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Changement de spéciation des éléments traces métalliques lors de la remise en suspension de sédiments de barrages

Abstract : The resuspension of the contaminated sediments may promote the remobilization of trace metals to the dissolved phase, threatening the water quality. The dam reservoirs sometimes need to be fully drawn down and being able to anticipate the release of the contaminants is essential to improve the management of reservoirs and assess the risk of water quality degradation. Surface sediments were collected in three contaminated dam reservoirs and aliquots of wet sediments were resuspended for a week in a reactor. The pH and the redox potential were continuously measured, dissolved samples were collected and the evolution of dissolved trace elements concentrations were measured. Depending on the elements, different temporal trends can be highlighted during the resuspension experiments. These evolutions were reproducible, regardless of the mass of sediment used from 2 to 9 g/L. 1) Cd, Cr and Zn were not released; 2) Mn, Fe, Co, Pb and As for two reservoirs, increased and then decreased during the experiments and were regulated by the Fe- and Mn-oxyhydroxides and the redox potential; 3) Al, Mo, or As for one reservoir, were still increasing at the end of the experiments, showing slower release processes and the stabilization of these elements under dissolved forms. For theses three reservoirs, As showed the greatest and the most prolonged release during resuspension. The experimental trends of dissolved metals were used in the firts calibration steps of a new chemical speciation model developped by EDF, which takes several kinetic rates into account for the exchange reactions of dissolved metal between water and three types of solid phases.
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Lucie Monnin. Changement de spéciation des éléments traces métalliques lors de la remise en suspension de sédiments de barrages. Géochimie. Aix Marseille Université, 2018. Français. ⟨tel-02080573⟩

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