Mineralizer-assisted low-temperature rapid synthesis of Zr(1-x)NdxSiO4-based glass-ceramic waste forms with high waste loading

To lower the reaction temperature and enhance the waste incorporation rate of ZrSiO 4 , this study developed a novel low-temperature synthesis strategy. MgF 2 was used as a mineralizer to optimize the synthesis of ZrSiO 4 . Ceramics are successfully prepared by sintering at 1000 °C for 6 h. The role of MgF 2 in promoting the reaction is also investigated. At 1000 °C, MgF 2 reacts with SiO 2 to form amorphous Mg 2 SiO 4 . The Mg 2 + ions released in this process promote the phase transformation from m-ZrO 2 to t-ZrO 2 . The t-ZrO 2 then reacts with SiO 4 4- , thereby forming ZrSiO 4 . Under the same conditions, Nd x Zr (1-x) SiO 4 ceramic waste forms are synthesized for the immobilization of Nd 2 O 3 , which simulates high-level radioactive waste. XRD results show that a single-phase zircon structure is maintained when x ≤ 0.35. However, when x > 0.35, a small amount of Mg 2 SiO 4 is detected as a secondary phase. This indicates that some SiO 2 remains unreacted, and part of the Nd 2 O 3 is not incorporated into the crystal structure. Based on these findings, the sample with the maximum solid solution (x = 0.35) is selected and combined with lead-containing borosilicate glass to produce glass-ceramic waste forms. Leaching tests show that the normalized release rate of Nd 3+ gradually decreases as the glass content increases. With a glass content of 90 wt%, the material exhibits outstanding aqueous durability, as evidenced by a negligible Nd 3+ leaching rate of merely 1.57 × 10 −6 g·m −2 ·d −1 after 2 8 days. In conclusion, MgF 2 acts as an effective mineralizer, enabling a substantial reduction in both the synthesis temperature and duration required for ZrSiO 4 formation.