The effect of magnesium on the local structure and initial dissolution rate of simplified UK Magnox waste glasses

Guo, R. and Brigden, C.T. and Gin, S. and Swanton, S.W. and Farnan, I. (2018) The effect of magnesium on the local structure and initial dissolution rate of simplified UK Magnox waste glasses. Journal of Non-Crystalline Solids, 497. pp. 82-92. ISSN 00223093 DOI https://doi.org/10.1016/j.jnoncrysol.2018.03.002

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Official URL: https://doi.org/10.1016/j.jnoncrysol.2018.03.002

Abstract

A series of simplified glasses were prepared to mimic the United Kingdom's Magnox radioactive waste glasses and determine the separate effect of the presence of Mg on the glass structure and the initial dissolution rate. These glasses had an alkaline earth (Ca/Mg) content of 6.5 mol% and relative ratios of Si, B and Na similar to 25 wt% waste loaded Magnox waste glass simulant. Each simplified glass had similar macroscopic properties, differing only in Ca/Mg ratio. 25Mg magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of the simplified Mg endmember (MgEM) glass (with no Ca) and the full-component simulant glass were similar, consistent with the similar Mg local environments in both glasses. 11B MAS NMR spectra of the series of simplified glasses showed a systematic increase in the amount of three-coordinated boron ([3]B) with increasing amounts of Mg. A clear change in the charge balancing of four-coordinated boron ([4]B) by Mg compared with Ca is observed. However, 11B NMR measurements of the leached material showed that the additional [3]B was not preferentially leached from the Mg containing samples. Despite the structural changes in the glass induced by Ca/Mg substitution, initial dissolution rates (r0) remained invariant, within error, with Ca/Mg ratio. This indicates that the poorer aqueous durability of Mg-containing Magnox waste glass measured experimentally in long-term leaching experiments, compared with SON68 glass containing Ca, is not caused by a primary structural effect in the glass.

Item Type: Article
Uncontrolled Keywords: 2018AREP, IA72
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
08 - Green Open Access
Journal or Publication Title: Journal of Non-Crystalline Solids
Volume: 497
Page Range: pp. 82-92
Identification Number: https://doi.org/10.1016/j.jnoncrysol.2018.03.002
Depositing User: Sarah Humbert
Date Deposited: 08 Feb 2019 12:04
Last Modified: 08 Feb 2019 12:04
URI: http://eprints.esc.cam.ac.uk/id/eprint/4420

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