Bentonite – geotechnical barrier and source for microbial life

Due to their properties, namely a high swelling capacity and a low hydraulic conductivity, bentonites fulfil as geotechnical barrier a sealing and buffering function in a high-level waste repository. Depending on the mineral composition, bentonites contain many suitable electron-donors and –acceptors, enabling potential microbial life. For the potential repository of highly radioactive waste, the microbial mediated transformation of bentonite could influence its properties as a barrier material. Microcosms were set up containing bentonite and anaerobic synthetic Opalinus-clay pore water solution under an N2/CO2 gas atmosphere to elucidate the microbial potential within selected bentonites. Substrates like acetate, lactate and hydrogen were supplemented as electron donors to stimulate potential microbial activity. First results show that bentonites represent a source for microbial life, demonstrated by the consumption of lactate and the formation of pyruvate and hydrogen sulphide.