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Uranium (U) mining and milling activities, as well as mineral processing plants, raise environmental concerns due to the possible release of radioactive and other potentially toxic elements. To understand their fate in the environment and evaluate their potential impact, the main scientific challenge calls for identifying their solubility, mobility and bioavailability in the environment. Around former U mining and processing plants, wetlands prove to be specific zones with significant amounts of U. This is partly explained by the reduction of the mobile U(VI) into U(IV) due to strongly reducing conditions related to the microbial activity and/or by complexation with the organic matter occurring with high concentrations in wetlands. At the center of the ancient mining district of Lachaux in France (45.994°N, 3.596°E), the site of Rophin (within the ZATU: Uranium Working Zone = Long Term Socio-Ecological Research Tool of CNRS, Fig.1.a) is characterized by a wetland area with large U concentrations up to 16 g.kg-1 of dry mass of soil [1]. Several cross-analyses indicate that U was transported in particulate forms into the wetland during the exploitation of U(VI) phosphate minerals [1]. The Rophin site therefore provides the opportunity to study the stability of these U minerals over almost 70 years in a non-manipulated wetland since the closure of the mine. In this context, the main challenge is to describe the behavior of U (and decay products of interest) in the wetland using a predictive model that combines transport and chemical speciation. The overall adopted scientific approach is to propose a mechanistic description of the mobility of these elements, from the molecular scale (speciation) to in natura behavior (lability), by coupling field investigations and laboratory experiments. A simplified three-layer model describes the soil profile of the Rophin wetland, with variable U concentrations and specific physico-chemical soil properties (Fig.1.b). Analyses carrie

Geochemical and biological processes controlling NOR mobility are studied within the RadoNorm project to derive more robust distribution coefficients Kd. To achieve this (i) the effect of microorganisms on NOR mobility in uranium (U) mine waters is studied, (ii) new datasets of NOR sorption and desorption parameters are acquired, (iii) a methodology for the determination of site-specific Kd values is evolved and (iv) models able to predict Kd (NOR) in relevant scenarios are developed. The impact of microbes on the speciation of U in U mine waters is characterized by a multidisciplinary approach providing insights into the microbe/U interaction mechanisms needed to predict the effect of microbial processes on the mobility of this radionuclide. Laboratory studies are performed to identify the soil properties that govern NOR interactions in soils. Sorption and desorption Kds for representative soils are determined, also considering soil aging effects. Chemical analogy between NOR and stable elements (e.g., Ba vs. Ra) is also examined, with new data and additional values gathered from literature. Considering the dynamics of sorption-desorption reactions, studies are carried out at the Zatu site (France) to develop a method to determine site-specific Kds. Experiments with soil core samples are performed to determine the amount of desorbed U, Ra and Pb and to derive apparent Kd values. The validity of this approach will be confirmed combining these results with in situ studies (Zatu site). Two approaches are followed to derive models for Kd (NOR) prediction. The first one is the “smart Kd” model, which is based on a realistic description of chemical reactions of NOR in liquid and solid phases. The second one is constructing simple, multivariate Kd prediction models based on soil properties governing NOR interaction. Water transport models with different levels of complexity are applied to describe the transport of NOR at the Zatu site in consistency with site-specific Kds

Geochemical and biological processes controlling NOR mobility are studied within the RadoNorm project to derive more robust distribution coefficients Kd. To achieve this (i) the effect of microorganisms on NOR mobility in uranium (U) mine waters is studied, (ii) new datasets of NOR sorption and desorption parameters are acquired, (iii) a methodology for the determination of site-specific Kd values is evolved and (iv) models able to predict Kd (NOR) in relevant scenarios are developed. The impact of microbes on the speciation of U in U mine waters is characterized by a multidisciplinary approach providing insights into the microbe/U interaction mechanisms needed to predict the effect of microbial processes on the mobility of this radionuclide. Laboratory studies are performed to identify the soil properties that govern NOR interactions in soils. Sorption and desorption Kds for representative soils are determined, also considering soil aging effects. Chemical analogy between NOR and stable elements (e.g., Ba vs. Ra) is also examined, with new data and additional values gathered from literature. Considering the dynamics of sorption-desorption reactions, studies are carried out at the Zatu site (France) to develop a method to determine site-specific Kds. Experiments with soil core samples are performed to determine the amount of desorbed U, Ra and Pb and to derive apparent Kd values. The validity of this approach will be confirmed combining these results with in situ studies (Zatu site). Two approaches are followed to derive models for Kd (NOR) prediction. The first one is the “smart Kd” model, which is based on a realistic description of chemical reactions of NOR in liquid and solid phases. The second one is constructing simple, multivariate Kd prediction models based on soil properties governing NOR interaction. Water transport models with different levels of complexity are applied to describe the transport of NOR at the Zatu site in consistency with site-specific Kds