Reduction mechanism of high-chromium vanadium–titanium magnetite pellets by H2–CO–CO2 gas mixtures

Abstract

The reduction of high-chromium vanadium–titanium magnetite as a typical titanomagnetite containing 0.95wt% V2O5 and 0.61wt% Cr2O3 by H2–CO–CO2 gas mixtures was investigated from 1223 to 1373 K. Both the reduction degree and reduction rate increase with increasing temperature and increasing hydrogen content. At a temperature of 1373 K, an H2/CO ratio of 5/2 by volume, and a reduction time of 40 min, the degree of reduction reaches 95%. The phase transformation during reduction is hypothesized to proceed as follows: Fe2O3 → Fe3O4 → FeO → Fe; Fe9TiO15 + Fe2Ti3O9 → Fe2.75Ti0.25O4 → FeTiO3 → TiO2; (Cr0.15V0.85)2O3 → Fe2VO4; and Cr1.3Fe0.7O3 → FeCr2O4. The reduction is controlled by the mixed internal diffusion and interfacial reaction at the initial stage; however, the interfacial reaction is dominant. As the reduction proceeds, the internal diffusion becomes the controlling step.