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Open AccessArticle

Electrochemical, Spectroscopic, and Computational Investigations on Redox Reactions of Selenium Species on Galena Surfaces

Department of Earth and Environmental Sciences, University of Michigan, Room 2534, North University Bldg., 1100 N University Ave, Ann Arbor, MI 48109-1005, USA
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Author to whom correspondence should be addressed.
Present address: Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, TN 37830, USA.
Minerals 2019, 9(7), 437; https://doi.org/10.3390/min9070437
Received: 15 June 2019 / Revised: 11 July 2019 / Accepted: 13 July 2019 / Published: 15 July 2019
(This article belongs to the Special Issue Selenide Mineralization )
Despite previous studies investigating selenium (Se) redox reactions in the presence of semiconducting minerals, Se redox reactions mediated by galena (PbS) are poorly understood. In this study, the redox chemistry of Se on galena is investigated over a range of environmentally relevant Eh and pH conditions (+0.3 to −0.6 V vs. standard hydrogen electrode, SHE; pH 4.6) using a combination of electrochemical, spectroscopic, and computational approaches. Cyclic voltammetry (CV) measurements reveal one anodic/cathodic peak pair at a midpoint potential of +30 mV (vs. SHE) that represents reduction and oxidation between HSeO3 and H2Se/HSe. Two peak pairs with midpoint potentials of −400 and −520 mV represent the redox transformation from Se(0) to HSe and H2Se species, respectively. The changes in Gibbs free energies of adsorption of Se species on galena surfaces as a function of Se oxidation state were modeled using quantum-mechanical calculations and the resulting electrochemical peak shifts are (−0.17 eV for HSeO3−/H2Se, −0.07 eV for HSeO3−/HSe, 0.15 eV for Se(0)/HSe, and −0.15 eV for Se(0)/H2Se). These shifts explain deviation between Nernstian equilibrium redox potentials and observed midpoint potentials. X-ray photoelectron spectroscopy (XPS) analysis reveals the formation of Se(0) potentials below −100 mV and Se(0) and Se(−II) species at potentials below −400 mV. View Full-Text
Keywords: selenium redox transformation; galena; elemental selenium; selenide; electrochemistry; computational modeling selenium redox transformation; galena; elemental selenium; selenide; electrochemistry; computational modeling
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Cook, P.; Kim, Y.; Yuan, K.; Marcano, M.C.; Becker, U. Electrochemical, Spectroscopic, and Computational Investigations on Redox Reactions of Selenium Species on Galena Surfaces. Minerals 2019, 9, 437.

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