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.
Keywords: Ti-bearing blast furnace slag; TiO2; hydrothermal hydrolysis; impurity removal; thermodynamic calculations.