Comprehending the stability of Sr2+ immobilization in chemically bonded phosphate ceramic system: A mechanism study

Chemically bonded phosphate ceramics (CBPC) are a promising matrix for the immobilization of Sr2+ in medium-and low-level liquid radioactive waste. Understanding the stability of immobilization is crucial, especially when distinguishing the mechanism of chemical immobilization from that of physical encapsulation. However, the mechanisms underlying these processes remain unclear. In this study, & UDelta;Eaq, & UDelta;E, and & UDelta;E & PRIME; were calculated to study the stability of the immobilization. CBPC samples were synthesized to confirm the calculated results. A negative & UDelta;E-aq value accounts for the dominant mechanism of chemical immobilization. Negative & UDelta;E and & UDelta;E' values indicate that physical encapsulation also contributes to the stability of immobilization, because Sr2+ could induce brucite to cover the K-struvite matrix. Corresponding experiments confirmed the mechanism of immobilization.