Effect of Aluminum Occurrence State on the Formation of Calcium Ferrites in the Sintering Process of Iron Ore Fines

摘要

High basicity sinter is a major iron bearing material used in blast furnace for ironmaking in Asia-Pacific countries. The strength and reducibility of sinter have been paid more attention in recent studies because they affect the efficiency of blast furnace production. The indexes are mainly influenced by the nature, abundance and morphology of mineral phases existing in the high basicity sinter, especially the silico-ferrite of calcium and aluminum (SFCA) as a primary bonding phase which determines the quality of high basicity sinter. Al_2O_3 is an important component of SFCA, the occurrence states of Al_2O_3is mainly divided into two types, one is existing in the iron ore as gangue whose main forms are gibbsite (Al(OH)_3) and kaolinite (Al_2Si_2O_5(OH)_4), the other one is dissolved in the iron oxides like the Al-containing hematite and goethite. In recent years, much works have been done on the effect of Al_2O_3 on formation mechanism of SFCA. Most studies adopted the gibbsite and Al_2O_3pure reagent as the source of alumina. Although the phenomenon of solid solution in iron oxides has been noticed decades ago, almost no related research has focused on the effect of aluminum occurrence state on the formation of calcium ferrite so far. In this experiment it was conducted to investigate the effect of aluminum occurrence state, the wrapping and solid solution into hematite, on the formation of calcium ferrite in sintering process of iron ore fines by simulating the solid-solid and solid-liquid state sintering process. X-ray diffraction, optical microscope and SEM-EDS were used to characterize the phase change of the sintered samples. The results show that in the sintering process of CaO-Fe_2O_3-Al_2O_3 ternary system, the aluminum dissolved in Fe_2O_3 as a solid solution plays a more prominent role in increasing the CFA content, especially in the solid-liquid reactions. Simultaneously, aluminum in solid solution state is easier to enter into CFA in solid state reactions. Therefore, in the sintering process of CaO-Fe_2O_3-Al_2O_3-SiO_2 quaternary system, the generation amount of SFCA in solid solution group is more than that in wrapping group, but the difference between the two groups is not as large as that in ternary system due to the addition of SiO_2.