Methods for simultaneous leaching and extraction of precious metals

Abstract

The present application relates to methods for the simultaneous leaching and extraction of precious metals. For example, the present application relates to methods of leaching and extracting gold and/or palladium from a substance comprising gold and/or palladium such as a gold and/or palladium-containing ore in one step using a compound of Formula I: (I).

Claims

1. A method of leaching and extracting gold and/or palladium from a substance comprising gold and/or palladium, the method comprising: treating the substance with a mixture comprising an aqueous phase and an organic phase, wherein the aqueous phase comprises an acid and an oxidizing agent, and the organic phase comprises a water-immiscible organic solvent and a compound of Formula I: ##STR00024## wherein R.sup.1 is —NR.sup.4R.sup.5 or aryl; R.sup.2 and R.sup.3 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl; or R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl, or a heterocycloalkyl or a heteroaryl substituted at one or more carbon atoms with C.sub.1-4 alkyl; R.sup.4 and R.sup.5 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl; or R.sup.4 and R.sup.5 together with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl, or a heterocycloalkyl or a heteroaryl substituted at one or more carbon atoms with C.sub.1-4alkyl; X is O or S; Y is S, NR.sup.6 or CR.sup.6R.sup.7; and R.sup.6 and R.sup.7 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl, and the treating is under conditions to leach the gold and/or palladium from the substance and extract the leached gold and/or palladium by forming a complex between the leached gold and/or palladium and the compound of Formula I, in a single reaction vessel; wherein the substance is an anode slime, electronic scrap, jewelry scrap, palladium-containing ore, or ore comprising gold and palladium.

2. The method of claim 1, wherein the compound of Formula I is a compound of Formula I(a): ##STR00025## wherein R.sup.2, R.sup.3, R.sup.4, R.sup.5 and Y are as defined in claim 1.

3. The method of claim 2, wherein only one of R.sup.2, R.sup.3, R.sup.4 and R.sup.5 is H.

4. The method of claim 2, wherein R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form a heterocycloalkyl or a substituted heterocycloalkyl, wherein the heterocycloalkyl is selected from aziridinyl, azetidinyl, pyrrolidinyl, piperidinyl, azepanyl, azocanyl, imidazolidinyl, oxazolidinyl, thiazolidinyl, piperazinyl, hexahydropyrimidinyl, morpholinyl, 1,3-oxazinanyl, thiomorpholinyl, 1,3-thiazinanyl, 1,3-diazepanyl, 1,3-oxazepanyl, 1,3-thiazepanyl, 1,4-diazepanyl, 1,4-oxazepanyl, 1,4-thiazepanyl, 1,3-diazocanyl, 1,3-oxazocanyl, 1,3-thiazocanyl, 1,4-diazocanyl, 1,4-oxazocanyl, 1,4-thiazocanyl, 1,5-diazocanyl, 1,5-oxazocanyl and 1,5-thiazocanyl.

5. The method of claim 4, wherein R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form morpholinyl, pyrrolidinyl or 4-methylpiperidinyl.

6. The method of claim 2, wherein R.sup.4 is H and R.sup.5 is C.sub.1-6 alkyl or C.sub.3-8 cycloalkyl.

7. The method of claim 1, wherein Y is NR.sup.6.

8. The method of claim 7, wherein R.sup.6 is H, C.sub.1-6 alkyl or C.sub.3-8 cycloalkyl.

9. The method of claim 1, wherein the compound of Formula I is a compound of Formula I(a)(i), I(a)(ii), I(a)(iii) or I(a)(iv): ##STR00026##

10. The method of claim 9, wherein the compound of Formula I is the compound of Formula I(a)(i): ##STR00027##

11. The method of claim 1, wherein the compound of Formula I is a compound of Formula I(b)(i): ##STR00028##

12. The method of claim 1, wherein the molar ratio of the compound of Formula Ito the gold and/or palladium is about 3:1 to about 4:1.

13. The method of claim 1, wherein the acid in the mixture is a hydrogen halide, chlorous acid, chloric acid, bromous acid, bromic acid, iodous acid, iodic acid, perchloric acid, sulfuric acid, nitric acid, oxalic acid, phosphoric acid, an organic acid, or combinations thereof.

14. The method of claim 13, wherein the acid is selected from HCl, H.sub.2SO.sub.4, HBr, HNO.sub.3, H.sub.3PO.sub.4 and HI.

15. The method of claim 14, wherein the acid is HCl having a concentration in the aqueous solution of about 0.75 M to about 3 M.

16. The method of claim 1, wherein the oxidizing agent is ozone, nitric acid, hydrogen peroxide, O.sub.2, bubbled air, I.sub.2, Br.sub.2, Cl.sub.2, potassium monopersulfate, an ammonium polyatomic salt, calcium hypochlorite, a sodium polyatomic salt, a potassium polyatomic salt, manganese oxide, a tetraalkylammonium salt, peroxomonosulfuric acid, urea, peracetic acid, an alkanesulfonic acid, an aromatic sulfonic acid, or combinations thereof.

17. The method of claim 16, wherein the oxidizing agent in the mixture is selected from HNO.sub.3, or MnO.sub.2.

18. The method of claim 17, wherein the oxidizing agent is HNO.sub.3 having a concentration in the aqueous solution of about 0.1 M to 2.0 M.

19. The method of claim 1, wherein the water-immiscible organic solvent is selected from dichloromethane, chloroform and chlorobenzene.

20. The method of claim 1, wherein the conditions to leach the gold and/or palladium from the substance and extract the gold and/or palladium by forming a complex between the leached gold and/or palladium and the compound of Formula I in one step comprise stirring the mixture for a time of about 2 hours to about 10 hours at a temperature of about 10° C. to about 40° C.

21. The method of claim 20, wherein the conditions to leach the gold and/or palladium from the substance and extract the gold and/or palladium by forming a complex between the leached gold and/or palladium and the compound of Formula I in one step comprise stirring the mixture at a temperature of about 20° C. to about 25° C.

22. The method of claim 1, wherein the method further comprises separating the mixture into an aqueous phase and an organic phase comprising the complex between the leached gold and/or palladium and the compound of Formula I.

