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|Title: ||Uranium solubility, speciation and complexation at high pH|
|Authors: ||Sutton, Mark|
|Keywords: ||Uranium compounds|
|Issue Date: ||1999|
|Publisher: ||© Mark Sutton|
|Abstract: ||Low level nuclear waste arising from UK nuclear sites, research establishments,
hospitals and industry is currently disposed of at the Drigg Disposal Facility in
Cumbria. Waste is packed into steel canisters before being compacted and grouted
into larger steel storage containers. The aqueous chemistry of wastes, especially
radionuclides, in the presence of grout material is of major interest. The gout used
at the Drigg site is a mixture of Ordinary Portland Cement and Pulverised Fly Ash
additive, from which ingressing water will leach high levels of calcium, sodium
and potassium and produce waters of a high pH. Aerobic environments are
expected to dominate over the early period of the vault life, after which the
combined effect of canister corrosion and microbial activity will lead to anaerobic
conditions. After a much longer period (100,000 years) anaerobic conditions may
cease and yield once again an aerobic environment where migration of
radionuclides may be sorption-controlled rather than on hydroxide precipitation at
Work has been performed under both aerobic and anaerobic conditions to study
uranium solubility in the presence of complexing ligands that may be present in the
waters of the nearfield of a low-level waste disposal vault. Eleven ligands have
been investigated: carbonate, phosphate, chloride, sulphate, acetate, citrate, EDTA,
NTA and organic matter- humic acid, fulvic acid and iso-sacchannic acid.
Anaerobic conditions were achieved by two different procedures; the first used
ferrous ions in hydroxide solution and the second used dithionite in hydroxide
solution. Both methods produce reducing electrode potentials and high pH.
Computer software has been used to model experimental results, thereby predicting
uranium solubilities and speciation, and to propose new formation constants to fit
the experimental results more closely.
Studies have also been perforined to measure uranium sorption by grout material at
high pH in the presence of the above ligands.
This work makes a significant contribution to the understanding of uranium
solubility and speciation in waters. at high pH and under conditions relevant to low
level nuclear waste disposal.|
|Description: ||Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Chemistry)|
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