Aqueous leaching process for recovery of precious metals with addition of di-thiooxamide ligand
This invention relates to a process for the recovery of precious metal/s from a precious metal-containing material in an aqueous leach slurry or solution. The process includes the step of contacting the precious metal/s in the leach slurry or solution with a ligand selected from dithiooxamide (rubeanic acid), or a substituted dithiooxamide. The leaching of PGMs, gold and silver from their ores using the ligand of the present invention may take place under aqueous alkaline conditions, avoiding both corrosive acidic conditions and the use of cyanide.
1. A process for the recovery of precious metal/s from a precious metal-containing material in an aqueous leach slurry or solution, the process including a step of contacting the precious metal/s in the leach slurry or solution with a ligand,
wherein the ligand is dithiooxamide, or substituted dithiooxamide, and
wherein the leach solution or slurry is maintained at conditions which result in a deprotonation of the ligand.
2. A process as claimed in claim 1 , wherein a pH of the leach solution or slurry is above 7.
3. A process as claimed in claim 1 , wherein the ligand is dithiooxamide.
4. A process as claimed in claim 3 , wherein a pH of the leach or slurry solution is above 9.
5. A process as claimed in claim 4 , wherein the pH of the leach or slurry is 10 or above.
6. A process as claimed in claim 1 , wherein the ligand is added at a concentration above a stoichiometric amount required for extraction of the precious metal/s and up to a solubility limit of the ligand.
7. A process as claimed in claim 1 , wherein the ligand is added at a molar ratio of ligand to precious metal/s of 2:1 to 11000:1.
8. A process as claimed in claim 7 , wherein the ligand is added at a molar ratio of ligand to precious metal/s of 60:1 to 800:1.
9. A process as claimed in claim 1 , wherein an electrochemical potential (Eh) of the leach solution or slurry is controlled to be above 0 mV versus a Standard Hydrogen Electrode (SHE).
10. A process as claimed in claim 9 , wherein the electrochemical potential (Eh) of the leach solution or slurry is controlled to be above 40 and less than 200 mV.
11. A process as claimed in claim 10 , wherein the electrochemical potential (Eh) of the leach solution or slurry is controlled to be above 60 and less than 150 mV.
12. A process as claimed in claim 1 , wherein the ligand is added to the slurry dissolved in an aqueous solution.
13. A process as claimed in claim 12 , wherein the ligand is dithiooxamide which is dissolved into the aqueous solution at a temperature below 40° C., and a pH above 13 up to 14.
14. A process as claimed in claim 13 , wherein the ligand is dithiooxamide which is dissolved into the aqueous solution at a temperature from 20 to below 40° C. and a pH from 13.5 to 14.
15. A process as claimed in claim 1 , wherein the leach slurry or solution is contacted with activated carbon and the precious metal/s is/are adsorbed onto the activated carbon.
16. A process as claimed in claim 1 , wherein the precious metal is gold and the precious metal-containing material is ore, concentrates or tailings.
17. A process as claimed in claim 16 , wherein a pH of the leach or slurry solution is from 10 to 15.
18. A process as claimed in claim 17 , wherein the pH of the leach slurry or solution is 12 to 14.
19. A process as claimed in claim 18 , wherein a temperature of the leach slurry or solution is from 20 to less than 40° C.
20. A process as claimed in claim 19 , wherein the temperature of the leach slurry or solution is from 20 to 30° C.
21. A process as claimed in claim 16 , wherein the a ligand concentration in the leach solution or slurry is from 0.002 to 12 g/l.
22. A process as claimed in claim 16 , wherein a ligand concentration in the leach solution or slurry is at a ratio of 0.1 to 1 g/l ligand per mg/g gold.
23. A process as claimed in claim 1 , wherein the precious metal/s is/are selected from the group consisting of silver, PGMs, PGMs and gold, PGMs and silver and PGMs and gold and silver, and the precious metal-containing material is selected from the group consisting of ore, concentrates and tailings.
24. A process as claimed in claim 23 , wherein a pH of the leach slurry or solution is from 10 to 14.
25. A process as claimed in claim 24 , wherein the pH of the leach or slurry is from 10.5 to 13.
26. A process as claimed in claim 23 , wherein a temperature of the leach solution or slurry is from 20 to less than 70° C.
27. A process as claimed in claim 23 , wherein a ligand concentration in the leach solution or slurry is from 0.001 to 36 g/l.
28. A process as claimed in claim 23 , wherein a ratio of a concentration of ligand in the leach slurry or solution, in g/l, to a concentration of silver, PGMs, PGMs and gold, PGMs and silver, or PGMs and gold and silver in the leach slurry or solution, in mg/g, is 0.02 to 0.4.
29. A process as claimed in claim 1 , wherein the precious metal/s are in elemental form.
30. A process as claimed in claim 29 , wherein a pH of the leach or slurry solution is from 10 to 15.
31. A process as claimed in claim 29 , wherein a ligand concentration in the leach solution us from 0.002 to 12 g/l.
32. A process as claimed in claim 29 , wherein a ligand concentration in the leach solution is at a ratio of 0.1 to 1 g/l ligand per mg/g elemental precious metal/s.
33. A process as claimed in claim 1 , wherein the substituted dithiooxamide ligand is a compound represented by
where R1,2,3,4 are independently —H, alkyl, substituted alkyl, aryl, or substituted aryl; or
where X is —CO—, —CS—, —CH2-, -—O—, —S—, —CH═CH—, or —NH—; or
where X is —CO—, —CS—, —CH2-, —O—, —S—, or —NH—.
34. The method of claim 33 , wherein the substituted dithiooxamide ligand is the compound represented by
where R1,2,3,4 are independently —H, —COOH, —CH2COOH, or —(CH2)2SO3H.