Effect of CaCl₂ addition on decontamination of radioactive Cs in soil via heat treatment

The effectiveness of CaCl₂ addition in thermal soil decontamination was investigated by performing heat treatment on radioactive Cs-contaminated Fukushima soil under both atmospheric and vacuum conditions, and comparing the results with NaCl addition. When CaCl₂ was added, a decontamination ratio exceeding 95% was achieved at approximately 740°C under both atmospheric and vacuum conditions, showing slightly higher efficacy than NaCl addition. For the removal of non-radioactive Cs adsorbed onto weathered biotite by heat treatment, CaCl₂ exhibited a distinctly greater effect than NaCl. While NaCl induces rapid ion exchange (RIE) in clay minerals of the soil under vacuum conditions, CaCl₂ was found to trigger RIE at the initial stage of the heat treatment under both atmospheric and vacuum conditions, subsequently promoting the decomposition and phase transformation of clay minerals leading to the removal of radioactive Cs. These results indicate that CaCl₂ is an effective additive for heat treatment even when used alone.