Effects of CaF₂ and La₂O₃ on the phase structure of rare earth in CaO–SiO₂–La₂O₃–CaF₂ slags

The rare earth in the rare earth slag can be separated and enriched by heating and melting the rare earth slag and then slowly cooling crystallisation. In this process, it is of great significance to study the effect of chemical composition on the crystallisation of rare earth phase in slag and the effect of slag viscosity on crystal growth. The rare earth slag melt samples were prepared according to the main chemical composition of rare earth slag by using an analytical pure reagent. The effects of CaF 2 and La 2 O 3 contents on the phase structure and morphology of rare earth phase in CaO–SiO 2 –La 2 O 3 –CaF 2 slags were studied by SEM-EDS and XRD. The relationship between the viscosity of the slag and the crystal growth behaviour was studied by measuring the melt viscosity with the cylinder rotation method. The results show that the rare earth in CaO–SiO 2 –La 2 O 3 –CaF 2 slags exists in the form of CaLa 4 (SiO 4 ) 3 O. The change of CaF 2 and La 2 O 3 content has no effect on the structure of rare earth phase, but the size of rare earth crystal phase changes obviously. With the increase of CaF 2 and La 2 O 3 content, the size of rare earth crystal phase increases gradually. CaF 2 and La 2 O 3 can reduce the viscosity transition temperature of slag melt and increase the crystallisation temperature range of rare earth phase to promote crystal growth.