23. The method of claim 22, wherein the method further comprises stripping the gold and/or palladium from the complex between the compound of Formula I and the leached gold and/or palladium by a method comprising contacting the organic phase with an aqueous solution comprising an acid and thiourea under conditions to obtain a gold and/or palladium-containing strip solution and a gold and/or palladium-reduced organic phase comprising the compound of Formula I.

24. The method of claim 23, wherein the method further comprises separating the gold and/or palladium-containing strip solution from the gold and/or palladium-reduced organic phase comprising the compound of Formula I and recovering gold and/or palladium from the gold and/or palladium-containing strip solution by electrowinning or reduction.

25. The method of claim 23, wherein the method further comprises recycling the compound of Formula I from the gold and/or palladium-reduced organic phase.

26. The method of claim 22, wherein the method further comprises recovering gold and/or palladium from the organic phase by direct reduction.

27. The method of claim 1, wherein the method further comprises, prior to contacting with the mixture, crushing and/or grinding the substance comprising gold and/or palladium into particles.

28. The method of claim 27, wherein the size of the particles of the substance comprising gold and/or palladium is less than or equal to about 75 microns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present application will now be described in greater detail with reference to the drawings in which:

(2) FIG. 1 shows a schematic representation of a process of gold recovery using cyanide leaching according to the prior art.

(3) FIG. 2 is a plot showing Au Recovery (%) as a function of time (hours) for simultaneous leaching and extraction according to an embodiment of a method of the present application in comparison to conventional leaching.

(4) FIG. 3 shows a schematic representation of a method of leaching and extracting gold from a gold-containing substance according to an embodiment of a method of the present application.

DETAILED DESCRIPTION

I. Definitions

(5) Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the present application herein described for which they are suitable as would be understood by a person skilled in the art.

(6) The term “compound of the present application” and the like as used herein refers to a compound of Formula I as defined herein.

(7) In understanding the scope of the present application, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. The term “consisting” and its derivatives, as used herein, are intended to be closed terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The term “consisting essentially of”, as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and/or steps as well as those that do not materially affect the basic and novel characteristic(s) of features, elements, components, groups, integers, and/or steps.

(8) Terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

(9) The term “and/or” as used herein means that the listed items are present, or used, individually or in combination. In effect, this term means that “at least one of” or “one or more” of the listed items is used or present.

(10) As used in this application, the singular forms “a”, “an” and “the” include plural references unless the content clearly dictates otherwise. For example, an embodiment including “a compound” should be understood to present certain aspects with one compound or two or more additional compounds.

(11) In embodiments comprising an “additional” or “second” component, such as an additional or second compound, the second component as used herein is chemically different from the other components or first component. A “third” component is different from the other, first, and second components, and further enumerated or “additional” components are similarly different.

(12) In embodiments of the present application, the compounds described herein have at least one asymmetric center. Where compounds possess more than one asymmetric center, they may exist as diastereomers. It is to be understood that all such isomers and mixtures thereof in any proportion are encompassed within the scope of the present application. It is to be further understood that while the stereochemistry of the compounds may be as shown in any given compound listed herein, such compounds may also contain certain amounts (for example, less than 20%, suitably less than 10%, more suitably less than 5%) of compounds of the present application having alternate stereochemistry. It is intended that any optical isomers, as separated, pure or partially purified optical isomers or racemic mixtures thereof are included within the scope of the present application.

(13) The term “suitable” as used herein means that the selection of specific reagents or conditions will depend on the reaction being performed and the desired results, but none-the-less, can generally be made by a person skilled in the art once all relevant information is known.

(14) The term “immiscible” as used herein when referring to two liquid phases means that the two liquid phases cannot be mixed to form a solution having a single phase under the conditions used, such as the relative proportions of the two liquid phases and/or the temperature, etc. Two immiscible liquid phases will, for example separate into two liquid phases after mixing. Each of these two liquid phases may, for example contain small amounts of the other liquid phase. Accordingly, a “water-immiscible” liquid such as a “water-immiscible organic solvent” is a liquid that cannot be mixed with water to form a solution having a single phase under the conditions used but that may, for example contain small amounts of water after being mixed with water.

(15) The term “alkyl” as used herein, whether it is used alone or as part of another group, means straight or branched chain, saturated alkyl groups. The number of carbon atoms that are possible in the referenced alkyl group are indicated by the numerical prefix “C.sub.n1-n2”. For example, the term C.sub.1-10 alkyl means an alkyl group having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms.

(16) The term “alkylene” as used herein, whether it is used alone or as part of another group, means straight or branched chain, saturated alkylene group, that is, a saturated carbon chain that contains substituents on two of its ends. The number of carbon atoms that are possible in the referenced alkylene group are indicated by the numerical prefix “C.sub.n1-n2”. For example, the term C.sub.1-6 alkylene means an alkylene group having 1, 2, 3, 4, 5 or 6 carbon atoms.

(17) The term “cycloalkyl,” as used herein, whether it is used alone or as part of another group, means saturated alkyl groups having at least one cyclic ring. The number of carbon atoms that are possible in the referenced cycloalkyl group are indicated by the numerical prefix “C.sub.n1-n2”. For example, the term C.sub.3-10 cycloalkyl means a cycloalkyl group having 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms.

(18) The term “heterocycloalkyl” as used herein, whether it is used alone or as part of another group, refers to a non-aromatic, ring-containing group having one or more multivalent heteroatoms, independently selected from N, O and S, as a part of the ring structure and including at least 3 and up to 20 atoms in the ring(s). Heterocycloalkyl groups are either saturated or unsaturated (i.e. contain one or more double bonds) and may contain more than one ring.

(19) The term “aryl” as used herein, whether it is used alone or as part of another group, refers to cyclic groups that contain at least one aromatic ring. In an embodiment of the application, the aryl group contains from 6, 9, 10 or 14 atoms, such as phenyl, naphthyl, indanyl or anthracenyl.

(20) The term “heteroaryl” as used herein, whether it is used alone or as part of another group, refers to an aromatic, ring-containing group having one or more multivalent heteroatoms, independently selected from N, 0 and S, as a part of the ring structure and including at least 5 and up to 20 atoms in the ring(s). Heteroaryl groups may contain more than one ring.

