Reduction Rate of Dense Wustite with CO-CO₂ Gas Mixtures

Abstract

The reduction rate of dense wustite plates to iron with CO-CO₂-Ar gas mixtures has been measured at 1203, 1273 and 1323K by using a thermobalance. The effects of partial pressures of CO and CO₂/CO ratios in the reducing gas on the reduction rate and the morphology of the iron formed on the wustite were investigated. The reduction proceeded in two consecutive stages. In the initial stage, no formation of metallic iron was observed and the reduction rate was slow. The iron ion concentration at the wustite surface, estimated from the lattice parameter, increased with increasing reduction time and reached eventually to the concentration equilibrated with iron. In the next stage, metallic iron was formed and the reduction rate became markedly higher than that of the initial stage. The reduction rate was affected by the morphology of formed iron and the deposited carbon. On the conditions that porous iron layer was formed uniformly and carbon deposition was negligible, the reduction rate was controlled by the chemical reaction process at the interface. The reduction rate r (kg-oxygen/m²·s) was expressed by the following equation, r=kc·(1-α/Ke)·Pco where Ke and α are the equilibrium constant for the chemical reaction and Pco₂/Pco ratio in the gas phase, respectively. The temperature dependence of the apparent chemical reaction rate constant kc (kg-oxygen/m²·s·Pa) was expressed by the following equation kc=3.84×10^-6·exp(-9.42×10⁴/RT).