Patent ID: 8398954

Claim:
A process for the production of a white titanium dioxide pigment, the process comprising the steps of: (a) reacting a titanium ore containing iron with an aqueous NH 4 F solution at 100-120° C. and at a pressure of 1-2 bar to obtain an aqueous suspension; (b) filtering the aqueous suspension into a sludge fraction and a filtrate fraction, the filtrate fraction comprising ammonium oxofluorotitanate; (c) subjecting the filtrate fraction to a hydrolysis reaction to obtain an aqueous dispersion; (d) filtering the aqueous dispersion prior to a first thermal hydrolysis reaction to obtain a solid component comprising ammonium oxofluorotitanate; (e) subjecting the solid component to the first thermal hydrolysis reaction in a first reactor in the presence of steam to release a first quantity of HF and NH 4 F from the ammonium oxofluorotitanate, the first reactor being maintained at a temperature of up to 350° C.; (f) passing the solid component to a second reactor connected in series with the first reactor; (g) subjecting the solid component to a second thermal hydrolysis reaction in a second reactor in the presence of steam to release a second quantity of HF and NH 4 F from the ammonium oxofluorotitanate to obtain a white titanium dioxide pigment, the second reactor maintained at a temperature of up to 900° C.; wherein in steps (e) and (g) the HF and NH 4 F are vented from the respective reactor.