II. Methods and Uses of the Application

(21) In the methods of the present application, both leaching and extraction of metal steps are done simultaneously which can increase the overall efficiencies of the process over known methods for leaching and extracting metals such as gold in which these steps are conducted separately. Using the methods of the present application, greater than 99.9% gold recovery has been achieved with gold powder in only four hours using very low concentrations of acid (1 M HCl) at room temperatures. Increasing HCl concentration to 2 M reduced gold recovery times to two hours. To investigate the selectivity of the methods of the present application, a mixture of different metals was treated. The method was found to be highly selective for gold in the presence of large amounts of transition metal impurities such as Fe, Cu, Zn and Ag. Compared to known methods, on top of eliminating the need for cyanide and activated carbon, the methods of the present application also can eliminate the need for an acid washing step to remove impurities.

(22) Accordingly, the present application includes a method of leaching and extracting gold and/or palladium from a substance comprising gold and/or palladium, the method comprising:

(23) treating a mixture comprising an aqueous phase comprising an acid, an oxidizing agent and the substance, and an organic phase comprising a water-immiscible organic solvent and a compound of Formula I:

(24) ##STR00008##
wherein

(25) R.sup.1 is —NR.sup.4R.sup.5 or aryl;

(26) R.sup.2 and R.sup.3 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl; or

(27) R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl, or a heterocycloalkyl or a heteroaryl substituted at one or more carbon atoms with C.sub.1-4alkyl;

(28) R.sup.4 and R.sup.5 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl; or

(29) R.sup.4 and R.sup.5 together with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl, or a heterocycloalkyl or a heteroaryl substituted at one or more carbon atoms with C.sub.1-4 alkyl;

(30) X is O or S;

(31) Y is S, NR.sup.6 or CR.sup.6R.sup.7; and

(32) R.sup.6 and R.sup.7 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl, under conditions to leach the gold and/or palladium from the substance and extract the gold and/or palladium by forming a complex between the leached gold and/or palladium and the compound of Formula I, in one step.

(33) In an embodiment, R.sup.1 is —NR.sup.4R.sup.5.

(34) In an alternative embodiment, R.sup.1 is aryl. In another embodiment, R.sup.1 is C.sub.6-10 aryl. In a further embodiment, R.sup.1 is phenyl.

(35) In another embodiment, the compound of Formula I is a compound of Formula I(a):

(36) ##STR00009##
wherein R.sup.2, R.sup.3, R.sup.4, R.sup.5 and Y are as defined for the compound of Formula I.

(37) In an embodiment of the present application, for example, in the compound of Formula I(a), only one of R.sup.2, R.sup.3, R.sup.4 and R.sup.5 is H.

(38) In another embodiment of the present application, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl, or a substituted heterocycloalkyl or a substituted heteroaryl.

(39) In an embodiment, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form a heterocycloalkyl or a substituted heterocycloalkyl. In another embodiment, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form a heterocycloalkyl or a substituted heterocycloalkyl, wherein the heterocycloalkyl is selected from aziridinyl, azetidinyl, pyrrolidinyl, piperidinyl, azepanyl, azocanyl, imidazolidinyl, oxazolidinyl, thiazolidinyl, piperazinyl, hexahydropyrimidinyl, morpholinyl, 1,3-oxazinanyl, thiomorpholinyl, 1,3-thiazinanyl, 1,3-diazepanyl, 1,3-oxazepanyl, 1,3-thiazepanyl, 1,4-diazepanyl, 1,4-oxazepanyl, 1,4-thiazepanyl, 1,3-diazocanyl, 1,3-oxazocanyl, 1,3-thiazocanyl, 1,4-diazocanyl, 1,4-oxazocanyl, 1,4-thiazocanyl, 1,5-diazocanyl, 1,5-oxazocanyl and 1,5-thiazocanyl. In a further embodiment, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form morpholinyl, pyrrolidinyl or 4-methylpiperidinyl. In an embodiment, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form morpholinyl. In another embodiment, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form pyrrolidinyl. In a further embodiment, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form 4-methylpiperidinyl.

(40) In an embodiment, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form a heteroaryl or a substituted heteroaryl. In another embodiment of the present application, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form a heteroaryl. In a further embodiment, for example, in the compound of Formula I(a), R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached form a heteroaryl selected from pyrrolyl, imidazolyl, pyrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, 1,2,3-triazolyl, 1 ,2,4-triazolyl, furazanyl, pyridinyl, pyrazinyl, pyrimidinyl, pyridazinyl, 1,2,3-triazinyl, 1,2,4-triazinyl and 1,3,5-triazinyl.

(41) In an embodiment, for example, in the compound of Formula I(a), R.sup.4 is selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl. In another embodiment, for example, in the compound of Formula I(a), R.sup.4 is selected from H, C.sub.1-6 alkyl, C.sub.3-8 cycloalkyl, C.sub.1-4 alkylene C.sub.3-8 cycloalkyl, heterocycloalkyl and phenyl. In a further embodiment, for example, in the compound of Formula I(a), R.sup.4 is selected from H, C.sub.1-6 alkyl and C.sub.3-8 cycloalkyl. It is an embodiment that, for example, in the compound of Formula I(a), R.sup.4 is selected from H and C.sub.1-4 alkyl. In another embodiment of the present application, for example, in the compound of Formula I(a), R.sup.4 is H.

(42) In an embodiment, for example, in the compound of Formula I(a), R.sup.5 is selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl. In another embodiment, for example, in the compound of Formula I(a), R.sup.5 is selected from C.sub.3-10 alkyl, C.sub.3-8 cycloalkyl, C.sub.1-4 alkylene C.sub.3-8 cycloalkyl, heterocycloalkyl and phenyl. In a further embodiment, for example, in the compound of Formula I(a), R.sup.5 is selected from C.sub.1-6 alkyl and C.sub.3-8 cycloalkyl. It is an embodiment, for example, in the compound of Formula I(a), that R.sup.5 is isopropyl or cyclohexyl. In another embodiment, for example, in the compound of Formula I(a), R.sup.5 is isopropyl. In a further embodiment, for example, in the compound of Formula I(a), R.sup.5 is cyclohexyl.

(43) In an embodiment, at least one of any one of R.sup.1 to R.sup.7 is aryl. In another embodiment, at least one of any one of R.sup.1 to R.sup.7 is phenyl.

