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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	Spectroscopic identification of Ca-bearing uranyl silicates formed in C–S–H systems Antonia S. Yorkshire , Martin C. Stennett , Brant Walkley , John L. Provis , Luke T. Townsend , Latham T. Haigh , Neil C. Hyatt , Lucy M. Mottram , Claire L. Corkhill Scientific Reports 13 DOI: 10.1038/s41598-023-30024-0 Diamond Proposal Number(s): [17782] Open Access Show Abstract ▼ Abstract: Portland cement-based grouts used for radioactive waste immobilisation contain a Ca- and Si-rich binder phase, known as calcium–silicate–hydrate (C–S–H). Depending on the blend of cement used, the Ca/Si ratio can vary considerably. A range of C–S–H minerals with Ca/Si ratios from 0.6 to 1.6 were synthesised and contacted with aqueous U(VI) at 0.5 mM and 10 mM concentrations. Solid-state 29Si MAS-NMR spectroscopy was applied to probe the Si coordination environment in U(VI)-contacted C–S–H minerals and, in conjunction with U LIII-edge X-ray absorption spectroscopy analysis, inferences of the fate of U(VI) in these systems were made. At moderate or high Ca/Si ratios, uranophane-type uranyl silicates or Ca-uranates dominated, while at the lowest Ca/Si ratios, the formation of a Ca-bearing uranyl silicate mineral, similar to haiweeite (Ca[(UO2)2Si5O12(OH)2]·3H2O) or Ca-bearing weeksite (Ca2(UO2)2Si6O15·10H2O) was identified. This study highlights the influence of Ca/Si ratio on uranyl sequestration, of interest in the development of post-closure safety models for U-bearing radioactive waste disposal.	Feb 2023
B18-Core EXAFS	Spectroscopic evaluation of UVI-cement mineral interactions: ettringite and hydrotalcite Antonia S. Yorkshire , Martin C. Stennett , Brant Walkley , Sarah E. O'Sullivan , Lucy M. Mottram , Daniel J. Bailey , John L. Provis , Neil C. Hyatt , Claire L. Corkhill Journal Of Synchrotron Radiation 29 DOI: 10.1107/S1600577521011553 Diamond Proposal Number(s): [17782] Open Access Show Abstract ▼ Abstract: Portland cement based grouts used for radioactive waste immobilization contain high replacement levels of supplementary cementitious materials, including blast-furnace slag and fly ash. The minerals formed upon hydration of these cements may have capacity for binding actinide elements present in radioactive waste. In this work, the minerals ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and hydrotalcite (Mg6Al2(OH)16CO3·4H2O) were selected to investigate the importance of minor cement hydrate phases in sequestering and immobilizing UVI from radioactive waste streams. U LIII-edge X-ray absorption spectroscopy (XAS) was used to probe the UVI coordination environment in contact with these minerals. For the first time, solid-state 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was applied to probe the Al coordination environment in these UVI-contacted minerals and make inferences on the UVI coordination, in conjunction with the X-ray spectroscopy analyses. The U LIII-edge XAS analysis of the UVI-contacted ettringite phases found them to be similar (>∼70%) to the uranyl oxyhydroxides present in a mixed becquerelite/metaschoepite mineral. Fitting of the EXAFS region, in combination with 27Al NMR analysis, indicated that a disordered Ca- or Al-bearing UVI secondary phase also formed. For the UVI-contacted hydrotalcite phases, the XAS and 27Al NMR data were interpreted as being similar to uranyl carbonate, that was likely Mg-containing.	Jan 2022
I11-High Resolution Powder Diffraction	Early age hydration and application of blended magnesium potassium phosphate cements for reduced corrosion of reactive metals Laura J. Gardner , Claire L. Corkhill , Sam A. Walling , James E. Vigor , Claire A. Murray , Chiu C. Tang , John L. Provis , Neil C. Hyatt Cement And Concrete Research 143 DOI: 10.1016/j.cemconres.2021.106375 Diamond Proposal Number(s): [10038] Open Access Show Abstract ▼ Abstract: Magnesium potassium phosphate cements (MKPC) were investigated to determine their efficacy towards retardation of reactive uranium metal corrosion. Optimised low-water content, fly ash (FA) and blast furnace slag (BFS) blended MKPC formulations were developed and their fluidity, hydration behaviour, strength and phase assemblage investigated. In-situ time resolved synchrotron powder X-ray diffraction was used to detail the early age (~60 h) phase assemblage development and hydration kinetics, where the inclusion of BFS was observed to delay the formation of struvite-K by ~14 h compared to FA addition (~2 h). All samples set within this period, suggesting the possible formation of a poorly crystalline binding phase prior to struvite-K crystallisation. Long-term corrosion trials using metallic uranium indicated that MKPC systems are capable of limiting uranium corrosion rates (reduced by half), when compared to a UK nuclear industry grout, which highlights their potential application radioactive waste immobilisation.	May 2021

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