Abstract
Zirconolite is a candidate wasteform for actinides (U/Pu/Th), and glass incorporation to form glass-ceramics provides flexibility to accommodate heterogeneous wastes while simplifying processing requirements; however, the glass content required to optimise these benefits remains unestablished. This systematic study investigated the effect of glass content on zirconolite crystallisation, phase assemblage, phase composition, cerium valence states and partitioning. Cerium-bearing zirconolite glass-ceramics were fabricated by targeting zirconolite (Ca0.8Ce0.2ZrTi1.6Al0.4O7; Ce as actinide surrogate) with varying amounts (0–100 vol%) of glass addition (NaAl1.5B0.5Ca0.7Ti0.2Si2O8.6). Differential scanning calorimetry data revealed that glass addition lowered the zirconolite crystallisation temperature (1283°C to 1200°C). X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy analyses showed that glass addition lowered the temperature (1320°C to 1270°C) required to fabricate phase-pure zirconolite glass-ceramics and minimise CeO2/ZrO2 phases, with > 90 % of cerium preferentially partitioned into zirconolite. X-ray absorption near edge spectroscopy data showed predominantly Ce4+ within zirconolite as targeted.
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