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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-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 lM 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.more » 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:
 [1];  [1];  [2]
  1. Argonne National Laboratory (ANL)
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
930801
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochimica et Cosmochimica Acta; Journal Volume: 71; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; ABSORPTION SPECTROSCOPY; CALCIUM COMPLEXES; SODIUM COMPLEXES; URANYL CARBONATES; GROUND WATER; RADIOECOLOGICAL CONCENTRATION; BACTERIA; BIOREMEDIATION; X-RAY SPECTROSCOPY; GEOCHEMISTRY

Citation Formats

Kelly, Shelly D, Kemner, Kenneth M, and Brooks, Scott C. 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, Shelly D, Kemner, Kenneth M, & Brooks, Scott C. X-ray Absorption Spectroscopy Identifies Calcium-Uranyl-Carbonate Complexes at Environmental Concentrations. United States. doi:10.1016/j.gca.2006.10.013.
Kelly, Shelly D, Kemner, Kenneth M, and Brooks, Scott C. 2007. "X-ray Absorption Spectroscopy Identifies Calcium-Uranyl-Carbonate Complexes at Environmental Concentrations". United States. doi:10.1016/j.gca.2006.10.013.
@article{osti_930801,
title = {X-ray Absorption Spectroscopy Identifies Calcium-Uranyl-Carbonate Complexes at Environmental Concentrations},
author = {Kelly, Shelly D and Kemner, Kenneth M and Brooks, Scott C},
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-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 lM 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.},
doi = {10.1016/j.gca.2006.10.013},
journal = {Geochimica et Cosmochimica Acta},
number = 4,
volume = 71,
place = {United States},
year = 2007,
month = 1
}
  • 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.more » 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.« less
  • BS>A new reaction was found by passing CO/sub 2/ through an aqueous suspension of a particularly reactive form of UO/sub 3/. The reaction leads to the whole dissolution of the suspended dihydroxiuranyl through complex formation. The process was submitted to careful investigation by proper selection of different instrumental techniques. A theoretical treatment of the question is laid down to account for the variety of phenomena observed, in connection with the most recent aspects on the chemistry of uranium in solution. The existence of a complex uranyl carbonate compound, showing a CO/sub 3/: lJ relation equal to 1 is postulated. Themore » stability of the llevow complex solutions is but limited, solid products precipitating therefrom after elapsing a definite time interval. In dilute solution, the complex compound seems to tend irreversibly toward a dinuclear structure. in more concentrated solution toward a tetranuclear arrangement. Both processes, leading to uranyl carbonate complexes with COg: U relations 1:2 and 1: 4 respectively, are presumably governed by a cores + links'' type of mechanism. (auth)« less
  • No abstract prepared.
  • An in situ procedure for quantifying total organic and inorganic Cl concentrations in environmental samples based on X-ray absorption near-edge structure (XANES) spectroscopy has been developed. Cl 1s XANES spectra reflect contributions from all Cl species present in a sample, providing a definitive measure of total Cl concentration in chemically heterogeneous samples. Spectral features near the Cl K-absorption edge provide detailed information about the bonding state of Cl, whereas the absolute fluorescence intensity of the spectra is directly proportional to total Cl concentration, allowing for simultaneous determination of Cl speciation and concentration in plant, soil, and natural water samples. Absolutemore » Cl concentrations are obtained from Cl 1s XANES spectra using a series of Cl standards in a matrix of uniform bulk density. With the high sensitivity of synchrotron-based X-ray absorption spectroscopy, Cl concentration can be reliably measured down to the 5-10 ppm range in solid and liquid samples. Referencing the characteristic near-edge features of Cl in various model compounds, we can distinguish between inorganic chloride (Cl{sub inorg}) and organochlorine (Cl{sub org}), as well as between aliphatic Cl{sub org} and aromatic Cl{sub org}, with uncertainties in the range of {approx}6%. In addition, total organic and inorganic Br concentrations in sediment samples are quantified using a combination of Br 1s XANES and X-ray fluorescence (XRF) spectroscopy. Br concentration is detected down to {approx}1 ppm by XRF, and Br 1s XANES spectra allow quantification of the Br{sub inorg} and Br{sub org} fractions. These procedures provide nondestructive, element-specific techniques for quantification of Cl and Br concentrations that preclude extensive sample preparation.« less