Quantitative Zn speciation in a contaminated dredged sediment by μ-PIXE, μ-SXRF, EXAFS spectroscopy and principal component analysis |
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Authors: | Marie-Pierre Isaure Agnès LaboudigueAlain Manceau Géraldine SarretChristophe Tiffreau Patrick TrocellierGéraldine Lamble Jean-Louis HazemannDaniel Chateigner |
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Institution: | 1 CNRSSP, 930 boulevard Lahure, BP537, 59505 Douai cedex, France 2 Environmental Geochemistry Group, LGIT, University J. Fourier and CNRS, BP53, 38041 Grenoble cedex 9, France 3 Laboratoire Pierre Süe, CEA-CNRS, Centre d’Etudes de Saclay, 91191 Gif-sur-Yvette cedex, France 4 Advanced Light Source, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA 5 LPEC, Université du Maine-Le Mans, av. O. Messiaen, BP535, 72085 Le Mans cedex, France |
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Abstract: | Dredging and disposal of sediments onto agricultural soils is a common practice in industrial and urban areas that can be hazardous to the environment when the sediments contain heavy metals. This chemical hazard can be assessed by evaluating the mobility and speciation of metals after sediment deposition. In this study, the speciation of Zn in the coarse (500 to 2000 μm) and fine (<2 μm) fractions of a contaminated sediment dredged from a ship canal in northern France and deposited on an agricultural soil was determined by physical analytical techniques on raw and chemically treated samples. Zn partitioning between coexisting mineral phases and its chemical associations were first determined by micro-particle-induced X-ray emission and micro-synchrotron-based X-ray radiation fluorescence. Zn-containing mineral species were then identified by X-ray diffraction and powder and polarized extended X-ray absorption fine structure spectroscopy (EXAFS). The number, nature, and proportion of Zn species were obtained by a coupled principal component analysis (PCA) and least squares fitting (LSF) procedure, applied herein for the first time to qualitatively (number and nature of species) and quantitatively (relative proportion of species) speciate a metal in a natural system.The coarse fraction consists of slag grains originating from nearby Zn smelters. In this fraction, Zn is primarily present as sphalerite (ZnS) and to a lesser extent as willemite (Zn2SiO4), Zn-containing ferric (oxyhydr)oxides, and zincite (ZnO). In the fine fraction, ZnS and Zn-containing Fe (oxyhydr)oxides are the major forms, and Zn-containing phyllosilicate is the minor species. Weathering of ZnS, Zn2SiO4, and ZnO under oxidizing conditions after the sediment disposal accounts for the uptake of Zn by Fe (oxyhydr)oxides and phyllosilicates. Two geochemical processes can explain the retention of Zn by secondary minerals: uptake on preexisting minerals and precipitation with dissolved Fe and Si. The second process likely occurs because dissolved Zn and Si are supersaturated with respect to Zn phyllosilicate. EXAFS spectroscopy, in combination with PCA and LSF, is shown to be a meaningful approach to quantitatively determining the speciation of trace elements in sediments and soils. |
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