We are pleased to announce a Petrology Lunch with Professor Claire Corkhill, School of Earth Sciences at University of Bristol. The topic will be: Elucidating the role of zinc in borosilicate glass dissolution.

Abstract:

The UK high level waste glass composition – an alkali-aluminoborosilicate – has been modified by Sellafield Ltd to incorporate Ca and Zn, with the purpose of enhancing MoO₄^‑ radionuclide retention in a final product that meets processing requirements. We have undertaken a broad range of studies to elucidate the role of CaO and ZnO on the structure and dissolution kinetics of these glasses, with the latter being important for understanding the long-term behaviour of the glasses in a geological disposal facility. It was found that replacing ZnO for CaO, up to only several mol.%, results in significant changes to both structure and dissolution behaviour in 6-component simplified glasses as well as fully-waste loaded simulant glasses; for example, in the forward rate of dissolution, analysed using the single-pass flow through method, the addition of Zn enhanced durability as a consequence of a more polymerised glass network (as determined by ²⁹Si MAS NMR and XAS analysis). However, in the residual rate, the precipitation of the phyllosilicate clay mineral, sauconite Na_0.3Zn₃(Si,Al)₄O₁₀(OH)₂·4H₂O, drives enhanced dissolution for Zn-rich glass compositions. Most intriguingly, glasses with high replacements of ZnO for CaO exhibit rate resumption behaviour (i.e., glass dissolution increases after a period of stability) after several years. Using µ-XAS techniques we tentatively assign this behaviour to the nucleation of poorly crystalline Zn-containing secondary phases within the gel layer.

For the Zoom link:

Meeting ID: 963 6392 3854

Passcode: 574401