Simultaneous CO₂ mineral sequestration and rutile beneficiation by using titanium-bearing blast furnace slag: Process description and optimization

CO₂ mineral sequestration is a promising method for abating global warming. Mineral carbonation with titanium-bearing blast furnace slag (TBFS) can offer a sustainable option for simultaneous CO₂ emission reduction and comprehensive utilization of solid waste. In this study, a novel process combining CO₂ mineral sequestration and rutile beneficiation was proposed by using TBFS and copperas as feedstocks. TBFS and copperas were roasted at 550–750 °C to convert the calcium and magnesium into the corresponding sulfates, while titanium in the TBFS was beneficiated to rutile. The roasted slag was then subjected to carbonation followed by recovery of rutile and hematite through flotation and magnetic separation, respectively. The effects of process parameters were studied systematically. It was found that addition of Na₂SO₄ significantly enhanced the conversion efficiency of Ti (from 53% to 98%). The mechanism revealed that the addition of Na₂SO₄ promoted the formation of molten Na₃Fe(SO₄)₃, and gas-liquid-solid reactions proceeded much faster and efficiently. The carbonation of sulfated TBFS results indicated that the optimal CO₂ storage capacity can reach 187 kg t⁻¹ TBFS. In this process, two solid wastes were utilized for CO₂ mineralization, realizing the multiple benefits of CO₂ emission reduction, solid waste disposal as well as valuable byproducts recovery.