Effect of Pre-reduction on the Reduction of Hematite Powder by H<SUB>2</SUB>-H<SUB>2</SUB>O Mixtures

The effect of pre-reduction of sintered hematite powder on the subsequent reduction to iron was investigated. Both the pre-reduction and the subsequent reduction were carried out at 900°C, but the ratio of the partial pressures, pH2/pH2O, in the reducing gas mixtures changed very widely.When the hematite powder was pre-reduced to magnetite, the rate of the subsequent reduction from magnetite to wustite as well as that from wustite to iron was retarded significantly. And topochemical progress of iron-wustite interface could be observed as in the case of the reduction of original hematite without pre-reduction.By pre-reducing the hematite powder to wustite, the subsequent reduction proceeded much faster than the reduction of hematite without pre-reduction, especially when the concentration of hydrogen was much higher than that of water vapor. Under such conditions, the reduction from wustite to iron progressed nontopochemically. As the concentration of water vapor became high, however, the reduction began to progress rather topochemically.By plotting the rate of reduction from wustite to iron against the ratio of hydrogen to water-vapor concentrations, it was found that the equilibrium between wustite and iron shifted apparently to the side of high concentration of hydrogen by such pre-reduction.