Browsing by Author "Comarmond, MJ"

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    Applicability of surface area normalised distribution coefficients (Ka) for uranium sorption
    (Elsevier, 2011-10-01) Payne, TE; Vinzenz, B; Nebelung, C; Comarmond, MJ
    Adsorption of radionuclides on soils and sediments is commonly quantified by distribution coefficients (Kd values). This paper examines the relationship between Kd values for uranium(VI) adsorption and the specific surface area (SSA) of geologic materials. We then investigate the potential applicability of normalising uranium (U) Kd measurements using the SSA, to produce ‘Ka values’ as a generic expression of the affinity of U for the surface. The data for U provide a reasonably coherent set of Ka values on various solid phases, both with and without ligands. The Ka representation provides a way of harmonising datasets obtained for materials having different specific surface areas, and accounting for the effects of ligands in different systems. In addition, this representation may assist in developing U sorption models for complex materials. However, a significant limitation of the Ka concept is that sorption of radionuclides at trace levels can be dominated by interactions with specific surface sites, whose abundances are not reflected by the SSA. Therefore, calculated Ka values should be interpreted cautiously. © 2011, Elsevier
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    Applicability of surface area normalised distribution coefficients (Ka) in interpreting measurements of radionuclide sorption
    (South Pacific Radioactivity Association, 2008-11-26) Payne, TE; Brendler, V; Comarmond, MJ
    The mobility of radionuclides in the environment is a key issue in assessing the future performance of nuclear waste repositories and modelling the movement of radionuclides in contaminated sites. There have been numerous experimental studies of the adsorption of radionuclides, however, it remains difficult to model the uptake of radionuclides by soils and other complex multi-component geologic materials. Although it would be desirable to utilise mechanistic sorption models (such as surface complexation models) in environmental radionuclide transport modelling, these require a large amount of experimental data and involve considerable mathematical complexity. Therefore, they are not yet available for predictive modelling of complex systems. As a result, predictions of the mobility of radionuclides in the environment generally rely on descriptive measured parameters, such as the solid-liquid distribution coefficient (Kd value) for which various compilations of data values are available (e.g. Sheppard and Thibault, 1990). In order to better understand the mobility of radionuclides in the environment, it has been proposed to utilise a surface area normalised distribution coefficient (Ka value) in which the Kd values are normalised by the measured sample surface area (Pabalan et al., 1998). The concept is developed in this paper by analysing radionuclide sorption measurements from several data sets, including experimental data for well characterised geological materials that were obtained from candidate low-level nuclear repository sites in Australia. In addition, several data-sets summarised in the extensive RES3T database (Brendler et al., 2003) are also utilised in determining whether the K, would be an applicable tool to constrain the ranges of sorption values expected for natural materials in the environment. Finally, we discuss the conditions under which the K, value provides useful insights into radionuclide mobility and possible limitations in its applicability.
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    Assessment of surface area normalisation for interpreting distribution coefficients (Kd) for uranium sorption
    (Elsevier B. V., 2011-10) Payne, TE; Brendler, V; Comarmond, MJ; Nebelung, C
    Adsorption of radionuclides on soils and sediments is commonly quantified by distribution coefficients (Kd values). This paper examines the relationship between Kd values for uranium(VI) adsorption and the specific surface area (SSA) of geologic materials. We then investigate the potential applicability of normalising uranium (U) Kd measurements using the SSA, to produce ‘Ka values’ as a generic expression of the affinity of U for the surface. The data for U provide a reasonably coherent set of Ka values on various solid phases, both with and without ligands. The Ka representation provides a way of harmonising datasets obtained for materials having different specific surface areas, and accounting for the effects of ligands in different systems. In addition, this representation may assist in developing U sorption models for complex materials. However, a significant limitation of the Ka concept is that sorption of radionuclides at trace levels can be dominated by interactions with specific surface sites, whose abundances are not reflected by the SSA. Therefore, calculated Ka values should be interpreted cautiously. © 2010 Elsevier Ltd.
