Influence of Oxygen Partial Pressure on Oxidation Reaction of Iron-bearing Materials in Iron Ore Sintering Bed

Abstract

In the sintering process of iron ores, coke breeze is utilized as a main agglomeration agent. Its replacement with iron-bearing materials such as metallic iron scraps and magnetite ore seem to be a promising way to reduce CO₂ emissions. When using iron-bearing materials together with coke breeze, however, their oxidation reaction appears to be suppressed, since coke combustion tends to decrease in oxygen partial pressure. Therefore, it is necessary to understand the effect of oxygen pressure on the oxidation behavior of the iron-bearing materials. In this study, the oxidation experiments of metallic iron were carried out under the different oxygen partial pressure.

A thin plate sample of metallic iron was heated up to the holding temperature, 1200°C, under N₂ atmosphere. Then, the atmosphere was changed to the oxygen partial pressure of 0.001 - 0.21 atm, which was controlled by using N₂ or CO₂ gas mixture. Oxidation ratio and the thickness of wustite layer formed through the oxidation of metallic iron follows a parabolic manner under P_O2 = 0.21 atm. The thickness of wustite layer decreases after 300 s under P_O2 = 0.21 atm, while the thicknesses of magnetite and hematite layers increase. It appears that the rate-controlling step changes when all metallic iron is oxidized to wustite. Under the condition of P_O2 = 0.01 atm, only wustite layer is observed and the oxidation proceeds faster in CO₂ base than in N₂. It implies that O₂ consumed by oxidation reaction is quickly supplied by the decomposition reaction of CO₂ gas.