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La Recherchev2

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Zn and Cd retention by a calcareous fluvio-glacial deposit in the presence of Pb: experiments, modelling and microanalysis


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Titre du congrès :9th ICOBTE (International Conference on the Biogeochemistry of Trace Elements) Ville du congrès :Pékin Date du congrès :15/07/2007

Résumé

We studied the simultaneous transfer of Zn, Cd and Pb in a calcareous substrate, extracted from a fluvio-glacial deposit that is used to infiltrate stormwater. Laboratory column experiments showed that Pb retention was the strongest, as expected. However, Zn and Cd retentions were almost equal, in disagreement with conventional modelling assumptions. Investigations based on PHREEQC reactive modelling and both scanning electron microscopy (SEM) and PIXE / RBS analysis (nuclear microprobe) proved that Zn and Cd did not precipitate separately as smithsonite and otavite as usually observed under these experimental conditions. These investigations point at a surface substitution process in which Ca is successively replaced by metals such as Zn and Cd on surface sites, followed by diffusion of these metals into the lattice of the calcareous particles.