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

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 → Fe_2.75Ti_0.25O₄ → FeTiO₃ → TiO₂; (Cr_0.15V_0.85)₂O₃ → Fe₂VO₄; and Cr_1.3Fe_0.7O₃ → 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.