Process for recovering titanium dioxide
An improved process for recovering a titanium dioxide product from a titanium oxide-containing roasted mass of the type derived from roasting an ilmenite, anatase or perovskite ore by exploiting an organic acid, such as mixture of oxalic acid and ascorbic acid.
1. A process for recovering a titanium dioxide product from a titanium oxide-containing roasted mass comprising:
(a) subjecting the titanium oxide-containing roasted mass or a substantially water-insoluble residue thereof to leaching in an organic acid solution which is a mixture of oxalic acid and ascorbic acid to produce an acid leachate and the titanium dioxide product.
2. A process as claimed in claim 1 wherein the titanium oxide-containing roasted mass is the product of roasting a titanium oxide-containing composition, wherein the titanium oxide-containing composition is an ore selected from the group consisting of ilmenite, anatase and perovskite.
3. A process as claimed in claim 1 or claim 2 wherein step (a) is preceded by:
(a0) providing a titanium oxide-containing composition with one or more alkali salts to produce a charge; and
(a01) oxidatively roasting the charge to produce the titanium oxide-containing roasted mass.
4. The process as claimed in claim 3 wherein the charge is without an alumina-containing additive and a calcium oxide-containing additive.
5. The process as claimed in claim 3 wherein the one or more alkali salts is a potassium salt.
6. The process as claimed in claim 3 wherein the one or more alkali salts is an OH-containing salt.
7. The process as claimed in claim 3 wherein the one or more alkali salts is a hydroxide or bicarbonate.
8. The process as claimed in claim 1 wherein in step (a) the titanium oxide-containing roasted mass comprises particles and the particles are in suspension in the organic acid solution.
9. A process as claimed in claim 8 wherein in step (a) the organic acid solution is at a pH of 4 or less.
10. A process as claimed in claim 9 wherein in step (a) the organic acid solution is at a pH in the range 3 to 4.
11. A process as claimed in claim 1 further comprising:
(b) adding an alkaline solution to maintain the pH of the organic acid solution in the range 3 to 4.
12. A process as claimed in claim 1 wherein step (a) is carried out anaerobically.
13. A process as claimed in claim 1 wherein step (a) is preceded by:
(a02) washing the roasted mass with an aqueous medium to produce an aqueous solution and a substantially insoluble residue of the roasted mass.
14. A process as claimed in claim 13 wherein the aqueous solution supports a colloidal layer rich in rare-earth oxides.
15. A process as claimed in claim 14 further comprising:
(a03) isolating said colloidal layer from the aqueous solution; and
(a04) recovering said rare-earth oxides from the colloidal layer.
16. A process as claimed in claim 15 further comprising:
(c) washing the titanium dioxide product in a mineral acid.
17. A process as claimed in claim 1 or claim 16 wherein the titanium dioxide product consists essentially of TiO 2 with a purity of 92 wt % or more.
18. A process as claimed in claim 17 wherein the titanium dioxide product is in the form of synthetic rutile or synthetic anatase or a mixture thereof.