Impact of Redox on Glass Durability: The Glass Selection Process

PEELER, DAVID

Savannah River Site (S.C.)

关键词: Sludges;    Waste Processing;    Hydroxides;    Waste Forms;    Redox Reactions;   

DOI  :  10.2172/827204
RP-ID  :  WSRC-TR-2004-00135
RP-ID  :  AC09-96SR18500
RP-ID  :  827204

美国|英语

来源: UNT Digital Library

【 摘 要 】

Recent glass formulation activities have focused on developing alternative frit compositions for use with specific sludge batches to maximize melt rate and/or waste throughput. The general trend has been to increase the total alkali content in the glass through the use of a high alkali based frit, a less washed sludge, or a combination of the two. As a result, predictions of durability have become a limiting factor in defining the projected operating windows for the Defense Waste Processing Facility (DWPF) for certain systems. An additional issue for these high alkali glasses has been the effect of REDuction/OXidation (REDOX) on the durability of the glass. Recent analyses have indicated that the application of the durability model's value without consideration of the overall glass composition may lead to a more significant shift (larger magnitude) than needed. Therefore, activation of the REDOX term in the Product Composition Control System (PCCS) may have a significant impact on the predicted operational windows based on model predictions, but may not represent the realistic impact on the measured durability. In this report, two specific issues are addressed. First, a review of the data used to develop PCCS (in particular the durability model) showed the potential for a REDOX interaction that is not accounted for. More specifically, three terms were added to the current model and were found to be statistically significant at a confidence level of 95 per cent. These results suggest a possible interaction between REDOX and glass composition that is not accurately captured leading to potentially conservative decisions regarding the durability of reduced glasses. The second issue addressed in this report is the development of a 45 glass test matrix to assess the effect of REDOX on durability as well as to provide insight into specific interactive compositional effects on durability. The glasses were selected to support the assessment of the following specific objectives: (1) the impact of REDOX on glass durability (as measured by the Product Consistency Test (PCT)) and (2) the interactive effects that may mitigate the predicted negative impacts based on current free energy of hydration model theory. These glasses will be batched and melted under conditions that target both the projected compositions and intended REDOX states. Durability (as measured by the PCT) will be experimentally determined for each glass in triplicate using standard procedures. The measured response will then be compared to model based predictions to assess the applicability and/or potential conservatism of the model under REDOX activated conditions.