Alteration of bentonite by hyper alkaline fluids: the role of secondary minerals

Concerns over the chemical compatibility of cement and bentonite in engineered barrier systems for the geological disposal of radioactive wastes necessitate a comprehensive understanding of the potential rate and nature of bentonite alteration in the long-term. Due to the paucity of relevant natural systems, the current emphasis lies predominantly with predictive numerical modelling. Previous studies of this type have shown that the degree of bentonite alteration is sensitive to a number of factors, such as the precise rate and mechanism of montmorillonite dissolution close to equilibrium, the variation of bentonite transport properties with time, the composition of cement pore fluids, and the assumed crystallinity and types of secondary minerals. This latter issue is the subject of the present communication. (authors)