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Title: Radionuclide biogeochemistry in UK contaminated land scenarios
Author: Begg, James David
ISNI:       0000 0001 3453 8894
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2008
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Technetium and uranium are radionuclides found in groundwaters at sites where nuclear wastes have been processed or stored. As a result, increasing understanding of the mobility of these radioactive contaminants in the environment is required in order to predict their movement in the sub-surface and to develop efficient remediation of contaminated environments. The redox chemistry of both technetium and uranium exerts a strong control on their environmental behaviour. Unde~ oxic conditions, mobile Tc(VII) and U(VI) species dominate. In contrast, under reducing conditions the Tc(IV) and U(IV) oxidation states predominate and are poorly soluble. A change in oxidation state of both Tc and U can be effected by indigenous microbial activity in natural soils and sediments. As a result, indigenous microbes may play an important role in controlling the environmental behaviour of both these redox active radionuclides. Here, a multidisciplinary approach is applied in order to identifY biogeochemical factors that control the redox state and environmental behaviour of Tc and U in soil from the UKAEA operated site at Dounreay, UK. Microcosm experiments containing soil from the site' at Dounreay showed that indigenous microbial activity caused removal of Tc(VII) from solution during anaerobic incubation and was most likely mediated by '~'-------abiotic~reauCtiori-of-Tc(VII)-wiih microbially -pro-dilced---Fe(II).--X,:ray -absc)rptiori--------------- spectroscopy (XAS) analysis confirmed reduction of Tc(VII) to Tc(IV) in microcosm experiments. Tc was found to be partially remobilised following exposure of reduced Tc(IV)-labelled soils to _air, but was not significantly remobilised following exposure to nitrate. In uranium experiments, uptake of U(VI) by soil was rapid and complete under oxic conditions from artificial groundwater and in experiments with groundwater amended with ethylenediaminetetraacetic acid (EDTA). By contrast, uptake was slower in systems amended with bicarbonate. XAS experiments confirmed that uranium was adsorbed to soil as U(VI) in all three groundwater systems. After anaerobic. incubation for 120 days and the development of microbially-mediated Fe(III)- and sol- reducing conditions, XAS analysis showed that soil-associated uranium was present as U(IV) in all three systems. Further investigation of unamended artificial groundwater systems indicated that reduction of sorbed U(VI) required an active microbial population. These findings suggest that indigenous soil microorganisms in a Dounreay-type soil environment will exert a strong control on the fate ofTc and U.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available