.