EFFECT OF RAW-MATERIAL COMPOSITION ON THE MINERAL PHASES IN LIME-FLUXED IRON-ORE SINTER

In this study small tablet specimens of powdered commercial iron ores mixed with fluxes and kaolin were heated in a reducing atmosphere and then cooled slowly in air to simulate industrial sintering. The effect of different ore and flux compositions on the phases found in the sinter bond was studied. An increase in basicity (CaO/SiO2) favoured the formation of calcium ferrite and densification of the bond at a low sintering temperature. The amount of calcium ferrite decreased as the Al2O3 content decreased and the amount of reoxidized hematite produced on cooling decreased. A decrease in Al2O3 content promoted a densification of the bond. An increase in MgO content, introduced by addition of dolomite, decreased the amount of calcium ferrite slightly. When MgO was added in the form of serpentine the calcium ferrite content increased considerably. Increase in MgO markedly reduced the amount of reoxidized hematite but produced a less dense bond. Generally the same composition and sintering temperature produced similar mineral compositions in the bond independent of the iron ore used. The only exception was when an ore with coarse dense hematite was used, in which case the bond contained some unreacted hematite. The porosity of the bond did vary with the type of ore used. Limonitic ore produced a bond with closed pores and less reoxidized hematite at lower temperature and basicity than did hematite ores.