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.