Effect of fluxing agents on the swelling behavior of hematite pellets

• Effect of different fluxes on microstructure and swelling was examined.
• Limestone decreased swelling at lower basicity but showed highest at 0.6 basicity.
• Addition of magnesite and pyroxenite considerably decreased swelling.
• Swelling decreased due to formation of magnesioferrite and high melting point slag.

Pellet properties are largely governed by the form and degree of bonding achieved between ore particles during induration and the stability of these bonding phases during reduction. Fluxing agents play an important role in forming these bonds by forming different phases depending on the type of flux. In the present study, effect of different fluxing agents, viz., limestone, magnesite and pyroxenite, on melt formation & microstructure during the induration and on swelling behavior during reduction, was examined. Optical microstructural studies with image analysis were carried out to estimate the amount of different phases. SEM-EDS analysis was done to measure 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 limestone addition decreased the swelling at lower basicity but exhibited highest swelling at 0.6 basicity and decreased thereafter. Formation of low melting point calcium olivines between Fe2SiO4 and Ca2SiO4 can be attributed to the highest swelling at 0.6 basicity. With increasing addition of magnesite and pyroxenite, pellet swelling found to be decreased considerably. Formation of magnesioferrite phase and high melting point slag formed during induration could be attributed to the improved swelling of magnesite and pyroxenite fluxed pellets. Limestone fluxed pellets at 0.8 basicity, pyroxenite fluxed pellets at 1.5% MgO and magnesite fluxed pellets at 1.0% MgO exhibited low swelling behavior among all the pellets studied.