Non-isothermal reduction kinetics of oolitic iron ore in ore/coal mixture

Abstract

Mixtures of oolitic iron ore and coal with different C/O molar ratios (1.5, 2.0, 2.5, and 3.0) were heated from 600 to 1300 °C at four heating rates (5, 10, 15, and 20 °C min−1). The degree of reduction and reduction rate were calculated from the measurements of weight loss and off-gas composition using thermogravimetry technique and NDIR gas analyzer. The kinetic parameters (the activation energy, pre-exponential factor, and reduction model) were determined by Ozawa–Flynn–Wall kinetic method and by Satava–Sestak method. It was found that, as temperature increased, the degree of reduction increased, while the reduction rate rapidly increased first, subsequently stabilized, and then decreased. The non-isothermal reduction of oolitic iron ore with coal was significantly influenced by both heating rate and C/O molar ratio, although the impact of the latter was much less. The values of activation energy estimated by Ozawa–Flynn–Wall method ranged from 159.2 to 169.6 kJ mol−1. The mechanism function for the non-isothermal coal-based reduction of oolitic iron ore was D5 reaction model. The non-isothermal kinetic models for coal-based reduction of oolitic iron ore were proposed based on the obtained kinetic parameters. The iron oxide in the oolitic ore was reduced to metallic iron in the sequence of Fe2O3 → Fe3O4 → FeO (FeAl2O4, Fe2SiO4) → Fe. Phase change and reduction mechanism shift were observed during the reduction.