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Title: Characterisation and remediation of depleted uranium munitions residues and aqueous chromium (VI)
Author: Crean, Daniel
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2013
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Depleted uranium (DU) munitions particles and aqueous chromium(VI) are hazardous and challenging toxic metal contaminants. This thesis develops new approaches for remediating these pollutants, and provides insight into the long term behaviour of DU contamination by characterisation of environmentally aged residues. DU munitions particles exposed to the environment for ~25 years were studied using synchrotron X-ray chemical imaging. Micron-scale domains of U speciation were resolved in particles, indicating heterogeneous formation conditions and a variable extent of particle weathering. Two soil samples from a UK firing range were shown to have different U speciation, linked to environmentally mediated alteration in one soil. This study represents a novel application of X-ray chemical imaging to U in environmental materials, allowing domains of U(IV), U(V) and U(VI) to be resolved. An aged particle containing UFeO4 was shown to contain U(V), providing new evidence for the stability of this oxidation state under environmental conditions. Remediation of DU contaminated soils was studied by chemical extraction using bicarbonate, sulfric acid and citric acid lixivants. Single batch extraction in bicarbonate was the most effective, and able to remove 50% total DU. Residual particles showed partially leached microstructures, and the formation of secondary phases. An alternating pH multi-batch extraction was developed to promote secondary phase dissolution and improve the decontamination yield to a maximum of 87% total DU. In the last section, remediation of aqueous Cr(VI) was studied by reduction to insoluble Cr(III) using a hybrid Pd functionalised biomineral, magnetite. A means to increase the reactive capacity of the Pd-magnetite was demonstrated by addition of sodium formate, and the system performance was not affected by dissolved oxygen or nitrate. Using advanced spectroscopic and microscopic techniques, analysis of the reacted mineral showed Cr(III) was retained in the magnetite structure, and Pd recrystallisation resulted in a loss of reductive capacity.
Supervisor: Hyatt, Neil ; Livens, Francis Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available