Synthesis and hydrothermal stability of U doped zirconolite–sphene composite materials

Abstract

Two series of U doped zirconolite–sphene composite materials were prepared by solid state reaction method: CaZr_(1−m)U_mTi₂O₇−(1−m) Ca_(1−x)U_xAl_2xTi_(1−2x)SiO₅ (m = 7x) and Ca_(1−n)U_6nZr_(1−5n)Al_2nTi_(2−2n)O₇−(1−5n) Ca_(1−y)U_yAl_2yTi_(1−2y)SiO₅ (n = 5y/6). The effects of U content on the phase structure of the composite materials were mainly investigated. The results show that the optimal synthesis temperature of the composite material is ∼1230°C. In comparison with the incorporation of U in the Zr site of zirconolite, U incorporation in the Ca site of zirconolite using Al as charge compensating ions was not very efficient. Hydrothermal stability of the U doped zirconolite–sphene composite material was examined by modified product consistency test method at 90°C in deionised water (pH 7). The normalised U leach rate is fairly constant in a low value below 10⁻⁵ g m⁻² day⁻¹ after 28 days.

Keywords:

• Zirconolite
• Sphene
• Uranium
• Hydrothermal stability

Acknowledgements

Financial support by the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials (Southwest University of Science and Technology, grant no. 11zxfk26) is greatly appreciated.