A Model for The Recovery of Titanium From Mixtures of Ilmenite and Hematite by Hydrochloric Acid Leaching

Abstract

A partial equilibrium model has been developed to describe the leaching of FeTiO₃-Fe₉O mixtures by aqueous HC1. The model couples the rates of leaching of the minerals to changes in the solution species concentrations; 23 species concentrations were calculated as a function of leaching time. Solution reactions included in the model include (1) the redox reaction converting Ti(IV) and Fe(II) to Ti(III) and Fe(III); (2) formation of chloro complexes; (3) hydrolysis; and (4) dissociation of H₂O. Ilmenite is more rapidly depleted than hematite, and available data indicate that the time dependence of the leaching reactions is different. Modeling results show that the Ti/Fe concentration ratio drops steeply initially but then gradually rises as the leaching rates change. Of the two oxides, FeTiO₃ is consumed first, and thereafter the Ti/Fe ratio again declines. The Fe(II)/Fe(III) concentration ratio behaves similarly. The Ti/Fe and Fe(II)/Fe(III) ratios have simultaneous extrema and plots of these ratios vs. time can, with appropriate adjustments in vertical scale, virtually be superimposed. These changes are greatest when the initial molar amounts of FeTiO₃ and Fe₂O₃ are approximately equal. They are qualitatively the same, but of much smaller magnitude, when the initial FeTiO₃ /Fe₃O₃ molar ratio is far from 1.0. The species distributions change in a complex way during leaching; typically, hydroxo species become more important but chloro species become less so. Implications of these results for the selective recovery of titanium will be discussed.