Hydrogen-based fluidization direct reduction of high purity iron concentrate: Experimental optimization and mechanism analysis

Abstract

China had a large number of high-grade iron concentrate powder available for utilization, and the process of smelting them using blast furnaces resulted in substantial emissions of CO₂. Compared to carbon reduction, hydrogen reduction could greatly reduce the emission of greenhouse gases and harmful gases. To efficiently convert high-purity iron concentrate into metallic iron, the process and mechanism of direct reduction of high-purity iron concentrate under hydrogen atmosphere were systematically investigated in this paper. Experimental results revealed that the metallization rate of the product could reach 95.26 % under the optimum conditions of reduction temperature of 575 °C, H₂ concentration of 60 vol% and reduction time of 60 min. Thermodynamic calculations, phase transformation analyses, and studies of microstructure evolution indicated that temperature has a considerable impact on the reduction of iron concentrate, and that the final reduction products exhibited great differences in phase and microstructure at different temperatures. Reduction of the iron ore progressed from the exterior to the interior within the temperature range of 500–575 °C, leading to increasing degrees of reduction and continuous formation of sponge-like metallic iron. The particle surfaces are covered with cross-shaped cracks. As the reduction temperature is further increased, the reduction reaction changes, forming intermediate product wüstite. Particles displayed a dense state where metallic iron surrounded wüstite, with numerous pores formed on the particle surfaces.