Borosilicate glass alteration driven by magnesium carbonates

International audienceGeochemical modeling of glass and silicate mineral alteration is a major challenge for understanding natural processes in the earth sciences (e.g. chemical compositions of natural waters and oceans...). In confined media, solids reactivity quickly controls solution compositions. The alteration of a simplified synthetic glass, representative of the French reference nuclear glass in the presence of a simple Mg- bearing phase is a key step towards the understanding of the interactions between nuclear glass and nearfield materials in geological repository. Indeed, magnesium in solution is one of the elements known to potentially enhance glass alteration. In a first study, hydromagnesite was chosen as the simplest and as the most reactive Mg bearing carbonate. Experiments were performed in closed system at 90°C and characterized by SEM, XRD and TofSIMS. They revealed that glass alteration is enhanced in presence of hydromagnesite at 90°C. Geochemical modeling was performed using the GRAAL model implemented within the CHESS/HYTEC reactive transport code. The model was efficient enough for quantifying the amount of present solids, the pH and the elements concentration with time whatever the glass/hydromagnesite ratio. Future experimental and modeling work will concern more representative solids, like dolomite and smectites