The immobilisation of uranium is an important issue within the nuclear industry due to contaminated land from accidental spillage, weapons testing or mining activities. Within the environment uranium is most commonly found in the +VI oxidation state as the mobile uranyl cation [UO2]2+. Alternatively, the +IV oxidation state can also be found in the environment, forming either an insoluble crystalline uraninite phase, or a more soluble molecular uranium(IV) species. Many endogenous subsurface bacteria can bind and accumulate actinide ions through biosorption and can reduce mobile uranyl(VI) species down to immobile uranium(IV) compounds and mineral phases. This work presents an investigation into the bioreduction process by two anaerobic Gram-negative bacteria, Geobacter sulfurreducens and Shewanella oneidensis MR-1. Luminescence spectroscopy is used to monitor the intensity of uranyl(VI) emission in situ over the course of a 24 hour bioreduction experiment with uranyl(VI) acetate as the electron acceptor and either acetate or lactate as the electron donor. An increase in intensity of the emission around hour three or four during the reduction, followed by an overall decrease, is attributed as the disproportionation of an unstable uranyl(V) intermediate. The role of inner and outer membrane c-typecytochromes as well as flavin secretion is also investigated using three deletion mutants of the S. oneidensis bacteria, which shows that in their absence, the reduction of uranyl(VI) does not occur over the course of 24 hours. The emission of uranium(IV) is also investigated during bioreduction in phosphate media and results show that emission can be observed in aqueous solutions at pH 7 pointing to the presence of a molecular product. One photon confocal and two photon fluorescence microscopy has been utilised for the very first time to directly optically image the bioreduction of uranyl(VI) in combination with luminescence lifetime mapping. The sorption of uranyl(VI) onto the surface of the bacteria with differing lifetimes indicates a direct interaction between uranyl(VI) and surface bound c-type cytochromes, since this variation was not observed in mutant S. oneidensis strains where the cytochromes were not present. Combined, these results have established the applicability of optical spectroscopy and microscopyin tracking the bioreduction of uranium in situ.

Unconformity-related uranium deposits in the Athabasca Basin represent a significant global resource of uranium. One such deposit, the Phoenix Deposit, discovered in 2007 on Denison Mine’s Wheeler River property, shares similarities with other deposits in the Basin. The Phoenix Deposit is located at the apex between a basement shear structure, and the unconformity between the crystalline basement and overlying sandstones. The shear structure extends into the sandstones, this structure controls the distribution of alteration minerals in the basement and early alteration phases in sandstones. The shear structure extending to sandstones is not spatially associated with late alteration phases associated with the uranium deposit, suggesting that the structure was not important for uranium mineralisation. Bulk rock compositions of sandstones show chimney-like distribution of elements above the uranium deposit. The most notable ones are the distribution of yttrium, and boron. Rare earth elements and yttrium are not soluble in aqueous fluids at low temperatures and they are enriched in uranium ore. Therefore, the chimney-like distribution of elements are attributed to uraniferous hydrothermal activity in sandstones. Petrographic and chemical analysis of alteration associated with the Phoenix Deposit shows two types of tourmaline, a pre-ore (Tur 1) in the basement, which is likely a metamorphic product (Tur1) and a syn-ore magnesiofoitite (Tur 2) in the basement and the sandstones. Three generations of chlorite are identified within the alteration halo of the Phoenix Deposit; an early Fe-rich clinochlore (C1) in the basement and sandstones, the second generation, Mg-rich sudoitic chlorite (C2) in the basement, and a late, sudoitic chlorite (C3) in the basement and sandstones. Illite shows three types; an early and late M1 and a late M2. M1 is found as two polytypes, 1Mc and 1Mt, in the basement and sandstones, with the 1Mt having a spatial relationship with the uranium deposit. Late M2 illite is coarse-grained and occurs in the basement and sandstones. Near Infrared (NIR) spectra of sandstones overlying the deposit shows absorption features between 600 and 700 nm. It is considered that these absorption features appear to have been produced during late hydrothermal activity and may have a temporal as well as spatial relationship with uranium mineralisation.

No description available.

Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO22+aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.

Reproduction de : Thèse de doctorat : Terre solide et enveloppes superficielles : Poitiers : 2008. / Titre provenant de l'écran-titre. Bibliogr. 111 réf.

Reproduction de : Thèse doctorat : Chimie : Lyon 1 : 2003. / Titre provenant de l'écran titre. 87 Réf. bibliogr.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on January 21, 2010). Thesis advisor: Dr. Gary Solbrekken. Includes bibliographical references.

Thesis (M.S. in environmental science)--Washington State University, December 2009. / Title from PDF title page (viewed on Jan. 26, 2010). "School of Earth and Environmental Sciences." Includes bibliographical references (p. 48-51).

Thesis (Ph. D.)--Lehigh University, 2002. / Includes vita. Includes bibliographical references (leaves 128-134).

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains x, 230 p. : col. ill., col. maps. Includes abstract. Includes bibliographical references (p. 198-209).