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    Biogeochemical mobility of contaminants from a replica radioactive waste trench in response to rainfall-induced redox oscillations
    (American Chemical Society, 2021-06-10) Kinsela, AS; Bligh, MW; Vázquez-Campos, X; Sun, Y; Wilkins, MR; Comarmond, MJ; Rowling, B; Payne, TE; Waite, TD
    Results of investigations into factors influencing contaminant mobility in a replica trench located adjacent to a legacy radioactive waste site are presented in this study. The trench was filled with nonhazardous iron- and organic matter (OM)-rich components, as well as three contaminant analogues strontium, cesium, and neodymium to examine contaminant behavior. Imposed redox/water-level oscillations, where oxygen-laden rainwater was added to the anoxic trench, resulted in marked biogeochemical changes including the removal of aqueous Fe(II) and circulation of dissolved carbon, along with shifts to microbial communities involved in cycling iron (Gallionella,Sideroxydans) and methane generation (Methylomonas,Methylococcaceae). Contaminant mobility depended upon element speciation and rainfall event intensity. Strontium remained mobile, being readily translocated under hydrological perturbations. Strong ion-exchange reactions and structural incorporation into double-layer clay minerals were likely responsible for greater retention of Cs, which, along with Sr, was unaffected by redox oscillations. Neodymium was initially immobilized within the anoxic trenches, due to either secondary mineral (phosphate) precipitation or via the chemisorption of organic- and carbonate-Nd complexes onto variably charged solid phases. Oxic rainwater intrusions altered Nd mobility via competing effects. Oxidation of Fe(II) led to partial retention of Nd within highly sorbing Fe(III)/OM phases, whereas pH decreases associated with rainwater influxes resulted in a release of adsorbed Nd to solution with both pH and OM presumed to be the key factors controlling Nd attenuation. Collectively, the behavior of simulated contaminants within this replica trench provided unique insights into trench water biogeochemistry and contaminant cycling in a redox oscillatory environment. © 2024 American Chemical Society.
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    Contaminant 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, TD
    Numerous 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.
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    Correction: Emerging investigator series: a holistic approach to multicomponent EXAFS: Sr and Cs complexation in clayey soils
    (Royal Society of Chemistry, 2021-07-13) Bots, P; Comarmond, MJ; Payne, TE; Gückel, K; Lunn, RJ; Rizzo, L; Schellenger, AEP; Renshaw, JC
    Correction for ‘Emerging investigator series: a holistic approach to multicomponent EXAFS: Sr and Cs complexation in clayey soils’ by Pieter Bots et al., Environ. Sci.: Processes Impacts, 2021, DOI: 10.1039/D1EM00121C. - Open Access CC-BY
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    Effects of pH, competing ions and aging on arsenic(V) sorption and isotopic exchange in contaminated soils
    (Elsevier, 2019-06) Rahman, MS; Clark, MW; Yee, LH; Comarmond, MJ; Payne, TE; Burton, ED
    Cattle tick control in Australia using arsenicals from early 1900s to 1955 has led to the existence of some 1600 contaminated sites in northern New South Wales alone. Sorption processes play key roles in controlling arsenic (As) accessibility and subsequent mobility in these dip soils. As(V) sorption and accessibility in three As-contaminated soils and two uncontaminated soil types (ferralitic and sandy soils) are investigated utilizing batch sorption experiments and isotopic exchange techniques. The aged contaminated soils displayed little or no ability to sorb additional As(V), and increasing the soil pH caused a substantial reduction in As(V)-sorption and resulting in As(V)-release. Isotope exchange experiments further supported that any further exposure of the aged-contaminated-soils to additional As(V) increased As-mobilization potential. Amendments of phosphate greatly decreased As(V) sorption in aged-contaminated-soils where As-sorption sites were more highly saturated, whereas phosphate had little effect on As(V) sorption in pristine soils. Similarly, sulfate reduced As(V) sorption, but these effects were less marked than those for phosphate, hence, the application of both PO43− and SO42− in As(V)-contaminated-soils may lead to potential As(V)- mobilization. Conversely, Ca2+ increases As(V)-sorption, which is consistent with expected changes in the surface charge characteristics from Ca2+ sorption, and/or Ca-AsO4 precipitations, consequently Ca2+ amendments may improve As-retention, thereby decreasing As accessibility from cattle dip soils. Therefore, the detailed knowledge presented here provides new insights that may be useful for the assessment and management of the As-contaminated soils. © 2019 Elsevier Ltd.
