Bentonite Geomicrobiology

Bentonites may be used as a buffer and backfill material in future deep geological repositories of high-level radioactive waste. These clay formations have been reported to host different metabolically active microorganisms with the potential to affect the biogeochemical cycles of carbon, phosphorus and sulfur. Therefore, low porosity bentonites with high swelling capacity might prevent several microbial processes, such as corrosion. In addition, microorganisms occurring in bentonite may be able to interact with released radionuclides affecting their fate and behavior and leading to their mobilization or immobilization.
This chapter reviews the latest findings on the structure and composition of microbial communities in bentonites under repository relevant conditions (high temperature, high pressure, presence of electron donors/acceptors, etc.), to underline the importance of the microbial activity for the long-term effectiveness of the repository. Both, laboratory and large-scale experiment results will be summarized and discussed. In addition, the impact of microbial processes on the mobilization of radionuclides at the bentonite/microbe/radionuclide interface will be reviewed. A multidisciplinary approach combining microscopy, spectroscopy, radiochemistry and microbiology-based techniques used to study the speciation of radionuclides will be highlighted.