Browsing by Author "Schellenger, AEP"

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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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    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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    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.