The role of Zn in model nuclear waste glasses studied by XAS

It has been suggested that small additions of zinc increases the durability of oxide glasses of interest for radioactive waste immobilisation. However, the structural environment of Zn in such glasses is not fully understood. To understand the mechanisms by which Zn increases glass durability, a suite of Zn doped model silicate glasses was investigated by Zn K-edge X-ray absorption spectroscopy (XAS) together with a mineral specimen of hemimorphite - Zn4Si2O7(OH)2·H2O and a simulant UK HLW glass. Fitting of XAS data from the mineral standard permitted reliable determination of four-fold co-ordinate Zn in the model and simulant HLW glasses. XAS data show evidence of intermediate range order, in FT χ(k) plots, consistent with Zn-O-Si linkages in all glasses. Thus, Zn is understood to adopt a network intermediate role in model and simulant HLW silicate glasses.