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

With the intensified depletion of high-grade iron ores, the increased aluminum content in iron ore concentrates has become unavoidable, which is detrimental to the pelletization process. Therefore, the effect mechanism of aluminum on pellet quality must be identified. In this study, the influence of aluminum occurrence and content on the induration of hematite (H) and magnetite (M) pellets was investigated through the addition of corresponding Al-containing additives, including alumina, alumogoethite, gibbsite, and kaolinite. Systematic mineralogical analysis, combined with the thermodynamic properties of different aluminum occurrences and the quantitative characterization of consolidation behaviors, were conducted to determine the related mechanism. The results showed that the alumina from various aluminum occurrences adversely affected the induration characteristics of pellets, especially at an aluminum content of more than 2.0wt%. The thermal decomposition of gibbsite and kaolinite tends to generate internal stress and fine cracks, which hinder the respective microcrystalline bonding and recrystallization between Fe2O3 particles. The adverse effect on the induration characteristics of fired pellets with different aluminum occurrences can be relieved to varying degrees through the formation of liquid phase bonds between the hematite particles. Kaolinite is more beneficial to the induration process than the other three aluminum occurrences because of the formation of more liquid phase, which improves pellet consolidation. The research results can further provide insights into the effect of aluminum occurrence and content in iron ore concentrates on downstream processing and serve as a guide for the utilization of high-alumina iron ore concentrates in pelletization.