Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort–Lot River system | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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  Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort–Lot River system

Type de publication:

Journal Article

Source:

Volume 255, Ticket 3/4, p.295 (Soumis)

ISBN:

00092541

URL:

http://search.ebscohost.com/login.aspx?direct=true&site=eds-live&db=a9h&AN=34534055

Mots-clés:

ANALYTICAL geochemistry, AVEYRON (France), GEOCHEMICAL modeling, METALLURGICAL analysis, ZINC ores

Résumé:

Abstract: Zn isotopes were used to trace the anthropogenic sources in the Lot watershed (Aveyron, SW France) where a small river, the Riou Mort drains an industrial exploitation of zinc ore. The zinc isotopes in industrial tailings are highly fractionated relatively to Zn ore (δ 66Zn∼0.16‰), due to metallurgical processes, reaching δ 66Zn values up to +1.49‰. Zn extraction yields for these samples were calculated using presumable conservative elements (Fe, Ca, Mg, K, Na and Mn) and vary from 95.4% to 99.4%. Extraction yields are related to the intensity of Zn isotopic fractionation. Different Rayleigh isotope fractionation scenarios for Zn refining yielded α ore-tailings ranging from 1.00012 to 1.00062. The δ 66Zn of the Riou Mort sediments downstream from the former Zn-ore facility is presently +0.91±0.04‰, i.e. significantly different from the signature of upstream sediments and of the regional geochemical background, +0.31±0.06‰, (2SD, n =3). Sediment core δ 66Zn values in the 40 km downstream Cajarc hydroelectric reservoir are also consistently ‘heavier’ (+0.75 to +1.35‰) than the regional geochemical background. Both top-core Zn concentrations and isotopic signatures can be explained by the contribution of 9% of present-day Riou Mort sediments. δ 66Zn variations in the 137Cs-dated downcore sediments are suggested to reflect historical changes in metallurgical processes of the Viviez facility, such as improved Zn extraction efficiency and the related evolution of tailings. In sediments deposited during 1952–1972, the mean δ 66Zn is +0.95±0.08‰, representative of the combined electrolysis and thermal process used at that time for the Zn extraction. In sediments deposited during the late seventies, δ 66Zn increases, reaching a maximum of 1.35‰ during the eighties. These heavier δ 66Zn are likely related to further increased Zn extraction after replacement of thermal waste processing by electrolysis in 1976/77. The nature of the extraction processes, especially electrolysis, may therefore play a major role in the Zn isotopic fractionation produced. The soils located on the Lot riverbanks have chemical and Zn isotopic compositions (+0.74‰ to +0.96‰) close to the Cajarc sediments, indicating that they were also impacted by tailings erosion and leaching. The soils located in the vicinity of the plant display lower δ 66Zn (+0.40‰ to 0.48‰). That corresponds to mixtures of several atmospheric sources like coal fly ashes, ore and tailing dusts. The relation between Zn isotopic fractionation, extraction yields and/or extraction processes clearly demonstrates the efficiency of δ 66Zn as tracer of environmental contamination. [Copyright &y& Elsevier]<i>Copyright of Chemical Geology is the property of Elsevier Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)