Sodium zirconium phosphate-based glass-ceramics as potential wasteforms for the immobilization of nuclear wastes

A comprehensive study on the development of sodium zirconium phosphate (NZP)-based glass-ceramic composites as potential wasteforms for the immobilization of nuclear wastes is reported. Two complementary waste treatment routes, the ex situ and in situ crystallisation of NZP with a sodium aluminoborosilicate glass, were investigated with various processing conditions including sintering temperature, cooling rate and NZP to glass ratios. While the ex situ route with mixing of pre-made NZP and glass is a robust and reliable means of producing the glass-ceramic composites, the in situ crystallisation of NZP from an amorphous NZP precursor is a more realistic processing route. The formation of ZrO2 as a minor phase was observed especially for high NZP to glass ratios due to the solubility difference between Zr and P oxides in glass. The addition of extra phosphate can overcome this and yield glass-ceramic composites with appropriate NZP stoichiometry. Overall, the NZP glass-ceramic system is versatile offering multiple processing options for nuclear waste management.