Browsing by Author "Pham, AN"

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    Influence of dissolved silicate on rates of Fe(II) oxidation
    (American Chemical Society, 2016-10-05) Kinsela, AS; Jones, AM; Bligh, MW; Pham, AN; Collins, RN; Harrison, JJ; Wilsher, KL; Payne, TE; Waite, TD
    Increasing concentrations of dissolved silicate progressively retard Fe(II) oxidation kinetics in the circum-neutral pH range 6.0–7.0. As Si:Fe molar ratios increase from 0 to 2, the primary Fe(III) oxidation product transitions from lepidocrocite to a ferrihydrite/silica-ferrihydrite composite. Empirical results, supported by chemical kinetic modeling, indicated that the decreased heterogeneous oxidation rate was not due to differences in absolute Fe(II) sorption between the two solids types or competition for adsorption sites in the presence of silicate. Rather, competitive desorption experiments suggest Fe(II) was associated with more weakly bound, outer-sphere complexes on silica-ferrihydrite compared to lepidocrocite. A reduction in extent of inner-sphere Fe(II) complexation on silica-ferrihydrite confers a decreased ability for Fe(II) to undergo surface-induced hydrolysis via electronic configuration alterations, thereby inhibiting the heterogeneous Fe(II) oxidation mechanism. Water samples from a legacy radioactive waste site (Little Forest, Australia) were shown to exhibit a similar pattern of Fe(II) oxidation retardation derived from elevated silicate concentrations. These findings have important implications for contaminant migration at this site as well as a variety of other groundwater/high silicate containing natural and engineered sites that might undergo iron redox fluctuations. © 2016 American Chemical Society
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    Movement of a tritium plume in shallow groundwater at a legacy low-level radioactive waste disposal site in eastern Australia over four decades
    (South Pacific Radioactivity Association, 2008-11-23) Hughes, CE; Cendón, DI; Collins, RN; Hankin, SI; Harrison, JJ; Hoffmann, EL; Loosz, T; Payne, TE; Pham, AN; Twining, JR; Vine, M; Waite, TD
    Between 1960 and 1968 radioactive Wastes with low levels of activity were buried by the Australian Atomic Energy Commission in a series of shallow trenches in bushland near the Lucas Heights facility, on the outskirts of Sydney. Groundwater monitoring carried out since the mid 1970’s has found that no radioactivity, with the exception of tritium, has been detected outside the immediate vicinity of the trenches. However, over this period of more than 40 years, a plume of tritiated water has migrated om the trenched area and extends at least 100 m from the source. The peak tritium activity detected in the mid l970’s was 390 kBq/L directly adjacent to the trenches. Modem tritium activity in the groundwater is less than the drinking water standard of 7.6 kBq/L and poses no radiological risk to the community or local environment. The tritium dataset will be presented and analysed to determine the effects of rainfall and drought periods on tritium levels and plume transport.