Effect of phase evolution and acidity on the chemical stability of Zr1-xNdxSiO4-x/2 ceramics

Abstract Zircon ceramics (ZrSiO 4 ) are promising candidates for actinide immobilization. Here, a series of Zr 1- x Nd x SiO 4- x /2 ( x  = 0, 0.02, 0.20, and 1.0) ceramics are prepared to study the effects of phase evolution and acidity on the chemical durability of ZrSiO 4 -based nuclear waste forms. The results show that the chemical stability of the single-phase ZrSiO 4 sample is better than that of the biphasic Zr 0.8 Nd 0.2 SiO 3.9 sample due to the existence of a secondary highly soluble phase (Nd 2 Si 2 O 7 ), which increases the contact area with leachate. The normalized release rates of both zirconium (Zr) and neodymium (Nd) in the Zr 1- x Nd x SiO 4- x /2 ceramic waste forms increase with increasing Nd loading and acid concentration. LR Zr in ZrSiO 4 ceramics and LR Nd in Zr 0.98 Nd 0.02 SiO 3.99 ceramics are the lowest, while LR Zr and LR Nd reach the highest values in the Zr 0.8 Nd 0.2 SiO 3.9 and Nd 2 Si 2 O 7 ceramics, respectively. The normalized release rates of Zr are lower than those of Nd due to the difference in the energies of their bonds with oxygen atoms. Moreover, the changes in the surfaces of the leached ceramics are consistent with their leaching results.