GB934626A - Manufacture of titanium dioxide - Google Patents

Abstract

Titanium dioxide suitable for incorporation in vitreous enamels is prepared by mixing a hydrous precipitated titanium dioxide of coarse particle size such that before and after calcination and dressing alone (if so treated) more than 50% by weight of the particles are within the range of 5 to 20 microns, with a hydrous precipitated titanium dioxide of fine particle size such that before and after calcination and grinding alone (if so treated) it consists of particles of a size not exceeding 3 microns, preferably not exceeding 1 micron. The mixture contains 2,5-50% of the fine size calculated as TiO2, and is then subjected to calcination. The hydrous precipitates may be prepared by the hydrolysis of aqueous solutions of titanium sulphate obtained by the sulphation of ilmenite or enriched material prepared therefrom. The coarse particled material may be prepared by carrying out the hydrolysis of titanium sulphate solution at a concentration of dissolved and undissolved titanium calculated as TiO2 of 40-125 g.p.l. and at a factor of activity not exceeding 100%, preferably at a temperature above 90 DEG C. Desirably the initial solution is prepared by adding a concentrated solution of titanium sulphate to hot water over a period of 5-40 minutes. The fine particled material may be prepared by effecting the hydrolysis of titanium sulphate solution at a concentration of dissolved and undissolved titanium calculated as TiO2 higher than 150 g.p.l., desirably in the presence of hydrous titanium dioxide nuclei.