Solidification and stabilization of strontium and chloride ions in thermally treated calcium aluminate cement modified with or without sodium polyphosphate

Cementation of aqueous radioactive waste contaminated with a significant 90Sr is challenging due to the potential radiolysis of water contents. Utilization of calcium aluminate cement (CAC) modified with sodium polyphosphate (CAP) is interesting as its water content can be reduced by thermal treatment. The present study investigated solidification and stabilization of Sr2+ and Cl− ions in CAC and CAP with or without thermal treatment. A leaching test showed a superior Sr2+ ion stabilization in CAP: apparent diffusion coefficient of Sr2+ was smaller than in the CAC by 5 orders of magnitude. CAC cured at 20 °C had the best stabilization for Cl− ions among the samples tested. Friedel's salt formed in CAC may have contributed to the immobilization of Cl− ions. The stabilization of Cl− ions by CAP was significantly improved by the thermal treatment likely because of the improvement in the microstructure previously reported.