Abstracts Category : Other

Uranium(VI) uptake by geological materials,characterisation by luminescence spectroscopy

by Mark Williams

Many of the wastes associated with the nuclear fuelcycle are toxic to the biosphere; advancing the use of highresolution spectroscopy applied to these materials will provide thechemical speciation of the interaction between nuclear waste andgeological material, improving confidence in a permanent disposalmethod and informing clean-up operations. Luminescence spectroscopyof uranyl(VI) is a well-established technique for the molecularspeciation of uranium-mineral interactions. This work explores theuse of both micro- and macroscopic luminescence spectroscopy toexpose uranyl(VI) speciative heterogeneity in a range of mineralswhich have been exposed to uranyl(VI) salt solutions. Acomprehensive review of the available literature on the interactionof uranyl(VI) with a range of geological media is assessed andcompared. The review finds considerable ambiguity in the speciationof uranyl(VI) at the mineral water interface. A database reportingthe multi parametric luminescence properties of uranyl(VI) withsilica gel, quartz, bayerite, boehmite, muscovite, kaolinite andmontmorillonite (SWy-2 and STx-1b) is presented and discussed.Although some of the results are consistent with previouslyreported values, many newly identified species are reported andtheir identification speculated. Parallel factor analysis is usedto deconvolute the excitationemission matrix of uranyl(VI) sorbedto silica gel between pH 3 and pH 10. The results are used toidentify the spectroscopic properties of complexes >(SiO)2UO2and >(SiO)2UO2OH and thus new complexation coefficients (log(K))for their formation with the silica gel surface are determined,log(K1) = 9.22 0.02 and log(K2) = 3.45 0.01, respectively.The investigation also provides insight into the fundamentalproperties of uranyl(VI) excitation pathways, which are not yetfully understood. Confocal microscopy and phosphorescent lifetimeimage mapping (PLIM) is used to expose the sub-micron heterogeneityof uranyl(VI) sorption complexation across mineral surfaces ofsilica gel, bayerite and montmorillonite (STx-1b). The resultssuggest that changes in the uranyl(VI) lifetime can be used toobserve and understand submicron changes in uranyl(VI) complexationat hitherto unknown temporal resolution.Advisors/Committee Members: BURTON, NEIL NA, SHAW, SAM S, Natrajan, Louise, Burton, Neil, Shaw, Sam.