Reduction kinetics of hematite ore fines with H^sub 2^ in a rotary drum reactor

Porous hematite ore was prepared by the dehydration of low-grade limonite ore with high moisture content. In this study, the mechanisms and kinetics of the isothermal reduction of hematite ore fines by hydrogen–nitrogen gas mixtures were investigated using a rotary drum reactor in the temperature range of 700–900 °C. The reduction rate and degree of reduction initially increased with H2 content and temperature, and subsequently, the reduction rate decreased with the increasing reduction reactions of iron oxide. Our results indicate that the dehydration significantly increases the specific surface area of the original limonite ore, creating nanopores. We found that the reduction of hematite (Fe2O3) to metallic iron (Fe) was controlled by a first-order reaction model (one-dimensional formation and growth of nuclei) below 850 °C. However, at 900 °C, the reaction initially followed the above model and then shifted to follow a diffusion-controlled reaction model in the final stages of reduction owing to the low diffusion rate of oxygen in the formed dense iron layer. The value of the apparent activation energy for the overall reduction process of hematite to metallic iron was ~51 kJ/mol.