Immobilization of CeO2 using single-phase zirconolite and the chemical stability analysis

In this study, zirconolite-based ceramic powder was firstly fabricated from combustion reaction route. CeO2 was introduced as the surrogate of tetravalent actinides, which was directly immobilized by the single-phase zirconolite waste matrice. The results demonstrate that the crystalline incorporation of CeO2 is highly depended on the sintering temperature. 10 wt% CeO2 was directly immobilized into the zirconolite crystal structure under 1250 °C sintering, where Ce concurrently occupies the Ca and Zr sites. Higher CeO2 incorporation (15–25 wt%) leads to the formation of Ce-rich impurity phase and phase transformation from 2M-zirconolite to 3T-zirconolite. The Ce-bearing zirconolite waste forms exhibit the highest density and hardness after sintering at 1400 °C for 12 h. The aqueous durability was evaluated, where the 42 days LRCe values are 1.68 × 10–6 and 6.85 × 10–6 gm−2d−1 before and after the leachate treatment using nitric acid.