Low Temperature Glasses

TWRS wastes contain certain chemical components which, either because of their limited solubility or volatilization at high temperatures, present problems for conventional vitrification technologies. The current task completed by BNL concerns the use of low temperature glasses for tank waste remediation. A literature review of existing technologies highlighted lead-iron-phosphate glasses, with melt temperatures of around 900oC, as a significant improvement over existing borosilicate formulations. However, concerns over leachability of the high lead levels in the glass matrix has kindled interest in the development of lead-free phosphate glasses. As part of this current task, crucible studies were performed to scope the potential of advanced phosphate glasses. Based on pioneer work on iron-aluminum-phosphate and tin-phosphate glasses, new formulations were investigated, modified with cations to enhance chemical durability and reduce melt temperatures. Dissolution of matrix metals using a standard leach test, the Product Characterization Test (PCT), was the basis used to evaluate the new glasses. Cursory results indicate that low-temperature glasses can indeed be prepared with melt temperatures between 450 and 900oC. Durability of these glasses and composites compares favorably with lead-iron-phosphate glasses, and is an improvement over reference borosilicate formulations. The capacity to incorporate high percentages of sodium was demonstrated, however much wastespecific work will be required to further qualify and quantify treatability of tank waste components.