QUANTITATIVE ZN SPECIATION IN A CONTAMINATED DREDGED SEDIMENT BY μ-PIXE, μ-SXRF, EXAFS SPECTROSCOPY AND PRINCIPAL COMPONENT ANALYSIS

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 ship canal in northern france and deposited on an agricultural soil was determined by physical analytical techniques raw chemically treated samples. Zn partitioning between coexisting mineral phases its chemical associations were first micro-particle-induced x-ray emission micro-synchrotron-based radiation fluorescence. Zn-containing species then identified diffraction powder polarized extended absorption fine structure spectroscopy (exafs). the number, nature, proportion obtained coupled principal component analysis (pca) least squares fitting (lsf) procedure, applied herein for time to qualitatively (number nature species) quantitatively (relative speciate metal natural system.the coarse fraction consists slag grains originating nearby smelters. this fraction, is primarily present as sphalerite (ZnS) lesser extent 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.