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Title: X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations.

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-UO{sub 2}-CO{sub 3} complex. However, the stoichiometry of the complex is poorly defined and may be complicated by the presence of a Na-UO{sub 2}-CO{sub 3} complex. Such a complex might exist even at high calcium concentrations, as some UO{sub 2}-CO{sub 3} 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 {micro}M 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 UO{sub 2}-CO{sub 3} complex to approximately 0.6more » and enables spectroscopic identification of the Na-UO{sub 2}-CO{sub 3} 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.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
940696
Report Number(s):
ANL/BIO/JA-57749
Journal ID: ISSN 0016-7037; GCACAK; TRN: US200824%%216
DOE Contract Number:  
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochim. Cosmochim. Acta; Journal Volume: 71; Journal Issue: 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
54 ENVIRONMENTAL SCIENCES; ABSORPTION; ABSORPTION SPECTROSCOPY; ATOMS; BACTERIA; BIOREMEDIATION; CALCIUM; ECOLOGICAL CONCENTRATION; FINE STRUCTURE; PH VALUE; SODIUM; STOICHIOMETRY; TRANSPORT; URANIUM; URANYL CARBONATES

Citation Formats

Kelly, S. D., Kemner, K. M., Brooks, S. C., Biosciences Division, and ORNL. X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations.. United States: N. p., 2007. Web. doi:10.1016/j.gca.2006.10.013.
Kelly, S. D., Kemner, K. M., Brooks, S. C., Biosciences Division, & ORNL. X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations.. United States. doi:10.1016/j.gca.2006.10.013.
Kelly, S. D., Kemner, K. M., Brooks, S. C., Biosciences Division, and ORNL. Mon . "X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations.". United States. doi:10.1016/j.gca.2006.10.013.
@article{osti_940696,
title = {X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations.},
author = {Kelly, S. D. and Kemner, K. M. and Brooks, S. C. and Biosciences Division and ORNL},
abstractNote = {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-UO{sub 2}-CO{sub 3} complex. However, the stoichiometry of the complex is poorly defined and may be complicated by the presence of a Na-UO{sub 2}-CO{sub 3} complex. Such a complex might exist even at high calcium concentrations, as some UO{sub 2}-CO{sub 3} 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 {micro}M 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 UO{sub 2}-CO{sub 3} complex to approximately 0.6 and enables spectroscopic identification of the Na-UO{sub 2}-CO{sub 3} 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.},
doi = {10.1016/j.gca.2006.10.013},
journal = {Geochim. Cosmochim. Acta},
number = 2007,
volume = 71,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}