Crystalline phase, microstructure, and aqueous stability of zirconolite–barium borosilicate glass-ceramics for immobilization of simulated sulfate bearing high-level liquid waste

Abstract The crystalline phase, microstructure, and aqueous stability of zirconolite–barium borosilicate glass-ceramics with different content (0–30 wt %) of simulated sulfate bearing high-level liquid waste (HLLW) were evaluated. The sulfate phase segregation in vitrification process was also investigated. The results show that the glass-ceramics with 0–20 wt% of HLLW possess mainly zirconolite phase along with a small amount baddeleyite phase. The amount of perovskite crystals increases while the amount of zirconolite crystals decreases when the HLLW content increases from 20 to 30 wt%. For the samples with 20–30 wt% HLLW, yellow phase was observed during the vitrification process and it disappeared after melting at 1150 °C for 2 h. The viscosity of the sample with 16 wt% HLLW (HLLW−16) is about 27 dPa·s at 1150 °C. The addition of a certain amount (≤20 wt %) of HLLW has no significant change on the aqueous stability of glass-ceramic waste forms. After 28 days, the 90 °C PCT-type normalized leaching rates of Na, B, Si, and La of the sample HLLW−16 are 7.23 × 10 −3 , 1.57 × 10 −3 , 8.06 × 10 −4 , and 1.23 × 10 −4  g·m −2 ·d −1 , respectively.