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→Fe O, and Fe O→Fe, which start at 912 K, 1255 K, and 1397 K, respectively. The CO content in the evolved gas is lower than the CO2content in the Fe2O3→Fe3O4stage but is substantially greater than the CO2 contents in the Fe3O4→Fe O and Fe O→Fe stages, where gasification starts at approximately 1205 K. The activation energy（E） of the three stages are 126–309 k J/mol, 628 k J/mol, and 648 k J/mol, respectively. The restrictive step of the total reduction is Fe O→Fe. If the rate of the total reduction is to be improved, the rate of the Fe O→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 FexOy reduction by CO, which are the restrictive step in the last two stages, require further study.