Mineralogical Aspects of Reducing Lump Iron Ore, Pellets, and Sinter with Hydrogen

Iron ore, pellets, and sinter were reduced with hydrogen at 800 degrees C to understand the degree of reduction and the mineralogical aspects. The weight loss of goethite and limonite iron ore was noticed to be lower than that of magnetite and hematite varieties. X-ray diffractometry (XRD) indicated 100 pct Fe in the case of hematite, 93 pct in magnetite, 53 pct in goethite, and as low as 15 pct in limonite. The phenomenon of cracking of pellets was not evidenced when reduced with hydrogen whereas cracks were noticed when reduced in 30 pct CO at 950 degrees C. Finer grains of 10 to 20 mu m in the case of lump ore and 40 to 100 mu m in the case of pellets were noticed. In the case of sinter, grain size up to 20 to 50 mu m was noticed. A maximum Fe up to 96 pct in some locations in pellets and 99 pct in sinter was observed when reduced with hydrogen. Applications of hydrogen/hydrogen-rich gas in the sinter plant and COREX were discussed briefly in this article. A unique zebra pattern of magnetite and silico ferrite of calcium and aluminum (SFCA) was observed when hydrogen-rich coke oven gas was injected into the sinter bed. Magnetite formation in sinter was predominant and is attributed to the high diffusion rate of hydrogen.