The effects of SiO₂ content on the compressive strength, reduction behavior and melting-dripping properties of the pellets were investigated under experimental conditions. The experimental results indicated that the compressive strength of pellets gradually decreased with increasing SiO₂ content, mainly because the pellets with high SiO₂ had poor crystallization capacity, a more liquid phase and more pores. With increasing SiO₂ content from 2.19 wt% to 8.13 wt%, the reduction degree of pellets descreased due to the generation of 2FeO·SiO₂. Based on the morphology analysis, inside of the pellets, 2FeO·SiO₂ caused the compact structure and fewer microspores with increasing SiO₂ content, which was unfavorable for the reduction process and resulted in the decrease of the reduction degree. Also, increasing the SiO₂ content had negative effects on the melting-dripping properties of pellets. The melting-dripping properties can be improved by adding some sinter with high basicity in the mixed burden. The current work established the relation between SiO₂ content and reduction-melting behavior of pellets, which can provide theoretical and technical support for the effective utilization of pellets with different SiO₂ content in blast furnace process.

The induration process of oxidized pellet, containing the oxidation of magnetite phase (Fe₃O₄) and the sintering of oxidized magnetite phase (hematite–Fe₂O₃), is significant to obtain sufficient pellet strength. The current study focuses on the induration mechanisms of MgO flux pellet in terms of the oxidation process of Fe₃O₄ and densification process of the pellet. It is found that MgO dosage negatively affects the oxidation of Fe₃O₄ into Fe₂O₃. The number of recrystallized grain of Fe₂O₃ in the MgO flux pellet is less than that in the Non-MgO flux pellet. Additionally, an unreacted core model was applied to consider and clarify the oxidation of Fe₃O₄. According to the verification experiments, the experimental data and calculated results fit well. Therefore, the unreacted core model can describe the oxidation of Fe₃O₄ in the pellet induration process. Moreover, based on the development of pore parameters during the pellet induration process, a new index, the so-called oxide densification index (ODI) was defined to profoundly specify the densification degree of the pellet. The results show that the ODI of the MgO flux pellet maintains at a lower level compared with that of the Non-MgO flux pellet. It illustrates that MgO can substantially restrain the pellet densification process.

With the gradual depletion of high-quality iron-ore resources, ironmaking blast furnaces have gradually shifted to using high-content Al₂O₃ iron ore. Under this condition, the addition of MgO in the slag is adopted to alleviate operation problems caused by the high content of Al₂O₃. However, the proper value of the MgO/Al₂O₃ ratio for blast-furnace slag systems (Al₂O₃ = 8–25%) is not systematically studied. In this paper, we discuss the proper MgO/Al₂O₃ ratio on the basis of blast-furnace slag systems under different Al₂O₃ contents. On the basis of thermodynamics and phase-diagram analysis, it could be concluded that: (1) the MgO/Al₂O₃ ratio is not limited when Al₂O₃ in slag is less than 14%, (2) the MgO/Al₂O₃ ratio is required to be in the range of 0.40–0.50 when Al₂O₃ in the slag is 15–17%, and (3) the MgO/Al₂O₃ ratio should be 0.45–0.55 when Al₂O₃ in the slag is larger than 18%. The proper MgO/Al₂O₃ ratio value has been established in various industries, and it has achieved significant economic and social benefits.