SREL Reprint #3288

Retention and chemical speciation of uranium in an oxidized wetland sediment from the Savannah River Site

Dien Li1, John C. Seaman2, Hyun-Shik Chang2, Peter R. Jaffe3, Paul Koster van Groos3,
De-Tong Jiang4, Ning Chen5, Jinru Lin6, Zachary Arthur4, Yuanming Pan6, Kirk G. Scheckel7,
Matthew Newville8, Antonio Lanzirotti8, and Daniel I. Kaplan1

1Savannah River National Laboratory, Aiken, SC 29808, USA
2Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, USA
3Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA
4Department of Physics, University of Guelph, Guelph, ON N1G 2W1, Canada
5Canadian Light Source Inc., Saskatoon, SK S7N 2V3, Canada
6University of Saskatchewan, Saskatoon SK S7N 5E2, Canada
7US Environmental Protection Agency, National Risk Management Research Laboratory,
Cincinnati, OH 45224-1702, USA
8University of Chicago, Chicago, IL 60637, USA

Abstract: 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.

Keywords: Wetland sediments, Uranium, Chemical speciation, Retention, Spectroscopy

SREL Reprint #3288

Li, D., J. C. Seaman, H. Chang, P. R. Jaffe, P. Koster van Groos, D. Jiang, N. Chen, J. Lin, Z. Arthur, Y. Pan, K. G. Scheckel, M. Newville, A. Lanxirotti, and D. I. Kaplan. 2014. Retention and chemical speciation of uranium in an oxidized wetland sediment from the Savannah River Site. Journal of Environmental Radioactivity 131(2014): 40-46.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).