Reduction and subsequent carburization of pre-oxidation magnetite pellets

Abstract

Magnetite is a kind of iron ore that is difficult to carburize. In order to improve the carburizing performance of magnetite pellet, pre-oxidation treatment was carried out, and the oxidation, reduction and carburization behaviors of magnetite pellet were investigated in this study. The magnetite pellet was oxidized in the air and carburized in CO-CO₂-H₂ gas mixtures, the oxidation, reduction and carburization behaviors were demonstrated by detecting phase change, microstructure, carburizing index via thermogravimetry, X-ray diffraction (XRD), infrared carbon-sulfur analyzer, and scanning electron microscope (SEM). The results show that the dense magnetite particles inside pellet are oxidized to porous hematite particles, and the Fe₃O₄ transforms to Fe₂O₃ with high lattice defect concentration during the pre-oxidation process. Then the porous hematite particles and newly formed Fe₂O₃ significantly promote the reduction efficiency. Porous metallic iron particles are produced in the reduction process. Finally, both high reduction efficiency and the porous structure of metallic iron particles dramatically enhance the carburization efficiency of pellet. High pre-oxidation temperature favors to the carburization of magnetite pellet. However, the carburized index decreases due to the recrystallization of iron oxide when the temperature extends to 1000 ° C. The optimum pre-oxidation temperature for magnetite pellet carburization is 900 °C.

Keywords

magnetite / pre-oxidation / carburization / porous particle / recrystallization

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