PREPARATION OF TITANIUM DIOXIDE
A method for the preparation of titanium dioxide, the method comprising the steps of subjecting a titanium containing leach residue to a concentrated sulfuric acid digest step; and in turn subjecting that residue to a leach in dilute sulfuric acid, whereby a black liquor is obtained and from which titanium dioxide is in turn obtained.
1 . A method for the preparation of titanium dioxide, the method comprising the steps of:
(i) subjecting a titanium containing leach residue to a concentrated sulfuric acid digest step; and
(ii) in turn subjecting that residue to a leach in dilute sulfuric acid to obtain a black liquor from which titanium dioxide is in turn obtained,
wherein the leach residue is a residue from a hydrochloric leach of a titanomagnetite-type ore.
2 . The method of claim 1 , wherein the titanium dioxide is utilised in the preparation of a titanium dioxide pigment.
3 . The method of claim 1 , wherein the concentration of hydrochloric acid ranges between:
(i) about 15% to 32% (w/w); or
(ii) about 15% to 20% (w/w).
4 . The method of claim 1 , wherein a feedstock for the leach of the titanomagnetite-type ore is the product of a ferric leach.
5 . The method of claim 1 , a feedstock for the leach of the titanomagnetite-type ore is the product of a ferric leach, the ferric leach step having been conducted with ferric chloride.
6 . The method of claim 5 , wherein the concentration of ferric chloride ranges between:
(i) about 10 to 40% w/w;
(ii) about 25 to 35% w/w; or
(iii) about 28% w/w.
7 . The method of claim 1 , wherein the titanium containing leach residue has a P 80 of:
(i) ≤125 μm;
(ii) ≤45 μm; or
(iii) <40 μm.
8 . The method of claim 1 , wherein recovery of titanium into the black liquor is at least 98%.
9 . The method of claim 1 , wherein the digest step is conducted at a temperature of:
(i) greater than 175° C.; or
(ii) about 190° C.
10 . The method of claim 1 , wherein the digest step is conducted over a period of:
(i) between about 3 to 4 hours; or
(ii) about 3 hours.
11 . The method of claim 1 , wherein the mix of leach residue to concentrated sulfuric acid in the digest step is in the ratio of about 1:1.27 (g/g).
12 . The method of claim 1 , wherein at least 1.9 g of concentrated sulfuric acid is provided in the digest step (i) for every gram of TiO 2 in the titanium containing leach residue.
13 . The method of claim 1 , wherein the dilute sulfuric acid of the leach step (ii) is about 6% sulfuric acid.
14 . The method of claim 1 , wherein the leach step (ii) is conducted at about 60° C.
15 . The method of claim 1 , wherein the leach step (ii) is conducted for a period of about 15 hours.
16 . The method of claim 1 , wherein the leach step (ii) is conducted at about 20% solids.
17 . The method of claim 1 , wherein the black liquor is recovered from a slurry produced by the leach step (ii) by filtration, and the solids washed to recover titanium.
18 . The method of claim 1 , wherein the digest step (i):
(i) proceeds in an autothermic manner;
(ii) further comprises an initial dilution of the acid; or
(iii) further comprises an initial dilution of the acid to about 88-92% with water.
19 . (canceled)
20 . (canceled)
21 . The method of claim 1 , wherein the black liquor is passed to hydrolysis and calcination for the recovery of titanium dioxide.