Browsing by Author "Collins, RN"

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    Analysis of hot particle characteristics affecting environmental fate and interaction with living organisms
    (SPERA, 2016-09-09) Johansen, MP; Child, DP; Collins, RN; Hotchkis, MAC; Howell, NR; Payne, TE; Ikeda-Ohno, A; Mokhber-Shahin, L
    The 2nd International Conference on the Sources, Effects and Risks of Ionizing Radiation (SERIR-2) and the 14th Biennial Conference of the South Pacific Environmental Radioactivity Association (SPERA-2016) and will be held in Bali, Indonesia 5-9 September 2016. The South Pacific Environmental Radioactivity Association (SPERA), in conjunction with the Indonesian National Nuclear Energy Agency (BATAN) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) made the decision to jointly hold these conferences in one week at the same venue to avoid topical overlap and to strengthen regional participation at both events. SERIR2 will be a 1-day conference (5 September) and deals with the efforts to enhance data collection and disseminate scientific findings related to the issues of sources, effects and risks of the ionizing radiation, as well as to seek ways of communicating with stakeholders (scientific communities, regulatory authorities and general public) on those issues. The 14th Biennial Conference of the South Pacific Environmental Radioactivity Association (SPERA), to be held 6-9 September, provides a platform for discussion and debate among scientists on the occurrence, behaviour, impact and measurement of radioactive species present in the environment through natural processes, or resulting from human activities. This international conference facilitates knowledge sharing on environmental radioactivity and related topics of local and global significance. The joint conference will be held 5-9 September 2016, with a welcome reception on 4 September, at the Sanur Paradise Plaza Hotel in Bali. The joint conference will include a one-day workshop on the 6 September on topic(s) to be decided.
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    Applications of time-resolved laser fluorescence spectroscopy to the environmental eiogeochemistry of actinides
    (American Society of Argonomy, 2011-05-01) Collins, RN; Saito, T; Aoyagi, N; Payne, TE; Kimura, T; Waite, TD
    Time-resolved laser fluorescence spectroscopy ( TRLFS) is a useful means of identifying certain actinide species resulting from various biogeochemical processes. In general, TRLFS diff erentiates chemical species of a fl uorescent metal ion through analysis of diff erent excitation and emission spectra and decay lifetimes. Although this spectroscopic technique has largely been applied to the analysis of actinide and lanthanide ions having fl uorescence decay lifetimes on the order of microseconds, such as UO(2)(2+), Cm(3+), and Eu(3+), continuing development of ultra-fast and cryogenic TRLFS systems off ers the possibility to obtain speciation information on metal ions having room-temperature fl uorescence decay lifetimes on the order of nanoseconds to picoseconds. Th e main advantage of TRLFS over other advanced spectroscopic techniques is the ability to determine in situ metal speciation at environmentally relevant micromolar to picomolar concentrations. In the context of environmental biogeochemistry, TRLFS has principally been applied to studies of ( i) metal speciation in aqueous and solid phases and ( ii) the coordination environment of metal ions sorbed to mineral and bacterial surfaces. In this review, the principles of TRLFS are described, and the literature reporting the application of this methodology to the speciation of actinides in systems of biogeochemical interest is assessed. Signifi cant developments in TRLFS methodology and advanced data analysis are highlighted, and we outline how these developments have the potential to further our mechanistic understanding of actinide biogeochemistry. © American Society of Agronomy
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    Aqueous phase speciation and chemistry of cobalt in terrestrial environments
    (Elsevier, 2010-05) Collins, RN; Kinsela, AS
    The solution speciation of a metal has a critical influence on its biological activity in the environment and is now an important focus of research. In this review, pertinent aspects related to the aqueous speciation and chemistry of cobalt (Co) in terrestrial environments are critically assessed. Although there is a lack of comprehensive data on aqueous Co concentrations in soil porewaters, groundwaters and surface waters, existing reports indicate that natural Co concentrations vary within a picomolar to micromolar range. Cobalt chemistry is dominated by the Co(II) oxidation state in the aqueous phase of terrestrial environments primarily due to the extremely low solubility of Co(III). There is no universal agreement on the importance of Co(II) complexation in the solution phase of terrestrial environments and, furthermore, on the nature of the major binding organic ligands. The kinetics of Co(II) complexation to, and dissociation from, natural organic complexing ligands are such that the speciation of Co is likely to significantly diverge from estimates based on thermodynamic equilibrium calculations. As a result, an accurate understanding of Co bioavailability, toxicity and transport in terrestrial aquatic environments will only be achieved when thermodynamics can be reconciled with reaction kinetics. © 2010, Elsevier Ltd.
