Stepwise reduction of CaO and/or MgO doped-Fe2O3compacts (hematite-wüstite-iron transformation steps)

Pure Fe 2 O 3 and Fe 2 O 3 doped with either 1.0% CaO and/or 1.0%MgO fired compacts were isothermally stepwisely reduced at 1173-1473K. At a given temperature, hematite was first reduced to wustite (Fe 0.934 O) in CO/CO 2 gas mixtures, then subsequently to iron in pure CO. The influence of doping oxide composition on the reduction behaviour of hematite to wustite and wustite to iron was intensively studied. The presence of CaO and/or MgO promoted the reduction rate of hematite at early stages. At ≥70% extents, the presence of MgO retarded the reduction of Fe 2 O 3 due to the formation of hardly reducible magnesioferrite phase. The reduction of hematite to wustite is controlled by a mixed reaction mechanism at early stages and by interfacial chemical reaction at later stages. The reduction of wustite to iron is also promoted at early stages in the presence of these doping oxides. At later stages, while the presence of CaO still promoted the reduction, the presence of MgO retarded the reduction, resulting in a slowing down in the rate at final stages. The wustite-iron transformation step is controlled by a mixed reaction mechanism at early stages. At later stages, the reduction of of CaO-doped compacts is controlled by interfacial chemical reaction, while solid-state diffusion is contributed to the interfacial chemical reaction in the reduction of pure and MgO-containing samples.