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    Electroacoustic isoelectric point determinations of bauxite refinery residues: different neutralisation techniques and minor mineral effects
    (American Chemical Society, 2012-08-14) Freire, TSS; Clark, MW; Comarmond, MJ; Payne, TE; Reichelt-Brushett, AJ; Thorogood, GJ
    5Bauxite refinery residue (BRR) is a highly caustic, iron hydroxide-rich byproduct from alumina production. Some chemical treatments of BRR reduce soluble alkalinity and lower residue pH (to values <10) and generate a modified BRR (MBRR). MBRR has excellent acid neutralizing (ANC) and trace-metal adsorption capacities, making it particularly useful in environmental remediation. However, soluble ANC makes standard acid-base isoelectric point (IEP) determination difficult. Consequently, the IEP of a BRR and five MBRR derivatives (sulfuric acid-, carbon dioxide-, seawater-, a hybrid neutralization, i.e, partial CO2 neutralization followed by seawater, and an activated-seawater-neutralized MBRR) were determined using electroacoustic techniques. Residues showed three significantly different groups of IEPs (p < 0.05) based around the neutralization used. Where the primary mineral assemblage is effectively unchanged, the IEPs were not significantly different from BRR (pH 6.6-6.9), However, neutralizations generating neoformational minerals (alkalinity precipitation) significantly increased the IEP to pH 8.1, whereas activation (a removal of some primary mineralogy) significantly lowered the IEP to pH 6.2. Moreover, surface charging curves show that surfaces remain in the +/-30 mV surface charge instability range, which provides an explanation as to why MBRRs remove trace metals and oxyanions over a broad pH range, often simultaneously. Importantly, this work shows that minor mineral components in complex mineral systems may have a disproportionate effect on the observable bulk IEP. Furthermore, this work shows the appropriateness of electroacoustic techniques in investigating samples with significant soluble mineral components (e.g., ANC). © 2012, American Chemical Society.
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    Emerging investigator series: a holistic approach to multicomponent EXAFS: Sr and Cs complexation in clayey soils
    (Royal Society of Chemistry, 2021-06-21) Bots, P; Comarmond, MJ; Payne, TE; Gückel, K; Lunn, RJ; Rizzo, L; Schellenger, AEP; Renshaw, JC
    Strontium and caesium are fission products of concern at many nuclear legacy sites and Cs is additionally a significant consideration at sites in the aftermath of nuclear accidents and incidents. Such sites require long-term management to minimize the risk of such contaminants to the environment and the public. Understanding the geochemical speciation of Sr and Cs in situ in the soils and groundwater is essential to develop engineered management strategies. Here we developed and utilized a comprehensive approach to fitting the EXAFS of Sr and Cs adsorption to single mineral phases and a composite clayey soil. First, a shell-by-shell fitting strategy enabled us to determine that Sr surface complexes involve the formation of bidentate edge sharing complexes with anatase and illite-smectite, and form at the silicon vacancy sites at the kaolinite basal surfaces. Cs surface complexes form at the silicon vacancy sites at the illite-smectite and kaolinite basal surfaces. Second, using a subsequent holistic approach we determined the predominance of these complexes within a composite clayey soil. Sr was dominated by complexation with illite-smectite (72–76%) and to a lesser extent with kaolinite (25–30%) with negligible complexation with anatase, while Cs complexed roughly equally to both illite-smectite and kaolinite. The presented approach to fitting EXAFS spectra will strengthen predictive modelling on the behaviour of elements of interest. For example, the details on Sr and Cs speciation will enable predictive modelling to characterise their long-term behaviour and the design and validation of evidence-based engineering options for long-term management of nuclear legacy sites. © Royal Society of Chemistry 2024 - Open Access CC-BY
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    Environmental mobility of cobalt-influence of solid phase characteristics and groundwater chemistry.
