Synthesis and characterization of zirconolite-sodium borosilicate glass-ceramics for nuclear waste immobilization

Abstract

Zirconolite-sodium borosilicate glass-ceramics were successfully prepared via slow-cooling methods, and the crystallization, microstructure and aqueous durability have been investigated with powder X-ray diffraction (XRD), backscattered scanning electron microscopy and energy dispersive spectroscopy (BSE-EDS), Raman spectroscopy and ASTM Product Consistency Test leaching method. The results show that the main crystalline phase in the prepared glass-ceramics is strip-shaped zirconolite phase and the quantitative fraction of the zirconolite phase is about 30 wt%, the chemical composition of zirconolite crystals grown from a glass matrix is determined by Rietveld refinement to be Ca0.93Zr0.76Ce0.31Ti1.95Al0.05O7 and 84.53% Ce are incorporated in zirconolite crystals. Moreover, the aqueous durability test shows the low normalized leaching rates of Si (LRSi), Ca (LRCa) and Ce (LRCe) of the glass-ceramics, and LRSi, LRCa and LRCe are about 4 × 10−4, 1 × 10−4 and 8 × 10−7 g m−2 d−1, respectively after 56 leaching days. The obtained conclusions provide useful information for the immobilization of high-level radioactive wastes by using borosilicate glass-ceramic as potential matrix through one-step method.