Preparation of Hydrated TiO2 Particles by Hydrothermal Hydrolysis of Mg/Al-Bearing TiOSO4 Solution

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.

Co-Removal of Fe/V Impurity in H2TiO3 Synthesized from Ti-Bearing Blast Furnace Slag

Ti-bearing blast furnace slag (TBFS) can be converted to impurity bearing TiOSO4 solution for TiO2 pigment production. However, the H2TiO3 (MTA) hydrolyzed from the solution has too high Fe/V impurity to meet the standard for TiO2 pigment. In this study, we found that Fe3+ and V3+ were easily hydrolyzed and entered the MTA lattice, and hence could not be removed by washing. Furthermore, Fe/V was hard to co-remove by the traditional reduction method. Therefore, the Fe/V non-hydrolysis condition (Ti3+ = 0.01 M, F = 3.0, T = 130 °C; Ti3+ = 0.01 M, F = 3.5, T = 150 °C) was determined by thermodynamic calculations. However, at these conditions, the Ti hydrolysis ratio was low or the reaction time was long. Therefore, a new two-step hydrothermal hydrolysis process was proposed. Step 1 (130 °C, 2 h) ensured the non-hydrolysis of V3+, and Ti was partially hydrolyzed to increase the H2SO4 concentration. Step 2 (150 °C, 2 h) ensured a high Ti hydrolysis ratio (>0.95) and short total reaction time (4-6 h). Finally, a high-purity MTA was obtained (Fe = 21 ppm, V = 145 ppm). These results provide new insights into the control of the hydrolysis of impurity ions in solutions and help to optimize the process of TiO2 pigment preparation from TBFS.