Effects of MgO on the mineral structure and softening-melting property of Ti-containing sinter

Certain requirements regarding the chemical composition of slag have to be satisfied to perform a stable blast furnace operation. Particularly, the ratio of MgO to Al₂O₃ in the slag is observed to have a significant influence on the fluidity and desulfurization ability of the slag, along with the the stability of the blast furnace. However, the amount of MgO in the ore could not satisfy the smelting requirement of the blast furnace. Thus, Mg-containing flux has to be added into the ferrous burden. In the ferrous burden structure of the blast furnace that is observed in China, sinter generally accounts for more than 70%. Therefore, the effects of various concentrations of MgO on the quality of sinter are of great significance and must be investigated in further detail. In this study, the influence of MgO on the mineral structure and softening-melting property of Ti-containing sinter were investigated using scanning electronic microscopy (SEM)-energy dispersive spectrometer (EDS) and drop testing. The results depict that increasing the concentration of MgO from 2.04% to 3.96% results in a decrease in the contents of hematite and complex calcium ferrite in the sinter, whereas there is an increase in the mass of liquid phase, magnetite, and silicate. Further, the pore size also gradually increases. Additionally, the hematite content reduces from 13.57% to 9.99%, and the complex calcium ferrite in sinter reduces from 38.7% to 30.17%. Therefore, the increase of MgO in sinter is unfavorable for the development of a liquid phase, which depicts a negative effect on the tumbler strength and reduction index of sinter. Mg in sinter is mainly distributed in complex calcium ferrite. Further, an increase in the concentration of MgO causes a gradual increase in the concentration of magnetite. Additionally, it also causes a part of Mg to be dissolved in magnetite. An olivine solid solution, which contains a minor amount of Mg and Ti, can be observed in high-Mg sinter. Finally, by increasing the concentration of MgO in the sinter, the softening temperature can increase, which is observed to be greater than 1120℃. Further, the softening interval (Δt_A) of the sinter is observed to increase gradually with an increasing MgO content.