Manufacture of High Pure Titanium(IV) Oxide by the Chloride Process. I. Kinetic Study on Leaching of Ilmenite Ore in Concentrated Hydrochloric Acid Solution

Abstract

Kinetic study of the leaching of powdered ilmenite ore was carried out in highly concentrated hydrochloric acid (11.3–11.6 mol dm−3) at temperatures of 30 to 80 °C. The changes in shape and grain size of the ore particles with progress of the leaching was simultaneously observed with X-ray diffraction and electron microscope techniques. Titanium and iron were dissolved in a nearly stoichiometric ratio; the rate of the dissolution was significantly affected by the temperature of the acid solutions. From the analysis of the dissolution rates on the basis of the core-model, it was found that the dissolution rates at temperatures of 30 to 50 °C were well expressed by the rate equation based on the rate-determining step of the surface chemical reaction. The apparent activation energies were 81.2 kJ mol−1 for titanium and 73.2 kJ mol−1 for iron. The rate-determining step of the dissolution was changed at a temperature of about 50–60 °C; the dissolution rates at temperatures of 60 to 80 °C were limited by the diffusion of the dissolved metal ions through a residual layer of the ore. However, the rates after 2 or 3 h at high temperatures deviated from the rate equation because of the precipitation of hydrous titanium(IV) oxide on the surface of the ore by hydrolysis of the dissolved titanium(IV) ion.