STEPWISE REDUCTION OF CAO AND OR MGO DOPED FE2O3 COMPACTS TO MAGNETITE THEN SUBSEQUENTLY TO IRON AT 1173-1473 K/

Compacts of pure Fe2O3 and Fe2O3-doped with either of 1.0% CaO and/or 1.0% MgO, sintered at 1 473 K for 20 h, were isothermally reduced at 1 173-1 473 K with 1.O%CO-90%CO2 to magnetite then to metallic iron wit h purified CO. The oxygen weight-loss resulted from Fe2O3-Fe3O4 or Fe3 O4-Fe reduction steps was continuously recorded as a function of time. Chemical and X-ray analyses, microscope examination and pore size ana lyzer were used to characterize the fired and reduced compacts. The in fluence of CaO and/or MgO on the reduction behaviour of Fe2O3 and Fe3O 4 was intensively studied. The reduction mechanisms predicted from bot h of apparent activation energy values and heterogeneous gas-solid mat hematical models were correlated with the microstructures of partially reduced samples. The results obtained showed that the doping of these fluxing oxides promoted the reduction of Fe2O3 at 1173-1473 K. The re duction of pure and doped Fe2O3 compacts is controlled by gaseous diff usion at early stages and by interfacial chemical reaction at later st ages. In Fe3O4-Fe reduction step, the doping of CaO and/or MgO enhance d the reduction at early stages which is temperature and compact compo sition dependent. With progress in reduction, the presence of MgO reta rded the reduction of Fe3O4 at less than or equal to 1 273 K resulting a slowing down in the rate at latter stages. This was attributed to f ormation of entrapped lower oxide relies which hindered gaseous diffus ion. At early stages, the reduction of pure and doped Fe3O4 compacts i s controlled by mixed control reaction mechanism. At latter stages, in terfacial chemical reaction is the rate determining step for pure and CaO-containing samples, whereas solid-state diffusion is the rate cont rolling step for MgO-doped compacts.