2015 Volume 55 Issue 4 Pages 751-757
Comprehensive utilization of low grade ludwigite is critical important for the safe supply of boron resource of China. Boron-bearing iron concentrate is the intermediate product of the ore dressing process of crude low grade ludwigite and extracting boron from it has great effect on the total boron yield. Pre-reduction of the boron-bearing iron concentrate is one of the important steps of the pyrometallurgical boron and iron separation process. The carbothermal reduction study of boron-bearing iron concentrate was carried out in the present work. The reduction rate was improved with the increasing of heating temperature and carbon content. The appropriate temperature and C/O (mole ratio of fixed carbon to reducible oxygen) were 1200 to 1300°C and 0.8 to 1.2, respectively. In addition, the microstructure and phase evolution of the pellet during the reduction process were characterized by means of SEM and XRD. The apparent activation energy of the iron oxide reduction in the composite pellet was 114.32 kJ/mol based on the first-order reaction model. The iron and slag separate well when the reduced pellets were heated at 1550°C. The B2O3 content of the slag and the boron element content of the pig iron were 10.8 wt% and 0.74 wt%, respectively. The main minerals in the slag were olivine, kotoite, periclase and spinel after slow cooling, and the efficiency of extraction of boron (EEB) of the slag was 68.4%. The boron-rich slag and boron-bearing pig iron can be used as the raw materials for boron extraction and steel making.