Effect of reduction behavior from Fe2O3 to FeO on the formation of metallic Fe in multi-stage reduction

The current study investigated the reduction behavior of iron ore using hydrogen in four-stage reduction processes. Reduction reactions from Fe2O3 to Fe3O4 and from Fe3O4 to FeO proceeded at the first and second stages, respectively. The third and fourth stages subsequently reduced FeO to metallic iron. Iron ore mixture of hematite and goethite achieved the final reduction degree to be 87% by multi-stage reduction processes. As the duration of reduction at the first stage was decreased, the final reduction degree was improved. The first reduction stage produced the most stable iron oxides as magnetite, while the second reduction stage corresponded to the reduction condition where wustite is the most stable. Decreasing the duration time of the first reduction stage resulted in the decrease of stable magnetite formation, consequently increasing the surface area of reduced iron ore. The omission of the first reduction stage resulted in the highest degree of final reduction of 95%. Kinetic analyses for each reduction reaction were performed to derive the optimal reduction conditions. The reduction of hematite to magnetite at the initial stage of iron oxide was controlled by diffusion, and the rate-controlling step of reduction was gradually shifted to chemical reaction in the reduction from FeO to metallic iron.