Spectroscopic identification of Ca-bearing uranyl silicates formed in C–S–H systems

DOI: 10.1038/s41598-023-30024-0

Authors: Antonia S. Yorkshire (University of Sheffield) , Martin C. Stennett (University of Sheffield) , Brant Walkley (University of Sheffield) , John L. Provis (University of Sheffield) , Luke T. Townsend (University of Sheffield) , Latham T. Haigh (University of Sheffield) , Neil C. Hyatt (University of Sheffield) , Lucy M. Mottram (University of Sheffield) , Claire L. Corkhill (University of Sheffield)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Scientific Reports , VOL 13

State: Published (Approved)
Published: February 2023
Diamond Proposal Number(s): 17782

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.

Journal Keywords: Nuclear chemistry; Nuclear waste

Subject Areas: Materials, Chemistry, Environment


Instruments: B18-Core EXAFS

Other Facilities: 6BM at National Synchrotron Light Source II

Added On: 06/03/2023 09:12

Documents:
s41598-023-30024-0.pdf

Discipline Tags:

Earth Sciences & Environment Radioactive Materials Chemistry Materials Science Chemical Engineering Engineering & Technology Nuclear Waste Inorganic Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS) X-ray Absorption Near Edge Structure (XANES)