Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Environmental pollution by metals and radionuclides is one of the biggest challenges which have to be solved globally. In the uranium mine of the Wismut GmbH near Königstein (Germany) uranium production was achieved by leaching the sandstone with sulfuric acid. As a consequence the geochemical nature of the mine water has been substantially changed leading to an increase in sulfate, metals and uranium concentrations. For remediation purposes the mine is currently in the process of being flooded. Mine water is pumped to the surface, where it is treated by a conventional water treatment plant which is cost-intensive and long-lasting. For that reason, biological concepts for remediation could be appropriate alternatives.
In our studies, we designed a pilot plant for a bioremediation approach using the mine water with the naturally occurring microorganisms. We added 10 mM glycerol to 100 L of the mine water and incubated the solution over six weeks at ambient temperature. During this time, we performed online-measurements of pH, redox potential (Eh) and temperature. The uranium concentration as well as the iron(II) and sulfate concentrations were measured periodically. Within the six weeks of incubation, we monitored a drastic decrease of Eh, from 650 mV to 80 mV. Theoretical predictions showed that this decrease could be associated with a uranium(VI) reduction. Thus, the prediction was confirmed using UV-vis and EXAFS/ XANES measurements. After 17 days of incubation uranium(IV) was detectable. In addition to the uranium(VI) reduction, we detected an iron(III) to iron(II) reduction during the first three weeks as well as a slight sulfate reduction after 30 days of incubation.
In summary, our results demonstrate a biological influence within the mine water of the former uranium mine only by adding 10 mM glycerol. As a result, uranium(VI) is reduced to uranium(IV). The investigation in pilot-plant scale confirmed our previous lab scale experiments. We were able to prove the microbial induced reduction of uranium(VI) which could by a possible bioremediation approach in combination with or instead of conventional water treatment.