Effect of compaction on bisulfide diffusive transport through MX-80 bentonite

Chowdhury, F.; Rashwan, T. L.; Mondal, P.; Behazin, M.; Keech, P. G.; Sharma, J. S. and Krol, M. (2024). Effect of compaction on bisulfide diffusive transport through MX-80 bentonite. Journal of Contaminant Hydrology, 264, article no. 104341.

DOI: https://doi.org/10.1016/j.jconhyd.2024.104341


Canada's deep geological repository (DGR) design includes an engineered barrier system where highly compacted bentonite (HCB) surrounds the copper-coated used fuel containers (UFCs). Microbial-influenced corrosion is a potential threat to long-term integrity of UFC as bisulfide (HS-) may be produced by microbial activities under anaerobic conditions and transported via diffusion through the HCB to reach the UFC surface, resulting in corrosion of copper. Therefore, understanding HS- transport mechanisms through HCB is critical for accurate prediction of copper corrosion allowance. This study investigated HS- transport behaviour through MX-80 bentonite at dry densities 1070-1615 kg m-3 by performing through-diffusion experiments. Following HS- diffusion, bromide (Br- ) diffusion and Raman spectroscopy analyses were performed to explore possible physical or mineralogical alterations of bentonite caused by interacting with HS-. In addition, accessible porosity (ε) was estimated using extended Archie's law. Effective diffusion coefficient of HS- was found 2.5 × 10-12m2s-1 and 5.0 × 10-12m2s-1 for dry densities 1330 and 1070 kg m-3, respectively. No HS- breakthrough was observed for highly compacted bentonite (1535-1615 kg m-3) over the experimental timeframe (170 days). Raman spectroscopy results revealed that HS- reacted with iron in bentonite and precipitated as mackinawite and, therefore, it was immobilized. Finally, results of this study imply that HS- transport towards UFC will be highly controlled by the available iron content and dry density of the buffer material.

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