(44) In an embodiment, for example, in the compound of Formula I(a), R.sup.4 is H or C.sub.1-4 alkyl and R.sup.5 is C.sub.1-6 alkyl or C.sub.3-8 cycloalkyl. In another embodiment, for example, in the compound of Formula I(a), R.sup.4 is H and R.sup.5 is C.sub.1-6 alkyl or C.sub.3-8 cycloalkyl. In a further embodiment of the present application, for example, in the compound of Formula I(a), R.sup.4 is H and R.sup.5 is C.sub.1-6 alkyl. It is an embodiment, for example, in the compound of Formula I(a), that R.sup.4 is H and R.sup.5 is C.sub.3-8 cycloalkyl. In another embodiment, for example, in the compound of Formula I(a), R.sup.4 is H and R.sup.5 is isopropyl. In a further embodiment, for example, in the compound of Formula I(a), R.sup.4 is H and R.sup.5 is cyclohexyl.

(45) In an embodiment, X is O. In another embodiment, X is S.

(46) In an embodiment, Y is NR.sup.6.

(47) In an embodiment, R.sup.6 is selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl. In another embodiment, R.sup.6 is selected from H, C.sub.1-6 alkyl, C.sub.3-8 cycloalkyl, C.sub.1-4 alkylene C.sub.3-8 cycloalkyl and heterocycloalkyl. In a further embodiment, R.sup.6 is H, C.sub.1-6 alkyl or C.sub.3-8 cycloalkyl. It is an embodiment that R.sup.6 is H. In another embodiment R.sup.6 is C.sub.1-6 alkyl. In another embodiment of the present application, R.sup.6 is C.sub.3-8 cycloalkyl. In a further embodiment, R.sup.6 is isopropyl. It is an embodiment that R.sup.6 is cyclohexyl.

(48) In an embodiment, Y is CR.sup.6R.sup.7.

(49) In an embodiment, R.sup.6 and R.sup.7 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl. In another embodiment, R.sup.6 and R.sup.7 are each independently selected from H, C.sub.1-6 alkyl, C.sub.3-8 cycloalkyl, C.sub.1-4 alkylene C.sub.3-8 cycloalkyl and heterocycloalkyl. In a further embodiment, R.sup.6 and R.sup.7 are each independently H, C.sub.1-6 alkyl or C.sub.3-8 cycloalkyl.

(50) In an embodiment, the compound of Formula I is a compound of Formula I(a)(i), I(a)(ii), I(a)(iii) or I(a)(iv):

(51) ##STR00010##

(52) In another embodiment of the present application, the compound of Formula I is the compound of Formula I(a)(i):

(53) ##STR00011##

(54) In another embodiment of the present application, the compound of Formula I is the compound of Formula I(a)(ii):

(55) ##STR00012##

(56) In another embodiment of the present application, the compound of Formula I is the compound of Formula I(a)(iii):

(57) ##STR00013##

(58) In another embodiment of the present application, the compound of Formula I is the compound of Formula I(a)(iv):

(59) ##STR00014##

(60) In another embodiment, the compound of Formula I is a compound of Formula I(b)(i):

(61) ##STR00015##

(62) In another embodiment, the compound of Formula I is a compound of Formula I(c)(i), I(c)(ii), I(c)(iii) or I(c)(iv):

(63) ##STR00016##

(64) wherein in each of the compounds of Formula I(c)(i), I(c)(ii), I(c)(iii) or I(c)(iv) independently, one of Z.sup.1 and Z.sup.2 is O and the other of Z.sup.1 and Z.sup.2 is S.

(65) In an embodiment, the molar ratio of the compound of Formula I to the gold and/or palladium is about 1:10 to about 50:1. In another embodiment, the molar ratio of the compound of Formula I to the gold and/or palladium is about 1:1 to about 20:1. In a further embodiment, the molar ratio of the compound of Formula Ito the gold and/or palladium is about 2:1 to about 10:1. It is an embodiment that the molar ratio of the compound of Formula I to the gold and/or palladium is about 3:1 to about 4:1. In another embodiment, the molar ratio of the compound of Formula Ito the gold and/or palladium is about 3:1. In a further embodiment, the molar ratio of the compound of Formula I to the gold and/or palladium is about 4:1.

(66) The acid can be any suitable acid. In an embodiment, the acid is a hydrogen halide (e.g., HCl, HBr or HI), chlorous acid, chloric acid, bromous acid, bromic acid, iodous acid, iodic acid, perchloric acid, sulfuric acid, nitric acid, oxalic acid, phosphoric acid, an organic acid (e.g., benzenesulfonic acid) or combinations thereof. In another embodiment, the acid is HCl. In another embodiment, the acid is HCl having a concentration in the aqueous solution of about 0.1 M to about 10 M. In a further embodiment, the acid is HCl having a concentration in the aqueous solution of about 0.5 M to about 5 M. It is an embodiment that the acid is HCl having a concentration in the aqueous solution of about 0.75 M to about 3 M. In another embodiment, the acid is HCl having a concentration in the aqueous solution of about 1 M to about 2 M. In a further embodiment, the acid is HCl having a concentration in the aqueous solution of about 1 M. It is an embodiment that the acid is HCl having a concentration in the aqueous solution of about 2 M.

(67) The oxidizing agent can be any suitable oxidizing agent. In an embodiment, the oxidizing agent is ozone, nitric acid (HNO.sub.3), hydrogen peroxide (H.sub.2O.sub.2), O.sub.2, bubbled air, I.sub.2, Br.sub.2, Cl.sub.2, oxone™, an ammonium polyatomic salt (e.g., ammonium chlorite, ammonium periodate (NH.sub.4IO.sub.3), ammonium perborate (NH.sub.4BO.sub.3), ammonium chlorate (NH.sub.4ClO.sub.3), ammonium persulfate (NH.sub.4).sub.2S.sub.2O.sub.8), ammonium hypochlorite or ammonium nitrate), calcium hypochlorite, a sodium polyatomic salt (e.g., sodium persulfate (Na.sub.2S.sub.2O.sub.8), sodium nitrate or sodium hypochlorite), a potassium polyatomic salt (e.g., potassium permanganate, potassium persulfate, potassium iodate, potassium hypochlorite or potassium nitrate), manganese oxide, a tetraalkylammonium salt (e.g., tetramethylammonium chlorite (N(NH.sub.3).sub.4)ClO.sub.2) or tetramethylammonium periodate (N(NH.sub.3).sub.4)IO.sub.4)), peroxomonosulfuric acid, urea, peracetic acid, an alkanesulfonic acid (e.g., methane sulfonic acid), an aromatic sulfonic acid (e.g., benzenesulfonic acid) or combinations thereof.

