Reductive ammoniacal leaching of nickel and cobalt bearing materials

1. A process for the recovery of nickel and/or cobalt from an impure nickel, cobalt or mixed nickel/cobalt material including the steps of:

a) providing a nickel, cobalt or mixed nickel/cobalt material; and

b) contacting the nickel, cobalt or mixed nickel/cobalt material with a feed ammoniacal ammonium carbonate solution and a reductant in a leach step, wherein the reductant is selected from a mixed cobalt/nickel sulphide, cobalt sulphide or hydroxylamine.

2. A process according to claim 1 , wherein the nickel, cobalt or mixed nickel/cobalt material is either a nickel, cobalt or mixed nickel/cobalt hydroxide, carbonate, basic carbonate or basic sulphate material.

3. A process according to claim 1 , wherein the nickel, cobalt or mixed nickel/cobalt material is a mixed nickel/cobalt hydroxide material.

4. A process according to claim 1 , wherein the feed ammoniacal ammonium carbonate solution is a process liquor from a Caron process.

5. A process according to claim 1 , wherein the reductant is a mixed cobalt/nickel sulphide and is produced by contacting a cobalt/nickel containing ammoniacal ammonium carbonate solution with ammonium hydrosulphide or sodium hydrosulphide, to precipitate a mixed cobalt/nickel sulphide.

6. A process according to claim 5 , wherein the cobalt/nickel containing ammoniacal ammonium carbonate solution is a portion of the process liquor of a Caron process used as the feed ammoniacal ammonium carbonate solution, or a portion of any selected cobalt/nickel containing process liquor.

7. A process according to claim 1 wherein the feed ammoniacal ammonium carbonate solution and the cobalt/nickel containing ammoniacal ammonium carbonate solution contain 8 to 16% by wt ammonia, 4 to 12% by wt carbon dioxide, 0.5 to 1.5% by wt nickel and 0.02 to 0.2% by wt cobalt.

8. A process according to claim 1 wherein the mixture of the nickel, cobalt or mixed nickel/cobalt material, the feed ammoniacal ammonium carbonate solution and reductant is agitated for a period of from 30 minutes to 12 hours at a temperature of from 30 to 90° C. at atmospheric or elevated pressure.

9. A process according to claim 8 wherein air or oxygen containing gas is injected into the mixture after a period of at least 10 minutes anaerobic agitation.

10. A process according to claim 1 , wherein the leach step includes:

a) a primary leach step wherein the nickel, cobalt or mixed nickel/cobalt material is contacted with a feed ammoniacal ammonium carbonate solution to produce a product solution and a residue;

b) separating the residue from the product solution; and

c) a secondary leach step wherein the residue is contacted with fresh ammoniacal ammonium carbonate solution and a reductant to produce a secondary product solution containing dissolved nickel and cobalt and a secondary leach residue;

wherein the reductant is selected from a mixed nickel/cobalt hydroxide, cobalt sulphide or hydroxylamine.

11. A process according to claim 10 , wherein the nickel, cobalt or mixed nickel/cobalt material is either a nickel, cobalt or mixed nickel/cobalt hydroxide, carbonate, basic carbonate or basic sulphate material.

12. A process according to claim 10 , wherein the material is a mixed nickel/cobalt hydroxide material.

13. A process according to claim 10 wherein the feed ammoniacal ammonium carbonate solution is a process liquor from a Caron process.

14. A process according to claim 10 wherein the secondary product solution is returned and combined with the feed ammoniacal ammonium carbonate solution for the primary leach step.

15. A process according to claim 10 including the further step wherein the secondary leach residue is subjected to a third leach step by subjecting the secondary leach residue to prolonged contact with a strong ammoniacal ammonium carbonate solution.

16. A process according to claim 15 , the strong ammoniacal ammonium carbonate solution contains 8 to 16 wt % ammonia, 4 to 12 wt % carbon dioxide, 0 to 1.0 wt % nickel, and 0 to 0.1 wt % cobalt.

17. A process according to claim 10 wherein the reductant is a mixed cobalt/nickel sulphide and is produced by contacting a cobalt/nickel containing ammoniacal ammonium carbonate solution with ammonium hydrosulphide or sodium hydrosulphide to precipitate a mixed cobalt/nickel sulphide.

18. A process according to claim 17 , wherein the cobalt/nickel containing ammoniacal ammonium carbonate solution is a portion of the process liquor of a Caron process used as the feed ammoniacal ammonium carbonate solution, or a portion of any selected cobalt/nickel containing process liquor.

19. A process according to claim 10 wherein the feed ammoniacal ammonium carbonate solution and the cobalt/nickel containing ammoniacal ammonium carbonate solution contains 8 to 16% by wt ammonia, 4 to 12% by wt carbon dioxide, 0.5 to 1.5% by wt nickel and 0.02 to 0.2% by wt cobalt.

20. A process according to claim 10 wherein the fresh ammoniacal ammonium carbonate leach solution for the secondary leach step contains from 8 to 16% by wt ammonia and 4 to 12% by wt carbon dioxide with only trace amounts of nickel and cobalt.

21. A process according to claim 10 wherein the mixture of the fresh ammoniacal ammonium carbonate leach solution, the residue of the primary leach step and the reductant is agitated for a period of from 30 minutes to 12 hours at a temperature of from 30 to 90° C. at atmospheric or elevated pressure.

22. A process according to claim 21 wherein air or oxygen containing gas is injected into the mixture after a period of at least 10 minutes anaerobic agitation.