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in compacted sodium montmorillonite as a function of porewater salinityTachi, Yukio; Yotsuji, Kenji
Proceedings of 5th International Meeting on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement (USB Flash Drive), p.899 - 900, 2012/10
Sorption and diffusion of radionuclides in compacted bentonite are key processes in the safe geological disposal. The effects of porewater salinity on Sr diffusion and sorption in compacted montmorillonite were investigated by experimental and modeling approaches. Effective diffusion coefficients (De) and distribution coefficients (Kd) of Sr in montmorillonite compacted to dry density of 800 kg/m
were measured under four different salinities (0.01-0.5 M NaCl). The De decreased drastically with increasing porewater salinity. The Kd values decreased with increasing salinity, which are consistent with Kd values obtained by batch sorption. These results were interpreted by the ISD model coupling the thermodynamic sorption model and the EDL diffusion model in narrow pores. The ISD model can be basically applicable for divalent cations, however is needed to modify for better agreement at low salinity conditions by considering additional factors.
Yotsuji, Kenji; Tachi, Yukio; Nishimaki, Yuichiro*
Proceedings of 5th International Meeting on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement (USB Flash Drive), p.427 - 428, 2012/10
We have developed integrated sorption and diffusion model (ISD model) for assessment of diffusion parameters consistent with sorption processes in compacted bentonite. Conventional ISD model is unsatisfactory because for multivalent cation/anion and complex ion model predictions disagree with experimental data, and because the model contains additional non-physical fitting parameter. Accordingly we extract the factors influencing the assessment from fundamental assumptions of the conventional ISD model. In this study we incorporated the excluded volume effect and the dielectric saturation effect into ISD model. As results of numerical analysis of these models the considering factors influence hardly the effective diffusivity. Therefore it does not mean that the disagreement with experimental data are caused by considering factors in this report.