Process for recovering precious metals from clay-containing ores

1. A method for heap leaching of precious metal from day containing ore comprising:

forming a heap of ore on a leach bed;

percolating a leach solution through said heap wherein said leach solution comprises:

cyanide;

a wetting agent; and

a clay stabilizing polymer wherein said clay stabilizing polymer is selected from the group consisting of a polyalkylene oxide copolymer, a propoxylated glycol and a polyamine copolymer;

thereby forming a pregnant leach solution comprising said precious metal; and

removing said precious metal from said pregnant leach solution.

2. A method for heap leaching of precious metal from day containing ore of claim 1 wherein said metal is selected from the group consisting of gold, silver, copper and uranium.

3. A method for heap leaching of precious metal from day containing ore of claim 1 wherein said leach solution has a pH of at least 8 to no more than 11.

4. A method for heap leaching of precious metal from clay containing ore of claim 3 wherein said leach solution has a pH of at least 9.5 to no more than 10.5.

5. A method for heap leaching of precious metal from clay containing ore of claim 1 wherein said leach solution comprises at least 50 ppm cyanide to no more than 1000 ppm cyanide.

6. A method for heap leaching of precious metal from clay containing ore of claim 5 wherein said leach solution comprises at least 200 ppm cyanide to no more than 800 ppm cyanide.

7. A method for heap leaching of precious metal from day containing ore of claim 1 wherein said polyalkylene oxide copolymer is defined by:

R 1 —R 2 —R 3 —R 4 —R 5

wherein:

R 1 and R 5 are terminal groups independently selected from the group consisting of H, hydroxyl, saturated or unsaturated aliphatic of 1 to 30 carbons, —OC(O)R 6 wherein R 6 is a hydrogen or a saturated or unsaturated aliphatic of 1 to 30 carbons;

at least one of R 2 , R 3 or R 4 is polypropylene oxide (PO) with 1 to 100 PO groups;

R 2 , R 3 or R 4 is otherwise independently selected from the group consisting of: polyethylene oxide (EO) with 1 to 100 EO groups;

polypropylene oxide (PO) with 1 to 100 PO groups with the proviso that at least one of R 2 , R 3 and R 4 is not PO; polyester defined by—(OC(O)R 7 C(O)O) z —wherein R 7 is aromatic with at least one to no more than four aromatic rings or a saturated or unsaturated aliphatic with 1 to 20 carbons and z is an integer of 1 to 100.

8. A method for heap leaching of precious metal from clay containing ore of claim 7 wherein said R 2 , R 3 or R 4 is ethylene oxide with 2 to 100 EO groups.

9. A method for heap leaching of precious metal from day containing ore of claim 7 wherein said R 2 , R 3 or R 4 is propylene oxide with 2 to 100 PO groups.

10. A method for heap leaching of precious metal from day containing ore of claim 7 wherein z is an integer of 2 to 100.

11. A method for heap leaching of precious metal from clay containing ore of claim 7 wherein R 3 is PO and R 2 , R 3 and R 4 are independently selected from EO and polyester.

12. A method for heap leaching of precious metal from clay containing ore of claim 1 wherein said propoxylated glycol is defined by the formula:

X[(CH 2 CHR 17 O) s R 18 ] t

wherein X is a linking group derived from an organic compound containing at least two hydroxyl or amine groups capable of reacting with ethylene oxide;

each R 17 is independently —H or —CH 3 , branched or linear aryl or alkyl moieties of 2-22 carbons which can be unsubstituted or substituted, and may also be —CH 2 OR 19 groups such as those arising from the reaction of an alkyl or aryl glycidyl ether with the proviso that at least one R 17 is not hydrogen;

each R 18 is independently —H, unsubstituted or substituted aryl or alkyl hydrocarbon chains of 1-25 carbons which may be saturated or unsaturated, or an ester group —C(═O)R 20 ;

R 19 is a branched or linear aryl or alkyl moiety of 1-22 carbons which can be substituted or unsubstituted;

R 20 is unsubstituted or substituted aryl or alkyl hydrocarbon chain of 1-25 carbons which may be saturated or unsaturated;

s is an integer of 3-300;

t is an integer of 2-12.

