Hydrated-layer formation during dissolution of complex silicate glasses and minerals

The characteristics of aqueous dissolution of three complex silicate glasses (rhyolitic, basaltic, and simulated nuclear-waste glass) have been investigated by analytical techniques based on energetic ion beams, which provide depth profiles of various elements including hydrogen, on the altered surface of the materials. The two main corrosion features of this type of glass have been extensively documented: the build-up of a hydrated layer and the surficial accumulation of transition and heavy elements. Comparison with the corrosion behavior of ion-bombarded silicate minerals and study of the influence of solution temperature (in the range 60–200°C) and chemistry (effect of high sodium concentration) allow a better understanding of the corrosion mechanism. It is shown that hydration involves two different processes simultaneously, namely ion exchange between hydrogen and glass network modifiers and permeation of molecular water, their respective importance depending markedly on temperature and solution chemistry. Heavy element accumulation is explained by the precipitation of hydroxides or complex hydrosilicates, the latter possibly resulting also from ion exchange with major cations of primary hydrosilicates.