Uranium repartitioning during microbial driven reductive transformation of U(VI)-sorbed schwertmannite and jarosite

Weathering of sulfide-containing soils, bedrock, and mining wastes at numerous sites worldwide releases large amounts of acidic sulfate-rich drainages with elevated levels of the highly carcinogenic and toxic radionuclide uranium into the surrounding ecosystems. The release of acidic sulfate-rich drainage leads to the formation of Fe oxyhydroxysulfates (dominated by schwertmannite and jarosite) as mineral encrustations on the surfaces of rock grains and soil macropores or colloidal precipitates in recipient watercourses. Microorganisms are key biological factors driving the reductive dissolution/transformation of Fe(III) oxyhydroxysulfates. Incubation experiments show that natural consortia of anaerobic microorganisms trigger and sustain a rapid and efficient reduction of Fe and sulfate bound to schwertmannite under acidic conditions. Here, two incubation experiments were conducted with U(VI)-sorbed schwertmannite and jarosite that were mixed with artificial acidic groundwater and subsequently exposed to a natural consortium of anaerobic microorganisms. The overall aim was to explore how the reductive transformation of these two oxyhydroxysulfates and co-linked microbial communities regulated the mobility, redox status, and repartitioning of co-associated U.