Thermodynamic and Experimental Studies of Selective Decomposition of Diopside in Ti-Bearing Blast Furnace Slag

Titanium-bearing blast furnace slag (TBFS) is formed during the smelting of vanadium-titanium magnetite ore, containing more than 10 wt % Ti. The metal resource in TBFS has not yet been utilized because of the difficulty of extracting the objective phase from the complex eutectic. In this work, thermodynamic and experimental studies of selective leaching of diopside phase in TBFS in 20 wt % H₂SO₄ were conducted. The Gibbs free energy of reaction with H₂SO₄ calculated by applying a mechanical mixture model was in the order of Ti-bearing diopside < MgAl₂O₄ < Ti-rich diopside < CaTO₃. The extraction rate of Ti ions was controlled by the leaching temperature and leaching time in 20 wt % H₂SO₄. The extraction rate of Ti reached as high as 0.50 under optimal conditions. The diopside phases in TBFS were completely decomposed, while the perovskite (CaTiO₃) was almost unaffected by 20 wt % H₂SO₄. The experimental results agreed with the trend of thermodynamic calculations, supporting their validity. The hydrolysis of TiOSO₄ showed the possibility of obtaining high-purity TiO₂. This work shows the selective leaching of the diopside phase in TBFS and suggests an environmentally friendly method for utilizing Ti-bearing blast furnace slag and waste acid.