13. A method for heap leaching of precious metal from clay containing ore of claim 1 wherein said propoxylated glycol is defined by the formula:

R 10 —CH 2 —CH(OR 12 )CH 2 (OCH 2 CH(OR 13 )CH 2 ) n OR 11

wherein R 10 and R 11 are terminal groups independently selected from selected from the group consisting of H, hydroxyl and saturated or unsaturated aliphatic of 1 to 30 carbons or OC(O)R 15 wherein R 15 is a hydrogen or a saturated or unsaturated aliphatic of 1 to 30 carbons;

R 12 , R 13 are independently selected from polyethylene oxide (EO) with 1 to 100 EO groups; polypropylene oxide (PO) with 1 to 100 PO groups or —(CH 2 CHR 16 O) r —;

R 16 is independently hydrogen or methyl;

r is an integer of 1 to 100; and

n is an integer of 1 to 4.

14. A method for heap leaching of precious metal from clay containing ore of claim 13 wherein r is an integer of 2 to 100.

15. A method for heap leaching of precious metal from day containing ore of claim 13 wherein said R 12 , R 13 are independently ethylene oxide having 2 to 100 EO groups.

16. A method for heap leaching of precious metal from day containing ore of claim 13 wherein said R 12 , R 13 are independently propylene oxide having 2 to 100 PO groups.

17. A method for heap leaching of precious metal from clay containing ore of claim 1 wherein said polyamine comprises dicyandiamide, formaldehyde and ammonia.

18. A method for heap leaching of precious metal from clay containing ore of claim 17 wherein said polyamine has a hydroxyl number of at least 20 to no more than 35.

19. A method for heap leaching of precious metal from clay containing ore of claim 17 wherein said polyamine has a hydroxyl number of at least 26 to no more than 31.

20. A method for heap leaching of precious metal from day containing ore comprising:

forming a heap of ore on a leach bed;

percolating a leach solution through said heap wherein said leach solution comprises:

cyanide;

a wetting agent; and

a clay stabilizing polymer;

thereby forming a pregnant leach solution comprising said precious metal; and

removing said precious metal from said pregnant leach solution; and

wherein said wetting agent is selected from the group consisting of alcohol ethoxylates; polyethylene glycol esters, hydrophilic modified silicones, and fatty amine ethoxylates.

21. A method for heap leaching of precious metal from clay containing ore of claim 20 wherein said clay stabilizing polymer is selected from the group consisting of polyalkylene oxide copolymer; propoxylated glycols; polyamine copolymer comprising dicyandiamide, formaldehyde and ammonia; polyvinyl alcohol; partially hydrolyzed polyvinyl acetate; polyacrylamide; quaternary amines; carboxymethyl cellulose; methacrylate copolymers; hydroxyaldehydes; hydroxyketones; and copolymers of anionic or cationic monomers.

22. A method for heap leaching of precious metal from clay containing ore of claim 20 wherein said polyethylene glycol esters has 3 to 20 polyethylene groups.

23. A method for heap leaching of precious metal from clay containing ore of claim 22 wherein said polyethylene glycol esters has 7 to 12 polyethylene groups.

24. A method for heap leaching of precious metal from clay containing ore of claim 20 wherein said alcohol ethoxylate has an alkyl chain with 5-20 carbon atoms.

25. A method for heap leaching of precious metal from clay containing ore of claim 24 wherein said alcohol ethoxylate has an alkyl chain with 10-15 carbon atoms.

26. A method for heap leaching of precious metal from clay containing ore of claim 20 wherein said alcohol ethoxylate has 2 to 20 ethylene oxide units.

27. A method for heap leaching of precious metal from clay containing ore of claim 26 wherein said alcohol ethoxylate has 3 to 14 ethylene oxide units.

28. A method for heap leaching of precious metal from day containing ore of claim 20 comprising:

mixing said cyanide;

said wetting agent and said clay stabilizing polymer at a pH below 7; and

adjusting to a pH above 8.

29. A method for heap leaching of precious metal from day containing ore of claim 21 wherein said quaternary amines are tetramethylammonium salts.