Effects of Water Chemistry on the Leach Resistance of Synroc C

Abstract

ABSTRACTThe chemical durability of SYNROC C has been measured as a function of repository conditions, namely, temperature, surface/volume ratio, groundwater pH and composition. The leach rate of SYNROC C is less dependent on temperature than borosilicate glasses; activation energies range from 15-25 kJ mol-1 compared to 33-74 kJ mol-1 for glass. The rate of release from SYNROC C is very low and independent of solution composition for the solutions studied. There is little variation in leach rate over the pH range 4-9, but at pH 2 the rate is up to 10 times higher. SYNROC C leach rate is independent of flow rate or surface/volume ratio for the mobile waste elements because of the unimportance of solution saturation effects owing to the low concentration of dissolved solids. The differential leach rate decreases rapidly with time because, after initial leaching from grain boundaries and metastable minor phases, the highly insoluble matrix protects the more leachable elements from further attack.