Synergistic solidification of radioactive waste salts by thermal synthesis of sodalite derived from kaolinite

Capturing and solidifying the fission elements in radioactive waste salt is an urgent task for the safe treatment and final disposal of spent fuels. In this paper, we present a synergistic method that combines low-temperature solution-based precursor preparation with high-temperature solid-phase sintering to synthesize sodalite while simultaneously solidifying radioactive waste salts in situ using kaolinite, a clay mineral that is economically viable and widely available. Various material characterization methods were employed to elucidate the mechanism of sodalite’s solidification of fission elements. The results demonstrated that a sodalite solidified body with strong thermal stability and high mechanical strength could be achieved when the precursor was sintered at 800℃ for 2 h. Normalized leaching rate experiments indicated that the solidification effect of sodalite on Cs, Sr, Ba, and Ce was significant, with the normalized leaching rate remaining well below 5 × 10 -4 g·cm −2 ·d -1 after 28 days. Furthermore, the solidification of these four fission elements by sodalite involves mechanisms such as ion exchange, lattice solidification, coordination chelation, and physical and chemical adsorption. In summary, the sodalite synthesized by this method exhibited excellent curing performance without the need for additional sintering agents or secondary glass coatings. The findings of this study will serve as a valuable reference for the final disposal of irradiated nuclear fuels.