PNNL

Abstract

Leaching of the International Simple Glass (ISG) under a range of pH conditions, from acidic to hyperalkaline, has been examined. Forward rate measurements consistent with some literature data have been obtained over a range of temperatures (23 – 90°C) and pH values (pH(RT) = 4.5 to 11.0) using the dynamic testing SPFT protocol. Rate model parameters for B, Na and Si have been derived for the basic regime; the errors in the rates predicted using these parameters at high pH and temperatures are shown to be significant because the data fit is conducted using logarithmic data. Possible evidence of localized preferential attack on ISG during the SPFT measurements has been observed. Additionally, the effects of hyperalkaline conditions imposed by a cementitious environment, representative of geological disposal conditions for nuclear waste, have been investigated using both the PCT and MCC-1 static testing protocols with Ca(OH)2 solutions. In hyperalkaline conditions dissolution was incongruent in both test protocols for all elements at all time points . Calcium silicate hydrate (C-S-H) alteration products were observed on the MCC-1 monoliths from 180 days onwards and the presence of both zirconia-rich and zirconia-poor silica-alteration layers was observed on all monoliths at all time points, indicating the occurrence of a self-organisation phenomenon during leaching.