PNNL

Abstract

Silicate glasses are an accepted option for immobilizing nuclear waste and are often deposited in a near-surface environment. Therefore, it is important to understand glass alteration mechanisms since this is fundamental for predicting glass corrosion rates upon disposal. Microbial activity at or near the glass surface may influence glass alteration biomechanically and biochemically. However, waste glass chemical durability is evaluated using specified tests that do not explicitly consider microbial alteration. In this study, four glass compositions were tested in three solutions with and without a subsurface Paenibacillus bacterium to compare the extent of leaching from the glass over 100 to 200 days. The results found that the presence of this microbe not only influenced the extent of glass alteration but also increased the soluble fractions of specific elements such as boron, iron, sodium, and silicon. This was due to microbial metabolic products (e.g. organic acids), which decrease the pH, being countered by abiotic glass dissolution, which increases the pH, resulting in a net neutral or slightly acidic bulk solution that could promote further glass alteration. However, the extent of elemental release was dependent on the glass and solution composition and was element specific. Overall, this study revealed a dynamic relationship between the elemental release, microbial growth, and corresponding changes in solution pH, and shows that microbial processes can indirectly accelerate glass alteration by changing the surrounding pH. This work will support a greater understanding of microbially-influenced glass alteration and support the development of standardized durability testing procedures to assess the influence of microbial communities at a specified disposal facility.