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.