Migration Behavior of Fe, Cu, Zn, and Mo in Alkaline Tailings from Lanjiagou Porphyry Molybdenum Deposits, Northeast China
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The migration behavior of Fe, Cu, Zn, and Mo within an inactive tailings impoundment in Lanjiagou molybdenum mining area, northeast China, is investigated by mineralogical and geochemical methods. XRD results show that carbonate minerals consume the liberated protons during sulfide minerals oxidation and subsequent hydrolysis of secondary phase. Meanwhile, the tailings impoundment maintains an alkaline condition because of the hydrolysis of carbonate minerals (paste pH=7.3-8.24). Analyses and comparison of geochemical behavior of heavy metals show that concentrations of Fe, Cu and Zn reachmaximum values between 30 and 60 cm below the surface of tailings impoundment but there is hardly any bioavailable fraction of the three metals in the tailings impoundment. Fe, Cu and Zn are retained in the tailings impoundment for precipitation, co-precipitation, adsorption, complexation and ion exchange mechanisms and a weak cemented layer is formed at the lowest part of oxidation zone accordingly. The results demonstrate that the alkaline condition becomes a natural factor for retaining Fe, Cu and Zn in Lanjiagou tailings pounds. The concentrations of Mo significantly increase with depth (1090-1146 μg•g-1 at 200 cm deep) and so does the proportions of bioavailable Mo fraction (34-37% at 200 cm deep) in the tailings impoundment, which further reveals that the alkaline condition is helpful to increase the solubility of molybdate and the adsorption of iron (hydr)oxides on Mo becomes weaker at pH > 7. Mo can leach from Lanjiagou Mo tailings pounds into outside environment and may pose a high risk to the local ecological system.
- 2010-05-06
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