Glass Dissolution Kinetics Research Articles

Oscillations in the dissolution kinetics of silicate glass in tris-buffered aqueous media

The dissolution of soda-lime glass in aqueous media was monitored as a function of time at 90°C. The introduction of the cationic buffer, tris (abbreviated name for tris[hydroxymethyl] aminomethane or H 2NC[Ch 2OH 3), in order to maintain a pH value of 8.1 resulted in the formation of a surface layer which caused a decrease in the extent of glass dissolution relative to that observed in tris-free media. This surface layer exhibited periodic cracking, which was correlated with sharp ‘spikes’ when the concentration of the leachates was monitored as a function of time. The presence of Mg in the tris-based leachants resulted in reduced ‘spike’ frequency. On the other hand, the use of the anionic buffer, CAPS (abbreviated name for 3-(cyclohexylamino)-1-propanesulfonic acid or C 6H 11NH[CH 2] 2] 3SO 3H), to maintain a pH level of 9.5 was not observed to cause oscillations associated with surface passivation and cracking. Likewise, such oscillations were not observed in solutions buffered at pH 8.1 using sodium borate instead of tris.

Analysis of high-level waste glass performance by the physical and geochemical simulation code STRAG4

A source term release analysis code for high-level waste glass has been developed for simulation of long-term dissolution behavior under repository conditions. The STRAG4 code consists of models for (a) element diffusion in both the bulk glass and surface layer, (b) glass dissolution kinetics at the interface between glass and water, and (c) geochemical reactions of dissolved elements in underground water. The simulations for various conditions of glass dissolution, including a static and dynamic system, show accordance with the experimental observations even in the relatively complicated case where bentonite is present. Long-term dissolution analyses of a borosilicate waste glass were carried out as preliminary study. The calculations were achieved by considering detrimental effects due to interactions between the glass and surrounded materials which are presumed to be in a repository environment (i.e., compacted bentonite, corrosion products from the iron overpack, and underground water). The environmental conditions such as temperature and geochemical reactions are also taken into account in the calculations. The results suggest the life of the waste glass would be more than 50,000 years even if the glass surface area increased by a factor of 10 due to crack formation.

Water chemistry and dissolution kinetics of waste-form glasses

A simplified water chemistry program was developed for determining the chemical speciation of a solution. This was combined with a linear, first-order kinetic equation to produce a model of the kinetics of dissolution of a nuclear waste glass which includes effects of groundwater flow. Calculations are presented for four waste glasses, giving the rate of glass dissolution in both pure water and a solution intended to simulate basalt groundwater. The calculations are performed for the case of dissolution in a static volume of groundwater and for the case of steady-state dissolution in flowing groundwater. Inclusion of the effects of water chemistry on the solubility of silicon is found to increase the rate of glass dissolution in the case of pure water but to either increase or decrease it in the case of the simulated groundwater, depending upon the glass composition. Implications of the results for prediction of the long-term behavior of a nuclear waste glass are discussed.