Abstract
Current research on bioremediation of uranium-contaminated groundwater focuses on supplying indigenous metal-reducing bacteria with the appropriate metabolic requirements to induce microbiological reduction of soluble uranium(VI) to poorly soluble uranium(IV). Recent studies of uranium(VI) bioreduction in the presence of environmentally relevant levels of calcium revealed limited and slowed uranium(VI) reduction and the formation of a Ca-UO2-CO3 complex. However, the stoichiometry of the complex is poorly defined and may be complicated by the presence of a Na-UO2-CO3 complex. Such a complex might exist even at high calcium concentrations, as some UO2-CO3 complexes will still be present. The number of calcium and/or sodium atoms coordinated to a uranyl carbonate complex will determine the net charge of the complex. Such a change in aqueous speciation of uranium(VI) in calcareous groundwater may affect the fate and transport properties of uranium. In this paper, we present the results from X-ray absorption fine structure (XAFS) measurements of a series of solutions containing 50 μM uranium(VI) and 30 mM sodium bicarbonate, with various calcium concentrations of 0-5 mM. Use of the data series reduces the uncertainty in the number of calcium atoms bound to the UO2-CO3 complex to approximately 0.6 and enables spectroscopic identification of the Na-UO2-CO3 complex. At nearly neutral pH values, the numbers of sodium and calcium atoms bound to the uranyl triscarbonate species are found to depend on the calcium concentration, as predicted by speciation calculations.
| Original language | English |
|---|---|
| Pages (from-to) | 821-834 |
| Number of pages | 14 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 71 |
| Issue number | 4 |
| DOIs | |
| State | Published - Feb 15 2007 |
Funding
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, Environmental Remediation Sciences Program. MRCAT operations are supported by the U.S. DOE and the MRCAT member institutions. Advance Photon Source is supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, under contract W-31-109-ENG-38. Special appreciation is extended to E.J. O’Loughlin and M. Boyanov for assistance with the uranium XAFS data collection. Finally, the authors wish to thank William M. Murphy and two anonymous reviewers for their insightful review comments. The submitted manuscript has been created by the University of Chicago as operator of Argonne National Laboratory under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the government.
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| Office of Science | |
| Basic Energy Sciences | W-31-109-ENG-38 |
| Biological and Environmental Research | |
| Argonne National Laboratory | |
| University of Chicago |
