Improvement of sinter strength and reducibility through promotion of magnetite ore oxidation by use of separate granulating method

In general, Fe content in iron ore is gradually decreasing. This fact affects worse performance of BF operation, for example, increase of RAR and Slag ratio. Depletion of high grade iron ore deposits is moving us to use concentrates in sintering process. Through magnetite concentration deteriorates reducibility because of high FeO content in sinter product. Such situation makes it to promote oxidation of magnetite iron ore during sintering process for improving sinter reducibility. In addition, promoting oxidation of magnetite possibly increases sinter strength with using oxidation heat. ISIJ sinter research group for utilization of magnetite concentration suggests that restricting melt formation is critical for promoting oxidation of magnetite concentration. In this paper, It is confirmed that “Separate Granulation” has been examined to apply their suggestion by sinter pot test. The main results obtained are described as follows: (1) “Separate Granulation” in case that magnetite is pre-granulated with high Al₂O₃ iron ore without limestone and coke breeze resulted in decrease of FeO in sinter and improvement of both sinter reducibility and sinter strength. (2) Sinter micro structure featured restriction of pore, low circle factor and small mineral texture, which supported that melting restriction worked during sintering. (3) Magnetite decreased and hematite increased as sinter mineral, which corresponded with decrease of FeO content. (4) These facts shown (1) to (3) concluded that “Separate Granulation” is effective to improve both sinter reducibility and sinter strength due to restriction of melting during sinter reaction.