The digestion of New Zealand ilmenite by hydrochloric acid

• We measure the kinetics of digestion of ilmenite in hydrochloric acid.
• Unusually, reduction of the ilmenite is not required before digestion.
• The kinetics of the reaction is modeled.
• It is possible to achieve a high digestion and avoid hydrolysis of Ti.

Ilmenite (FeTiO3) is an important source of titanium, for which the main application is TiO2 pigment. One route to the production of TiO2 from ilmenite may be the digestion of both the Fe and Ti components in hydrochloric acid and the subsequent direct hydrolysis of the Ti. The process requires that the Ti be solubilized. A kinetic study is performed of the leaching of New Zealand (Barrytown) placer ilmenite (ground to a 10 μm median particle diameter) by hydrochloric acid in a stirred reactor. Around 90% extraction of both Fe and Ti is achieved with a 32% w/w HCl concentration, with a 2:1 w/w ratio of HCl to FeTiO3 over the temperature range 60 to 90 °C. The shrinking sphere model is a good representation of the kinetics if particle size distribution is accounted for. The reaction rate is estimated to be 4th order in HCl concentration. The temperature rise due to an exothermic reaction is calculated to be c. 41 °C. Undesirable, in situ hydrolysis of Ti during digestion can be limited by control of temperature, reaction time and acid concentration. The data and models presented may facilitate the preliminary design of an industrial process to digest ilmenite to dissolve and retain Ti in solution.

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