Zirconolite Matrices for the Immobilization of REE-Actinide Wastes

The structural and chemical properties of zirconolite (ideally CaZrTi2O7) as a host phase for separated REE-actinide-rich wastes are considered. Detailed analysis of both natural and synthetic zirconolite-structured phases confirms that a selection of zirconolite polytype structures may be obtained, determined by the provenance, crystal chemistry, and/or synthesis route. The production of zirconolite ceramic and glass-ceramic composites at an industrial scale appears most feasible by cold pressing and sintering (CPS), pressure-assisted sintering techniques such as hot isostatic pressing (HIP), or a melt crystallization route. Moreover, we discuss the synthesis of zirconolite glass ceramics by the crystallization of B-Si-Ca-Zr-Ti glasses containing actinides in conditions of increased temperatures relevant to deep borehole disposal (DBD).