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Zinc speciation in mining and smelter contaminated overbank sediments by EXAFS spectroscopy |
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| Authors: | An Van Damme Erik Smolders Géraldine Sarret Rudy Swennen |
| Institution: | a Geology Section, Department of Earth and Environmental Sciences, K.U.Leuven, Celestijnenlaan 200E bus 2408, 3001 Heverlee, Belgium b Division Soil and Water Management, Department of Earth and Environmental Sciences, K.U.Leuven, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium c Environmental Geochemistry Group, LGIT, University Joseph Fourier and CNRS, 38041 Grenoble Cedex 9, France d Mineralogy & Environments, LGCA, University Joseph Fourier and CNRS, 38041 Grenoble Cedex 9, France |
| Abstract: | Overbank sediments contaminated with metalliferous minerals are a source of toxic metals that pose risks to living organisms. The overbank sediments from the Geul river in Belgium contain 4000-69,000 mg/kg Zn as a result of mining and smelting activities, principally during the 19th century. Three main Zn species were identified by powder Zn K-edge EXAFS spectroscopy: smithsonite (ZnCO3), tetrahedrally coordinated sorbed Zn (sorbed IVZn) and Zn-containing trioctahedral phyllosilicate. Smithsonite is a primary mineral, which accounts for approximately 20-60% of the Zn in sediments affected by mining and smelting of oxidized Zn ores (mostly carbonates and silicates). This species is almost absent in sediments affected by mining and smelting of both sulphidic (ZnS, PbS) and oxidized ores, presumably because of acidic dissolution associated with the oxidation of sulphides, as suggested by the lower pH of this second type of sediment (pH(CaCl2) <7.0 vs. pH(CaCl2) >7.0 for the first type). Thus, sulphide minerals in sediment deposits can act as a secondary source of dissolved metals by a chemical process analogous to acid mine drainage. The sorbed IVZn component ranges up to approximately 30%, with the highest proportion occurring at pH(CaCl2) <7.0 as a result of the readsorption of dissolved Zn2+ on sediments constituents. Kerolite-like Zn-rich phyllosilicate is the major secondary species in all samples, and in some the only detected species, thus providing the first evidence for pervasive sequestration of Zn into this newly formed precipitate at the field scale. |
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