Effect mechanism of aluminum occurrence and content on the induration characteristics of iron ore pellets

With a growing depletion of high-grade iron ores, the increased aluminum content in the iron ore concentrates is unavoidable, which is detrimental to the pelletizing process. Therefore, it is essential to discover the effect mechanism of aluminum on pellet quality. In this paper, the effect of aluminum occurrence and content on the induration of both hematite and magnetite pellets was investigated by adding corresponding Al-containing additives including alumina, alumogoethite, gibbsite and kaolinite. The related mechanism was also revealed through not only systematic process mineralogy analyses combined with the thermodynamic properties of different aluminum occurrence, but also the quantitative characterization of consolidation behaviors. The results show that the alumina from different aluminum occurrence had an adverse effect on the induration characteristics of pellets, especially when the aluminum content was more than 2.0wt%. The thermal decomposition of gibbsite and kaolinite will tend to generate internal stress and fine cracks, which go against the respective formation of microcrystalline bonding and recrystallization between the Fe₂O₃ particles. The adverse effect on the induration characteristics of fired pellets with different aluminum occurrence can be relieved to varying degrees through the formation of slag bonds of CaO-Fe₂O₃-Al₂O₃-SiO₂ polybasic eutectoid between the hematite particles. The kaolinite is more beneficial to the induration process than other three aluminum occurrence because of formation of more liquid phase which improves the consolidation of pellets. The research results can help to further understand the effect of aluminum occurrence and content in iron ore concentrates on downstream processing, and then provide a good guidance for the utilization of high-alumina iron ore concentrates in pelletizing.