Effect of Alumina on Liquid Phase Formation in Sintering Process of Iron Ore Fines

The formation of liquid phase is of great significance for improving the quality of high basicity sinter which is widely used as raw materials in blast furnace ironmaking. As an important component of gangue in iron ore, alumina affects the amount of liquid phase by influencing the formation of calcium ferrites-bonding phase. In this work, the hematite solid solution with aluminum (H-ss) was prepared and sintered with CaO to investigate the effect of alumina on liquid phase formation in sintering process of iron ore fines. Three homogeneous phases of CaFe2O4 (CF), Ca2Fe15.57O25.56 (CF3.9), and Ca3.18Fe15.48Al1.34O28 (CFA) are prepared to determine the melting temperature by using DSC method. XRD, SEM-EDS, and optical microscope are used to characterize the change of mineral and microstructure of sintered samples. The results show that an Fe-rich calcium ferrite CF3.9 is produced above 1200 degrees C in Fe2O3-CaO binary system. The liquid phase formation temperature can be reduced to 1206 degrees C when CF3.9 and CF coexist. The ternary calcium ferrite CFA, which has a eutectic temperature of 1201 degrees C with CF, is generated above 990 degrees C in Fe2O3-CaO-Al2O3 ternary system. The formation of liquid phase is promoted by adding alumina in moderation through changing the mass ratio of CF to CFA, and the largest amount of liquid phase is produced when the ratio is 8:2.