Improved Process for Separating TiO2 from an Oxalic-Acid Hydrothermal Leachate of Vanadium Slag

In the present study, a process of separating high-quality TiO2 from an oxalic-acid leachate of vanadium slag was proposed. It consists of two steps; oxalic acid was firstly recovered from the leachate by the cooling-crystallization method, and subsequently TiO2 was separated from the oxalic-acid recovered leachate by the hydrothermal precipitation method. The experimental results indicate that oxalic acid can be recovered from the leachate by cooling crystallization at 5 °C, and after the recovery of oxalic acid, the purity of final TiO2 product can also be improved. For example, when the leachate was cooled directly at 5 °C for 5 h, about 7% of oxalic acid was recovered, and the purity of final TiO2 product improved from 95.7% to 96.6%. Furthermore, it was found that when some HCl solution was added to the leachate, both the recovery percentage of oxalic acid and the purity of TiO2 product increased. For instance, when 15 vol% of HCl solution relative to pregnant leachate was added, about 35% oxalic acid was recovered by cooling crystallization at 5 °C for 3 h, and the anatase TiO2 product with a purity of 99.2% was obtained by hydrothermal precipitation at 140 °C for 2.5 h.