Recovery of TiO.sub.2 from ilmenite-type ore by a membrane based electrodialysis process

In a process for producing titanium dioxide from ilmenite-type ore including the steps of

• (a) digesting ilmenite ore with aqueous hydrogen fluoride to form a solution of titanium fluoride compounds and soluble iron fluoride impurities;
• (b) adding aqueous ammonium fluoride and ammonium hydroxide to substantially precipitate iron-ammonium fluoride impurities from the solution;
• (c) separating the remainder of the iron fluoride impurities by precipitating with ammonium sulfide and filtering off;
• (d) adding ammonium hydroxide to precipitate hydrated titanium dioxide and to form aqueous ammonium fluoride;
• (e) calcining the hydrated titanium dioxide to form pigmentary titanium dioxide;
• and
• (f) converting the precipitated iron-ammonium fluoride impurities from step (b) to form iron oxide and aqueous ammonium fluoride, the improvement which comprises subjecting the combined ammonium fluoride solutions from steps (d) and (f) to electrodialytic water-splitting to form an aqueous solution of ammonium hydroxide and an aqueous solution of hydrogen fluoride and recycling said aqueous ammonium hydroxide to step (d), and said aqueous hydrogen fluoride to step (a).