Phase evolution and chemical stability of Nd-doped natural garnet waste form by microwave sintering

Advanced materials and processes are needed to immobilize fission products in the form of chemically durable waste. Nd-doped Ca3Zr2Fe2SiO12 (GZG) ceramics with different sintering temperatures (1100–1300 °C), sintering times (0.5–6 h) and solid solutions (0 ≤ x ≤ 2.5) were prepared by microwave sintering. The results show that by adjusting a series of key parameters, natural garnet structures with excellent chemical stability are obtained. XRD shows that a single phase of solid solution can be obtained by increasing the sintering temperature and controlling the actinide solid solution below the solid solution limit. The sintering temperature only affects the compactness of the solid solution. Thermodynamic calculations show that high temperature is favorable for the synthesis of GZG, and it is positive and irreversible. The normalized leaching rate of Nd3+ in the GZG structure is approximately ∼ 10−6 g m−1 d−1. The release form of Nd in aqueous solution is inner diffusion. The experimental results show that the naturally occurring garnet structure is an excellent waste form.