Low-temperature zircon-based glass-ceramic synthesis for high Sm3+ immobilization

Zircon (ZrSiO 4 ), due to its excellent thermal stability and chemical durability, is an efficient solidification matrix for high-level radioactive waste (HLW). However, the traditional solid-state method has problems such as high synthesis temperature (>1600 °C), long reaction time (>24 h), and insufficient product purity. Thus in this study, the synthesis conditions were optimized to 1400 °C/6 h by adding 10 wt% MgO as a mineralizer, significantly reducing the reaction temperature and time. The mechanism of MgO as a mineralizer was investigated. XRD revealed that MgO promoted the transformation of m-ZrO 2 (monoclinic zirconia) to t-ZrO 2 (tetragonal zirconia) and reacted with SiO 2 to form MgSiO 3 , jointly lowering the reaction temperature and time. Based on this, the lattice substitution strategy was used to immobilize Sm 3+ (simulating trivalent actinides) in Sm x Zr (1-x) SiO 4 (0 < x < 0.5) solid solutions. XRD indicated that when x ≤ 0.45, a stable coexistence phase of Sm x Zr (1-x) SiO 4 (zircon structure) and m-ZrO 2 (monoclinic zirconia) was formed, and Sm 3+ successfully replaced Zr 4+ . When x > 0.45, the structure collapsed, with peak broadening and the appearance of a second phase. The maximum component (x = 0.45) was combined with borosilicate glass to prepare glass-ceramic solidification bodies. In the 90 °C static leaching test, the 28-day normalized leaching rate of Sm 3+ ( LR Sm ) was ∼10 −6  g m −2  d −1 . This strategy provides a new solution for the long-term immobilization of fission element.