Inhibiting the reoxidation of directly reduced iron by vapour phase inhibitors

Abstract

The inhibition of the reoxidation of direct reduced iron was investigated by establishing different contents of vapour phase inhibitors in oxidising gas mixture He‐O2 at 150 and 200 °C. The raw materials were iron oxide powder and iron ore pellets which were first pre‐reduced by H2 at 500 °C and then reoxidised. Three stages of oxidation are identified, a rapid initial stage, an intermediate stage in which the rate of reoxidation decreases significantly, and a final stage, in which the rate of oxidation is very low. The length of each stage and the rate of reoxidation are related to temperature and to the status of raw materials.Four inhibitors were tested. Benzylamine, ammonium benzoate, and the commercial VCI cortec 101 exert a good inhibition on the reoxidation of iron. The inhibition by ammonia, however, is not significant. Presence of water vapour enhances the reoxidation. XPS analysis reveals amines on the surface when benzylamine is added in the oxidation gases.The ignition temperature of reduced iron decreases with the addition of inhibitors in the oxidation gas atmosphere. This unwanted effect probably is due to organic deposits on iron surface, initiating the burning of iron. The extent of reoxidation, however, is significantly diminished by the inhibitors, thus heating of the material is suppressed and the danger of ignition is decreased.