Tracing molybdenum attenuation in mining environments using molybdenum stable isotopes
Date
2019-04-18
Authors
Skierszkan, Elliott K.
Robertson, Jared M.
Lindsay, Matthew
Stockwell, Justin S.
Dockrey, John W.
Das, Soumya
Weis, Dominique
Beckie, Roger D.
Mayer, K. Ulrich
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American Chemical Society
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Article
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Abstract
Molybdenum contamination is a concern in mining regions worldwide. Better understanding of processes controlling Mo mobility in mine wastes is critical for assessing potential impacts and developing water-quality management strategies associated to this element. Here, we used Mo stable isotope (δ98/95Mo) analyses to investigate geochemical controls on Mo mobility within a tailings management facility (TMF) featuring oxic and anoxic environments. These isotopic analyses were integrated with X-ray absorption spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and aqueous chemical data. Dissolved Mo concentrations were inversely correlated with δ98/95Mo values such that enrichment of heavy Mo isotopes in solution reflected attenuation processes. Inner-sphere complexation of Mo(VI) with ferrihydrite was the primary driver of Mo removal and was accompanied by a circa 1 ‰ isotope fractionation. Limited Mo attenuation and isotope fractionation was observed in Fe(II)- and Mo-rich anoxic TMF seepage, while attenuation and isotope fractionation were greatest during discharge and oxidation of this seepage after discharge into a pond where Fe-(oxyhydr)oxide precipitation promoted Mo sorption. Overall, this study highlights the role of sorption onto Fe-(oxyhydr)oxides in attenuating Mo in oxic environments, a process which can be traced by Mo isotope analyses.
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Keywords
mine waste, molybdenum, isotopes, groundwater, iron (oxyhydr)oxides
Citation
Skierszkan, E.K., Robertson, J.M., Lindsay, M.B.J., Stockwell, J.S., Dockrey, J.W., Das, S., Weis, D., Beckie, R.D., & Mayer, K.U., (2019). Tracing molybdenum attenuation in mining environments using molybdenum stable isotopes. Environmental Science and Technology 53, 5678–5686. https://doi.org/10.1021/acs.est.9b00766
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Citation
Skierszkan, E.K., Robertson, J.M., Lindsay, M.B.J., Stockwell, J.S., Dockrey, J.W., Das, S., Weis, D., Beckie, R.D., & Mayer, K.U., (2019). Tracing molybdenum attenuation in mining environments using molybdenum stable isotopes. Environmental Science and Technology 53, 5678–5686. https://doi.org/10.1021/acs.est.9b00766
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DOI
10.1021/acs.est.9b00766