Browsing by Author "Waite, TD"
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- ItemApplications 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, TDTime-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
- ItemAssessment 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, TDNot available
- ItemCharacterisation of natural substrates with regard to application of surface complexation models(OECD, 2001) Waite, TD; Fenton, BR; Payne, TE; Lumpkin, GR; Davis, JA; McBeath, MWhile good correspondence between laboratory sorption data and surface complexation modelling results has been obtained for single oxide phase, much poorer correspondence has been obtained for natural substrates. This result arises, at least in part, from the difficulty in ascertaining the identity of sorbing surfaces and in assigning appropriate values for sorbing surface site concentrations. In an attempt to clarify the nature of possible sorbing phases, we have used a variety of techniques to investigate the surfaces of natural solid substrates from the Koongarra weathered zone. Based on insights gained from the surface characterisation studies, we have then proceeded to assess the applicability of various surface complexation modelling approaches as applied to U(VI) uptake. © 2001 OECD
- ItemContaminant release, mixing and microbial fluctuations initiated by infiltrating water within a replica field-scale legacy radioactive waste trench(Elsevier B. V., 2022-12-10) Kinsela, AS; Payne, TE; Bligh, MW; Vázquez-Campos, X; Wilkins, MR; Comarmond, MJ; Rowling, B; Waite, TDNumerous legacy near-surface radioactive waste sites dating from the mid 20th century have yet to be remediated and present a global contamination concern. Typically, there is insufficient understanding of contaminant release and redistribution, with invasive investigations often impractical due to the risk of disturbing the often significantly radiotoxic contaminants. Consequently, a replica waste trench (~5.4 m3), constructed adjacent to a legacy radioactive waste site (Little Forest Legacy Site, LFLS), was used to assist our understanding of the release and mixing processes of neodymium (Nd) — a chemical analogue for plutonium(III) and americium(III), two significant radionuclides in many contaminated environments. In order to clarify the behaviour of contaminants released from buried objects such as waste containers, a steel drum, representative of the hundreds of buried drums within the LFLS, was placed within the trench. Dissolved neodymium nitrate was introduced as a point-source contaminant to the base of the trench, outside the steel drum. Hydrologic conditions were manipulated to simulate natural rainfall intensities with dissolved lithium bromide added as a tracer. Neodymium was primarily retained both at its point of release at the bottom of the trench (>97 %) as well as at a steel container corrosion point, simulated through the emplacement of steel wool. However, over the 8-month field experiment, advective mixing initiated by surface water intrusions rapidly redistributed a small proportion of Nd to shallower waters (~1.5–1.7 %), as well as throughout the buried steel drum. Suspended particulate forms of Nd (>0.2 μm) were measured at all depths in the suboxic trench and were persistent across the entire study. Analyses of the microbial communities showed that their relative abundances and metabolic functions were strongly influenced by the prevailing geochemical conditions as a result of fluctuating water depths associated with rainfall events. The site representing steel corrosion exhibited divergent biogeochemical results with anomalous changes (sharp decrease) observed in both dissolved contaminant concentration as well as microbial diversity and functionality. This research demonstrates that experimental trenches provide a safe and unique method for simulating the behaviour of subsurface radioactive contaminants with results demonstrating the initial retention, partial shallow water redistribution, and stability of particulate form(s) of this radioactive analogue. These results have relevance for appropriate management and remediation strategies for the adjacent legacy site as well as for similar sites across the globe. © 2022 Elsevier B.V.
- ItemEffect 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, TDIt 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
- ItemFerric 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, TDDefinitive 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.