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    Assessment of radionuclide distributions at an Australian legacy radioactive waste site
    (South Pacific Radioactivity Association, 2010-09-01) Payne, TE; Cendón, DI; Collins, RN; Dore, M; Hankin, SI; Harrison, JJ; Hughes, CE; Johansen, MP; Thiruvoth, S; Twining, JR; Wilsher, KL
    During the 1960s, low level radioactive waste was buried in shallow trenches at a disposal site in south-eastern Australia, known as the Little Forest Burial Ground. This paper discusses preliminary findings of research into the distribution of radionuclides at the site, including soils, groundwater and biota. In particular, we are studying the mobility of radionuclides; and their uptake by plants, insects and small animals. Groundwater monitoring indicates that there has been limited movement of radioactivity, other than a tritium plume that extends at least 100 m. The tritium results are being used to define the groundwater flowpaths, and the effects of seasonal and climatic factors. The pattern of tritium distribution suggests that the source of tritium is predominantly within the waste materials. However, tritium derived from a nearby municipal landfill contributes to tritium concentrations in some groundwaters, with smaller amounts from cosmogenic tritium and atmospheric deposition originating from the nearby HIFAR reactor (shut down in 2007). The tritium data provide a record of water movement against which the relative mobility of other radionuclides can be assessed. There are measurable amounts of 60Co, 90Sr, 137Cs and traces of actinides in some soils, groundwater and vegetation samples taken in close proximity to the disposal area. Isotopic ratios such as δ13C, δ180, δ2H, δ34S and 87Sr/86Sr are being measured in groundwater, in addition to the radioactive isotopes originating from the disposed wastes. Synchrotron EXAFS and XANES studies are being applied to study elemental chemical environments and oxidation states in the soils at the site. We have recently undertaken a major geophysical investigation and drilling program; and installation of an improved array of water sampling boreholes is planned. Therefore, many more samples of groundwater and soils are becoming available for analysis.
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    Assessment of radionuclide movement at an Australian legacy radioactive waste site
    (EMSL, 2009-09-20) Payne, TE; Cendón, DI; Collins, RN; Hankin, SI; Harrison, JJ; Hughes, CE; Johansen, MP; Twining, JR; Waite, TD
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    Characterization of foliar manganese (Mn) in Mn (hyper)accumulators using x-ray absorption spectroscopy
    (Wiley-Blackwell, 2010-12-01) Fernando, DR; Mizuno, T; Woodrow, IE; Baker, AJM; Collins, RN
    Plant hyperaccumulation of the essential nutrient manganese (Mn) is a rare phenomenon most evident in the Western Pacific region, and differs from hyperaccumulation of other elements. Mn hyperaccumulators employ a variety of species-dependent spatial distribution patterns in sequestering excess foliar Mn, including primary sequestration in both nonphotosynthetic and photosynthetic tissues. This investigation employed synchrotron X-ray absorption spectroscopy (XAS) in a comparative study of Mn (hyper)accumulators, to elucidate in situ the chemical form(s) of foliar Mn in seven woody species from Australia, New Caledonia and Japan. Foliar Mn was found to predominate as Mn(II) in all samples, with strong evidence of the role of carboxylic acids, such as malate or citrate, as complexing ligands. Overall, the X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure spectroscopy (EXAFS) data appeared weighted against previous observations that oxalate binds excess Mn in Mn-(hyper)accumulating species. © 2010, Wiley-Blackwell.
