An Investigation of Actinide Interactions With Humic Substances

Graham, Margaret C (1995) An Investigation of Actinide Interactions With Humic Substances. PhD thesis, University of Glasgow.

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Saltmarsh and intertidal areas in SW Scotland and NW England receive inputs of natural and anthropogenic radionuclides from a number of sources. Discharges of low level liquid radioactive waste from the Sellafield nuclear fuel reprocessing plant, with maximum releases in the 1970s, have resulted in contamination of the offshore sediment in the proximity of the discharge point with the anthropogenic nuclides, 238Pu, 239u, 240Pu and 241Am and 237Np. Dispersal and redeposition of the contaminated sediment has resulted in continuous input of these nuclides to soils and sediments in coastal areas over the past 40 years which will continue for the forseeable future. Natural decay series radionuclides are subject to similar deposition processes following their discharge from a phosphate refinery at Whitehaven. Additionally, natural decay series radionuclides occur at enhanced levels in saltmarsh sediments of the Solway Firth as a consequence of deposition from natural uranium mineralisations. Previous studies, involving sequential extraction of components of soils and sediments, have highlighted the importance of the organic fraction in binding significant proportions of actinides present in these environments. This thesis presents a study of three locations - a saltmarsh in SW Scotland, a floodplain soil (R. Esk, W Cumbria) and a highly organic soil on the bank of the R. Esk, W Cumbria. The saltmarsh sediments and the Esk soils vary in the degree of marine inundation experienced and provide contrasting environmental conditions which in turn affect actinide geochemistry. Gel filtration chromatography, FTIR, UV and Fluorescence spectroscopy, alpha spectrometry and ICP-MS were used to investigate the influential role of the organic fraction, and in particular humic substances, in determining actinide behaviour. Specifically, these techniques were used to investigate humic properties including structural characteristics and actinide binding ability. An important part of this work involved the evaluation of traditional extraction methodology and, following the observation that humic substances were irreversibly altered during the separation of humic and fulvic acids, both in terms of their actinide binding capacity and chemical characteristics, the application of new methodology was developed to minimise these etfects. Conclusions from this study are as follows: i) the sum of properties of humic acid and fulvic acid is not equal to those of humic substances: ii) humic substances from diverse locations are compositionally different retlecting the variations in the source of the precursor material, iii ) humic substances comprise only a minor component of the total soil mass but account disproponionately for a significant amount of the actinide binding capacity the soil or sediment, iv) gel chromatographic separation of humic substances provides fractions which are less heterogeneous than the bulk material , v) gel fractionation is unsuitable for size determination of humic materials since certain humic components are retarded by the gel resulting in their elution at greater volumes than proposed purely on the basis of size, VI) characterisation of fractions of humic substances showed that they vary in chemical composition and in their actinide binding capacity. This provided evidence of discrete associations of actinide elements with fractions of humic substances indicating that a single parameter describing their interaction with the bulk humic material is inadequate, vii) characterisation of fractions also shows that actinide associations with humic material are influenced by the composition and the degree of diagenetic alteration of the humic material. In summary, this study has provided evidence of discrete associations of actinide elements with fractions of humic substances and that different components of the humic fraction have widely varying actinide binding capacities. The chemical characteristics of these molecules are vitally important in determining the mobility of these species in the environment.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Roger Scott
Keywords: Ecology, Biogeochemistry, Nuclear chemistry, Soil sciences
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-75344
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 20:28
Last Modified: 19 Nov 2019 20:28

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