The Effect of Compaction of Na-montmorillonite on the Solubility, Diffusivity, and Sorption Capability of Ions due to Specific Pore Water Chemistry

Abstract

Compacted bentonite is a potential candidate buffer material for use in high-level radioactive waste disposal. Although the physico-chemical properties for the compacted form are required to assure the safety function of the system, experimental evidence is quite limited. Electro-migration experiments using tetra-alkyl-ammonium cations having different hydrated ionic radii and osmotic pressure measurements were performed to receive information on the solid/liquid interface in pore water under non-destructive conditions of the highly compacted bentonite (Na-montmorillonite 99%). The results indicated the pore water was strongly influenced by the solid surface and may not be treated as common free water. The geochemical code MINEQL was significantly revised to model the solubility, diffusivity and sorption coefficient simultaneously under consolidated condition. Calculations showed good accordance with the experimental information and the validity of the revision of MINEQL was demonstrated.