Effects of CaF 2 and La 2 O 3 on the phase structure of rare earth in CaO–SiO 2 –La 2 O 3 –CaF 2 slags

Abstract

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 CaF₂ and La₂O₃ contents on the phase structure and morphology of rare earth phase in CaO–SiO₂–La₂O₃–CaF₂ 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–SiO₂–La₂O₃–CaF₂ slags exists in the form of CaLa₄(SiO₄)₃O. The change of CaF₂ and La₂O₃ 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 CaF₂ and La₂O₃ content, the size of rare earth crystal phase increases gradually. CaF₂ and La₂O₃ can reduce the viscosity transition temperature of slag melt and increase the crystallisation temperature range of rare earth phase to promote crystal growth.