An ultra-durable ZIT glass-ceramic composite for immobilization of radioactive mixed lanthanide oxides

Zinc Titanate (ZIT) glass-ceramic composite is a potential candidate waste form for immobilizing radioactive lanthanide oxides due to its relatively high lanthanide embedding capacity and low reaction temperature. However, the composition of lanthanide oxides after electrolytic refining is very complex and the immobilization mechanism of lanthanide oxides by ZIT composite is not clear. Herein, we prepared ZIT-PrEu glass-ceramic waste forms by a solid-phase sintering method at 1200 °C for 4 h using mixed lanthanide oxides of Pr 6 O 11 and Eu 2 O 3 simulated as radioactive waste. The XRD and SEM results show that different mixed lanthanide oxide ratios have very little effect on the composition and microstructure of ZIT-PrEu waste forms with different waste embedding rates. With the increase of waste embedding rate, the density of the ZIT-PrEu glass-ceramic waste forms with different mixed lanthanide oxide ratios first increases and then decreases. When the embedding rate increases to 25 wt%, the density of ZIT-PrEu waste forms with different mixed lanthanide oxide ratios reaches a maximum. The ZIT-PrEu glass-ceramic waste forms embedded with 25 wt% waste exhibit excellent chemical durability, and the leaching rates of Pr ion and Eu ion are only 10 −6 - 10 −7  g m −2  d −1 after 28 days at 90 °C. Moreover, the phase evolution of the ZIT composites immobilizing lanthanide oxides at different temperatures is revealed by XRD and FT-IR measurements. The lanthanides (Ln) are mainly present in the form of LnPO 4 monazite phases.