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

Irisawa, Keita  ; Namiki, Masahiro*; Taniguchi, Takumi ; Garcia-Lodeiro, I.*; Kinoshita, Hajime*

Cementation of aqueous radioactive waste contaminated with a significant Sr is challenging, and utilization of calcium aluminate cement (CAC) modified with sodium polyphosphate (CAP) is interesting. The present study investigated solidification and stabilization of Sr and Cl ions in CAC and CAP cured in open system at 90C and in closed system at 20C. A leaching test showed that Sr ion could be stabilized more effectively in the CAP than in the CAC. On the other hand, the CAC cured at 20C had the best stabilization for Cl ion among the samples. Friedel's salt formed in the CAC may have contributed to the immobilization of Cl ion. Although the stabilization of Cl ion by CAP was less effective than CAC, it was significantly improved by the thermal treatment. The results may suggest that Cl ion in the CAP was incorporated in the poorly crystalline apatite structure.