Determination of early stages of glass dissolution by pH titration

The early stages of glass dissolution are marked by rapid changes in pH for leach solutions with low buffer capacity. Consideration of both dissolution reactions and the electrical neutrality requirement allow the calculation of exchanged cation equivalents from the depletion of the H+-ion reservoir. Comparison was made between sodium trisilicate glass, a commercial waste glass (PNL 76-68), and the defense waste reference glass. The released Na+ calculated from the pH curve of sodium trisilicate glass has the expected parabolic dependence on time. The nuclear waste glasses react with H+ more slowly and the pH - time plots do not have the shape of a titration curve. The equivalents of cations released follow a power law function, the exponent of which depends on initial pH. There are two distinct rate regimes for all glasses with initial fast rates related to consumption of H+ and later, slower rates nearly independent of H+ activity. 9 refs., 7 figs