GB1023275A - Production of titanium dioxide - Google Patents

Abstract

In the production of titanium dioxide by thermal hydrolysis of aqueous titanium tetrachloride the aqueous hydrochloric acid separated from the titanium dioxide is contacted with titanium tetrachloride to form gaseous hydrogen chloride and aqueous titanium tetrachloride. Mineral rutile or ilmenite or leucoxene is chlorinated and the resulting titanium tetrachloride, which may be purified by distillation in the presence of hydrocarbons, mineral oils, soaps and/or sulphides, and should contain less than 100 p.p.m. of Fe, Cr, V, Nb is dissolved in at least 20% hydrochloric acid solution to give a final concentration of 100-300 gm./1. at 35-60 DEG C. depending on acid concentration. Gaseous hydrogen chloride is evolved, dried to less than 2% water and passed over a catalyst whence chlorine is produced and used in the production of further titanium tetrachloride. The remaining titanium tetrachloride solution is added to boiling water and retained for at least seventy minutes, peptisation of the hydrous titanium dioxide being prevented by addition of polyvalent anions, e.g. sulphuric acid as flocculating agents before or during recovery. The aqueous hydrochloric acid separated from the recovered precipitate may be concentrated by addition of part of the gaseous hydrogen chloride liberated in the titanium tetrachloride dissolution before recycling to the dissolution step. The recovered hydrated titanium dioxide is calcined at 800-850 DEG C., or additioned, calcined, leached wet or dry milled in a fluid energy mill, hydroclarified, coated with hydrated oxides of Al, Ti, Zr, Si Ce, PO4 alcohols and/or alkanolamines and/or remilled to form pigmentary TiO2.