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    Effect of amorphous Fe(III) oxide transformation on the Fe(II)-mediated reduction of U(VI).
    (American Chemical Society, 2011-02-15) Boland, DD; Collins, RN; Payne, TE; Waite, TD
    It has recently been reported that the Fe(II)-catalyzed crystallization of 2-line ferrihydrite to goethite and magnetite can result in the immobilization of uranium. Although it might be expected that interference of the crystallization process (for example, by the presence of silicate) would prevent uranium immobilization, this has not yet been demonstrated. Here we present results of an X-ray absorption spectroscopy study on the fate of hexavalent uranium (U(VI)) during the Fe(II)-catalyzed transformations of 2-line ferrihydrite and ferrihydrite coprecipitated with silicate (silicate−ferrihydrite). Two-line ferrihydrite transformed monotonically to goethite, whereas silicate−ferrihydrite transformed into a form similar to ferrihydrite synthesized in the absence of silicate. Modeling of U L(III)-edge EXAFS data indicated that both coprecipitated and adsorbed U(VI) were initially associated with ferrihydrite and silicate−ferrihydrite as a mononuclear bidentate surface complex. During the Fe(II)-catalyzed transformation process, U(VI) associated with 2-line ferrihydrite was reduced and partially incorporated into the newly formed goethite mineral structure, most likely as U(V), whereas U(VI) associated with silicate−ferrihydrite was not reduced and remained in a form similar to its initially adsorbed state. Uranium(VI) that was initially adsorbed to silicate−ferrihydrite did, however, become more resistant to reductive dissolution indicating at least a partial reduction in mobility. These results suggest that when the Fe(II)-catalyzed transformation of ferrihydrite-like iron oxyhydroxides is inhibited, at least under conditions similar to those used in these experiments, uranium reduction will not occur. © 2011, American Chemical Society
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    Ferric iron geometry and coordination during hydrolysis and ferrihydrite precipitation
    (Mineralogical Society of Great Britain & Ireland, 2011-10-01) Collins, RN; Rose, AL; Glover, CJ; Boland, DD; Payne, TE; Waite, TD
    Definitive structural characterisation of ferrihydrite has challenged scientists primarily due to its nanosized particles and inherent long-range structural disorder which challenges analytical methodology (and modelling) typically employed to determine the structure of minerals. Here we report on the application of a synchrotron quick-scanning X-ray absorption spectroscopy (XAS) approach, which allows the collection of Extended X-ray Absorption Fine Structure (EXAFS) spectral data to k = 15 Å-1 in < 1 minute, to obtain unparalleled iron Kedge data on the hydrolysis of FeIII(H2O)6 and ferrihydrite precipitation. Modelling of the pre-edge and EXAFS data: 1) supports theoretical studies which have suggested the existence of a monomeric penta-coordinated FeIII hydrolysis species and; 2) corroborates recently proposed structural models of ferrihydrite that contain tetrahedral FeIII. Modelling results indicate that ferrihydrite consists of 15 to 25 % tetrahedral FeIII and suggest that this geometry must be included in any comprehensive structural model of ferrihydrite and, furthermore, should be considered when evaluating the reactivity, stability and other structure-property relationships of this mineral. © 2011 The Authors.
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    Influence of calcium and silica on hydraulic properties of sodium montmorillonite assemblages under alkaline conditions
    (Elsevier, 2010-03-01) Kinsela, AS; Tjitradjaja, A; Collins, RN; Waite, TD; Payne, TE; Macdonald, BCT; White, I
    A sodium-washed montmorillonite was exposed to calcium and silica under alkaline conditions in order to gain insight into possible interactions of engineered clay barriers and cementitious leachates found in many waste storage facilities. The changes in physico-chemical properties of the material were investigated using a combination of dead-end filtration, electrophoresis and scanning electron microscopy. The results show minimal differentiation between unaltered Na-montmorillonite samples at the two pH values tested (9 and 12), with the structure of the resulting assemblages arising from repulsive tactoid interactions. The addition of calcium (50 mM) greatly decreases the size of the structural network, and in doing so, increases the hydraulic conductivity ~65-fold, with the effect being greatest at pH 12. Whilst the addition of silica alone (10 mM) produced little change in the hydraulic properties of montmorillonite, its combined effect with calcium produced alterations to the structural assemblages that could not be accounted for by the presence of calcium alone. The likely binding of calcium with multiple silanol groups appears to enhance the retention of water within the Na-montmorillonite assemblage, whilst still allowing the fluent passage of water. The results confirm that polyvalent cations such as Ca2+ may have a dramatic effect on the structural and hydraulic properties of montmorillonite assemblages while the effects of solutions containing both silicate and calcium are complex and influenced by silica–cation interactions. © 2010, Elsevier Ltd.
