Manufacture of Pure Titanium(IV) Oxide by the Chloride Process. III. Precipitation of Hydrous Titanium(IV) Oxide in Hydrochloric Acid Solution at Elevated Temperatures

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Abstract
Thermal hydrolysis of titanium(IV) in hydrochloric acid solutions (0.2 mol dm−3 in Ti(IV); 2 mol dm−3 in HCl) was carried out at temperatures up to 110 °C to investigate the effects of heating rate, heating temperature, aging time, and coexisting ions on the particle shape, size, crystal form, crystalline size, and content of water of the hydrous titanium(IV) oxide precipitated. The resulting polycrystalline particles having rutile structure were all distorted ellipsoids at the beginning of the hydrolysis, and gradually changed to spheres with rising temperature or with the duration of time. However, no effects of heating rate on the particle shape and size distribution were observed at the beginning of the hydrolysis. On the other hand, the precipitation rate of titanium(IV) measured at a constant temperature remarkably depended on the temperature; marked changes in the particle size distribution and mean particle size were observed during the reaction. The precipitation rate was well expressed by the rate equation based on the rate-determining step of the surface chemical reaction. The apparent activation energy was 111 kJ mol−1. Although no effects of coexisting cations such as iron(III) and aluminium(III) were recognized, the presence of sulfate and fluoride ions significantly affected the particle shape and size of such precipitates. Anatase-type hydrous titanium(IV) oxide consisting of spherical particles of narrow size distribution was also obtained in the presence of fluoride ion.