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Quantitative Investigation of MgO, Al2O3 and SiO2 Effects on Solid-State Formation of Secondary Hematite in Sintering Process of Iron Ore Fines

Secondary hematite (SH) is a serious factor resulting in reduction degradation of iron ore sinter in a blast furnace; however, until now, a quantitative study for SH formation had not been reported. In this work, the effects of gangue composition, including MgO, Al2O3 and SiO2, on the solid-state formation in the sintering process of iron ore fines were investigated quantitatively. It shows that the SH formation decreased from 67.84% to 46.11%, 35.44% and 22.37% after adding 1.0%, 3.0% and 5.0% MgO, respectively, while for Al2O3, the amount increased to 69.38%, 69.98% and 70.56%, respectively. For SiO2, the amount changed to 68.14%, 61.59% and 47.96%, respectively. Simultaneously, the magnetite (magnesioferrite) formation increased from 8.24% to 34.79%, 50.26% and 70.45% after adding 1.0%, 3.0% and 5.0% MgO, respectively. For Al2O3 and SiO2, the amount changed to 8.95%, 8.37%, 7.62% and 7.62%, 11.10%, 18.77%, respectively, compared with no gangue. This indicates that the SH formation increased with decrease in magnesioferrite. It was found that the decrease in SH formation relates to the diffusion of Mg2+ in magnesioferrite, which inhibits the solid-state formation of SH kinetically. A supposition was suggested that a maghemite existed at a high temperature, and decreased with an increase in MgO addition. This would be another reason to improve the degradation performance of iron ore sinter.