Mechanism of Variable Valence Elements in TRPO on Phase Transformation and Comprehensive Properties of Gd2Zr2O7 Waste Matrix

The treatment of high-level radioactive waste with trialkyl phosphine oxide (TRPO) results in radioactive residues, necessitating the effective management of TRPO process waste to protect the environment. In this study, TRPO waste was immobilized in Gd 2 Zr 2 O 7 for the first time using solid-state reactive sintering at 1300 °C. XRD and Raman analysis results demonstrate that the waste solubility exceeds 50 wt .%, indicating a high incorporation capacity. With increasing TRPO waste addition, the pyrochlore phase initially transitioned to fluorite before reverting to pyrochlore. Valence state analysis suggests that fluorite-to-pyrochlore transition was driven by redox reactions of Ce at high temperatures, where Ce 4+ was reduced to Ce 3+ . The incorporation of Ce 3+ into the A-site of Gd 2 Zr 2 O 7 led to an increase in the r A /r B ratio, reaching a range of 1.46 to 1.78. In sample N5 (50 wt .% waste content), a Vickers hardness of 12.03 GPa was achieved, corresponding to the largest grain size and highest densification. Leaching experiments indicated that the normalized leaching rates of Nd and Ce after 42 d were both 10 -6 g·m -2 ·L -1 . These results suggest that variable valence elements in TRPO waste significantly influence the Gd 2 Zr 2 O 7 structure, and that samples synthesized under low-temperature sintering conditions exhibit excellent mechanical and chemical stability.