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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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    Inhibition of uranium (VI) sorption on titanium dioxide by surface iron (III) species in ferric oxide/titanium dioxide systems
    (American Chemical Society, 2012-10-16) Comarmond, MJ; Payne, TE; Collins, RN; Palmer, G; Lumpkin, GR; Angove, MJ
    Uranium (U(VI)) sorption in systems containing titanium dioxide (TiO2) and various Fe(M)-oxide phases was investigated in the acidic pH range (pH 2.5-6). Studies were conducted with physical mixtures of TiO2 and ferrihydrite, TiO2 with coprecipitated ferrihydrite, and with systems where Fe(III) was mostly present as crystalline Fe(III) oxides. The presence of ferrihydrite resulted in decreased U(VI) sorption relative to the pure TiO2 systems, particularly below pH 4, an unexpected result given that the presence of another sorbent would be expected to increase U(VI) uptake. In mixtures of TiO2 and crystalline Fe(III) oxide phases, U(VI) sorption was higher than for the analogous mixtures of TiO2 with ferrihydrite, and was similar to U(VI) sorption on TiO2 alone. X-ray absorption spectroscopy of the TiO2 system with freshly precipitated Fe(III) oxides indicated the presence Fe(III) surface phase that inhibits U(VI) sorption-a reaction whereby Fe(III) precipitates as lepidocrocite and/or ferrihydrite effectively blocking surface sorption sites on the underlying TiO2. Competition between dissolved Fe(III) and U(VI) for sorption sites may also contribute to the observed decrease in U(VI) sorption. The present study demonstrates the complexity of sorption in mixed systems, where the oxide phases do not necessarily behave in an additive manner, and has implications for U(VI) mobility in natural and impacted environments where Fe(III) (oxyhydr)oxides are usually assumed to increase the retention of U(VI). © 2012, American Chemical Society.
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    Inhibitory effect of silicate on the Fe(II)-catalysed sequestration of U by Fe(III) oxides
    (Elsevier; Cambridge Publications, 2010-06-17) Boland, DD; Collins, RN; Payne, TE; Waite, TD
    It has recently been reported that the natural Fe (II)- catalysed transformation of Fe (III) minerals to more crystalline forms can result in the sequestration of uranium [1], thus potentially leading toward a solution to the universal and emotive problem of uranium contamination. While this process may reduce uranium migration, there is no clear knowledge of its viability in conditions which inhibit the transformation of iron oxides. Here we present XAS results of Fe (II)-catalysed transformations in systems containing 2-line ferrihydrite, silicate and uranium as U (VI). The chemical environment of both co-precipitated and adsorbed U (VI) bound by 2-line ferrihydrite was initiallyidentical, in both cases being associated with the iron oxides as a surface complex. Upon addition of aqueous Fe (II) in anoxic conditions, 2-line ferrihydrite with associated U (VI) transformed to goethite. Ab initio modelling of EXAFS data indicated that U (VI) associated with 2-line ferrihydrite was incorporated into the newly formed goethite mineral structure. In contrast, silicate-ferrihydrite only transformed to ferrihydrite with the associated U (VI) remaining in a form similar to its initial state. The adsorbed U (VI) did however become more resistant to reductive dissolution indicating at least a partial reduction in mobility. These results demonstrate that the Fe (II)-catalysed crystallisation of iron oxides may not always induce uranium reduction or immobilisation in relevant environmental conditions. The precise mechanism of the inhibitory effect of silicate, with a focus on how to control conditions to reduce this effect, must be resolved before this process may be considered a reliable means of preventing sub-surface uranium transport. © 2020 Elsevier B.V.
