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

Abstract

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.