Evidence for indigenous sulphate-reducing bacteria in commercial Wyoming bentonite MX-80

Journal article, 2010

The activity of sulphate reducing bacteria (SRB) in Wyoming bentoniteMX-80 saturated with groundwater from 450mundergroundwas investigated in situ. The bentonitewas compacted to densities of 1.5,1.8, and 2.0 g cm−3. Lactatewas added to the bentonite as a source of energy and organic carbon for SRB. Radioactive sulphur (35SO42−) was used as a tracer of sulphide production. The copper sulphide (Cux 35S) that was produced was localized and quantified using electronic autoradiography. The mean copper sulphide production rates observedwere 1.5×103, 3.1×102, and3.4×101 fmol CuxSmm−2 day−1 at densities of 1.5,1.8, and 2.0 g cm−3, respectively. The use of sterilefiltered (0.2 μm) groundwater resulted in sulphide production of 1.5×102 and 2.4×101 fmol CuxSmm−2 day−1 at densities of 1.8, and 2.0 g cm−3, respectively. Additional in situ experiments were performed with sterile-filtered (0.2 μm) groundwater and bentonite that had been heated to 120 °C for 15 h. Sulphide production rates in the heated bentonitewere 1.3–16 times lower than in controls treated at 25 °C. These results reveal bentonite to be a source of SRB, in addition to the groundwater. Furthermore, all experiments demonstrated that increasing bentonite density correlated with decreasing copper sulphide production rates. According to the results presented here, sulphide production rates in bentonite compacted to 2.0 g cm−3 are hundred to thousands of times below the rate needed to corrode through the copper capsule over 100000 years.