    (Elsevier Ltd, 2008-05) Payne, TE; Itakura, T; Comarmond, MJ; Harrison, JJ
    The adsorption of cobalt on samples from a potential waste repository site in an arid region was investigated in batch experiments, as a function of various solution phase parameters including the pH and ionic strength. The samples were characterized using a range of techniques, including BET surface area measurements, total clay content and quantitative X-ray diffraction. The statistical relationships between the measured cobalt distribution coefficients (Kd values) and the solid and liquid phase characteristics were assessed. The sorption of cobalt increased with the pH of the aqueous phase. In experiments with a fixed pH value, the measured Kd values were strongly correlated to the BET surface area, but not to the amount of individual clay minerals (illite, kaolinite or smectite). A further set of sorption experiments was undertaken with two samples of distinctive mineralogy and surface area, and consequently different sorption properties. A simple surface complexation model (SCM) that conceptualized the surface sites as having equivalent sorption properties to amorphous Fe-oxide was moderately successful in explaining the pH dependence of the sorption data on these samples. Two different methods of quantifying the input parameters for the SCM were assessed. While a full SCM for cobalt sorption on these complex environmental substrates is not yet possible, the basic applicability and predictive capability of this type of modeling is demonstrated. A principal requirement to further develop the modeling approach is adequate models for cobalt sorption on component mineral phases of complex environmental sorbents. © 2009, Elsevier Ltd.
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    An EXAFS study on Sr and Cs speciation in clayey soils at nuclear legacy sites
    (Geochemical Society, 2020-06-21) Bots, P; Lunn, RJ; Comarmond, MJ; Payne, TE; Renshaw, JC
    Through more than 60 years of nuclear power generation, and a longer history of nuclear research, many legacy waste sites with stored radioactive wastes exist throughout the world. Such legacy sites include Savannah River (NC, USA), Sellafield (Cumbria, UK) and the Little Forest Legacy Site (NSW, Australia). The location of such sites was often chosen based on the local geology and soil composition. For example, the Little Forest Legacy Site was chosen based on the clayey nature of the soils and rocks present (~50 % kaolinite and illite-smectite), limiting water movement and migration of radioactive contaminants. However, despite the clay-rich environment, radioactive contaminants (including fission products and actinides) have been detected in sediments, groundwater, surface runoff and vegetation at the Little Forest Legacy Site.4,5 In order to ensure continued safe management of the site, as well as to develop new engineering stategies for radwaste containment and / or cleanup, an improved understanding of the geochemistry of radioactive contaminants is required. For this presentation we focused on the geochemical speciation of Sr and Cs in contact with clay minerals and a composite clayey soil. We performed a comprehensive set of adsorption experiments and XAS analyses. Subsequently, in order to obtain detailed information we utilized two EXAFS fitting strategies. The first, a semi-shell-by-shell strategy of the EXAFS, was used to determine the Sr and Cs surface complexes on the clay minerals. The second (based on the identified surface complexes) provided details on the complexation / distribution of Sr and Cs within a clayey soil.
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    Geochemical evidence for the application of nanoparticulate colloidal silica gel for in situ containment of legacy nuclear wastes
    (Royal Rociety of Chemistry (RSC), 2020-03-30) Lunn, RJ; Bots, P; Renshaw, JC; Payne, TE; Comarmond, MJ; Schellenger, AEP; Pedrotti, M; Calì, E
    Colloidal silica is a nanoparticulate material that could have a transformative effect on environmental risk management at nuclear legacy sites through their use in in situ installation of injectable hydraulic barriers. In order to utilize such nanoparticulate material as a barrier, we require detailed understanding of its impact on the geochemistry of radionuclides in the environment (e.g. fission products such as Sr and Cs). Here we show, through combining leaching experiments with XAS analyses, that colloidal silica induces several competing effects on the mobility of Sr and Cs. First, cations within the colloidal silica gel compete with Sr and Cs for surface complexation sites. Second, an increased number of surface complexation sites is provided by the silica nanoparticles and finally, the elevated pH within the colloidal silica increases the surface complexation to clay minerals and the silica nanoparticles. XAS analyses show that Sr and Cs complex predominantly with the clay mineral phases in the soil through inner-sphere surface complexes (Sr) and through complexation on the clay basal surfaces at Si vacancy sites (Cs). For binary soil – colloidal silica gel systems, a fraction of the Sr and Cs complexes with the amorphous silica-like surfaces through the formation of outer-sphere surface complexes. Importantly, the net effect of nanoparticulate colloidal silica gel is to increase the retention of Sr and Cs, when compared to untreated soil and waste materials. Our research opens the door to applications of colloidal silica gel to form barriers within risk management strategies at legacy nuclear sites. © Royal Society of Chemistry 2024.
