Glass dissolution as a function of pH and its implications for understanding mechanisms and future experiments

R=kiexp-EaH+RTaHηH+exp-EaH2ORT+exp-EaOH-RTaOHηOHappears to be applicable to a broad range of glasses. Here, R is the rate of dissolution, mol/(m2·s) or similar; E is the activation energy associated with the acid, water, or hydroxide activated reactions, kJ/mol; a is the activity of H+, H2O, or OH−, unitless; η is the order of the reaction with respect to H+, H2O, or OH−; R is the gas constant, kJ/(mol·K); T is the temperature, Kelvin; and ki is the intrinsic rate constant, mol/(m2·s) or similar. The contribution to the overall rate from the 'water' term is evident as a minor contribution in the middle pH range for some glass compositions and a major contributor for others. One nuclear waste glass (the Japanese P0798), a basalt glass (Köhler et al., 2003), and a glass with a mineral composition (Bourcier, 1998) exhibit this contribution as a relatively flat response to changes in pH in the range of 5-8. However, to distinguish between the possible rate laws, more experiments and more carefully constrained experimentation are needed. These may include experiments at pH values that differ by as little as 0.25. Lastly, experiments with glasses of different compositions are needed to determine the dependence of the intrinsic rate constant on the glass composition and structure, i.e. non-bridging oxygens, Si-O-Si and Si-O-X (X = a matrix-forming element, e.g. Al or Fe), and other glass structural properties, e.g. binding energies.