- ItemFinal report for AWRAC project 85/05 on iron and maganese removal from water supplies(Australian Nuclear Science and Technology Organisation, 1990-12) Waite, TDThe objective of this research project is the examination of the major factors governing the efficiency of removal or iron and manganese from water supplies. This objective has been met through a multi-faceted study involving the following major components: review of problems created by iron and manganese in Australian water supplies with particular reference to selected water sources; review of methods used for removal of iron and manganese from water supplies; and detailed laboratory studies of the critical processes of Fe(II) and Ma(II) oxidation, iron and manganese oxide aggregation (coagulation/flocculation) and particle removal by filtration. The process studies indicated above have been undertaken under both simple, idealised conditions (i.e. using well characterised particulate oxides and relatively simple solution conditions) and under conditions more typical of a water treatment plant. The latter studies have been undertaken for the most part using the waters of Mardi Dam in the New South Wales shire of Wyong. In this report, the reviews of problems caused by iron and manganese and the methods available for the removal of these elements from water supplies are documented in the main body of the report. Particularly extensive studies have been undertaken of the aggregation of colloidal oxides and methods used and results of studies undertaken under relatively simple, well defined conditions are given in Appendix 1.
- ItemInfluence 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, IA 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.
- ItemInfluence 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, TDIncreasing 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
- ItemInhibitory 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, TDIt 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.
- ItemIs 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, TDThe 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.
- ItemIsotopically exchangeable A1 in coastal lowland acid sulfate soils(Elsevier, 2016-01-15) Yvanes-Giuliani, YAM; Fink, D; Rose, J; Waite, TD; Collins, RNPeriodic 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.
- ItemKinetics 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, TDAntimony 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
- ItemLigand effects on uranyl sorption - key processes and models(South Pacific Radioactivity Association, 2010-09-01) Payne, TE; Comarmond, MJ; Collins, RN; Waite, TDThe 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.
- ItemManipulation of planar oxygen defect arrangements in multifunctional magnèli titanium oxide hybrid systems: from energy conversion to water treatment(Royal Society of Chemistry, 2020-10-28) Liu, YC; Yang, J; Liu, Y; Zheng, J; Lee, W; Shi, JJ; Horlyck, J; Xie, JZ; Tay, YY; Tan, TT; Yu, DH; Mole, RA; McIntyre, GJ; Zhang, CY; Toe, CY; Waite, TD; Scott, J; Wang, Y; Wu, T; Han, SH; Li, SAn extremely close relationship exists between energy usage and water supply with a tremendous amount of energy being consumed to process water for drinking and other purposes. The current energy crisis and inefficient water management place enormous stress on the sustainability of our society and environment. As such, the development of high-efficiency, cost-effective, and environmentally friendly materials which possess co-existing functionalities for applications ranging from energy capture to water treatment in one material, provides an opportunity to achieve sustainable development. As multifunctional materials, the layer-structured Magnèli titanium oxides with stoichiometry of TinO2n−1 (n ≥ 2) have been extensively studied in view of their potential for photocatalytic, thermoelectric and photothermal applications over the past few years. This group of materials occurs naturally as layered structures with planar oxygen defects, however, understanding of the correlation between the planar arrangements of the oxygen defects and various energy-related properties remains limited. Here, we demonstrate how the formation of layer structured TinO2n−1 with various planar oxygen defect arrangements correlates with the changes of their physical and chemical properties. The experimental results from inelastic neutron scattering analysis and electrical characterizations provide evidence that the planar oxygen defects are responsible for phonon scattering and exert a strong influence on their electrical conductivities. Manipulating these planar defects allows interconversion between different phases, which changes the interplay between electronic and phononic sub-systems. These manipulations potentially enable optimization of the corresponding physical properties of these materials such that they are rendered suitable for applications that require co-operative multifunctionality. More specifically, the experimental results demonstrate that the valence band positions and the onset potentials in the materials are raised, further enhancing their ability for catalysis of electrochemical reactions. This work also demonstrates the combinational effects of the thermoelectric and photothermal properties of these materials on their photocatalytic and electrochemical performance thereby providing a novel means of controlling the multi-response functionality of these materials for a variety of applications in different environments. © The Royal Society of Chemistry 2020
- ItemMovement 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, TDBetween 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.