(68) The oxidizing agent is suitably added to the aqueous phase as an aqueous solution, or if using a gas, is bubbled through the aqueous phase. In another embodiment, the oxidizing agent is HNO.sub.3 or MnO.sub.2. In another embodiment, the oxidizing agent is HNO.sub.3. The concentration of oxidizing agent can be any suitable concentration. For example, above a certain concentration (for example, above about 0.5 M H NO.sub.3) the compound of Formula I can be oxidized which reduces the extraction efficiency. In a further embodiment, the oxidizing agent is HNO.sub.3 having a concentration in the aqueous solution of about 0.1 M to 2.0 M. In another embodiment, the oxidizing agent is HNO.sub.3 having a concentration in the aqueous solution of about 0.1 M to 1.0 M. In another embodiment, the oxidizing agent is HNO.sub.3 having a concentration in the aqueous solution of about 0.1 M to 0.5 M. In a further embodiment, the oxidizing agent is HNO.sub.3 having a concentration in the aqueous solution of about 0.15 M to 0.25 M.

(69) The water-immiscible organic solvent can be any suitable water-immiscible organic solvent. In an embodiment of the present application, the water-immiscible organic solvent is selected from dichloromethane (DCM), chloroform, dichloroethane, chlorobenzene, dichlorobenzene and toluene. In another embodiment, the water-immiscible organic solvent is selected from dichloromethane, chloroform and chlorobenzene. In a further embodiment, the water-immiscible organic solvent is dichloromethane.

(70) In an embodiment, the conditions to leach the gold and/or palladium from the gold and/or palladium-containing substance and extract the gold and/or palladium by forming a complex between the leached gold and/or palladium and the compound of Formula I in one step, comprise stirring the mixture for a time of about 2 hours to about 10 hours, about 2 hours to about 5 hours, or about 3 hours to about 4 hours at a temperature of about 10° C. to about 40° C. or about 20° C. to about 25° C.

(71) In an embodiment, the method further comprises separating the mixture into an aqueous phase and an organic phase comprising the complex between the leached gold and/or palladium and the compound of Formula I. Methods to separate mixtures comprising an aqueous phase and an organic phase into separate phases are well known in the art and the selection of a suitable method for use in the methods of the present application can be made by a person skilled in the art.

(72) In an embodiment, the method further comprises stripping the gold and/or palladium from the complex between the compound of Formula I and the gold and/or palladium by a method comprising contacting the organic phase with an aqueous solution comprising any suitable acid and thiourea under conditions to obtain a gold and/or palladium-containing strip solution and a gold and/or palladium-reduced organic phase comprising the compound of Formula I. In an embodiment, the conditions to obtain a gold and/or palladium-containing strip solution and a gold and/or palladium-reduced organic phase comprise stirring the organic phase with an aqueous solution comprising H.sub.2SO.sub.4, for example 1 M H.sub.2SO.sub.4 and thiourea, for example 0.7 M thiourea for a time of about 5 minutes to about 1 hour or about 15 minutes at a temperature of about 10° C. to about 40° C. or about 20° C. to about 25° C. Other suitable acids such as but not limited to HCl may be used in the stripping step. However, it will be appreciated by a person skilled in the art that HCl is corrosive and that HCl gas may come out from the solution during subsequent reduction or electrowinning.

(73) In an embodiment, the method further comprises separating the gold and/or palladium-containing strip solution from the gold and/or palladium-reduced organic phase comprising the compound of Formula I and recovering gold and/or palladium from the gold and/or palladium-containing strip solution by electrowinning or reduction. The gold and/or palladium-containing strip solution and the gold and/or palladium-reduced organic phase comprising the compound of Formula I are separated by any suitable means, the selection of which for use in the methods of the present application can be made by a person skilled in the art.

(74) In an embodiment, the gold and/or palladium is recovered from the gold and/or palladium-containing strip solution by electrowinning.

(75) In another embodiment, the gold and/or palladium is recovered from the gold and/or palladium-containing strip solution by reduction. The reducing agent can be any suitable reducing agent. In an embodiment, the reducing agent is oxalic acid, Zn powder, Fe powder or NaBH.sub.4. In an embodiment, the reducing agent is NaBH.sub.4 and a temperature of from about 10° C. to about 35° C. or about 20° C. to about 25° C. is used. In another embodiment, the reducing agent is oxalic acid and a temperature of from about 40° C. to about 60° C. or about 50° C. is used.

(76) In another embodiment of the present application, the method further comprises, subsequent to separating the mixture into the aqueous phase and the organic phase, recycling the aqueous phase for use, for example, in the step of contacting the gold and/or palladium-containing substance with the mixture. In another embodiment, the method further comprises, subsequent to stripping and/or direct reduction of gold and/or palladium, for example, with NaBH.sub.4 or oxalic acid, recycling the water-immiscible organic solvent from the organic phase for use, for example, in the step of contacting the gold and/or palladium-containing substance with the mixture. In a further embodiment, the method further comprises recycling the compound of Formula I from the gold and/or palladium-reduced organic phase for use, for example, in the step of contacting the gold and/or palladium-containing substance with the mixture.

(77) In an embodiment, the method further comprises recovering gold and/or palladium from the organic phase by direct reduction. The reducing agent can be any suitable reducing agent. In an embodiment, the reducing agent is oxalic acid, Zn powder, Fe powder or NaBH.sub.4. In an embodiment, the reducing agent is NaBH.sub.4 and a temperature of from about 10° C. to about 35° C. or about 20° C. to about 25° C. is used. In another embodiment, the reducing agent is oxalic acid and a temperature of from about 40° C. to about 60° C. or about 50° C. is used.

