Removal of trace metals by coprecipitation with Fe,Al and Mn from natural waters contaminated with acid mine drainage in the Ducktown Mining District,Tennessee |
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| Institution: | 1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;2. School of Environmental Studies, China University of Geosciences, Wuhan 430074, China;3. Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, China;4. Hubei Key Laboratory of Yangtze Catchment Environmental Aquatic Science, Wuhan 430074, China;5. Department of Earth Sciences, Oxford University, Oxford OX1 3PR, United Kingdom;1. Department of Energy & Resources Engineering at the College of Engineering of Kangwon National University kangwondegil, Chuncheon, South Korea;2. Earth and Environmental Research Division, Korea Institute of Geoscience and Mineral Resources, 92 Gwahang-no, Daejeon, South Korea;3. Research Development Officer Research, Innovation and Enterprise Services, Cardiff University, Cardiff, UK |
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| Abstract: | This study examined the sorption of trace metals to precipitates formed by neutralization of 3 natural waters contaminated with acid mine drainage (AMD) in the former Ducktown Mining District, Tennessee. The 3 water samples were strongly acidic (pH 2.2 to 3.4) but had distinctively different chemical signatures based on the mole fractions of dissolved Fe, Al and Mn. One sample was Fe-rich (Fe=87.5%, Al=11.3%, and Mn=1.3%), another was Al-rich (Al=79.4%, Mn=18.0%, and Fe=2.5%), and the other was Mn-rich (Mn=51.4%, Al=25.7%, and Fe=22.9%). In addition, these waters had high concentrations of trace metals including Zn (37,700 to 17,400 μg/l), Cu (13,000 to 270 μg/l), Co (1,500 to 520 μg/l), Ni (360 to 75 μg/l), Pb (30 to 8 μg/l), and Cd (30 to 6 μg/l). Neutralization of the AMD-contaminated waters in the laboratory caused the formation of either schwertmannite at pH<4 or ferrihydrite at pH>4. Both phases were identified by XRD analyses of precipitates from the most Fe-rich water. At higher pH values (～5) Al-rich precipitates were formed. Manganese compounds were precipitated at pH～8. The removal of trace metals depended on the precipitation of these compounds, which acted as sorbents. Accordingly, the pH for 50% sorption (pH50) ranged from 5.6 to 7.5 for Zn, 4.6 to 6.1 for Cu, 5.4 to 7.7 for Ni, 5.9 to 7.9 for Co, 3.1 to 4.3 for Pb, and 5.5 to 7.7 for Cd. The pH dependence of sorption arose not only because of changes in the sorption coefficients of the trace metals but also because the formation and composition of the sorbent was controlled by the pH, the chemical composition of the water, and the solubilities of the oxyhydroxide-sulfate complexes of Fe, Al, and Mn. |
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