TY - JOUR
T1 - Se Isotopes as Groundwater Redox Indicators
T2 - Detecting Natural Attenuation of Se at an in Situ Recovery U Mine
AU - Basu, Anirban
AU - Schilling, Kathrin
AU - Brown, Shaun T.
AU - Johnson, Thomas M.
AU - Christensen, John N.
AU - Hartmann, Matt
AU - Reimus, Paul W.
AU - Heikoop, Jeffrey M.
AU - WoldeGabriel, Giday
AU - DePaolo, Donald J.
N1 - Funding Information:
This research was funded by the UC Laboratory Fees Research Program. We thank Uranium Resources, Inc. for providing site access and logistic support during sample collection and drilling. The U.S. Department of Energy provided salary support for D.J.D. and J.N.C. during the study period under contract no. DE-AC02-05CH11231.
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/10/18
Y1 - 2016/10/18
N2 - One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. In this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradient wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ϵ of -2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Furthermore, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.
AB - One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. In this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradient wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ϵ of -2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Furthermore, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.
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U2 - 10.1021/acs.est.6b01464
DO - 10.1021/acs.est.6b01464
M3 - Article
C2 - 27547844
AN - SCOPUS:84991745969
SN - 0013-936X
VL - 50
SP - 10833
EP - 10842
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 20
ER -