Abstract: Large quantities of CO₂ and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO₂ emission reduction and comprehensive utilization of the solid waste. This paper describes a novel route for indirect mineral carbonation of titanium-bearing blast furnace (TBBF) slag, in which the TBBF slag is roasted with recyclable (NH₄)₂SO₄ (AS) at low temperatures and converted into the sulphates of various valuable metals, including calcium, magnesium, aluminium and titanium. High value added Ti-and Al-rich products can be obtained through stepwise precipitation of the leaching solution from the roasted slag. The NH₃ produced during the roasting is used to capture CO₂ from flue gases. The NH₄HCO₃ and (NH₄)₂CO₃ thus obtained are used to carbonate the CaSO₄-containing leaching residue and MgSO₄-rich leaching solution, respectively. In this study, the process parameters and efficiency for the roasting, carbonation and Ti and Al recovery were investigated in detail. The results showed that the sulfation ratios of calcium, magnesium, titanium and aluminium reached 92.6%, 87% and 84.4%, respectively, after roasting at an AS-to-TBBF slag mass ratio of 2:1 and 350℃ for 2 h. The leaching solution was subjected to hydrolysis at 102℃ for 4 h with a Ti hydrolysis ratio of 95.7%and the purity of TiO₂ in the calcined hydrolysate reached 98 wt%. 99.7% of aluminium in the Ti-depleted leaching solution was precipitated by using NH₃. The carbonation products of Ca and Mg were CaCO₃ and (NH₄)₂Mg(CO₃)₂·4H₂O, respectively. The latter can be decomposed into MgCO₃ at 100-200℃ with simultaneous recovery of the NH₃ for reuse. In this process, approximately 82.1% of Ca and 84.2% of Mg in the TBBF slag were transformed into stable carbonates and the total CO₂ sequestration capacity per ton of TBBF slag reached up to 239.7 kg. The TiO₂ obtained can be used directly as an end product, while the Al-rich precipitate and the two carbonation products can act, respectively, as raw materials for electrolytic aluminium, cement and light magnesium carbonate production for the replacement of natural resources.

Key words: Mineral carbonation, CO₂ sequestration, Ti-bearing blast furnace slag, Ammonium sulphate, Titanium dioxide, Aluminium oxide

摘要： Large quantities of CO₂ and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO₂ emission reduction and comprehensive utilization of the solid waste. This paper describes a novel route for indirect mineral carbonation of titanium-bearing blast furnace (TBBF) slag, in which the TBBF slag is roasted with recyclable (NH₄)₂SO₄ (AS) at low temperatures and converted into the sulphates of various valuable metals, including calcium, magnesium, aluminium and titanium. High value added Ti-and Al-rich products can be obtained through stepwise precipitation of the leaching solution from the roasted slag. The NH₃ produced during the roasting is used to capture CO₂ from flue gases. The NH₄HCO₃ and (NH₄)₂CO₃ thus obtained are used to carbonate the CaSO₄-containing leaching residue and MgSO₄-rich leaching solution, respectively. In this study, the process parameters and efficiency for the roasting, carbonation and Ti and Al recovery were investigated in detail. The results showed that the sulfation ratios of calcium, magnesium, titanium and aluminium reached 92.6%, 87% and 84.4%, respectively, after roasting at an AS-to-TBBF slag mass ratio of 2:1 and 350℃ for 2 h. The leaching solution was subjected to hydrolysis at 102℃ for 4 h with a Ti hydrolysis ratio of 95.7%and the purity of TiO₂ in the calcined hydrolysate reached 98 wt%. 99.7% of aluminium in the Ti-depleted leaching solution was precipitated by using NH₃. The carbonation products of Ca and Mg were CaCO₃ and (NH₄)₂Mg(CO₃)₂·4H₂O, respectively. The latter can be decomposed into MgCO₃ at 100-200℃ with simultaneous recovery of the NH₃ for reuse. In this process, approximately 82.1% of Ca and 84.2% of Mg in the TBBF slag were transformed into stable carbonates and the total CO₂ sequestration capacity per ton of TBBF slag reached up to 239.7 kg. The TiO₂ obtained can be used directly as an end product, while the Al-rich precipitate and the two carbonation products can act, respectively, as raw materials for electrolytic aluminium, cement and light magnesium carbonate production for the replacement of natural resources.

关键词: Mineral carbonation, CO₂ sequestration, Ti-bearing blast furnace slag, Ammonium sulphate, Titanium dioxide, Aluminium oxide