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      Selenate removal by zero-valent iron under anoxic conditions: effects of nitrate and sulfate

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      Date
      2019-08-16
      Author
      Das, Soumya
      Lindsay, Matthew 
      Hendry, M. Jim
      Publisher
      Springer Nature
      Type
      Article
      Peer Reviewed Status
      Peer Reviewed
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      Abstract
      Batch experiments were conducted to examine aqueous Se(VI) removal by zero-valent iron (ZVI) under anoxic conditions in the presence and absence of NO3− and SO42−. Initial concentrations for Se(VI), SO4, and NO3–N of 5 mg L−1, 1800 mg L−1, and 13 mg L−1, respectively, were employed to mimic mine waters. In the control experiment, 90% Se(VI) removal occurred within 1.5 h without SO42− and NO3− (B1). This removal threshold was reached after 3 h with NO3− added (B3) and after 33 h with SO42− added (B2). Removal reached 90% after 42 h with both SO42− and NO3− added (B4). Modeled Se(VI) removal rates consistently followed first-order kinetics and revealed that the presence of SO42− and, to a lesser extent, NO3− inhibited Se(VI) removal. Increases in pH and Fe coupled with decreasing Eh are consistent with ZVI corrosion under anoxic conditions. Transmission electron microscopy, Raman spectroscopy, and X-ray diffraction revealed magnetite [Fe3O4] and lepidocrocite [γ-FeOOH] formed at ZVI surfaces during the experiments. X-ray absorption near edge structure spectroscopy indicated that Se(VI) was predominantly reduced to Se(0) (70–80%), but Se(IV) (10–13%) and Se(-II) (2–13%) were also detected at reacted ZVI surfaces. Overall, the results show that although SO42− and NO3− present in mine wastes can reduce reaction rates, Se(VI) removal by ZVI under anoxic conditions is associated with extensive reduction to insoluble Se(0).
      Citation
      Das, S., Lindsay, M.B.J., & Hendry, M.J. (2019). Selenate removal by zero-valent iron under anoxic conditions: Effects of nitrate and sulfate. Environmental Earth Sciences, 78, 528. https://doi.org/10.1007/s12665-019-8538-z
      URI
      http://hdl.handle.net/10388/12444
      DOI
      10.1007/s12665-019-8538-z
      Subject
      zero-valent iron
      selenium
      treatment
      geochemistry
      mine waste
      sulfate
      nitrate
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