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Ulrich K.-U.,Washington University in St. Louis | Ulrich K.-U.,BGD Soil and Groundwater Laboratory GmbH | Veeramani H.,Ecole Polytechnique Federale de Lausanne | Bernier-Latmani R.,Ecole Polytechnique Federale de Lausanne | Giammar D.E.,Washington University in St. Louis
Geomicrobiology Journal | Year: 2011

The kinetics of uranium(VI) reduction by Shewanella oneidensis strain MR-1 was studied for varied pH and concentrations of dissolved inorganic carbon (DIC) and calcium. These are key variables affecting U(VI) speciation in aqueous systems. For all conditions studied, a nearly log-linear decrease of [U(VI)] suggested pseudo-first-order kinetics with respect to U(VI). The reduction rate constants (k) decreased with increasing DIC and calcium concentration, and were sensitive to pH. A positive correlation was found between k and the logarithm of the total concentration of U(VI)-hydroxyl and U(VI)-organic complexes. Linear correlations of the rate constant with the redox potential (EH) of U(VI) reduction and the associated Gibbs free energy of reaction (ΔG r) were found for both Ca-free and Ca-containing systems. Both E H and ΔG r are strong functions of aqueous U(VI) speciation. Because the range in ΔG r among the experimental conditions was small, the differences in k are more likely to be due to differences in EH or to differences in individual rate constants of U(VI) species. Calculation of conditional reduction rate constants for the major groups of U(VI) complexes revealed highest constants for the combined groups of U(VI)-hydroxyl and U(VI)-organic species, lower rate constants for the U(VI)-carbonate group, and much lower constants for the Ca-U(VI)-carbonate group. Mechanistic explanations for these findings are discussed. © Taylor & Francis Group, LLC. Source


Ulrich K.-U.,BGD Soil and Groundwater Laboratory GmbH | Bethge C.,BGD Soil and Groundwater Laboratory GmbH | Guderitz I.,BGD Soil and Groundwater Laboratory GmbH | Heinrich B.,BGD Soil and Groundwater Laboratory GmbH | And 3 more authors.
Mine Water and the Environment | Year: 2012

The formerly highly acidic pit Lake Bockwitz south of Leipzig (Germany) has been repeatedly treated since 2004 with soda ash to meet water quality criteria for the lake effluent. Intense monitoring of water quality parameters showed that previous predictions underestimated the acid load into the lake. Field research and lab experiments were designed to identify and quantify the processes responsible for re-acidification. Monitoring data and key parameters from intermittent-flow column experiments were integrated in hydrogeochemical and physical transport models. The combined lake budget model indicated that re-acidification was dominated by leaching of acidic sulfide mineral weathering products from the Tertiary bank substrates. High inputs of iron, aluminum, and sulfate were generated by infiltrating rain water, interflow, and groundwater recharge. In contrast, acid loads from surface runoff and soil erosion were minor at this particular site. Based on this work, a methodology is proposed to obtain critical parameters from field and lab investigations and integrate those into hydrogeochemical and physical transport models. These process-based models offer tools to reliably predict the water quality of mining pit lakes, develop appropriate treatment measures for the rehabilitation period, and plan the requirements for cost-effective lake water conditioning. © 2012 Springer-Verlag. Source

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