R7T7 Glass Initial Dissolution Rate Measurements Using a High-Temperature Soxhlet Device

Abstract

ABSTRACTThe corrosion of glasses in aqueous media is described by the general rate equation proposed by Grambow. In its simplest form, this equation may be written as: V = Vo [1-a(H4SiO4)/a*(H4SiO4)]. The purpose of this investigation was to measure the initial dissolution rate (Vo) of R7T7 nuclear waste glass at temperatures between 90 and 250°C, and to determine activation energies of reaction.Leaching solutions were maintained far from equilibrium using a dynamic leaching apparatus: the High-Temperature Soxhlet device. The corrosion rates were defined by weight loss measurements and by silicon, boron, sodium and lithium analysis in the leachate. Throughout the test temperature range, the normalized mass losses were linear with time. The initial dissolution kinetics calculated from weight loss (before and after scraping off the surface layer) and from Si, B, Na and Li release, followed an Arrhenius relation. Activation energies range from 58 to 60 kJ·mol−1 depending on the element. This slight discrepancy is attributed to a more pronounced retention factor for certain elements In the alteration layer as the temperature rises. The mean activation energy of reaction (about 59 kJ·mol−1) Is typical of a surface-controlled reaction. This energy is unique in the temperature range investigated.