Anodic dissolution mechanisms of iron in bentonite slurries

The corrosion of iron or steel in contact with bentonite is a key factor affecting the long-term safety of radioactive waste disposal system. Previous studies focused on corrosion after long-term burial in compact bentonites, however, little work was dedicated to the corrosion of iron exposed to bentonite slurries, that can appear in case of fracture of the bentonite jacket separating steel from underground water. In this study, accelerated corrosion experiments were performed on pure iron in basic bentonite slurries (pH 9-10) using various electrochemical corrosion techniques. The anodic dissolution of iron was larger in more concentrated bentonite slurries and resulted in the formation of an acidic gel. This gel results from a cationic exchange between Fe²⁺ ions released by corrosion and protons from surface or edge locations in bentonite. Its growth appears to be governed by reactions at the gel-bentonite interface rather than diffusion processes.