- ItemPreferential association of adsorbed uranium with mineral surfaces: a study using analytical electron microscopy(Cambridge University Press/Springer Nature Limited, 1999-08-01) Lumpkin, GR; Payne, TE; Fenton, BR; Waite, TDAnalytical electron microscopy (AEM) has been employed to characterize the distribution of U(VI) on several mineral substrates, including standard kaolinite samples and weathered rock samples from Koongarra, Australia. Results of this study reveal that pre-existing impurity phases play a significant role in the uptake of U(VI) on standard kaolinite samples. Using a natural sample from the weathered zone of the Koongarra uranium deposit, we have also demonstrated that U(VI) sorption is controlled by iron oxyhydroxides (predominantly goethite) which constitute a small fraction of the sample. Limited sorption of U(VI) was observed on the clay minerals of this substrate. Uptake of U(VI) by goethite increases with total uranium content up to the point of uranium precipitation, after which it decreases dramatically. Uranium precipitation is indicated by the appearance of a uranyl oxyhydroxide phase. © 1999 Materials Research Society
- ItemReduction of U (VI) by Fe (II) during the Fe (II) - accelerated transformation of ferrihydrite(American Chemical Society, 2014-08-19) Boland, DD; Collins, RN; Glover, CJ; Payne, TE; Waite, TDX-ray absorption spectroscopy has been used to study the reduction of adsorbed U(VI) during the Fe(II)-accelerated transformation of ferrihydrite to goethite. The fate of U(VI) was examined across a variety of pH values and Fe(II) concentrations, with results suggesting that, in all cases, it was reduced over the course of the Fe(III) phase transformation to a U(V) species incorporated in goethite. A positive correlation between U(VI) reduction and ferrihydrite transformation rate constants implies that U(VI) reduction was driven by the production of goethite under the conditions used in these studies. This interpretation was supported by additional experimental evidence that demonstrated the (fast) reduction of U(VI) to U(V) by Fe(II) in the presence of goethite only. Theoretical redox potential calculations clearly indicate that the reduction of U(VI) by Fe(II) in the presence of goethite is thermodynamically favorable. In contrast, reduction of U(VI) by Fe(II) in the presence of ferrihydrite is largely thermodynamically unfavorable within the range of conditions examined in this study. © 2014, American Chemical Society.
- ItemRemoval of water impurities by hydrous oxides(Institution of Engineers, Australia, Institution of Chemical Engineers & Royal Australian Chemical Institute, 1991-09-19) Amal, R; Raper, JA; Waite, TDIn this study, the effects of adsorbed fulvic acid, a naturally occurring organic acid, on the kinetics of hematite aggregation and on the resulting structure of hematite aggregates are investigated. A model based on colloid stability theory which also accounts for the structure of the aggregates formed is used to describe the aggregation kinetics of these adsorbed particles. The study of aggregate structure shows that the fractal dimensions of hematite aggregates which are partially acid molecules are higher than those obtained with no adsorbed fulvic acid The scattering exponents obtained from static light scattering experiments of these aggregates range from 2.83 +- to 3.42 +- 0.1.
- ItemResponse of microbial community function to fluctuating geochemical conditions within a legacy radioactive waste trench environment(American Society for Microbiology, 2017-08-17) Vázquez-Campos, X; Kinsela, AS; Bligh, MW; Harrison, JJ; Payne, TE; Waite, TDDuring the 1960s, small quantities of radioactive materials were codisposed with chemical waste at the Little Forest Legacy Site (Sydney, Australia) in 3-meter-deep, unlined trenches. Chemical and microbial analyses, including functional and taxonomic information derived from shotgun metagenomics, were collected across a 6-week period immediately after a prolonged rainfall event to assess the impact of changing water levels upon the microbial ecology and contaminant mobility. Collectively, results demonstrated that oxygen-laden rainwater rapidly altered the redox balance in the trench water, strongly impacting microbial functioning as well as the radiochemistry. Two contaminants of concern, plutonium and americium, were shown to transition from solid-iron-associated species immediately after the initial rainwater pulse to progressively more soluble moieties as reducing conditions were enhanced. Functional metagenomics revealed the potentially important role that the taxonomically diverse microbial community played in this transition. In particular, aerobes dominated in the first day, followed by an increase of facultative anaerobes/denitrifiers at day 4. Toward the mid-end of the sampling period, the functional and taxonomic profiles depicted an anaerobic community distinguished by a higher representation of dissimilatory sulfate reduction and methanogenesis pathways. Our results have important implications to similar near-surface environmental systems in which redox cycling occurs. © 2017 Vázquez-Campos et al.