EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Pluri-millenial evolution of uranium speciation in lacustrine sediments

Pierre Lefebvre1, Alkiviadis Gourgiotis2, Arnaud Mangeret2, Pierre Le Pape1, Olivier Diez2, Pierre Sabatier3, Pascale Louvat4, Pauline Merrot1, Camille Baya1, Mathilde Zebracki2, Emmanuel Malet3, Didier Jézéquel4, Jean-Louis Reyss3, John Bargar5, Jérôme Gaillardet4, Charlotte Cazala2, and Guillaume Morin1
Pierre Lefebvre et al.
  • 1Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR 7590 Sorbonne Université-CNRS-MNHN-IRD, Paris, France
  • 2Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSE-ENV SEDRE/LELI, Fontenay-aux-Roses, France
  • 3Laboratoire Environnement, Dynamiques et Territoires de la Montagne (EDYTEM), UMR 5204 Université Savoie Mont-Blanc-Université Grenoble Alpes-CNRS, Le Bourget-Du-Lac, France
  • 4Université de Paris-Institut de Physique du Globe de Paris (IPGP)-CNRS, UMR 7154, Paris, France
  • 5Stanford Synchrotron Radiation Lightsource (SSRL), SLAC, Menlo Park, CA, USA

Uranium (U) is a toxic radionuclide which environmental dissemination must be limited. In this regard, understanding U immobilization mechanisms in reducing environments is essential for improving the management of radioactive waste and the remediation of contaminated sites. In particular, determining the long-term behavior of non-crystalline U(IV) species in (sub-)surface conditions is of growing importance, as these environmentally-relevant species have been recently showed to play a major role in U mobility. For this purpose, we investigated the evolution of U speciation over a pluri-millennial period in naturally U-enriched sediments from Lake Nègre (alt. 2354 m, Mercantour, France) as an analogue of contaminated systems. Several sediment cores were sampled at 24 m of water depth and preserved under anoxic conditions. Bottom sediments were dated back to 8700 cal BP. These organic- and Si-rich sediments display increasing U concentration with depth, from 350 to more than 1000 µg/g. Sequential ultrafiltration of surface waters and uranium isotopic ratios (238U/235U and (234U/238U)) of sediments and waters suggest that the deposition mode of U did not vary significantly with time, thus giving the opportunity to follow the effect of diagenesis on U speciation over more than 1000 years. Uranium LIII-edge X-Ray Absorption Near-Edge Structure (XANES) analysis shows that U is rapidly reduced in the upper sediment layers and is fully reduced at depth. Preliminary Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy data at the U LIII-edge reveals that U speciation evolved with depth in the sediment core, suggesting an effect of diagenesis in anoxic conditions on U solid speciation. Our results may help to design long-term storage conditions that are able to enhance the formation of poorly soluble U species in U-contaminated soils and sediments.

How to cite: Lefebvre, P., Gourgiotis, A., Mangeret, A., Le Pape, P., Diez, O., Sabatier, P., Louvat, P., Merrot, P., Baya, C., Zebracki, M., Malet, E., Jézéquel, D., Reyss, J.-L., Bargar, J., Gaillardet, J., Cazala, C., and Morin, G.: Pluri-millenial evolution of uranium speciation in lacustrine sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19811,, 2020


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