Metal extractant reagents having increased resistance to degradation

1. A solvent extraction composition comprising:

a) an orthohydroxyaryloxime extractant chosen from a member selected from the group consisting of:

i) an orthohydroxyarylketoxime compound according to Formula (1):

and salts, tautomers or metal complexes thereof,

wherein

R 1 is an optionally substituted C 1 -C 20 hydrocarbyl group; and

R 2 is an optionally substituted C 6 -C 20 orthohydroxyaryl group;

ii) an orthohydroxyarylaldoxime compound according to Formula (2):

and salts, tautomers or metal complexes thereof,

wherein

R 3 is an optionally substituted C 6 -C 20 orthohydroxyaryl group; and

iii) mixtures of (i) and (ii);

b) an anti-degradation agent chosen from a member selected from the group consisting of:

i) a phenol compound substituted with a member selected from the group consisting of:

2 t-butyl groups;

from 1 to 2 t-butyl groups and a C 1 -C 4 alkyl group;

from 1 to 3 alkaryl groups; and

a cumyl group;

ii) a catechol compound substituted with a solubilizing group selected from a member of the group consisting of: an optionally substituted C 6 -C 20 alkyl; and an optionally substituted C 6 -C 20 aryl;

iii) a resorcinol compound substituted with a solubilizing group selected from a member of the group consisting of: an optionally substituted C 6 -C 20 alkyl; and an optionally substituted C 6 -C 20 aryl; and

iv) mixtures of (i)-(iii); and

c) at least one water-immiscible organic solvent.

2. A solvent extraction composition according to claim 1 further comprising an equilibrium modifier chosen from a member selected from the group consisting of: alkylphenols; alcohols; esters; ethers; polyethers; carbonates; ketones; nitriles; amides; carbamates; sulphoxides; salts of amines and quaternary ammonium compounds; and mixtures thereof.

3. A solvent extraction composition according to claim 2 , wherein the equilibrium modifier is chosen from one or more compounds selected from the group consisting of: 2,2,4-trimethyl-1,3-pentanediol mono-isobutyrate; 2,2,4-trimethyl-1,3-pentanediol mono-benzoate; 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate; 2,2,4-trimethyl-1,3-pentanediol di-benzoate; butyl adipate; pentyl adipate; hexyl adipate; isobutyl heptyl ketone; nonanone; diundecyl ketone; 5,8-diethyldodecane-6,7-dione; tridecanol; and nonyl phenol.

4. A solvent extraction composition according to claim 1 , wherein the orthohydroxyaryloxime is chosen from a compound selected from the group consisting of: 5-(C 8 to C 14 alkyl)-2-hydroxyacetophenone oximes; 5-(C 8 to C 14 alkyl)-2-hydroxybenzaldoximes; and mixtures thereof.

5. A solvent extraction composition according to claim 1 , wherein the anti-degradation agent is chosen from a compound selected from the group consisting of:

and mixtures thereof.

6. A solvent extraction composition according to claim 5 , wherein the anti-degradation agent is chosen from a member selected from the group consisting of: mono-, di-, or tri-(1-phenylethyl)phenol; mixtures thereof; and isomers thereof.

7. A solvent extraction composition according to claim 1 , wherein the orthohydroxyaryl oxime is present in an amount of from 1% to 70% by weight of the total.

8. A solvent extraction composition according to claim 7 , wherein the orthohydroxyaryl oxime is present in an amount of from 5% to 50% by weight of the total.

9. A solvent extraction composition according to claim 8 , wherein the orthohydroxyaryl oxime is present in an amount of from 7.5% to 20% by weight of the total.

10. A solvent extraction composition according to claim 1 , wherein the oxime extractant is a mixture of aldoxime and ketoxime, and wherein the weight ratio of aldoxime:ketoxime is from 90:10 to 50:50.

11. A solvent extraction composition according to claim 1 , wherein the anti-degradation agent is present in an amount of from 0.1% to 20% by weight of the total.

12. A solvent extraction composition according to claim 11 , wherein the anti-degradation agent is present in an amount of from 0.5% to 10% by weight of the total.

13. A solvent extraction composition according to claim 1 , wherein the organic solvent has an aromatic hydrocarbon content of less than 30% w/w.

14. A solvent extraction composition according to claim 13 , wherein the organic solvent has an aromatic hydrocarbon content of less than 23% w/w.

15. A solvent extraction composition according to claim 1 , wherein the organic solvent is present in an amount of from 30% to 95% w/w.

16. A solvent extraction composition according to claim 15 , wherein the organic solvent is present in an amount of from 50% to 95% w/w.

17. A process for recovering a metal from an aqueous acidic solution comprising:

a) contacting an aqueous acidic solution containing a metal with a solvent extraction composition as defined by claim 10 , thereby forming a metal-solvent extractant complex in a water-immiscible phase; and

b) contacting the metal-solvent extractant complex in the water-immiscible phase with an aqueous acidic strip solution, thereby stripping the metal from the water-immiscible phase.

18. A process according to claim 17 , wherein the metal is chosen from a member selected from the group consisting of: copper; iron; cobalt; nickel; manganese; zinc; and mixtures thereof.

19. A process according to claim 18 , wherein the metal is copper.

20. A process according to claim 17 , wherein the volume ratio of solvent extractant to aqueous acidic solution is from 20:1 to 1:20.

21. A process according to claim 20 , wherein the volume ratio is from 5:1 to 1:5.

22. A process according to claim 17 further comprising recycling the solvent extractant or aqueous acidic solution.

23. A process according to claim 17 , wherein the aqueous acidic strip solution is a mineral acid chosen from a member selected from the group consisting of: sulfuric acid; nitric acid; hydrochloric acid; and mixtures thereof.