Reduction of CaO and/or MgO-doped Fe₂O₃ Compacts with Carbonmonoxide at 1173-1473 K

Abstract

Compacts of Fe₂O₃ doped with either (0.5-5.0%) CaO, 1.0% MgO and/or 1.0% CaO fired at 1473 K for 20 hr, were isothermally reduced with CO gas at 1173-1473 K. Thermogravimetric technique was used to follow up the oxygen weight-loss as a function of time. Partially and completely reduced samples were subjected to chemical and carbon analyses while their internal structure was examined by optical microscope. Pore size analyser was used to characterize pore structure and pore size distribution. The different phases developed during reduction were also identified by X-ray diffraction technique. It was observed that the doping of CaO revealed different effects on the reduction of pure Fe₂O₃ depending on CaO content, temperature and reduction extents. At lower temperatures (≤1273 K), the doping of ≤2.5% CaO promoted the reduction of Fe₂O₃ and a maximum effect was observed for compacts doped with 1.0% CaO. At ≥1373 K, the doping of CaO retarded the reduction of Fe₂O₃ at the latter stages due to the sintering and densification effects which increased with temperature. The influence of MgO on the reduction of Fe₂O₃ was discussed in another publication. The doping of 1.0% CaO with 1.0% MgO in Fe₂O₃ compacts greatly promoted the reduction of Fe₂O₃ at <1273 K and this effect decreased with temperature. Heterogeneous gas-solid raction formulations were examined and correlated with both of the apparent activation energies and the internal structures of partially reduced compacts to elucidate the corresponding reduction mechanisms.