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    A holistic approach to multicomponent EXAFS: Sr complexation in clayey soil
    (Geological Society of America, 2021-10-10) Bots, P; Comarmond, MJ; Payne, TE; Lunn, RJ; Schellenger, AEP; Renshaw, JC
    Strontium is a fission product of concern at many nuclear legacy sites, which require assessment and possibly engineered long-term management to minimize the risk of radionuclides to the environment and the public. One such site is the Little Forest Legacy Site (LFLS) in New South Wales, Australia. In the 60s low-level radioactive wastes were disposed at LFLS in unlined trenches. The location of LFLS was selected based on the clayey nature of the soils and rocks present (~50 % kaolinite and illite-smectite), limiting water movement and migration of radioactive contaminants [1,2]. Despite the clay-rich environment, radioactive contaminants (including fission products and actinides) have been detected in sediments, groundwater, surface runoff and vegetation at the Little Forest Legacy Site [2,3]. Understanding the geochemical speciation of radionuclides in the soils and groundwater at LFLS is essential to develop evidence-based engineered management strategies. In this study we investigated the geochemical speciation of Sr in clayey soils by performing a comprehensive set of adsorption experiments (on single minerals and a clayey soil) and subsequent X-ray absorption spectroscopy analyses. Furthermore, in order to fully benefit from such experimental and analytical methodologies, we developed and utilized a comprehensive dual/holistic approach to fitting multicomponent EXAFS. First, a shell-by-shell fitting strategy enabled us to determine Sr complexation with anatase and illite-smectite through bidentate edge sharing complexes and with kaolinite at the silicon vacancy sites on the basal surface [4]. Subsequently, we utilized a holistic approach to determine predominance of each of these complexes within a composite clayey soil to inform that Sr complexation with kaolinite (25-30%) and illite-smectite (72-76%) governs Sr speciation in clayey soils [4]. The presented surface complexation and dual/holistic approach to fitting EXAFS spectra will strengthen predictive modelling on the behaviour of elements of interest. © Copyright 2021 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes.
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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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    Installation of a pilot experimental trench at the Little Forest legacy site
    (Australian Nuclear Science and Technology Organisation, 2018-07-30) Payne, TE; Kinsela, AS; Rowling, B; Hankin, SI; Cendón, DI; Comarmond, MJ; Bligh, MW; Hughes, CE; Anderson, D; Wilsher, KL
    During 2017, a pilot experimental trench was constructed at the Little Forest Legacy Site (LFLS). The objective of installing this trench was to facilitate experimental field-work aimed at further characterising the site, in particular the hydrology of the excavated trenches and of the near-surface layers in which the trenches are located. The test trench is of similar depth to the waste disposal trenches at the legacy site (3 metres) and extends 6 m in length. However, unlike the disposal trenches, the experimental trench contains no waste materials of any kind. Instead, the trench contains a number of sampling points and other instrumentation, and is back filled with river gravel to provide a uniform composition and maintain structural stability. It is intended that the pilot trench will be followed by other trenches with specific experimental objectives. The purposes of this report are to discuss the background, rationale for, and implementation of the facility; to provide a detailed description of the pilot trench; and to compile information and photographs documenting the excavation process. Although some preliminary hydrological data and comparisons with the legacy trenches are presented, the scientific data will be fully discussed and interpreted in future scientific reports.