(78) The substance comprising gold and/or palladium can be any suitable substance comprising gold and/or palladium. In an embodiment, the substance comprising gold and/or palladium is selected from a gold-containing ore, anode slime, a platinum group metal (PGM)-containing substance such as a PGM concentrate, electronic scrap and jewelry scrap.

(79) In an embodiment, the substance comprising gold and/or palladium is a gold-containing substance. In another embodiment of the present application, the gold-containing substance is a gold-containing ore. In an embodiment, the gold ore is an oxidized gold ore. In another embodiment of the present application, the gold ore is a refractory gold ore.

(80) In an embodiment, the substance comprising gold and/or palladium is a palladium-containing substance. In another embodiment of the present application, the palladium-containing substance is a palladium-containing ore.

(81) In an embodiment, the substance comprising gold and/or palladium is a gold and palladium-containing substance. In another embodiment, the gold and palladium-containing substance is an ore that comprises gold and palladium.

(82) In an embodiment, the substance comprising gold and/or palladium is a platinum group metal-containing substance. In another embodiment, the platinum group metal-containing substance is a platinum group metal concentrate. It will be appreciated by a person skilled in the art that after dissolution of substances containing platinum group metals including platinum, palladium, rhodium, osmium, ruthenium and iridium the compounds of Formula I can selectively extract both palladium and gold into the organic phase and separate them from the rest of the platinum group metals..sup.44 .sup.44 Moradi, L. Salimi, H. Piltan, M. Yavari, I. United States Patent. Pub. No. US 2012/0228151 A1. Sep. 13, 2012.

(83) In another embodiment of the present application, the method further comprises crushing and/or grinding the substance comprising gold and/or palladium such as the gold-containing ore into particles prior to contacting with the mixture. In a further embodiment, the size of the particles of the substance comprising gold and/or palladium such as the gold-containing ore is less than or equal to about 75 microns.

(84) In an embodiment, the compounds of Formula I are commercially available or are prepared using methods known in the literature from commercially available materials. For example, a compound of Formula I(a) is prepared by adding an appropriately substituted amine to a mixture of CS.sub.2 and a carbodiimide in a suitable polar solvent, such as an alcoholic solvent, under conditions to form the compound of Formula I(a). The compound of Formula I(a) will generally precipitate from the reaction mixture and is isolated and, optionally, purified using known methods. In an embodiment, a slight excess, for example 1.05 to 1.5, suitably 1.1, equivalents of the amine and CS.sub.2 are used. In an embodiment, the suitable solvent is methanol or ethanol, suitably methanol. In an embodiment the reaction is performed at or around room temperature, however the temperature can be adjusted as needed by a person skilled in the art.

(85) The present application also includes a use of a compound of Formula I:

(86) ##STR00017##
wherein

(87) R.sup.1 is —NR.sup.4R.sup.5 or aryl;

(88) R.sup.2 and R.sup.3 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl; or

(89) R.sup.2 and R.sup.3 together with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl, or a heterocycloalkyl or a heteroaryl substituted at one or more carbon atoms with C.sub.1-4 alkyl;

(90) R.sup.4 and R.sup.5 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl; or

(91) R.sup.4 and R.sup.5 together with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl, or a heterocycloalkyl or a heteroaryl substituted at one or more carbon atoms with C.sub.1-4 alkyl;

(92) X is O or S;

(93) Y is S, NR.sup.6 or CR.sup.6R.sup.7; and

(94) R.sup.6 and R.sup.7 are each independently selected from H, C.sub.1-10 alkyl, C.sub.3-10 cycloalkyl, C.sub.1-6 alkylene C.sub.3-10 cycloalkyl, heterocycloalkyl and aryl, for leaching and extracting gold and/or palladium in one step from a substance comprising gold and/or palladium.

(95) It will be appreciated by a person skilled in the art that the embodiments of the uses for leaching and extracting gold and/or palladium in one step from a substance comprising gold and/or palladium of the present application can be varied as discussed herein for the embodiments of the methods of leaching and extracting gold and/or palladium from a substance comprising gold and/or palladium of the present application.

(96) The following non-limiting examples are illustrative of the present application:

EXAMPLES

Example 1: New Leaching Methods Employing Sulfur-based Ligands for Selective Extraction and Recovery of Gold

General Ligand Syntheses

(97) The ligands I(a)(i), I(a)(ii), I(a)(iii) and I(a)(iv) (Scheme 2) used in this research were synthesized by following reported literature procedures..sup.44 The ligand I(b)(i) (N-phenyl-N′-benzoylthiourea) was synthesized based on a reported procedure..sup.45 .sup.44 Moradi, L. Salimi, H. Piltan, M. Yavari, I. United States Patent. Pub. No. US 2012/0228151 A1. Sep. 13, 2012..sup.45 Vest, P. Schuster, M. Konig, K. H. Fresenius J Anal Chem. 1991, 341, 556-568.

(98) For example, for ligands I(a)(i)-I(a)(iv), in a round bottom flask, 1.1 equivalents of a substituted amine was added in small portions over a period of 1 hour to a mixture of 1.3 equivalents of CS.sub.2 and 1 equivalent of carbodiimide in methanol at room temperature. The reaction mixture was stirred for 4 hours, and then the resulting white precipitate was separated from the solution by filtration. Finally, it was washed with water and dried under vacuum.

Ligand I(a)(i) Synthesis

(99) In a round bottom flask, 2.02 g pyrrolidine was added in small portions over a period of 1 hour to a mixture of 2.80 g CS.sub.2 and 5.85 g of dicyclohexylcarbodiimide (DCC) in 30 ml methanol at room temperature. The reaction mixture was stirred for four hours, and then the resulting white precipitate was separated from the solution by filtration. Finally, it was washed with water and dried under vacuum. 8.93 g final product was isolated (yield: 89%).

