Improving the Reduction Swelling Behavior of Fired Hematite Pellets by Increasing Basicity

Oxide pellets are widely regarded as high-quality raw materials for BF ironmaking and direct reduction iron processes due to their excellent strength, performance and environmental properties. The decrease in the availability of magnetite resources has made the steel industry increasingly relying on hematite pellets. Therefore, understanding the reduction behavior, especially the swelling mechanism, and improving the reduction behavior of hematite pellets in coal-based reduction processes is of paramount importance. In this study, high grade hematite pellets were selected as the raw material, and the basicity was adjusted for the evaluation of coal-based reduction behavior. The results showed that natural basicity hematite pellets could achieve a maximum reduction expansion of 55.20%. Increasing the pellet basicity significantly improved the post-reduction swelling, ultimately leading to normal swelling, with a metallization rate exceeding 94%. Through mineral analysis and microscopic morphology analysis, it was found that an increase in basicity leads to a denser grain structure, reducing the reaction rate and thus decreasing the strain forces generated during reduction. Additionally, the growth of iron grains results in the formation of a denser iron layer after reduction, further lowering the RSI (Reduced Swelling Index).