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2014-09-18 - Colloque/Présentation - communication orale - Anglais - 1 page(s)

Chenoy Louise , De Weireld Guy , Hantson Anne-Lise , "Characterization and geochemical modelling of metallic trace element release from treated dredged sediments." in 4th International Symposium on Sediment Management (I2SM), Ferrara, Italie, 2014

  • Codes CREF : Environnement et pollution (DI3840)
  • Unités de recherche UMONS : Chimie et Biochimie appliquées (F504)

Abstract(s) :

(Anglais) Characterization and geochemical modelling of metallic trace element release from treated dredged sediments. L.Chenoy, G. De Weireld, A-L Hantson Waterways are generally recognized as the most economical and less polluting means of transport. 4 to 6 million m³ of sediments are to be dredged from waterways in Walloon Region to improve and promote this mode of transport. However about 65% of these sediments are polluted by heavy metals or organic compounds and are classified as waste materials according to the Walloon legislation (AGW 30/11/1995). In this context and in the framework of an ERDF funded project (SOLINDUS) an experimental treatment platform was developed to treat sediments by a mineralurgical treatment in order to reduce contamination and enable their beneficial reuse. The process relies on a granulometric separation (considering that contaminants are generally concentrated in fine fractions) followed or not by a flotation step. The aim of this research is to study the behavior of residual trace metals contained in the treated sediments. Indeed, these sediments still contain heavy metals (sometimes above the legal limit) and in order to reuse them (e.g. in landscape management), the environmental risks have to be evaluated, and particularly pollution risks of groundwater. In this purpose, laboratory experiments are conducted in parallel of geochemical modelling. Indeed, geochemical modelling is a useful tool to understand leaching processes of trace metals and to predict long term behavior of the sediments. The experiments conducted on the first sample of this study comprise analysis of total trace metal content (aqua regia digestion followed by ICP-OES analysis), BCR sequential extraction, batch leaching experiments with ultrapure water and in function of pH (TS 14429) and saturated column experiment (TS 14405). Geochemical modelling is conducted with PHREEQC v.3.0 [1]. The model allows inorganic speciation and mineral solubility calculation. It includes the generalized two layer model to consider surface complexation of ions to hydrous ferric oxides. The sorption of cations on organic matter (humic and fulvic acids) is taken into account by the use of the WHAM model [2]. In order to apply both models, the quantities of crystalline and amorphous Fe(hydr)oxides and of Al(hydr)oxides are estimated by selective extraction following ISO 12782-1,2,3, while the amounts of humic and fulvic acids in the solid phase are estimated following ISO 12782-4. This methodology will be further applied to other samples of treated sediment. In addition to be a useful tool for environmental risk assessments, the understanding of the leaching phenomena provided by modelling could also help to improve the treatment process. [1] D. L. Parkhurst and C. A. J. Appelo, “Description of Input and Examples for PHREEQC Version 3 — A Computer Program for Speciation , Batch-Reaction , One-Dimensional Transport , and Inverse Geochemical Calculations,” 2013. [2] E. Tipping and M. A. Hurley, “A unifying model of cation binding by humic substances,” Geochim. Cosmochim. Acta, vol. 56, pp. 3627–3641, 1992. Keywords: dredged sediment; geochemical modelling; trace metals; leaching; PHREEQC