Hydrochloric acid leaching behavior of different treated Panxi ilmenite concentrations

The effects of oxidation–reduction treatment and mechanical activation on the hydrochloric acid leaching performance of Panxi ilmenite concentration from Sichuan province of China were investigated. The results show that both of oxidation–reduction treatment and mechanical activation not only significantly accelerated the extraction of Fe, Ca and Mg from Panxi ilmenite concentration, but also apparently put forward the initial hydrolysis time of titanium ions in hydrochloric acid solution. In addition, oxidation–reduction treatment can obviously decrease the Ti extraction in hydrochloric acid solution. The formation of pseudobrookite by oxidizing at 900 °C is more favorable to upgrade Panxi ilmenite concentration to synthetic rutile. A process of “oxidation–reduction–mechanical activation–hydrochloric acid leaching” was proposed, and this process successfully prepared the synthetic rutile which meets the requirements of chlorination process. In this process, the Panxi ilmenite concentration is first oxidized at 900 °C in the presence of oxygen for 15 min, then reduced at 750 °C by hydrogen for 30 min. After cooled to room temperature in a nitrogen atmosphere, the oxidized–reduced ilmenite concentration obtained is milled in a planetary ball mill for 2 h under nitrogen atmosphere immediately. After the milling, the oxidized–reduced–mechanically activated ilmenite concentration proceeds to a leaching at ambient pressure using 20 wt.% hydrochloric acid for 10 h. Finally, the leached product is subjected to filtration, wash and calcination to produce a synthetic rutile containing 90.50 wt.% TiO2 and 1.37 wt.% total iron as well as combined CaO and MgO of 1.00 wt.%. The results demonstrate that the process of “oxidation–reduction–mechanical activation–hydrochloric acid leaching” can excellently upgrade ilmenite concentration with high content of gangue like Panxi ilmenite concentration into synthetic rutile which meets the requirements of chlorination process.

Research Highlights
► The initial hydrolysis time of titanium ions was put forward from 2 h to 0.5 h by mechanical activation.
► The oxidation–reduction pretreatment not only put forward the initial hydrolysis time of titanium ions remarkably, but also significantly decreased the Ti extraction in hydrochloric acid solution.
► The formation of pseudobrookite by oxidizing at 900 °C is more favorable to upgrade Panxi ilmenite concentration to synthetic rutile.
► A process of "oxidation–reduction–mechanical activation–hydrochloric acid leaching" was proposed.