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. 2019 Sep 20:522:26-37.
doi: 10.1016/j.chemgeo.2019.05.024. Epub 2019 May 20.

Reactivity of As and U co-occurring in Mine Wastes in northeastern Arizona

Johanna M Blake  1 , Sumant Avasarala  2 , Abdul-Mehdi S Ali  3 , Michael Spilde  3 , Juan S Lezama-Pacheco  4 , Drew Latta  5 , Kateryna Artyushkova  6 , Anastasia G Ilgen  7 , Christopher Shuey  8 , Christopher Nez  9 , José M Cerrato  2
Affiliations

Reactivity of As and U co-occurring in Mine Wastes in northeastern Arizona

Johanna M Blake et al. Chem Geol. .

Abstract

The reactivity of co-occurring arsenic (As) and uranium (U) in mine wastes was investigated using batch reactors, microscopy, spectroscopy, and aqueous chemistry. Analyses of field samples collected in proximity to mine wastes in northeastern Arizona confirm the presence of As and U in soils and surrounding waters, as reported in a previous study from our research group. In this study, we measured As (< 0.500 to 7.77 μg/L) and U (0.950 to 165 μg/L) in waters, as well as mine wastes (< 20.0 to 40.0 mg/kg As and < 60.0 to 110 mg/kg U) and background solids (< 20.0 mg/kg As and < 60.0 mg/kg U). Analysis with X-ray fluorescence (XRF) and electron microprobe show the co-occurrence of As and U with iron (Fe) and vanadium (V). These field conditions served as a foundation for additional laboratory experiments to assess the reactivity of metals in these mine wastes. Results from laboratory experiments indicate that labile and exchangeable As(V) was released to solution when solids were sequentially reacted with water and magnesium chloride (MgCl2), while limited U was released to solution with the same reactants. The predominance of As(V) in mine waste solids was confirmed by X-ray absorption near edge (XANES) analysis. Both As and U were released to solution after reaction of solids in batch experiments with HCO3 -. Both X-ray photoelectron spectroscopy (XPS) and XANES analysis determined the predominance of Fe(III) in the solids. Mössbauer spectroscopy detected the presence of nano-crystalline goethite, Fe(II) and Fe(III) in (phyllo)silicates, and an unidentified mineral with parameters consistent with arsenopyrite or jarosite in the mine waste solids. Our results suggest that As and U can be released under environmentally relevant conditions in mine waste, which is applicable to risk and exposure assessment.

Keywords: Arsenic; Iron species; Mine waste; Reactivity; Uranium.

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Figures

Fig. 1.
Fig. 1.
Microprobe image mapping of mine waste sample MW1. The backscatter black and white image shows a bright grain, on which elemental mapping was done, shown on the right.
Fig. 2.
Fig. 2.
57Fe Mössbauer spectroscopy temperature profile of mine waste sample MW3 with spectral fits shown.
Fig. 3.
Fig. 3.
XANES spectra (A) and linear combination fitting component weight (B and C) of MW4, MW5, and BRS samples. D and E show Fe XANES results. Sediment size of samples was < 63 μm.
Fig. 4.
Fig. 4.
A. XPS spectra on unreacted samples, and samples following the reaction with HCO3− for mine waste sample MW5. B. Sulfur standards showing binding energy locations. C. The table shows the percent of each element analyzed.
Fig. 5.
Fig. 5.
Sequential extraction results for As, Fe, U, and V of samples MW1, MW2, MW3, and BRS. Results are reported as percent of total extracted. Each extraction was analyzed in triplicate with the standard deviation shown.
Fig. 6.
Fig. 6.
Sequential extraction comparison of As and Fe and U and V. Results are reported in micromol per kilogram.
Fig. 7.
Fig. 7.
Batch experiments results for As, U, and Fe of extractant solution over time.
Fig. 8.
Fig. 8.
As speciation after sample reaction with HPLC mobile phase for 15 min.
See this image and copyright information in PMC

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