Effect of Hydrogen Concentration in Reducing Gas on the Changes in Mineral Phases during Reduction of Iron Ore Sinter

Abstract

In order to decrease CO₂ emission from the ironmaking process, an increasing use of hydrogen in blast furnace (BF) ironmaking is a promising way. In this case, the properties of iron ore sinter such as reducibility and strength need to be optimized because hydrogen reduction of iron oxide is an endothermic reaction and temperature distribution in BF drastically changes. In this study, the effect of hydrogen concentration in the reducing gas on the changes in mineral phases during reduction of iron ore sinter is evaluated. Mineral composition of the ten types of sinter samples was analyzed by XRD and image analysis. Sinter sample was reduced under the simulated conditions such as Low-H₂ (N₂ − 48%(CO + CO₂) − 5.8%(H₂ + H₂O)) and High-H₂ (N₂ − 48%(CO + CO₂) − 13%(H₂ + H₂O)). After reduction, microstructure of the sample was observed. Iron ore sinters usually consist of mineral phases such as hematite, magnetite, calcium-ferrites and slag. Furthermore, calcium-ferrite phases are roughly divided into four types: 1) acicular texture coexisted with primary hematite (1H-ACF), 2) columnar texture coexisted with secondary hematite (2H-CF), 3) small and 4) large columnar textures coexisted with magnetite (M-FCF and M-CCF). An increase in hydrogen concentration of reducing gas accelerates the reduction of hematite, 1H-ACF, and 2H-CF in all sinter samples, while it does not affect the reduction of magnetite, and calcium-ferrite coexisted with magnetite.