Lability of Uranium in a Mine-Impacted Wetland 70 Years after the Contamination

Understanding the behavior of contaminants in soils and their transport in water is crucial. This study focuses on the mobility of uranium (U) in a buried contaminated sediment layer, deposited in a wetland 70 years ago by the first U mining activities in France. U mobilization is kinetically limited in the contaminated layer with a small fraction of labile U as deduced from laboratory desorption-based studies and in situ studies performed by DET (Diffusive Equilibration in Thin films)/DGT (Diffusive Gradients in Thin films) passive sampler data monitored over time. The smart-K_d approach, combined with a comprehensive system characterization, identified this labile fraction as U(VI) primarily adsorbed on 2:1 clay minerals, which is in line with X-ray Absorption Spectroscopy (XAS) data. The inert fraction was found to correspond to U minerals and adsorbed U(IV) and U(VI) species exhibiting desorption hysteresis. Combining laboratory and field studies, this multiscale approach allows to connect molecular processes to operational K_d(labile) parameters.