Soutenance de thèse de Guillaume Othmane le 29 novembre 2012 à 14h

Amphithéâtre Jean Perrin du Campus Curie, 11 rue Pierre et Marie Curie, 75 005 PARIS

Spéciation de l'uranium dans l'environnement : application aux opales de Nopal I (Mexique) et aux résidus miniers de Gunnar (Canada)"

Abstract :
Understanding the processes of uranium migration and sequestration is an important issue for the prediction of radionuclide retardation in the vicinity of uranium mine tailings sites or for the safety assessment of potential high-level nuclear waste repositories. Uranium speciation, controlled by biotic and abiotic factors, represents a key parameter for the control of uranium transfer in the environment. This study firstly deals with uranium speciation in opals from the Nopal I uranium deposit (Mexico). Microscopic observations of opals at the nano-scale revealed the occurrence of vorlanite, cubic CaUO4. This was the first time this rare calcium uranate has been found displaying a cubic morphology, in agreement with its crystal structure. Association with opal zones enriched in Ca and U suggested that vorlanite formed at Nopal during late stage U-mobilization (54 ka) under oxidizing conditions and low (< 50 °C) temperature. Nopal I opals have been further investigated through time-resolved laser fluorescence spectroscopy. The opals spectra and their comparison with those of experimentally produced standards indicate occurrence of mono- or polymeric uranyl complexes (associated or not with calcium or phosphate) sorbed onto internal surface of opal around pH 7-8. Finally, the speciation of uranium was studied in mill tailings from Gunnar (Canada). Uranium mainly occurs as U(VI) sorbed or coprecipitated species onto iron oxyhydroxides and chlorite. Therefore uranium mobility in Gunnar is governed by sorption/desorption and dissolution/(co)precipitation processes.

Jury  :
Rizlan BERNIER-LATMANI, EPFL (Lausanne), rapportrice
Andreas SCHEINOST, HZDR (Dresden) et ESRF (Grenoble), rapporteur
Christophe MOULIN, CEA-DAM-Ile de France et CNAM, examinateur
Georges CALAS, IMPMC (UPMC), examinateur
Thierry ALLARD, IMPMC (CNRS), directeur de thèse
Nicolas MENGUY, IMPMC (UPMC), co-directeur de thèse