Se Isotopes as Groundwater Redox Indicators: Detecting Natural Attenuation of Se at an in Situ Recovery U Mine

Anirban Basu, Kathrin Schilling, Shaun T. Brown, Thomas M. Johnson, John N. Christensen, Matt Hartmann, Paul W. Reimus, Jeffrey M. Heikoop, Giday WoldeGabriel, Donald J. DePaolo

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Pages (from-to)10833-10842
Number of pages10
JournalEnvironmental Science and Technology
Volume50
Issue number20
DOIs
StatePublished - Oct 18 2016

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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    Basu, A., Schilling, K., Brown, S. T., Johnson, T. M., Christensen, J. N., Hartmann, M., Reimus, P. W., Heikoop, J. M., WoldeGabriel, G., & DePaolo, D. J. (2016). Se Isotopes as Groundwater Redox Indicators: Detecting Natural Attenuation of Se at an in Situ Recovery U Mine. Environmental Science and Technology, 50(20), 10833-10842. https://doi.org/10.1021/acs.est.6b01464