Processes for producing titanium dioxide

1. A process comprising:

a) digesting ilmenite ore with aqueous trimethylammonium hydrogen oxalate to form a leachate and an iron-rich precipitate;

b) separating said leachate from said iron-rich precipitate to form a separated leachate and a separated iron-rich precipitate;

c) hydrolyzing said separated leachate with trimethylamine or aqueous trimethylamine to form titanyl hydroxide and an oxalate-rich solution;

d) separating said titanyl hydroxide from said oxalate-rich solution to form a separated titanyl hydroxide;

e) washing said separated titanyl hydroxide with a material selected from the group consisting of water, trimethylamine and aqueous trimethylamine to form washed titanyl hydroxide; and

f) crystallizing titanium dioxide from said washed titanyl hydroxide.

2. The process of claim 1 further comprising adding a reducing agent to said separated leachate to form a reduced leachate and a second iron precipitate and separating said second iron precipitate from said reduced leachate to form a separated second iron precipitate and a separated reduced leachate.

3. The process of claim 1 further comprising:

oxidizing said separated iron-rich precipitate in an acidic trimethylammonium hydrogen oxalate solution to form an trimethylammonium iron(III) oxalate solution;

optionally, separating unreacted ore from said trimethylammonium iron(III) oxalate solution to form a separated trimethylammonium iron(III) oxalate solution;

adding a base to said separated trimethylammonium iron(III) oxalate solution to form an iron-rich hydroxide precipitate and a di-trimethylammonium oxalate solution;

separating said iron-rich hydroxide precipitate from said di-trimethylammonium oxalate solution to form a separated iron-rich hydroxide precipitate; and

optionally, calcining said separated iron-rich hydroxide precipitate.

4. The process of claim 1 , further comprising:

adding a base to said separated iron-rich precipitate to form an iron-rich hydroxide precipitate and a basic solution;

separating said iron-rich hydroxide precipitate from said basic solution to form a separated iron-rich hydroxide precipitate; and

optionally, calcining said separated iron-rich hydroxide precipitate.

5. The process of claim 1 , further comprising calcining said separated iron-rich precipitate.

6. The process of claim 1 , further comprising refluxing said di-trimethylammonium oxalate solution to obtain an aqueous trimethylamine distillate and an acidic trimethylammonium hydrogen oxalate solution.

7. A process comprising:

a) digesting ilmenite ore with aqueous trimethylammonium hydrogen oxalate to form a first leachate and an iron-rich precipitate;

b) separating said first leachate from said iron-rich precipitate to form a separated first leachate and a separated iron-rich precipitate;

c) optionally, adding a reducing agent to said separated first leachate to form a second iron-rich precipitate and a second leachate and separating said second iron-rich precipitate from said second leachate to form a separated second iron-rich precipitate and a separated second leachate;

d) hydrothermally crystallizing said separated first or second leachate in an autoclave for a period of one hour to 24 hours to form titanium dioxide and a hydrothermally treated solution; and

e) separating said titanium dioxide from said hydrothermally treated solution.

8. The process of claim 7 further comprising:

oxidizing said separated iron-rich precipitate in an acidic trimethylammonium oxalate solution to form a trimethylammonium iron(III) oxalate solution;

optionally, separating unreacted ore from said trimethylammonium iron(III) oxalate solution to form a separated trimethylammonium iron(III) oxalate solution;

adding a base to said separated trimethylammonium iron(III) oxalate solution to form an iron-rich hydroxide precipitate and a di-trimethylammonium oxalate solution;

separating said iron-rich hydroxide precipitate from said di-trimethylammonium oxalate solution to form a separated iron-rich hydroxide precipitate; and

optionally, calcining said separated iron-rich hydroxide precipitate.

9. The process of claim 7 , further comprising:

adding a base to at least one of said separated iron-rich precipitate from (b) and said separated iron-rich precipitate from (c) to form an iron-rich hydroxide precipitate and a basic solution;

separating said at least one of said separated iron-rich precipitate from (b) and said separated iron-rich hydroxide precipitate from said basic solution to form a separated iron-rich hydroxide precipitate; and

optionally, calcining said separated iron-rich hydroxide precipitate.

10. The process of claim 7 , further comprising calcining said separated iron-rich precipitate.

11. A process comprising:

a) digesting ilmenite ore with aqueous trimethylammonium hydrogen oxalate to form a leachate and an iron-rich precipitate;

b) separating said leachate from said iron-rich precipitate to form a separated leachate and a separated iron-rich precipitate; adding a reducing agent to said separated leachate to form a second iron-rich precipitate and a reduced leachate;

c) separating said second iron-rich precipitate from said reduced leachate of (b) to form a separated reduced leachate and a separated second iron-rich precipitate;

d) hydrolyzing said separated reduced leachate with aqueous trimethylamine to form titanyl hydroxide; and

e) hydrothermally crystallizing said titanyl hydroxide to form titanium dioxide and a di(trimethylammonium) oxalate solution.

12. The process of claim 11 further comprising:

oxidizing said separated second iron-rich precipitate of (c) in an acidic trimethylammonium oxalate solution to form a trimethylammonium iron(III) oxalate solution;

optionally, separating unreacted ore from said trimethylammonium iron(III) solution to form a separated trimethylammonium iron(III) oxalate solution;

adding a base to said separated trimethylammonium iron(III) oxalate solution to form an iron-rich hydroxide precipitate and an di-trimethylammonium oxalate solution;

separating said iron-rich hydroxide precipitate from said di-trimethylammonium oxalate solution to form a separated iron-rich hydroxide precipitate; and

optionally, calcining said separated iron-rich hydroxide precipitate.

13. The process of claim 11 , further comprising:

adding a base to at least one of said separated iron-rich precipitate from (b) and said separated second iron-rich precipitate from (c) to form an iron-rich hydroxide precipitate and a basic solution;

separating said at least one of said separated iron-rich precipitate from (b) and said separated iron-rich hydroxide precipitate from said basic solution to form a separated iron-rich hydroxide precipitate; and

optionally, calcining said separated iron-rich hydroxide precipitate.

14. The process of claim 11 , further comprising refluxing said di-trimethylammonium oxalate solution to obtain an aqueous trimethylamine distillate and an acidic trimethylammonium hydrogen oxalate solution.

15. The process of claim 11 , further comprising calcining said separated iron-rich precipitate.