Isothermal reduction kinetics and microstructure evolution of various vanadium titanomagnetite pellets in direct reduction

Abstract

Vanadium titanomagnetite (VTM) pellets is an important charge for utilizing VTM through the rotary kiln-electric furnace process, and its reduction characteristic is essential to industrial production. This paper investigated the reduction behaviors and mechanism of three types of fired VTM pellets, i.e. PA, PB and PC with 13.02%, 11.70% and 5.25% TiO2, respectively. Under the optimal conditions, which were reduced at 1423 K for 150, 120 and 100 min, respectively, they obtained more than 90% reduction degree. During reduction, PA exhibited excellent resistance to volume swelling and great morphology, while PB and PC displayed abnormal swelling and structural damage. Kinetic and microstructure studies indicated that the reduction of PA, which consisted of titanohematite and pseudobrookite, was controlled by the random nucleation and subsequent growth of metallic iron, whereas that of PB and PC, which mainly contained titanohematite, was controlled by intrinsic chemical reactions. Iron- and titanium-bearing oxides were reduced to metallic iron via two routes: titanohematite → titanomagnetite → wustite → metallic iron and pseudobrookite → metallic iron. These various compositions and grain sizes of iron- and titanium-bearing oxides led to different generation rates and morphologies of metallic iron, directly affecting the reduction characteristics and macroscopic performance of VTM pellets.