Solvent extraction of titanium from the simulated ilmenite sulfuric acid leachate by trialkylphosphine oxide

The extraction of Ti from the simulated ilmenite sulfuric acid leachate was investigated using TRPO-kerosene extraction system. The effects of stirring rate, contact time, TRPO concentration, phase ratio, and temperature were examined. Optimized extraction conditions were found to be: 25% (v/v) TRPO in kerosene, O/A 4:1, and temperature 30 °C. Under these conditions the extraction percentage of titanium was 78.5% with the extraction equilibrium and phase disengagement times of 40 min and 30 min, respectively. A continuous multi-stage extraction was unfeasible due to excessively long residence time. Upon the leachate being diluted by half and at the same time the sulfuric acid concentration increasing up to 150 g/L, the titanium extraction significantly rose to ~ 96% while the co-extracted iron was ~ 7%. A batch operation extraction was suggested on account of still long phase disengagement time. The co-extraction of iron resulted from air oxidation of ferrous to ferric during the extraction. Under N2 atmosphere the iron extraction decreased to 1%. Thus, an almost complete titanium and iron separation was realized with a separation factor of 2367. With 1.7% (w/w) sulfuric acid, 63% of the titanium loaded in organic phase was stripped through a single contact. McCabe–Thiele analysis predicts that the number of stripping stage is at least 5 under O/A phase ratio of 1:5 of operation line if a 90% of titanium stripping can be obtained. Further study showed that the extracted titanium species possibly included TiOSO4·TRPO besides TiO(HSO4)2·2TRPO under the conditions of high titanium ion concentration and relatively low concentrations of sulfuric acid and TRPO.