Noble metal extraction method and apparatus
A method for extracting noble metals from mining tailings and other solids is provided. The method uses a Lewis acid, Brønsted acid, complexing agent and oxygen to provide excellent extraction without the need for chorine gas or cyanide.
1. A method of separating bound noble metals from a solid, the method comprising:
mixing a solid comprising at least one noble metal (M) into an aqueous solution having a pH of less than 3.0 to form a slurry, the solution comprising a Brønsted acid, a Lewis acid, and a complexing agent;
contacting the slurry with an oxidant having a redox potential of greater than or equal to +0.77 V;
producing a soluble complex of the at least one noble metal (M) in the slurry; and
recovering at least 10% by weight of the at least one noble metal (M) from the solid.
2. The method of claim 1 wherein the Lewis acid comprises a salt.
3. The method of claim 2 wherein the Lewis acid comprises a metal halide salt.
4. The method of claim 3 wherein the metal of the metal halide salt is selected from iron, chromium, manganese and copper.
5. The method of claim 1 wherein the Lewis acid comprises an alkali metal cation and the complexing agent comprises the same alkali metal cation.
6. The method of claim 5 wherein the alkali metal cation is potassium or sodium.
7. The method of claim 1 wherein M is at least one of the platinum group metals.
8. The method of claim 1 wherein the Brønsted acid is a mineral acid.
9. The method of claim 1 wherein the Brønsted acid includes the same anion as does the Lewis acid and/or the complexing agent.
10. The method of claim 1 wherein the pH of the aqueous solution during mixing is less than 2.5.
11. The method of claim 1 wherein the bound noble metals are base metal sulfides, sulfates, phosphides, phosphates, carbonates, tellurides, arsenides or a mixture thereof.
12. The method of claim 1 wherein the temperature of the aqueous solution is less than 110° C.
13. The method of claim 1 wherein the temperature of the aqueous solution is greater than 40° C.
14. The method of claim 1 wherein the method comprises a batch process and the ratio of the solid to the aqueous solution is, by weight, greater than 1:10.
15. The method of claim 1 wherein the method comprises a batch process and the ratio of the solid to the aqueous solution is, by weight, less than 1:10.
16. The method of claim 1 wherein the slurry is mixed for greater than 1 minute.
17. The method of claim 1 wherein the Lewis acid is present in the slurry at a concentration of greater than 0.05 M.
18. The method of claim 1 wherein the complexing agent is present in the slurry at a concentration of greater than 0.001 M.
19. The method of claim 1 wherein the oxidant exhibits a positive redox potential of greater than +0.958 V.
20. The method of claim 1 wherein the method is void of gaseous oxidants other than oxygen.
21. The method of claim 1 wherein the method is void of chlorine gas.
22. The method of claim 1 wherein the solid comprises pentlandite, chalcopyrite and/or pyrite.
23. The method of claim 1 wherein the solid comprises mining tailings, dilute ore bodies, scrap material or material for recycling.
24. The method of claim 1 wherein the solution comprises a reduced species of the Lewis acid.
25. The method of claim 1 wherein the oxidant comprises peroxide, perchlorate or ozone.
26. The method of claim 1 wherein the oxidant is a gas.
27. The method of claim 26 wherein the gas comprises air, oxygen or ozone.
28. The method of claim 1 wherein the oxidant is dissolved in the solution.
29. The method of claim 28 wherein the oxidant comprises perchlorate, peroxide, persulfate or ozone.
30. The method of claim 1 wherein the method is void of gaseous oxidants except for oxygen, air and/or ozone.