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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	Emerging investigator series: A holistic approach to multicomponent EXAFS: Sr and Cs complexation in clayey soils Pieter Bots , M. Josick Comarmond , Timothy Payne , Katharina Gückel , Rebecca J. Lunn , Luca Rizzo , Alexandra E. P. Schellenger , Joanna Renshaw Environmental Science: Processes & Impacts DOI: 10.1039/D1EM00121C Diamond Proposal Number(s): [17114] Open Access Show Abstract ▼ Abstract: 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.	Jun 2021
B18-Core EXAFS	Geochemical evidence for the application of nanoparticulate colloidal silica gel for in-situ containment of legacy nuclear wastes Pieter Bots , Joanna C. Renshaw , Timothy Payne , M. Josick Comarmond , Alexandra E. P. Schellenger , Matteo Pedrotti , Eleonora Cali' , Rebecca J. Lunn Environmental Science: Nano DOI: 10.1039/D0EN00046A Diamond Proposal Number(s): [17114] Show Abstract ▼ Abstract: 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.	Mar 2020
I18-Microfocus Spectroscopy	Bacterially Produced Calcium Phosphate Nano-Biominerals: Sorption Capacity, Site Preferences and Stability of Captured Radionuclides Stephanie Handley-sidhu , Joe Hriljac , Mark Olaf Cuthbert , Joanna Renshaw , Richard Pattrick , John Charnock , Bjorn Stolpe , Jamie Lead , Stephen Baker , Lynne E. Macaskie Environmental Science & Technology 48 (12) DOI: 10.1021/es500734n Diamond Proposal Number(s): [6647] Open Access Show Abstract ▼ Abstract: A Serratia sp. bacterium manufactures amorphous calcium phosphate nanominerals (BHAP); this material has shown increased sorption capacity for divalent radionuclide capture. When heat-treated (≥450 °C) the cell biomass is removed and the biominerals are transformed to hydroxyapatite (HAP). Using a multimethod approach, we have elucidated both the site preferences and stability of analogue radionuclide incorporation for Sr, Co, Eu, and U. Strontium incorporates within the bulk amorphous inorganic phase of BHAP; however, once temperature modified to crystalline HAP, bonding was consistent with Sr substitution at the Ca(1) and/or Ca(2) sites. Cobalt incorporation occurs within the bulk inorganic amorphous phase of BHAP and within the amorphous grain boundaries of HAP. Europium (an analogue for trivalent actinides) substituted at the Ca(2) and/or the Ca(3) position of tricalcium phosphate, a known component of HAP grain boundaries. Uranium was surface complexed with no secondary minerals detected. With multiple sites for targeted radionuclide incorporation, high loadings, and good stability against remobilization, BHAP is shown to be a potential material for the remediation of aqueous radionuclide in groundwater.	May 2014

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