Redistribution of uranium and co-occurring metals from mining-inherited deposits recorded in a wetland

The legacy of former uranium (U) mining activities led to the dispersion of inherited materials enriched with U-series nuclides and metal-rich minerals. In this study, the fate of U and associated metals i.e. , copper (Cu) and lead (Pb) in a wetland located downstream of a former U mining site was evaluated. This assessment was conducted through the identification of U sources in wetland soils, the solid speciation of U and co-occurring metals, and their reactivity under oxidizing conditions. Our results confirmed that the mining materials in the wetland originated from the physical and chemical treatments of two U ores (Bois-Noirs-Limouzat and Rophin). The investigation of solid metal-bearing species revealed that, in the pure BNL-inherited layer, U, Cu, and Pb species were associated to amorphous and crystalline Fe oxyhydroxides and clay minerals and to a lesser extent, in the form of U oxides and chalcopyrite. For the Rophin-originated deposits, the absence of crystalline U-inherited minerals was highlighted, with a significant association of U and Pb with organic matter, Fe-bearing species, and/or the clay mineral fraction. These results suggested redistribution from primary to secondary phases during alteration and pedogenesis processes. Deionized water-normalized leaching tests indicated different mass amounts mobilized from the two types of U-mining materials identified. These differences could be attributed to i/ the occurrence of redox-sensitive minerals and ii/ the presence of organic matter, which led to the formation of secondary higher stable metal species. This study provided new insights into the post-depositional transformation of mining-derived materials and the need to consider the mineralogy of parent materials.