Cation Filtration of Montmorillonite on Hydraulic Conductivities of Some Bentonites in Artificial Seawater
Hideo Komine
Abstract
Bentonite is planned for use as a buffer for repositories of high-level radioactive waste (HLW) because the buffer must have extremely low hydraulic conductivity to seal wastes. A Japanese HLW disposal facility might be built in a coastal area to facilitate waste transportation. Therefore, it is important to investigate the influence of seawater on bentonite buffer materials. This study used experiments to investigate the influence of artificial seawater on the hydraulic conductivities of three sodium-type bentonites and one calcium-type bentonite. This study assessed the influence of artificial seawater on hydraulic conductivities of bentonites in terms of the kinds of bentonite such as exchangeable-cation type, montmorillonite content, and the bentonite buffer dry density. Experimentally obtained results indicate a low influence of artificial seawater on hydraulic conductivities of sodium-type bentonites, provided that the compacted bentonite dry density is high. Furthermore, the author has proposed a mechanism of bentonite behavior in artificial seawater that results from cation filtration of montmorillonite mineral layers in bentonite. This study has also clarified the validity of the cations’ filtration mechanism of montmorillonite mineral layers by comparing the calculated interlayer distance of montmorillonite minerals with the hydrated diameter of main cations in artificial seawater.