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    Is there a link between Fe(III) oxide reactivity, Fe(II)-catalysed crystallisation and U(VI) reduction?
    (Elsevier; Cambridge Publications, 2010-06-18) Collins, RN; Payne, TE; Waite, TD
    The discovery that Fe (II) catalyses the crystallisation of highly disordered Fe (III) oxides from years to hours has dramatically changed our perception of the time-scales that may be involved in the iron redox cycle with far-reaching ramifications to the kinetics of other globally important biogeochemical cycles such as carbon and sulfur [1] as well as that of redox sensitive elements such as uranium [2]. While we still explore the mechanisms of this potentially exciting new pathway in the iron redox cycle, in very simplified systems, one must ask of the relevance of such studies when these conditions are typically far-removed from those experienced in the natural environment. Indeed, when done so, it is observed that the Fe (II)-catalysed crystallisation process may not have global applicability [3, 4]. However, obtaining information on why a process does not work is often as enlightening as direct observation of the process in motion. Here we report on experiments which demonstrate that no relationship exists between Fe (III) oxide reactivity and its propensity for Fe (II)-catalysed crystallisation when the intrinsic reactivity of the Fe (III) oxide is induced by the presence of the sulfur tetrahedral oxyanion - SO4. We further demonstrate that Fe (III) oxide crystallinity is key for the Fe (II) reduction of U (VI) and, moreover, that (FeII)-U (VI) electron transfer is related to the redox potential of the Fe (II)- Fe (III) couple. In other words, U (VI) will not be reduced by Fe (II) when both are sorbed to highly disordered Fe (III) oxides such as ferrihydrite and/or schwertmannite.
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    Isotope exchange studies of contaminant availability in soils and sediments
    (ICI7 Organizing Committee, 2011-09-04) Payne, TE; Comarmond, MJ; Harrison, JJ; Clark, MW; Collins, RN; Angove, MJ; Palmer, G
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    Isotopically exchangeable A1 in coastal lowland acid sulfate soils
    (Elsevier, 2016-01-15) Yvanes-Giuliani, YAM; Fink, D; Rose, J; Waite, TD; Collins, RN
    Periodic discharges of high concentrations of aluminium (Al) causing fish kills and other adverse effects occur worldwide in waterways affected by coastal lowland acid sulfate soils (CLASS). The exchangeability — a metal's ability to readily transfer between the soil solid- and solution-phases — of Al in these soils is therefore of particular importance as it has implications for metal transport, plant availability and toxicity to living organisms. In the present study, the concentrations of isotopically exchangeable Al (E values) were measured in 27 CLASS and compared with common salt extractions (i.e. KCl and CuCl2) used to estimate exchangeable soil pools of Al. E values of Al were high in the soils, ranging from 357 to 3040 mg·kg− 1. Exchangeable concentrations estimated using 1 M KCl were consistently lower than measured E values, although a reasonable correlation was obtained between the two values (E = 1.68 × AlKCl, r2 = 0.66, n = 25). The addition of a 0.2 M CuCl2 extraction step improved the 1:1 agreement between extractable and isotopically exchangeable Al concentrations, but lead to significant mobilisation of non-isotopically exchangeable Al in surficial ‘organic-rich’ CLASS having E values < 1000 mg·kg− 1. It was concluded that currently used (i.e. 1 M KCl) methodology severely underestimates exchangeable Al and total actual acidity values in CLASS and should be corrected by a factor similar to the one determined here. © 2015 Elsevier B.V.
