Reduction behavior and kinetics of iron ore pellets under H2–N2 atmosphere

Abstract

Direct reduction behavior and dynamic characteristics of oxidized pellets under the 75%H2-25%N2 atmosphere at 760, 900, 1 000°C are studied in this paper. 500 g oxidized pellets in the size of 10–12.5 mm are reduced by gas with the flow rate of 12 L·min−1 for 1 hour. Weight loss during reduction was recorded and the model of un-reacted core was adopted for dynamic analysis. Morphology of metalized pellets was analyzed through optical microscope and scanning electron microscope. Compressive strength and degradation index were also detected. Results showed that both the reduction degree and reaction rate increased with the increasing temperature. The reduction rate was controlled by chemical reaction with the apparent activation energy of 40.954 kJ·mol−1. The chemical reaction resistance could be effectively reduced through appropriately raising the temperature. However, the effectiveness was weakened with the further increase of temperature. The reaction rate constant at 900°C was 0.025 m·s−1, which was slightly lower compared with reduction kinetics under pure hydrogen. The compressive strength decreased with the increasing temperature, and amounts of holes and cracks were observed at higher temperature. Reduction degradation behavior of pellets under this atmosphere was not obvious.