Patent ID: 7771680

Claim:
A process for the production of titanium dioxide comprising the following steps: (a) reacting a titanium ore containing iron with an aqueous NH 4 F and/or NH 4 HF 2 solution to produce an aqueous dispersion containing (NH 4 ) 2 TiF 6 and (NH 4 ) 3 FeF 6 ; (b) filtering the aqueous dispersion thus obtained with consequent separation of a solid residue and an aqueous solution containing titanium salts; (c) subjecting the aqueous solution thus obtained to hydrolysis, the hydrolysis comprising a first stage at pH 7.0-8.5, wherein the dispersion obtained from the first stage of the hydrolysis (c) is filtered to give an aqueous solution containing the titanium salt (NH 4 ) 2 TiF 6 and having a (NH 4 ) 3 FeF 6 concentration lower than 0.01% by weight, and a sludge fraction containing ammonium oxyfluorotitanate and (NH 4 ) 3 FeF 6 , and wherein said aqueous solution from the first stage is subjected to a second stage at pH 10.0-13.0; (d) filtering the aqueous dispersion thus obtained and the solid residue is subjected to pyrohydrolysis, the pyrohydrolysis comprising a first stage at a maximum temperature of 450° C. and a second stage at a maximum temperature of 1000° C.