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.
| Original language | English |
|---|---|
| Article number | 3374 |
| Journal | Scientific Reports |
| Volume | 13 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 28 Feb 2023 |
Bibliographical note
Funding Information:This research was performed in part at the HADES/MIDAS facility at the University of Sheffield established with financial support from the EPSRC and BEIS, under Grant No. EP/T011424/1 and also at the PLEIADES National Nuclear User Facility, established with funding from EPSRC under grant number EP/V035215/1, and the Henry Royce Institute for Advanced Materials Nuclear ICP-MS facility, under grant numbers EP/P02470X/1 and EP/P025285/1. We acknowledge financial support from the Nuclear Decommissioning Authority and the DISTINCTIVE consortium under EPSRC Grant No. EP/L01404/1. CLC would also like to thank the EPSRC for the award of an Early Career Research Fellowship under Grant No. EP/N017374/1. This research used beamline 6BM of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704 for U L-edge XAS data collection, in addition to Diamond Light Source at beamline B18 under proposal No. SP17782. Bruce Ravel, Stephen Parry and Giannantonio Cibin are gratefully acknowledged for their assistance with data collection. Collection of Si MAS-NMR data was performed at the Department of Chemistry, University of Sheffield by Sandra van Meurs and Craig Robertson. Sarah O’Sullivan is gratefully acknowledged for support with data analysis. III 29
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© 2023, The Author(s).