GB990419A - Improvements in the preparation of titanium dioxide pigments - Google Patents

Abstract

Rutile is prepared by calcination at or above about 1000 DEG C., of a hydrous titanium dioxide containing prior to calcination, rutile seeds, (in addition to those used in the initial hydrolysis) a water-soluble aluminium salt, a water-soluble phosphate and a basic potassium salt. The calcination is continued until the titanium dioxide is substantially completely converted into the rutile form. Ordinarily, the calcination is effected in the presence of 1-6% rutile seeds, 0.3-2.5% of a water-soluble aluminium salt (calculated as Al2O3) 0.1-0.5% of a watersolubl phosphate (calculated as P2O5) and 0.1-1.0% of a basic potassium salt (calculated as K2O) based by weight on the titanium dioxide. However, if the ore from which the titanium sulphate solution is obtained contains phosphorus, then the addition of extra phosphorus compounds may not be required. The seeds added before hydrolysis can be those obtained according to Example 1 of Specification 513,867, by halide hydrolysis in caustic soda and the seeds added after hydrolysis and before calcination, can be obtained by boiling washed hydrous titanium dioxide in a caustic soda solution for 4 hours, washing the precipitate, resuspending it in HCl solution and heating the suspension for 3 hours. In Example II, the rutile seeds are obtained by treating TiCl4 solution with a solution of caustic soda, neutralizing the suspension obtained, and then washing out 75% of the soluble salts present. The suspension thus obtained is added to titanium sulphate solution prior to hydrolysis to obtain hydrous titanium dioxide. The product is separated, washed and reslurried in water, to which is added rutile seeds as prepared in Specification 513,867, and an aluminium sulphate, mono-ammonium phosphate and potassium carbonate. The resulting mixture is dried and calcined at or above about 1000 DEG C.