Solubility constants of hydroxyl sodalite at elevated temperatures evaluated from hydrothermal experiments: Applications to nuclear waste isolation

The equilibrium constants obtained in this study have a wide range of applications, including synthesis of hydroxyl sodalite, de-silication in the Bayer process for extraction of alumina, and the performance of proposed sodalite waste forms in geological repositories in various lithologies including salt formations. The thermodynamic calculations based on the equilibrium constants obtained in this work indicate that the solubility products in terms of mΣAl×mΣSi for hydroxyl sodalite are very low (e.g., ∼10-13 [mol·kg-1]2 at 100 °C) in brines characteristic of salt formations, implying that sodalite waste forms would perform very well in repositories located in salt formations. The information regarding the solubility behavior of hydroxyl sodalite obtained in this study provides guidance to investigate the performance of other pure end-members of sodalite such as chloride- and iodide-sodalite, which may be of interest for geological repositories in various media.