Effect of Fe2O3 on the Immobilization of High-Level Waste with Magnesium Potassium Phosphate Ceramic

For the proposed novel procedure of immobilizing HLW with magnesium potassium phosphate cement (MKPC), Fe₂O₃ was added as a modifying agent to verify its effect on the solidification form and the immobilization of the radioactive nuclide. The results show that Fe₂O₃ is inert during the hydration reaction. It slows down the hydration reaction and lowers the heat release rate of the MKPC system, leading to a 3°C-5°C drop in the mixture temperature during hydration. Early comprehensive strength of Fe₂O₃ containing samples decreased slightly while the long-term strength remained unchanged. For the sintering process, Fe₂O₃ played a positive role, lowering the melting point and aiding the formation of ceramic structure. CsFe(PO₄)_2, or CsFePO_4, was generated by sintering at 900°C. These products together with the ceramic structure and absorption benefit the immobilization of Cs⁺. The optimal sintering temperature for heat treatment is 900°C; it makes the solidification form a fired ceramic-like structure.