[2M12-17] Bentonite

3:50 PM - 4:05 PM JST(6:50 AM - 7:05 AM UTC)

[2M13] Numerical Simulation of Ion Exchange Behavior in Buffer Materials Considering the Chemical Effects of Saltwater(1) Theoretical Analysis of Ca-Na Exchange Selectivity in Compacted Bentonite Using the Poisson-Boltzmann Equation

*Ryo Itoh¹, Tsuneyuki Memura¹, Kazuya Ono¹, Ryo Yasuda², Shingo Tanaka², Daisuke Hayashi² (1. Dia Nippon Engineering Consultants, 2. RWMC)

Keywords:

Geological disposal,coastal area,bentonite,ion exchange selectivity coefficient,Poisson-Boltzmann equation

To provide a theoretical explanation of the cation exchange selectivity coefficient (logK_GT) of compacted bentonite, theoretical logK_GT values for Ca over Na were derived using the Poisson-Boltzmann (P-B) equation and the relationship with dry density and ionic strength (IS) was investigated. Furthermore, the theoretical log K_GT values were compared with those obtained from infiltration tests (test values). An extended P-B equation, which considers ion size, yielded closer theoretical logK_GT values to the test values than the conventional P-B equation. The theoretical values were positively correlated with dry density and almost independent of IS. In contrast, the test values were positively correlated with IS, indicating the need to consider factors other than ion size to explain this IS dependence.