Effect of pellet basicity and MgO content on the quality and microstructure of hematite pellets

Quality of pellets is influenced by the nature of ore or concentrate, associated gangue, type and amount of fluxes added and their subsequent treatment to produce pellets. These factors in turn result in the variation of physicochemical properties of the coexisting phases and their distribution during pellet induration. In the present study, effect of pellet basicity and MgO content on the melt formation and microstructure during the induration was examined. Fired pellets with varying basicity (0 to 0.8) and MgO (0 and 1.5%) content were tested for cold strength, reduction degradation index, reducibility, swelling and softening-melting characteristics. Optical microscope studies with image analysis software were carried out to estimate the amount of different phases. SEM-EDS analysis was done to record the chemical analysis of oxide and slag phases. X-ray mapping was also carried out to understand the distribution of CaO, MgO, SiO2 and Al2O3 in different phases. From the results, it was observed that with increasing basicity, RDI and softening-melting characteristics of pellets found to be improved. Addition of MgO to both acid and limestone fluxed pellets considerably reduced their swelling tendency. Improved pellet quality could be attributed to the formation of sufficient amount of silicate melt in basic pellets and high melting point slag in MgO pellets. Limestone fluxed pellets at 0.8 basicity, pyroxenite fluxed pellets at 1.5% MgO and dolomite fluxed pellets at 0.4 basicity & 1.5% MgO exhibited optimum metallurgical properties among all the pellets studied. (C) 2011 Elsevier B.V. All rights reserved.