Purification of reduced upgraded titania slag by iron removal using mild acids

• 0.1 M HCl is optimal for combination of iron removal and titanium preservation.
• No additional iron is removed at the temperature above 140 °C.
• Limit of iron removal is near 90% if the titanium loss is kept below 1%.
• Model from factorial design of experiments is in good agreement with experiment data.

In this study, we focused on removal of iron from upgraded titania slag (UGS) that has been reduced by hydrogen gas, magnesium powder and salts at 750 °C for 5 h. Reduced UGS is mainly composed of titanium hydride and oxide impurities that include iron, silicon, aluminum, and magnesium. Mild concentrations of hydrochloric and boric acids were used in this investigation to remove iron from reduced UGS. The concentration of hydrochloric and boric acids and the leaching temperature have been chosen as the prime variables to identify the optimum conditions and leaching characteristics for purification of reduced UGS. Both ambient pressure leaching and elevated pressure leaching were performed to assess the rate of iron removal from reduced UGS without titanium loss. It was observed that under the constraint that 1% (w/w) of titanium hydride loss is the maximum amount tolerable, 0.1 M hydrochloric acid at 140 °C was found to be the most effective conditions for iron removal (87.63%). A factorial design of experiment for equation modeling with three main factors (temperature, concentration of hydrochloric and boric acids) was performed and associated modeling results were in good agreement with experimental data. The overall rate of reaction seems to follow interfacial reaction controlled kinetics. The calculated activation energy of the reaction is 73.9 kJ/mol.