GB970885A - Preparation of high purity titanium dioxide - Google Patents

Abstract

Pigment grade titanium dioxide is prepared by treating a titaniferous material with sulphuric acid at 40-80 DEG C., leaching with water, selectively extracting titanium values with a liquid mono- or di-alkyl orthophosphoric acid, or contaminants with an alkyl phosphate or alkyl amine; recovering titanium as the hydrated oxide, and calcining at above 800 DEG C. At least one equivalent of acid, preferably 90% or stronger, per equivalent of metal is used, and the material may be pretreated with an inorganic base. Contaminants are extracted if a trialkyl phosphate having alkyl groups with 4-8 carbon atoms, e.g. tributylphosphate, or an alkylamine having alkyl groups with 6-12 carbon atoms, e.g. triisooctylamine, is used as extractant; titanium is then precipitated from the acid leachate by digestion at 80-100 DEG C., preferably with an inorganic base, to give the hydrated oxide. Alternatively, titanium may be extracted from the leach liquor using a mono- or di-alkyl orthophosphoric acid having alkyl groups with 4-18 carbon atoms, e.g. di-(2-ethyl hexyl)-orthophosphoric acid, monododecyl orthophosphoric acid, and monoheptadecyl orthophosphoric acid; and any iron also extracted may be removed by scrubbing with 3-12M. HCl. Titanium is then recovered by adding an aqueous solution of either (1) an alkali metal or ammonium hydroxide or carbonate, or a mixture of ammonium hydroxide and carbonate, to precipitate hydrated titanium oxide; or (2) hydrogen fluoride or an alkali metal or ammonium fluoride or bifluoride, to precipitate a titanium-ammonium double fluoride, which is converted into the hydrated oxide by reaction with ammonia. The organic extractant is preferably carried in a water-immiscible solvent, e.g. kerosenes, toluene, benzene and halogenated and other aromatics, in 0.3-3.5M concentration. The organic/aqueous phase ratio may be from 1/10 to 1/1.