Reoxidation of direct reduced iron in ambient air

Abstract

Fresh reduced direct reduced iron pellets produced in a commercial furnace were reoxidised in ambient air for 1–50 days at an average temperature of 27°C. The degree of reoxidation was determined by weight gain. The reoxidation process is controlled by an irreversible first order reaction with respect to oxygen. A model based on reaction between gas and porous solid was used to calculate the degree of reoxidation with time. The calculation results agree satisfactorily with the experimental data. The apparent rate constant of reaction varies between 1·65×10⁻³ and 4·55×10⁻³ g/cm²/day, and is inversely proportional to the initial radius of the pellet. The effect of reoxidation on degree of metallisation and relative metallisation loss was also investigated. In all cases, two distinct groups of data resulted, reflecting the behaviour of the two types of oxide pellets charged in the furnace.