Geochemical and mineralogical characterization of streams and wetlands downstream a former uranium mine (Rophin, France)

The geochemical distribution of U and associated major and trace elements (As, Li, Pb, Sr, Zn) was studied at the former Rophin U mine (Puy-de-Dôme, France). Three zones of contrasting radiological settings were identified and sampled: a background area (1000 nSv·h−1). Sediment and water samples were collected both in a streambed located in the background area and in the streambed downslope the former mining area, and a soil sample was collected in the wetland downslope. Using both sequential and selective chemical extractions, and quantifying also the chemical reservoirs of As, Li, Pb, Sr, and Zn, it could be concluded that, in the streams, U was mainly bounded to primary ore minerals (phosphates) that were transported through particulate transport. It was also bound, to a lower extent, to clays, Mn oxyhydroxides and organic matter, certainly due to the sorption of aqueous U originating from partial dissolution or leaching of primary ore materials. Ore minerals remaining stable in the stream sediments were certainly included in a quartz matrix and hence were not in accessible for dissolution. In the wetland soil, selective extractions evidenced that U was about evenly distributed between humid/fulvic acids and organic matter unaffected by NH4OH 1M. [Display omitted] •Investigation of the radiological and geochemical settings downstream a former U mine.•In streams, U migration dictated by interplay between sorption of aqueous U and particulate transport.•In stream sediments, U primarily bound to ore material and to lesser extent clay, Fe/Mn hydroxides, and organic matter.•In a wetland soil, U bound to humic/fulvic acids and possibly lignin, clue for U uptake by plants.