Blast Furnace Ironmaking Process with Super High TiO2 in the Slag: High-Temperature Structure of the Slag

To increase the utilization fraction of V-Ti-Magnetite ore in the burden of the blast furnace over 80 pct, the technology of “replacing CaO with MgO” was discussed. The high content of TiO₂-bearing raw materials leads to a super high TiO₂ content in the blast furnace slag, which affects the normal operation of the blast furnace ironmaking process. The physicochemical properties of TiO₂-bearing blast furnace slag such as viscosity are fundamentally determined by the high temperature and structure of the slag. In this study, Raman spectroscopy focusing on the effect of TiO₂ and MgO/CaO ratio on the structure of super high TiO₂-bearing blast furnace slag was performed. The results indicate that most of the Ti⁴⁺ ions are in the tetrahedron unit, and a few of Ti⁴⁺ ions are in the octahedron unit with a coordination number of six; this is confirmed by the presence an emission spectrum related to Ti-O stretching vibrations at wavenumbers less than 700 cm⁻¹. The mole fraction of the band below 700 cm⁻¹, which is related to the coupling of Al-O stretch vibration and the Ti-O stretch vibrations of Ti⁴⁺ in sixfold coordination, increased from 0.14 to 0.19 as the TiO₂ content in CaO-SiO₂-TiO₂-MgO-Al₂O₃ slag increased from 20 to 34 mass pct. The (Q³)²/(Q²) ratio that is proposed as an index for the degree of polymerization (DOP) of melts decreased from 5.72 × 10⁻³ to 1.0 × 10⁻³ as the TiO₂ content increased. Increasing the MgO/CaO ratio caused a slight decrease in the fraction of the bands below 700 cm⁻¹ and resulted in the decrease of the (Q³)²/(Q²) ratio; thus, the DOP of the melts increased with increasing MgO/CaO ratio. The quantitative relationship, ln(η) = 0.91 + 0.11·ln((Q³)²/(Q²)), between the high-temperature structure information and the viscosity of TiO₂-bearing blast furnace slag was established.