Preparation of Gold Powder

(100) Gold powder was prepared by adapting the reported method from Jeffrey et al..sup.46. 1.000 g pure (99.9% purity) metallic gold was dissolved in 4 mL aqua regia (3 mL 37% HCl/1 mL 69% HNO.sub.3) and then diluted 5 times by adding distilled water. Sodium metabisulfite was gradually added to the solution while it was being stirred gently. Addition of Na.sub.2S.sub.2O.sub.5 was continued until all of the gold was precipitated out from the solution (the color changed from a yellow to a colorless solution). The resulting precipitate was isolated, washed with 1M HCl and then with distilled water and finally dried in an oven. 0.975 g light brown gold powder was obtained (yield: 97.5%). .sup.46 Jeffrey, M. Breuer, P. L. Chu, C. K. Int. J. Miner. Process. 2003, 72, 323-330.

(a) Simultaneous Leaching and Solvent Extraction

Effect of HCl Concentration

(101) 5.0 mg gold powder (0.025 mmol) was added to a vial containing 5 ml HCl solution with different concentrations (0.1, 0.5, 1, 1.5 and 2M) and 0.22 M HNO.sub.3. Then, 26.8 mg (0.075 mmol) ligand I(a)(i) was dissolved in 5 ml dichloromethane and added to the previous solution. The reaction mixture was stirred vigorously for different periods of time. When the reaction was completed, the two phases were separated and the organic phase was stripped with 5 ml H.sub.2SO.sub.4 (1 M) containing 0.7 M thiourea for 15 min.

(102) The gold content of the strip solutions was analyzed by AAS. Initial investigations (Table 1) showed that there was a significant difference between conventional leaching by HCl/HNO.sub.3 versus simultaneous leaching and extraction employing dithiobiuret ligands (entry 3 vs 4). While not wishing to be limited by theory, the initial tiny amount of leached gold is extracted into the organic phase by the sulfur-based ligands, pushing forward the gold leaching equilibrium (Scheme 1) which leads to increased leaching kinetics.

(103) ##STR00018##

(104) The results showed no significant gold recovery at low HCl concentration (entry 1, 2). However, by increasing HCl concentration gold could be completely recovered at 1 M HCl or higher. As can be seen in table 1, more than 99% recovery was achieved in 4 hours when HCl concentration was 1 M (entry 4), and at higher molarity the recovery time was shorter (entry 5, 6). Therefore, 1 mol/L HCl was chosen as an acid concentration for other experiments.

Effect of Stirring Time

(105) 5.0 mg gold powder (0.025 mmol) was added to a vial containing 5 ml 1 M HCl and 0.22 M HNO.sub.3. Then, 26.8 mg (0.075 mmol) ligand I(a)(i) was dissolved in 5 ml dichloromethane and added to the previous solution. The reaction mixture was stirred vigorously for different periods of time. When the reaction was completed, the two phases were separated and the organic phase was stripped with 5 ml H.sub.2SO.sub.4 (1M) containing 0.7 M thiourea for 15 min. The gold content of the strip solutions was analyzed by AAS. The results obtained (FIG. 2) showed that the gold recovery percentage increased quickly with the simultaneous leaching and extraction system until it reached 99% after 4 hours and remained constant. This is significantly quicker than conventional leaching systems with the same amount of HCl and HNO.sub.3. A useful leaching time for Au recovery using the present system was found to be 4 h in 1 M HCl solution.

(106) A comparison of the conventional leaching system to that of the present study shows that the dithiobiuret ligands can efficiently improve the rate of gold leaching with the least amount of acid and oxidizing reagent. In addition to the leaching step, the new technique recovers gold from aqueous solution at the same time; hence the overall time of gold recovery can be much shorter in comparison to cyanide leaching followed by activated carbon adsorption.

Effect of Ligand Concentration

(107) 5.0 mg gold powder (0.025 mmol) was added to a vial containing 5 ml 1M HCl and 0.22 M HNO.sub.3. Then, different amounts of ligand I(a)(i) (Table 2) were dissolved in 5 ml dichloromethane and added to the previous solution. The reaction mixture was stirred vigorously for 4h. When the reaction was completed, the two phases were separated and the organic phase was stripped with 5 ml H.sub.2SO.sub.4 (1 M) containing 0.7 M thiourea for 15 min. The gold content of the strip solutions was analyzed by AAS.

(108) Table 2 shows the gold recovery percentage with different ligand to Au ratios. With a 1:1 molar ratio, only 42% of gold was recovered with optimized HCl and oxidant concentrations. Gold recovery increased with increasing ligand concentration in organic solvent and substantially completed at a 3:1 molar ratio (Ligand: Au).

Efficiency of Different Ligand Derivatives

(109) Different derivatives of dithiobiuret ligand (I(a)(i), I(a)(ii), I(a)(iii) and I(a)(iv)) were synthesized and their capabilities were investigated for simultaneous leaching and extraction of gold in HCl media (Scheme 2). Compared to a monodentate thiourea derivative (L.sub.1) and conventional gold extractant, dibutylcarbitol (DBC), all of the dithiobiuret derivatives showed a higher percent gold recovery.

(110) ##STR00019##

(111) Among the different dithiobiuret derivatives, I(a)(i) showed the highest Au recovery %. DBC is the most common gold extractant which is used for selective extraction of gold from acidic solution. Although it is an effective gold extractant in conventional solvent extraction techniques, it showed very low gold recovery under the present simultaneous leaching and extraction conditions even at extremely high concentrations of extractant (entry 6, Table 3).

(112) The ligand I(b)(i) was also investigated. 5.0 mg gold powder (0.025 mmol) was added to a vial containing 5 ml HCl (1 M) and HNO.sub.3 (0.22 M). Then, 20.3 mg (0.075 mmol) of the synthesized ligand I(b)(i) was dissolved in 5 ml dichloromethane and added to the previous solution. The reaction mixture was stirred vigorously for 6 hours. When the reaction was completed, the two phases were separated and the organic phase was stripped with 5 ml H.sub.2SO.sub.4 (1 M) containing 0.7 M thiourea for 15 minutes. The gold content of the strip solutions was analyzed by AAS. The results showed that 99.0% of gold was recovered.

Selectivity

(113) To investigate the selectivity of the present technique, a mixture of different metals in chloride form was treated by the system. A mixture of Fe (1000 ppm), Cu (2000 ppm), Zn (500 ppm), Ag (200 ppm) and 0.5 mg gold powder was added to a vial containing 5 ml 1 M HCl and 0.2 M HNO.sub.3. Then, 26.8 mg of ligand I(a)(i) was dissolved in 5 ml dichloromethane and added to the previous solution. The reaction mixture was stirred vigorously for different periods of time. When the reaction was completed, the two phases were separated and the organic phase was stripped with 5 ml 1 M H.sub.2SO.sub.4 containing 0.7 M thiourea for 15 min. The metal content of the post extraction and strip solutions were analyzed by AAS.

