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Title: The biogeochemical behaviour of plutonium and americium in contaminated soils
Author: Kimber, Richard
ISNI:       0000 0004 2729 9145
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2012
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The biogeochemical behaviour of plutonium and americium was investigated in contaminated soils from the UK to help determine possible remediation and management options. Stimulating anoxic sediments from Aldermaston, through the addition of a carbon substrate (glucose), induced reducing conditions resulting in a negligible change in Pu mobility. This was despite a substantial shift in the bacterial profile from a diverse community to one dominated by fermentative Beta proteobacteria and Clostridia. The latter group also includes organisms associated with metal reduction, such as close relatives to Clostridium species, reported previously to facilitate the reduction of Pu(IV) to Pu(III). A sequential extraction was performed on soils from Aldermaston and the Esk Estuary to identify which selected fractions the Pu and Am are most strongly associated with. The majority of Pu was associated with the 'residual fraction': 63.8 – 85.5 % and 91.9 – 94.5 % in the Aldermaston and Esk Estuary soils respectively. Metals associated with this fraction are highly recalcitrant and are unlikely to be released into solution over a significant time span under most geological conditions. The Am was more evenly distributed with the 'organic fraction' being the most dominant. Degradation of organic matter under oxidising conditions may result in mobilization of metals associated with this fraction. The Aldermaston soil was also subjected to bioleaching using a sulfuric acid producing microbial community, which resulted in a maximum 0.18 % of Pu released into solution. However, up to 12.5% of Am was found in solution suggesting Am is more susceptible to mobilization than Pu. The potential for Pu mobilization through abiotic oxidative leaching was investigated using permanganate. Even when carbonate was added to act as a potential complexant for the Pu, less than 1% of the Pu was leached. Greater success was observed when leaching was attempted using citric acid; an estimated 25 – 30% of Pu was released into solution offering a potential route for remediation of Pu-contaminated soils. These data would suggest that the Pu is highly recalcitrant, and may exist in a small particulate form in the Aldermaston soils, possibly in the oxide form, and is unlikely to mobilize under natural biogeochemical conditions.
Supervisor: Livens, Francis; Lloyd, Jonathan Sponsor: Atomic Weapons Establishment ; EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: biogeochemistry ; bioremediation ; radionuclides ; contaminated