Blast Furnace Ironmaking Process with Super-High TiO₂ in the Slag: Sulfide Capacity

To increase the utilization of V-Ti-Magnetite ore in the burden of a blast furnace, we investigated replacing CaO with MgO. The high fraction of TiO₂-bearing raw materials leads to a super-high TiO₂ content in the blast furnace slag, typically above 30 wt pct, which affects normal blast furnace operation. The present study focuses on the sulfide capacity of slag containing a super-high TiO₂ content. The effects of TiO₂ content and the ratio of MgO to CaO (M/C) on the sulfide capacity of slag were examined using a gas-slag equilibrium method. In the CaO-SiO₂-TiO₂-MgO-Al₂O₃ slag system, as the content of TiO₂ in the slag increased from 20 to 34 wt pct, the sulfide capacity decreased from 6.25 × 10⁻⁵ to 2.86 × 10⁻⁵. Above 30 wt pct TiO₂, the influence of TiO₂ content on the sulfide capacity became negligible. Increasing the (M/C) ratio induced a non-monotonic trend in the sulfide capacity, which first increased and then decreased. Thermodynamic and structural analyses were employed to characterize the experimental results. Thermodynamically, decreasing the CaO activity reduced the free oxygen in the slag with increasing TiO₂ content. Furthermore, an increase of titanium suboxide slowed the reduction of the sulfide capacity. Mass substitution mainly influenced the availability of free oxygen in the slag, and then the sulfide stability and oxygen concentration worked together, resulting in a non-monotonic sulfide capacity when MgO was substituted for CaO. In addition, the sulfide capacity was dependent on the effect of both the quaternary molar basicity and the binary molar basicity. Finally, the structural analysis revealed that for a super-high TiO₂ content in the slag, both the structure of Ti and the depolymerization reaction of Ti had an extremely important effect on desulfurization.