In order to utilize niobium concentrate of Bayan Obo effectively, the effect of Nb2O5 and basicity on the viscosity of CaO-SiO2-Nb2O5-5.0 wt.% CeO2-5.0 wt.% CaF2 slag system was studied from 1653 to 1813 K in reducing atmosphere by rotating cylinder method. For the same condition, the as-quenched samples were investigated through X-ray diffraction and Raman spectroscopy. The results show that the viscosity, break temperature and activation energy of viscous flow decrease with the increase of Nb2O5 and basicity. Raman spectra show that the Nb4+ ions exist in the form of [NbO6] octahedron with different distortion and little [NbO4] tetrahedron in the slags. The Nb2O5 addition and basicity lower the degree of polymerization, where the complex Si-O network is depolymerized into simple structural units.

With the continued exploitation and utilization of high-grade rare earth ores, it is increasingly important to extract rare earths from separated slag containing low-grade rare earth. The X-ray powder diffraction, scanning electron microscopy, electron probe micro-analyzer and confocal laser scanning microscopy were used to explore the influence of TiO 2 and cooling rate on the crystallization of CaO-SiO 2 -TiO 2 -10 wt% P 2 O 5 -8 wt% Nb 2 O 5 -5 wt% CeO 2 -5 wt% CaF 2 slag system.In this study, the britholite was precipitated selectively as the Ce-enriched phase. When TiO 2 was added at less than 12 wt%, the britholite was promoted to crystallize meanwhile the Ca 2 Nb 2 O 7 was suppressed. However, CaTiSiO 5 inhibited the growth of britholite when the TiO 2 content exceeded 15 wt%. The non-isothermal crystallization kinetics had also been investigated for the TiO 2 content and cooling rate varied from 0-18 wt% and 10-40℃/min, respectively. The continuous cooling transformation diagram and the relative crystallinity of the primary crystals were also constructed.Based on the observation and measurement of crystallization process, the modified Avrami model was applied to determine the crystallization mode of britholite with 9 wt% TiO 2 addition . It was constant nucleation rate and one-dimensional growth with diffusion controlled. Considering the nucleation and growth of crystals, 20-30℃/min was preferred to be the reasonable parameter during cooling stage.

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