Carbothermic reduction behaviors of Ti–Nb-bearing Fe concentrate from Bayan Obo ore in China

Abstract

To support the development of technology to utilize low-grade Ti–Nb-bearing Fe concentrate, the reduction of the concentrate by coal was systematically investigated in the present paper. A liquid phase formed when the Ti–Nb-bearing Fe concentrate/coal composite pellet was reduced at temperatures greater than 1100°C. The addition of CaCO3 improved the reduction rate when the slag basicity was less than 1.0 and inhibited the formation of the liquid phase. Mechanical milling obviously increased the metallization degree compared with that of the standard pellet when reduced under the same conditions. Evolution of the mineral phase composition and microstructure of the reduced Ti–Nb-bearing Fe concentrate/coal composite pellet at 1100°C were analyzed by X-ray diffraction and scanning electron microscopy–energy-dispersive spectroscopy. The volume shrinkage value of the reduced Ti–Nb-bearing Fe concentrate/coal composite pellet with a basicity of 1.0 was approximately 35.2% when the pellet was reduced at 1100°C for 20 min, which enhanced the external heat transfer to the lower layers when reduced in a practical rotary hearth furnace. The present work provides key parameters and mechanism understanding for the development of carbothermic reduction technology of a Ti–Nb-bearing Fe concentrate incorporated in a pyrometallurgical utilization flow sheet.