Anodic dissolution mechanisms of iron in bentonite slurries

TL;DR

This study investigates how iron corrodes in bentonite slurries, which is important for radioactive waste disposal systems.

Contribution

The study reveals that anodic dissolution of iron in bentonite slurries leads to acidic gel formation due to cationic exchange.

Findings

Anodic dissolution of iron increases in more concentrated bentonite slurries.

The acidic gel forms from cationic exchange between Fe2+ ions and protons in bentonite.

Gel growth is governed by reactions at the gel-bentonite interface rather than diffusion.

Abstract

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.

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