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Characterization of Natural and Affected Environments
Tracing molybdenum attenuation in mining environments using molybdenum stable isotopes Elliott K Skierszkan, Jared Robertson, Matthew B.J. Lindsay, Justin S. Stockwell, John W. Dockrey, Soumya Das, Dominique Weis, Roger Daniel Beckie, and K. Ulrich Mayer Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b00766 • Publication Date (Web): 18 Apr 2019 Downloaded from http://pubs.acs.org on April 20, 2019
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Environmental Science & Technology
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Tracing molybdenum attenuation in mining environments using
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molybdenum stable isotopes
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Elliott K. Skierszkan,1,2,* Jared M. Robertson,3,4 Matthew B. J. Lindsay,3 Justin S. Stockwell,2
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John W. Dockrey,2 Soumya Das,3 Dominique Weis,1,5 Roger D. Beckie,1 and
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K. Ulrich Mayer1
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1Department
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Main Mall, Vancouver, BC, Canada, V6T 1Z4
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2Lorax
of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 2020-2207
Environmental Services Ltd., 2289 Burrard Street, Vancouver, BC, Canada, V6J 3H9
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3Department
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Canada, S7N 5E2
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4O’Kane
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5Pacific
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Sciences, University of British Columbia, 2020-2207 Main Mall, Vancouver, BC, Canada, V6T 1Z4
of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK,
Consultants Inc., 112 Research Drive, Saskatoon, SK, Canada, S7N 3R3
Centre for Isotopic and Geochemical Research, Department of Earth, Ocean and Atmospheric
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Corresponding Author
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*E-mail:
[email protected] 18
1 ACS Paragon Plus Environment
Environmental Science & Technology
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Abstract
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Molybdenum contamination is a concern in mining regions worldwide. Better
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understanding of processes controlling Mo mobility in mine wastes is critical for assessing
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potential impacts and developing water-quality management strategies associated to this element.
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Here, we used Mo stable isotope (δ98/95Mo) analyses to investigate geochemical controls on Mo
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mobility within a tailings management facility (TMF) featuring oxic and anoxic environments.
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These isotopic analyses were integrated with X-ray absorption spectroscopy, X-ray diffraction,
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Raman spectroscopy, transmission electron microscopy, and aqueous chemical data. Dissolved
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Mo concentrations were inversely correlated with δ98/95Mo values such that enrichment of heavy
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Mo isotopes in solution reflected attenuation processes. Inner-sphere complexation of Mo(VI)
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with ferrihydrite was the primary driver of Mo removal and was accompanied by a circa 1 ‰
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isotope fractionation. Limited Mo attenuation and isotope fractionation was observed in Fe(II)-
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and Mo-rich anoxic TMF seepage, while attenuation and isotope fractionation were greatest
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during discharge and oxidation of this seepage after discharge into a pond where Fe-
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(oxyhydr)oxide precipitation promoted Mo sorption. Overall, this study highlights the role of
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sorption onto Fe-(oxyhydr)oxides in attenuating Mo in oxic environments, a process which can
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be traced by Mo isotope analyses.
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Environmental Science & Technology
Graphical Abstract
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Introduction
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Oxidative weathering of sulfide mine wastes can release potentially hazardous elements
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including molybdenum (Mo) to the environment.1–4 Natural fresh waters typically contain
