Staged reaction kinetics and characteristics of iron oxide direct reduction by carbon

Staged reduction kinetics and characteristics of iron oxide direct reduction by carbon were studied in this work. The characteristics were investigated by simultaneous thermogravimetric analysis, X-ray diffraction (XRD), and quadrupole mass spectrometry. The kinetics parameters of the reduction stages were obtained by isoconversional (model-free) methods. Three stages in the reduction are Fe₂O₃→Fe₃O₄, Fe₃O₄→FeO, and FeO→Fe, which start at 912 K, 1255 K, and 1397 K, respectively. The CO content in the evolved gas is lower than the CO₂ content in the Fe₂O₃→Fe₃O₄ stage but is substantially greater than the CO₂ contents in the Fe₃O₄→FeO and FeO→Fe stages, where gasification starts at approximately 1205 K. The activation energy (E) of the three stages are 126–309 kJ/mol, 628 kJ/mol, and 648 kJ/mol, respectively. The restrictive step of the total reduction is FeO→Fe. If the rate of the total reduction is to be improved, the rate of the FeO→Fe reduction should be improved first. The activation energy of the first stage is much lower than those of the latter two stages because of carbon gasification. Carbon gasification and Fe_xO_y reduction by CO, which are the restrictive step in the last two stages, require further study.