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    Installation of an experimental trench at the Little Forest Legacy Site
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Payne, TE; Kinsela, AS; Bligh, M; Anderson, D; Rowling, B; Hughes, CE; Hankin, SI; Cendón, DI; Wilsher, KL; Comarmond, MJ
    During 2017, a pilot experimental trench was constructed at the Little Forest Legacy Site (LFLS), a 1960s era disposal site for low-level radioactive waste. The objective of installing this trench was to facilitate experimental field-work aimed at further characterising the site, in particular the hydrology of the excavated trenches and of the near-surface layers in which the trenches are located. The test trench is of similar depth to the waste disposal trenches at the legacy site (8 metres) and extends 6 m in length. However, unlike the disposal trenches, the experimental trench does not contain waste materials. instead, the trench contains a number of sampling points and other instrumentation, and is back filled with river gravel to provide a uniform composition and maintain structural stability. in this paper, the excavation of the trench is described, together with observations made during the excavation. in addition, some preliminary hydrological data and comparisons with the legacy trenches are presented.
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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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    The kinetics of chlorite dissolution
    (Elsevier, 2007-03-15) Lowson, RT; Brown, PL; Comarmond, MJ; Rajaratnam, G
    A model for the dissolution of chlorite has been developed based on fast ligand assisted proton attack of the alumina tetrahedra within the alumina-silica lattice followed by slower dissolution of the remnant silica lattice. While the rate determining step is within the silica dissolution regime, the rate is a function of the H+ and Al3+ concentrations and the dominant aqueous Al species. Individual rates may be described by a generic rate equation applicable across the spectrum of Al species: where rn is the rate subscripted for the nth Al species, k is the rate constant of the rate controlling step, K is the surface exchange constant, β is the solution stability constant subscripted for the Al species, a is the species activity subscripted for species and raised to the power of the stoichiometry, p and q are stoichiometric coefficients, z is the ligand charge and τ is the fractional coefficient for the precursor of the rate defining step. The observed rate is the sum of the individual rates. When the observed rate is in a domain of dominance for a single aluminium species and in the absence of strong complexing agents such as oxalate, the observed rate is proportional to (a3H+/aAl3+)τn. The model is supported by experimental data for the dissolution of chlorite over a pH range of 3–10 and temperature range 25–95°C. The results have hydrometallurgical application. © 2007, Elsevier Ltd.
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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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    Little Forest legacy site - technical report : dose rate estimates to humans and wildlife for a range of potential future scenarios
    (Australian Nuclear Science and Technology Organisation, 2020-03-10) Johansen, MP; Payne, TE; Comarmond, MJ; Harrison, JJ; Blackley, R; Kabir, A
    Purpose The objective of this report is to describe the human and wildlife dose-modelling used to compare various potential management options for the Little Forest Legacy Site (LFLS). Scope This work aligns with international standards and guidance which are primarily set forth in a series of documents published by the International Atomic Energy Agency (IAEA), Vienna (IAEA, 2011, 2012, 2014). The process envisioned by the IAEA was developed primarily for planned disposal facilities, but is also applicable to existing sites such as the LFLS: • SSG-23 (P.90, 6.86) “The approach to support the decision-making process . . . is also directly applicable to existing facilities (IAEA, 2011, 2012, 2014).” The IAEA documents address a scope that includes the Safety Case and Safety Assessment. This report focuses specifically on a human dose assessment for the post-closure period (assumed 100-year Institutional Control Period and through to 1000 years into the future). The dose work compares modelled radiological dose rates to hypothetical human receptors under a range of future management options and conditions at the LFLS. Five types of management options and multiple receptor types were evaluated. The approach used here is site-specific as it uses measurements of site samples, data from site documents, local meteorological and hydrological data as well as local site configuration and layout. The document also includes a wildlife dose assessment consistent with international best practice and, for Australia, the Radiation Protection of the Environment Guide (ARPANSA, 2015). The model results reported here address many different scenarios which, while not covering every possibility, are intended to provide a sufficient range of useful input data into selection of a sound management plan for the future of the LFLS. Following selection of an option a more detailed dose assessment should be performed to optimise the design. This dose assessment was conducted within, and relies on data from, a multi-year project that assessed the waste characteristics and environmental setting of the LFLS as described in a series of reports and papers (Johansen et. al., 2020).