Combined U-Pb isotopic signatures of U mill tailings from France and Gabon: A new potential tracer to assess their fingerprint on the environment

Aurélien Beaumais (1) , Arnaud Mangeret (1) , David Suhard (2) , Pascale Blanchart (3) , Mejdi Neji (4) , Charlotte Cazala (1) , Alkiviadis Gourgiotis (1)

1 IRSN/PSE-ENV/SEDRE/LELI - Laboratoire de recherche sur le devenir des pollutions de sites radioactifs
2 IRSN/PSE-SANTE/SESANE/LRSI - Laboratoire de recherche en Radiochimie, Spéciation et Imagerie
3 IRSN/PSE-ENV/SEDRE/USDR - Unité d'expertise des sites et des déchets radioactifs
4 IRSN/PSE-ENV/SEDRE/LETIS - Laboratoire d'étude et de recherche sur les transferts et les interactions dans les sous-sols

Uranium milling activities have produced high volumes of long-lived radioactive processed wastes stored worldwide in near surface environment. The aim of this study is to highlight relevant tracers that can be used for environmental impact assessment studies involving U mill tailings. A multi-tracer study involving elemental content, 238 U decay products disequilibria and stable Pb isotopes was performed in different types of U mill tailings (alkaline, acid, neutralized acid) collected from five Tailings Management Facilities in France (Le Bosc, L'Ecarpière, Le Bernardan, and Bellezane) and Gabon (Mounana). Our results showed that U and Pb concentrations range between 30-594 ppm and 66-805 ppm, respectively. These tailings have a strong disequilibrium of (234 U/ 238 U) and (230 Th/ 238 U) activity ratios (1.27-1.87 and 6-65, respectively), as well as higher 206 Pb/ 207 Pb (1.86-7.15) and lower 208 Pb/ 207 Pb (0.22-2.39) compared to geochemical background ((234 U/ 238 U) and (230 Th/ 238 U) equal to unity; 206 Pb/ 207 Pb = 1.20; 208 Pb/ 207 Pb = 2.47). In situ analyses (SEM, SIMS) showed that Pb-bearing phases with high 206 Pb/ 207 Pb are related to remaining U-rich phases, S-rich phases and potentially clay minerals or oxyhydroxides. We suggest that the combination of the 206 Pb/ 207 Pb with the (234 U/ 238 U) ratio is a relevant tool for the fingerprinting of the impact of U milling activities on the environment.

Domaines: Sciences de l'environnement

Aurélien Beaumais, Arnaud Mangeret, David Suhard, Pascale Blanchart, Mejdi Neji, et al.. Combined U-Pb isotopic signatures of U mill tailings from France and Gabon: A new potential tracer to assess their fingerprint on the environment. Journal of Hazardous Materials, 2022, 430, pp.128484. ⟨10.1016/j.jhazmat.2022.128484⟩. ⟨irsn-03814952⟩