Carbonization and nitridation of vanadium–bearing titanomagnetite during carbothermal reduction with coal

Direct reduction–magnetic separation followed by low temperature chlorination was a promising process to comprehensively utilize vanadium–bearing titanomagnetite (VTM). Herein, the conversion of titanium oxides to TiC/TiN/Ti(C,N) is extremely critical. In this study, the carbonization and nitridation of VTM during carbothermal reduction under different atmosphere was investigated. Thermodynamic analysis indicated that the reduction, carbonization and nitridation of VTM was feasible via carbothermal reduction by carbon. Introducing N2 into the reaction system was beneficial to decrease the equilibrium temperature by forming TiN instead of TiC. The experimental results showed that the Fe metallization ratio (MFe/TFe) reached about 100 wt% above 1150 °C regardless of the reduction atmosphere. The maximum carbonization ratio of Ti (TiC/TTi) was 98.55 wt% after roasting at 1300 °C for 2.5 h in Ar atmosphere. The total carbonization and nitridation ratio (TiN/TTi) was 99.55 wt% when reduced at 1300 °C for 2.5 h in N2 atmosphere. The main Ti–bearing phases were reduced and carbonized in the order of ilmenite (FeTiO3)→ ferropseudobrookite (FeTi2O5)→ Fe,Ti,Mg Oxide (Fe0.33Ti0.46Mg0.21)(Ti1.9Mg0.1)O5→ titanium carbide (TiC). TiC was further nitrided to form TiN, which combined with TiC as titanium carbonitride (Ti(C,N)). TiC/TiN/Ti(C,N) granules, with a particle size less than 10 μm, were mainly dispersedly distributed in metallic iron. They also gathered at the edge of metallic iron and part of them existed in the the interval between metallic iron and gangue minerals.