GB497694A - Improvements in and relating to the decomposition of titanium salt solutions by hydrolytic precipitation - Google Patents

Abstract

In a process for the production of titanium dioxide having the rutile crystalline structure wherein an aqueous solution of titanium tetrachloride, titanium fluoride, or a complex titanium fluoride compound is hydrolytically precipitated and the precipitate is calcined, hydrolysis is effected in the presence of a small amount of a negative polyvalent ion, which, with a titanium fluoride or complex fluoride solution, has a valency of two or more, and with a titanium tetra-chloride solution, has a valency of three or more, the substance from which the negative polyvalent ion is derived being present in an amount not greater than 0,01 mol of the substance to each mol of titanium reckoned as TiO2. The polyvalent ion may be obtained by adding oxalic, tartaric, sulphuric, arsenic, carbonic, phosphoric, or citric acid or an alkali metal salt of one of these acids to the solution. Hydrolysis may be effected by simple boiling, by addition of a solution containing the ion to the salt solution, or by adding the salt solution to the solution containing the ion. Preferably the acid or salt is dissolved in a large volume of water, the temperature raised, and the titanium salt solution then added. Examples are given of the hydrolysis of a tetrachloride solution and a solution of the compound TiF4.2NH3 in the presence respectively of citric acid and sodium sulphate. Specifications 308,725, [Class 1 (iii)], 433,960, and 481,892 are referred to. The Specification as open to inspection under Sect. 91, comprises also precipitation of the titanium dioxide by an alkaline hydroxide or ammonium carbonate in the presence of the polyvalent ion. This subject-matter does not appear in the Specification as accepted.