Aluminoborosilicate waste glass dissolution under alkaline conditions at 40°C: Implications for a chemical affinity-based rate equation

Single-pass flow-through experiments were conducted with aluminoborosilicate waste glasses to evaluate how changes in solution composition affect the dissolution rate (r) at 40°C and pH (23°C) ≤ 9.0. The three prototypic low-activity waste (LAW) glasses, LAWE-1A, -95A and -290A, used in these experiments span a wide range covering the expected processing composition of candidate immobilised low-activity waste (ILAW) glasses. Results suggest incongruent release of Al, B, Na, and Si at low flow-rate (q) to sample surface area (S), in units of (m s^?1), (log₁₀(q/S) < ?8.9) whereas congruent release is observed at high q/S (log₁₀(q/S) > ?7.9). Dissolution rates increase from log ₁₀(q/S) ? ?9.3 to ?8.0 and then become constant at log ₁₀(q/S) > ?7.9. Forward (maximum) dissolution rates, based on B release, are the same irrespective of glass composition, evident by the dissolution rates being within the experimental error of one another (r _1A ≤ 0.0301 ± 0.0153 g m^?2 day^?1, r_95A ≤ 0.0248 ± 0.0125 g m^?2 day^?1, and r_290A ≤ 0.0389 ± 0.0197 g m^?2 day ^?1). The results also illustrate that as the activity of SiO ₂(aq) increases, the rate of glass dissolution decreases to a residual rate. The pseudo-equilibrium constant, K_g, (log ₁₀(K_g) ≤ ?3.7) predicted with these results is slightly lower than the K for chalcedony (log₁₀(K) ≤ ?3.48) at 40°C. Finally, these results support the use of a chemical affinity-based rate law to describe glass dissolution as a function of solution composition.