Zinc speciation in mining and smelter contaminated overbank sediments by EXAFS spectroscopy
Date
2010
Authors
Van Damme, A.
Degryse, J.
Smolders, E.
Sarret, G.
Dewit, J.
Swennen, R.
Manceau, A.
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Journal article
Citation
Geochimica et Cosmochimica Acta, 2010; 74(13):3707-3720
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An Van Damme, Fien Degryse, Erik Smolders, Géraldine Sarret, Julie Dewit, Rudy Swennen, Alain Manceau
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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 4000-69,000mg/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 (ZnCO<inf>3</inf>), tetrahedrally coordinated sorbed Zn (sorbed <sup>IV</sup>Zn) 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(CaCl<inf>2</inf>) <7.0 vs. pH(CaCl<inf>2</inf>) >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 <sup>IV</sup>Zn component ranges up to approximately 30%, with the highest proportion occurring at pH(CaCl<inf>2</inf>) <7.0 as a result of the readsorption of dissolved Zn<sup>2+</sup> 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. © 2010 Elsevier Ltd.
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© 2010 Elsevier Ltd. All rights reserved.