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    Kinetics of coupled Fe(II)-catalysed ferrihydrite transformation and U(VI) reduction
    (Mineralogical Society of Greate Britian & Ireland, 2011-10-01) Boland, DD; Collins, RN; Glover, CJ; Payne, TE; Waite, TD
    Antimony is released into the environment in some natural and man-induced processes. [1]. Yet, its impact on the transformation processes of heavy metal-adsorbing minerals remains poorly understood. In acid-mine drainage systems and shooting ranges, the adsorption of antimony by iron oxides such as ferrihydrite can play a major role. The poorly crystalline 2-line ferrihydrite represents one of the most common Fe oxides in these settings and can transform to goethite (,-FeOOH) or hematite (,-Fe2O3) with time [2]. The rate of transformation depends on the pH, temperature, and on the ions and molecules present during the transformation process [3]. This study focuses on the transformation of synthetic ferrihydrite to crystalline iron oxides in the presence of Sb(V). Transformations were carried out for 1-16 days at 70 ºC and at pH 4, 7 and 12, with different concentrations of Sb(V) (0.00, 0.23, 0.75, 2.25 and 6.00 mM Sb). Samples taken from aqueous suspensions were washed, dried, and characterized by X-ray diffraction (XRD) and atomic absorption spectroscopy (AAS). At pH 12, goethite (Sb concentrations up to 3.7 mg Sb/g) is favored and the transformation is completed after one day. Only a concentration of 6 mM Sb retarded the transformation, where even after 8 days only 50 % of the ferrihydrite was transformed into goethite. Transformations at pH 7 led to a mixture of 75 % hematite and 25 % goethite (4.3 mg Sb/g). However, at concentrations of 6 mM Sb, feroxyhyte (!-FeOOH) (9.1 mg Sb/g) was favored instead. At pH 4, hematite (32.3 mg Sb/g) was favored except for concentrations of 6 mM Sb, were again feroxyhyte (141.1 mg Sb/g) occurred. We assume that increased Sb concentrations favor feroxyhyte and indicate the incorporation of Sb into the structure of feroxyhyte. © The Authors
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    Ligand effects on uranyl sorption - key processes and models
    (South Pacific Radioactivity Association, 2010-09-01) Payne, TE; Comarmond, MJ; Collins, RN; Waite, TD
    The mobility of uranium(Vl) is of concern in numerous natural and polluted environments. One of the main factors controlling uranyl mobility is the sorption of UVl on mineral surfaces, which is strongly dependent on aqueous chemistry, particularly the pH. However, many environmental systems contain a variety of organic and inorganic components, which can have a major effect on sorption. For example, many groundwaters in the Alligator Rivers region of the Northern Territory contain significant amounts of ligands, including carbonate and phosphate. These ligands can increase or decrease uranyl uptake through several possible processes, including competition for binding sites, complexation of aqueous uranyl, formation of ternary uranyl-ligand surface complexes, Vi 1 and precipitation. We have developed surface complexation models of U sorption on minerals including ferrihydrite, kaolinite, and more complex materials; utilising comprehensive U sorption databases and results from advanced spectroscopic techniques (e.g. EXAFS, TRLFS, and ATR-FTIR). These models require specific reactions to represent the effects of ligands. ln systems containing sulfate, it was necessary to consider complexation between U022+ and S042- as well as competition for surface sites, to model the U sorption data. To simulate U sorption data in the presence of carbonate, ternary surface complexes of the form (>S02)UOZCO32- were required (here >S represents a surface site). Similar ternary U-ligand-surface complexes appear to form in the presence of phosphate. The addition of citrate considerably reduced U sorption on both kaolinite and T ferrihydrite and caused dissolution of the solid in the latter case. Complexation of citrate with both uranyl and ferric ions was taken into account in modelling this system. The model required the optimisation of the formation constant for a postulated mixed metal (UVl/FeIII/citrate) aqueous e complex. The results emphasise the importance of considering interactions with ligands when modelling radionuclide sorption in environmental systems.
