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Evaluating chemical extraction techniques for the determination of uranium oxidation state in reduced aquifer sediments

Environmental Science and Technology

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, , , , , , , , , and
DOI: 10.1021/es401450v

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Abstract

Extraction techniques utilizing high pH and (bi)carbonate concentrations were evaluated for their efficacy in determining the oxidation state of uranium (U) in reduced sediments collected from Rifle, CO. Differences in dissolved concentrations between oxic and anoxic extractions have been proposed as a means to quantify the U(VI) and U(IV) content of sediments. An additional step was added to anoxic extractions using a strong anion exchange resin to separate dissolved U(IV) and U(VI). X-ray spectroscopy showed that U(IV) in the sediments was present as polymerized precipitates similar to uraninite and/or less ordered U(IV), referred to as non-uraninite U(IV) species associated with biomass (NUSAB). Extractions of sediment containing both uraninite and NUSAB displayed higher dissolved uranium concentrations under oxic than anoxic conditions while extractions of sediment dominated by NUSAB resulted in identical dissolved U concentrations. Dissolved U(IV) was rapidly oxidized under anoxic conditions in all experiments. Uraninite reacted minimally under anoxic conditions but thermodynamic calculations show that its propensity to oxidize is sensitive to solution chemistry and sediment mineralogy. A universal method for quantification of U(IV) and U(VI) in sediments has not yet been developed but the chemical extractions, when combined with solid-phase characterization, have a narrow range of applicability for sediments without U(VI).

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Evaluating chemical extraction techniques for the determination of uranium oxidation state in reduced aquifer sediments
Series title:
Environmental Science and Technology
DOI:
10.1021/es401450v
Volume
47
Issue:
16
Year Published:
2013
Language:
English
Publisher:
American Chemical Society
Contributing office(s):
National Research Program - Western Branch
Description:
8 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Environmental Science and Technology
First page:
9225
Last page:
9232
Country:
United States
State:
Colorado
City:
Rifle