Reduction of Fine Particle of Iron Oxides by H₂-H₂O Mixture

Abstract

Small α-hematite particles with mean diameter of 8.1μ were reduced at 900°C in a gas stream of hydrogen and water-vapour. The investigation was forcused on the effect of water-vapour on the reduction of wüs-wustite. The appearance of product iron, its growth, and the change of pore shapes were examined with both scanning electron and optical microscopes. The reduction rate was obtained by measuring the weight change of the solid sample due to the reduction.
When the partial pressure of water-vapour was less than 0.32 atm, the reduction rate was first order to the hydrogen partial pressure. Under those conditions, many spots of metallic iron could be observed on the surface of wastite particle. Then, they covered the whole surface in the early stage of reduction. After that, the reduction proceeded shell-likely.
However, when the partial pressure of water-vapour was more than 0.32atm, the reduction was retarded significantly by the water-vapour, especially at low fractional reduction, although the reductiontemperature was as high as 900°C. This gave remarkably sigmoid reducing curves. Under those conditions, a part of the outer surface of wastite particle was not covered with metallic iron, even when the reduction already proceeded into the inner part of wastite particle. It could be concluded that this kind of partial growth of product iron was one of the important factors to make the reducing curves sigmoid.