Precipitation of Rare Earth Slag and the Crystallization Behavior of Rare Earth Phase

Isothermal reduction experiments at 1400 °C, which used carbon-bearing pellets mainly made from Bayan Obo complex iron ore and pulverized coal, could effectively separate rare earth (RE) slag and iron. Different instruments were used to study the precipitation of RE slag and the growth behavior of the RE phase in RE slag during the process of cooling from 1400 °C. The experimental results show the presence of three main phases in the RE slag—the RE phase (Ca, Ce, La) 5 (SiO 4 ) 6 F, cuspidine (Ca 4 Si 2 O 7 F 2 ), and fluorite (CaF 2 ), which precipitated at 1352 °C, 1218 °C, and 1045 °C, respectively. The RE phase grew along a specific growth track and finally manifested with a hollow hexagon morphology. The edge nucleation layer-by-layer growth model was applied to explain the formation of the hollow crystal structure. Further, the growth kinetics of the RE phase formation from molten slag were also described.