At present, cost reduction and environmental protection are the mainstream of blast furnace (BF) development and the high lump ore ratio is an effective means. Therefore, it is significant to explore the relationship and mechanism of burden soft-melt dropping and its primary-slag formation behaviors under increasing lump ore ratio. In this paper, the melt–drop test is carried out on the single ore and mixed burden, and obtained primary-slag properties are subjected to analysis. The experimental results show that the primary-slag of lump ore contains a large amount of FeO and SiO₂, so it simply produces many low melting point compounds, which cause terrible soft-melt dropping properties and primary-slag formation behaviors. Notably, mixing with sinter and pellet can effectively improve both the properties. With the increase in lump ore ratio, the CaO in the primary-slag decreases, FeO and SiO₂ increase, resulting in the melting temperature of the primary-slag sequentially decreasing and the cohesive zone moves to the low temperature zone. In addition, the maximum pressure difference increases, and the gas permeability deteriorates. Increasing the sinter ratio can overcome the defect of high lump ore ratio that can effectively improve the poor softening performance, melting performance and the position and thickness of the cohesive zone. However, because of the pulverization performance, the maximum pressure difference and gas permeability of the burden become worse.

In order to clarify the effect of the MgO/Al₂O₃ ratio on the fluidity of a low-alumina blast furnace slag system, the influence law of slag fluidity with different MgO/Al₂O₃ ratios was studied based on the composition of blast furnace slag through a viscosity experiment and themodynamic software. By studying the effect of the MgO/Al₂O₃ ratio on the activation energy of viscous flow of slag combined with FT-IR, the effect of the MgO/Al₂O₃ ratio on the thermal-stability of low-aluminum slag was interpreted from the microstructure level. Results indicated that the viscosity and the melting temperature of slag both showed a gradual downward trend due to the increase of the MgO/Al₂O₃ ratio. Besides, the temperature stability of the low aluminum slag became more stable due to the depolymerization of the complex structure of slag. Considering the actual operating conditions of blast furnace, the MgO/Al₂O₃ ratio of slag was suggested to be controlled to 0.60 and the basicity to be no higher than 1.20 under the conditions of this investigation. Industrial test results showed that the coke rate could be saved as 3.49 kg/t when the MgO/Al₂O₃ ratio decreased from 0.70 to 0.58.

A low-cost and high-efficiency solid reaction method has been reported as an effective technology to synthesize manganese ferrite MnFe₂O₄ with a spinel crystal structure. This work clarified the underlying reason for the influence mechanism of SiO₂ and Al₂O₃ on the synthesis of MnFe₂O₄. Synthetic MnFe₂O₄ polyhedral microparticles with a saturated magnetization of 71.19 emu/g, a ratio of saturation magnetization to residual magnetization (Ms/Mr) of 0.062 and a coercivity (Hc) of 6.50 Oe were successfully obtained at an oxidization roasting temperature of 1100 °C for 60 min. The experimental results indicate that the tetrahedral Mn²⁺ ions and octahedral Mn³⁺ ions in the crystal structure of manganese ferrite MnFe₂O₄ were replaced by tetrahedral Si²⁺ ions and octahedral Al³⁺ ions from (Mn²⁺)_x(Fe²⁺)_y(Si²⁺)_1−x−y[Fe³⁺]₂O₄ and (Mn²⁺)[Fe³⁺]_2−x[Al³⁺]_xO₄, respectively. In addition, hercynite Fe_xMn_1−xAl₂O₄ with a spinel crystal structure and olivine Mn_xFe_2−xSiO₄ with an orthorhombic crystal structure were partially formed in the synthesis of manganese ferrite MnFe₂O₄, in which some Fe²⁺ ions were easily replaced by Mn²⁺ ions to form stable hercynite MnAl₂O₄ and olivine Mn₂SiO₄ in these crystal structures. The current research work provides comprehensive insights for synthesizing manganese ferrite MnFe₂O₄ and continuously advances its technical progress.