Influence of Oxide and Silicate Melt Phases on the RDI of Iron Ore Pellets Suitable for Shaft Furnace of Direct Reduction Process

Abstract

The temperature in iron ore pelletizing process is as high as 1300–1320°C, so that a significant amount of liquid slag forms in the pellets. The main components of the slag phases are SiO2, FeO, Al2O3, CaO and MgO in various proportions. The slag or melt phase wets the solid surface and facilitates the diffusion and grain growth. After cooling, melt phase solidifies and acts as important bonding phase in the finished pellets and influence high temperature properties, especially reduction degradation index (RDI) to a great extent. The resistance of pellets against degradation during reduction depends on the type of bonding and increases in the order of hematite, ferrite and silicate. In this study commercial pellets of different RDI rang-ing from 8.5 to 14.3 were characterized. Electron and optical micro structural studies with image analysis revealed that the amount and distribution of silicate melt, alumina content of hematite phase, porosity and pore density are vital in controlling the RDI. Residual magnetite in the core of the pellets was found detrimental to RDI. Distribution of different elements in the oxide and melt phase was identified by using X-ray mapping technique and chemistry of different phases was measured using SEM-EDS analysis.