Retention and chemical speciation of uranium in an oxidized wetland sediment from the Savannah River Site.
Uranium speciation and retention mechanisms onto Savannah River Site (SRS) wetland sediments was studied using batch (ad)sorption experiments, sequential extraction, U L3-edge X-ray absorption near-edge structure (XANES) spectroscopy, fluorescence mapping and μ-XANES. Under oxidized conditions, U was highly retained by the SRS wetland sediments. In contrast to other similar but much lower natural organic matter (NOM) sediments, significant sorption of U onto the SRS sediments was observed at pH < 4 and pH > 8. Sequential extraction indicated that the U species were primarily associated with the acid soluble fraction (weak acetic acid extractable) and organic fraction (Na-pyrophosphate extractable). Uranium L3-edge XANES spectra of the U-bound sediments were nearly identical to that of uranyl acetate. Based on fluorescence mapping, U and Fe distributions in the sediment were poorly correlated, U was distributed throughout the sample and did not appear as isolated U mineral phases. The primary oxidation state of U in these oxidized sediments was U(VI), and there was little evidence that the high sorptive capacity of the sediments could be ascribed to abiotic or biotic reduction to the less soluble U(IV) species or to secondary mineral formation. Collectively, this study suggests that U may be strongly bound to wetland sediments, not only under reducing conditions by reductive precipitation, but also under oxidizing conditions through NOM-uranium bonding.
Savannah River National Laboratory, Aiken, SC 29808, USA. Electronic address: Dien.Li@srs.gov.
Dien
D
Li
Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, USA.
John C
JC
Seaman
Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, USA.
Hyun-Shik
HS
Chang
Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA.
Peter R
PR
Jaffe
Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA.
Paul
P
Koster van Groos
Department of Physics, University of Guelph, Guelph, ON N1G 2W1, Canada.
De-Tong
DT
Jiang
Canadian Light Source Inc., Saskatoon, SK S7N 2V3, Canada.
Ning
N
Chen
University of Saskatchewan, Saskatoon SK S7N 5E2, Canada.
Jinru
J
Lin
Department of Physics, University of Guelph, Guelph, ON N1G 2W1, Canada.
Zachary
Z
Arthur
University of Saskatchewan, Saskatoon SK S7N 5E2, Canada.
Yuanming
Y
Pan
US Environmental Protection Agency, National Risk Management Research Laboratory, Cincinnati, OH 45224-1702, USA.
Kirk G
KG
Scheckel
University of Chicago, Chicago, IL 60637, USA.
Matthew
M
Newville
University of Chicago, Chicago, IL 60637, USA.
Antonio
A
Lanzirotti
Savannah River National Laboratory, Aiken, SC 29808, USA.
Daniel I
DI
Kaplan
D000327:Adsorption; D019015:Geologic Sediments / Q000737:chemistry*; D064371:Hazardous Waste Sites; D010084:Oxidation-Reduction; D011834:Radiation Monitoring; D011850:Radioactive Waste; D012990:Soil Pollutants, Radioactive / Q000032:analysis* / Q000737:chemistry; D013022:South Carolina; D014501:Uranium / Q000032:analysis* / Q000737:chemistry; D053833:Wetlands
D011850:Radioactive Waste; D012990:Soil Pollutants, Radioactive; D014501:Uranium
Chemical speciation; Retention; Spectroscopy; Uranium; Wetland sediments