Characterization and radionuclide sorption of suspended particulate matters in freshwater according to their settling kinetics

In freshwater, radionuclide transfers depend both on exchanges between liquid and solid phases and on mass transfers between suspended and bottom sediment. Whereas the former ones depend on chemical processes (sorption/desorption, complexation ...), the latter ones are regulated by hydrological and sedimentary considerations (dispersion, erosion, deposit ...) closely related to the interactions between flow, suspended matter and bed sediment. Previous studies highlight the need to consider the matter heterogeneity and its specific sediment dynamics to correctly report the in homogeneity of fluxes in time and in space. These considerations lead us to develop an experimental method to distinguish the different particle groups present in natural water, mainly according to their settling kinetics. In this context, this paper presents the experimental protocol TALISMEN to characterize a natural bulk suspension according to its main settling kinetics groups. In a first step, this identification is achieved by the use of a settling tank that allows the monitoring of the suspended solid concentrations at various depths, combined to a settling model applying a multi-class approach. In a second step, the particle groups are isolated and characterized. The sorption property of each group toward 137Cs is determined by estimation of its distribution coefficients (kd) and sorption kinetics