An assessment of selenate co-precipitation with gypsum |
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| Institution: | Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada |
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| Abstract: | In this study, we assessed the co-precipitation of selenate (SeO42?) with gypsum (CaSO4·2H2O) in controlled laboratory experiments. Batch testing was used to quantify the ability of CaSO4·2H2O to co-precipitate dissolved SeO42? over a range of dissolved SeO42?-Se concentrations (0–50 mg/L) and under slightly acidic (pH ～5.5–6.1) and oxic (Eh ～416?501 mV) conditions. Aqueous samples were analyzed using inductively coupled plasma optical emission spectrometry, solid samples using X-ray diffraction and Raman spectroscopy, and digests of selected CaSO4·2H2O precipitates using inductively coupled plasma-mass spectrometry. The concentration of Se co-precipitated in CaSO4·2H2O increased linearly with dissolved SeO42?-Se concentration. The aqueous analyses and calculations based on the CaSO4·2H2O digest data show between 14–19 % of the dissolved Se was removed during the co-precipitation experiments. The strong linear relationship between SeO42?-Se added to the test solutions and Se co-precipitated in CaSO4·2H2O can be used to estimate the concentration of co-precipitated SeO42- if the concentration of SeO42- in the associated porewater is known, and vice versa. Results indicate that <1% of SeO42-Se was removed from the test solutions during co-precipitation and the mass of Se in CaSO4·2H2O solids was low, ranging between 0?120 μg/g. These results were used in conjunction with field- and model-derived data to show co-precipitation of SeO42- with CaSO4·2H2O should be a minor SeO42- sequestration mechanism. The findings of this study should be applicable to mined rock dumps in North America and elsewhere. |
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| Keywords: | Co-precipitation Selenate Selenium Gypsum |
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