Carbothermal Reduction, Melting Separation, and Structural Analysis of Carbon-bearing Rare Earth Iron Ore Pellets

The slag of rare earth Bayan Obo complex iron ore (REBOCIO) after direct reduction and melting contains a lot of rare earth elements (REEs). In this work, the isothermal reduction and melting separation experiments of REEs-bearing iron carbon composite pellets and the detailed characterization of rare earth (RE) slag were conducted, with the aim at developing knowledge of the reduction mechanism and the behavior of REEs during the direct reduction and melting process. The results indicate that the pellets can be optimally reduced at 1200°C for 15 min with a C/O ratio of 1.2. The RE-containing phases differ depending on the reaction conditions. When the temperature is relatively low at 1100°C, the major RE phase in the slag is Ce4.67 (Si O4)3 O; while (Ca, Ce, La)5(SiO4)6F becomes the dominant RE phase in the slag at 1400°C. The main crystalline phase in the air-cooling slag are cuspidine (Ca4Si2O7F2), (Ca, Ce, La)5(SiO4)6F and fluorite (CaF2). The particle size of the RE phase increases as the cooling rate decreases. In the case of furnace cooling, the RE phase in the slag has a more complete structure, namely hexagonal prismatic. And the RE phase is hexagonal system with space group P 63/m and unitcell parameters a = 9.5908(3) Å, b = 9.5908(3) Å, c = 7.0268(2) Å, β = 90 (3)°, and V = 559.75(4) Å3.