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    Methods for isolating plutonium particles in Maralainga soils
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Mokhber-Shahin, L; Johansen, MP; Collins, RN; Payne, TE
    A combination of density-separation and gamma testing methods was used to isolate a plutonium (Pu)-containing particle from the host Maralinga soils. Such separation is necessary in order to reduce or eliminate interference from other elements in the host soils that may occur during analysis methods (e.g., synchrotron XANES) used for determining physico-chemical information such as compound speciation and oxidation state. Soil samples were obtained from the Taranaki test area, at Maralinga, South Australia, where Pu had been dispersed by high explosive detonation and through burning in the 1950s. Bulk soil samples were first screened using HPGe gamma-ray spectrometer for detection of Am-241 (0.060 MeV gamma emission) which co-exists with the Pu in the dispersed particles at a concentration ratio of approximately 1:7.5 (Am-241 to Pu-239). The sample was sieved (125 μm) to remove large sand particles and debris. Density separation was accomplished by repeated sonification (0.5 in. probe tip sonifier) and centrifugation of mixtures of soil and lithium heteropolytungstate (density of 2.9 g/ml). The various density fractions were tested for Am-241 through gamma counting. This process was repeated until a small mass (<0.01 g) of heavy particles remained. Further isolation was accomplished using microscope, physical separation, and gamma counting. The result of the process was isolation of a small particle, containing Am and Pu isotopes that had been originally part of a non-critical nuclear weapons test. The particle had been dispersed approximately two kilometres through the air pathway, and has been subjected to +60 years of weathering and chemical interaction processes. The isolation process allows for further testing of the Pu, without interference from natural soil elements, to provide a range of pathway, biological uptake, and dose information.
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    Modified bauxite refinery residues for immobilizing U(VI)
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Clark, MW; Payne, TE; Harrison, JJ; Cormarmond, MJ; Dore, MJ; Collins, RN
    Bauxite refinery residues (BRR) are a waste from the production of alumina using the Bayer process, which has high pH and soluble alkalinity. However, a modified BRR (MBRR) can be made using Mg and Ca to precipitate alkalinity as acid neutralizing capacity (ANC), which lowers pH from ≈13 to ≈8.5. The combined effects of a fine-grained mineral mix providing high surface area across a range of minerals for metal removal, and an ANC (3-5 mol/kg), gives MBRR potential for many environmental remediation and wastewater-treatment applications. We conducted several laboratory experiments that investigate and assess the application potential of MBRR for the environmental remediation U(VI). Isotopic exchange data show that U(IV) is, in part, irreversibly bound and that irreversibility increases with increased surface loading; it is also age- and temperature-sensitive. Synchrotron X-ray absorption techniques (EXAFS and XANES) suggest that a limited number of minerals bind U(VI), and the mechanisms and minerals involved are U(VI) concentration dependent. Data indicate that U(VI) binding is initiated by adsorption, largely to the hematite, but precipitation dominates as U(VI) concentration increases. This in turn suggests that irreversibility in the U(VI) binding is driven by precipitate re-crystallization rather than intra-particulate diffusion into adsorbing minerals. Moreover, the results of this work suggest that MBRR may well be useful in the environmental remediation of U(VI) contaminated soils and waters.
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    Movement of a tritium plume in shallow groundwater at a legacy low level radioactive waste disposal site in eastern Australia
    (Elsevier, 2011-10-01) Hughes, CE; Cendón, DI; Harrison, JJ; Hankin, SI; Johansen, MP; Payne, TE; Vine, M; Collins, RN; Hoffmann, EL; Loosz, T
    Between 1960 and 1968 low-level radioactive waste was buried in a series of shallow trenches near theLucas Heights facility, south of Sydney, Australia. Groundwater monitoring carried out since the mid1970s indicates that with the exception of tritium, no radioactivity above typical background levels hasbeen detected outside the immediate vicinity of the trenches. The maximum tritium level detected ingroundwater was 390 kBq/L and the median value was 5400 Bq/L, decay corrected to the time ofdisposal. Since 1968, a plume of tritiated water has migrated from the disposal trenches and extends atleast 100 m from the source area. Tritium in rainfall is negligible, however leachate from an adjacentlandfill represents a significant additional tritium source. Study data indicate variation in concentrationlevels and plume distribution in response to wet and dry climatic periods and have been used todetermine pathways for tritium migration through the subsurface.Crown Copyright © 2010 Published by Elsevier Ltd