(114) The obtained results, shown in Table 4, demonstrate that the simultaneous leaching and extraction technique employing dithibiuret ligands is highly selective for gold, so that only trace amounts of base metals was extracted even at the presence of high amount of free ligand. In contrast to the cyanidation process, the present technique can, for example eliminate the entire activated carbon step for separation of gold from other impurities.

Effect of Organic Solvent

(115) Simultaneous leaching and extraction tests were performed in the water-immiscible organic solvents shown in Table 5. The results show many organic solvents are suitable for extraction and recovery of gold. Among the investigated solvents, the highest percentages of Au recovery were obtained when dichloromethane (DCM), chlorobenzene, or chloroform were used as solvent.

(b) Gold Ore Treatment

(116) Crushed and ground gold ore with an average gold concentration of 7 ppm and an average particle size of 74 microns was obtained from Claude Resources from their Seabee gold mine operation located in the La Ronge Mining District at the north end of Laonil Lake approximately 125 kilometres northeast of the town of La Ronge, Saskatchewan.

General Experimental For Simultaneous Leaching and Solvent Extraction

(117) A method flow chart for the simultaneous leaching and solvent extraction technique 200 of the present example is shown in FIG. 3. In the method 200, crushed and ground gold ore 202 with an average particle size of 74 microns was subjected to a simultaneous leaching and extracting step 204 wherein the ore 202 was added to a 1 M HCl solution in the presence of HNO.sub.3; and a solution of ligand I(a)(i) in dichloromethane was then added to the aqueous solution 206. The resulting biphasic reaction mixture was stirred vigorously for 5 h. The mixture was then filtered to remove solid residue 208 and the phases separated 210 into an organic phase 212 and an aqueous phase 214. The aqueous phase 214 an be recycled for use in the simultaneous leaching and extracting step 204. he organic phase 212 was then stripped 216 with 1 M H.sub.2SO.sub.4 containing 0.7 M thiourea 218 for 15 min, and the gold content of the stripped solutions was analyzed by AAS showing gold recovery efficiencies consistently in the 95-97% range. Subsequent to the stripping step 216, the ligand and DCM can be recycled 220 for use in the simultaneous leaching and extraction step 204. An electrowinning or reduction step 222 can be carried out to isolate pure gold 224. Alternatively, instead of stripping step 216, the organic phase 212 can be reduced with an agent such as oxalic acid or NaBH.sub.4 226 to provide pure gold 228. If the organic phase is sensitive to a reducing agent, the use of thiourea stripping 216 of gold from the dithiobiuret gold complex may be used. However, the direct reduction 226 of the loaded organic phase may be more economical. For example, in methods 200 comprising stripping 216 the organic phase, a subsequent electrowinning or reduction step 222 is used to obtain the metallic gold 224 whereas in methods 200 comprising a direct reduction step 226, the metallic gold 228 can be obtained with one less step. In the present experiments, because low concentrations of gold in the samples were used, and the efficiency of the systems was measured, the final gold solutions were analyzed. Instead of weighing the precipitated gold, therefore the organic phase was typically stripped and its gold content measured by AAS.

Exemplary Experimental for Simultaneous Leaching and Solvent Extraction

(118) 5.0 g of crushed and ground gold ore with an average particle size of 74 microns was added to a vial containing 5 ml of 1 M HCl and 0.55 M HNO.sub.3. 27.8 mg of ligand I(a)(i) dissolved in 5 ml of dichloromethane was then added to the aqueous solution. The reaction mixture was stirred vigorously for 5h. The biphasic reaction mixture was then filtered and the organic phase was isolated. The organic phase was then stripped with 5 ml H.sub.2SO.sub.4 (1 M) containing 0.7 M thiourea for 15 min, and the gold content of the stripped solutions was analyzed by AAS. The final solution contained 6.7 ppm gold (96% gold recovery).

(c) Comparative Example: Gold Ore Treatment with Cyanide Solution

(119) 5.00 g gold ore was added to a vial containing 10 ml basic solution (pH=10.5, pH was adjusted by dissolving the appropriate amount of KOH in distilled water). 0.20 g KCN was added to the solution and the reaction mixture (open to air) was stirred vigorously for 24 hours. The reaction mixture was weighed before starting and after completion of the reaction to estimate the amount of water evaporated during the leaching process. Then the appropriate amount of water was added to the reaction mixture to keep the slurry's density constant. The gold content of the resultant solution was measured by atomic absorption spectroscopy.

(120) This experiment was conducted to determine the amount of gold in the ore sample and to compare the efficiency of the solvent extraction technique of the present studies with the cyanide leaching process. The cyanidation experiment was repeated 20 times on gold ore from the Claude Resources mine, and the results showed the average gold content was between 9.5 and 10 ppm.

(d) Discussion: Solvent Extraction Technique as a Leaching Technique

(121) Appropriate sulfur-containing compounds are useful candidates for gold recovery from ores, because in conformity with Pearson's concept of “hard acid/soft acid and hard base/soft base”, precious metals such as gold are typically classified as soft acids while sulfur containing compounds are classified as soft bases. Therefore, appropriate sulfur containing ligands, such as chelating ligands, can be used as highly selective extractants for extraction and recovery of gold.sup.44.

(122) ##STR00020##

(123) Compounds of Formula I wherein, for example, R.sup.1 is NR.sup.4R.sup.5; X is S; and Y and R.sup.2-R.sup.5 are as defined herein are useful for selective extraction of precious metals such as gold from aqueous solutions. Compounds of Formula I wherein, for example, R.sup.1 is aryl; X is O; and R.sup.1-R.sup.3 are as defined herein are also useful for selective extraction of precious metals such as gold from aqueous solution. For example, when X is S, the ligand has two strong donor sites (thiocarbonyl groups) to bind with precious metals which make it a strong bidentate ligand which can form highly stable six-membered ring complexes with precious metals like gold (e.g. compounds of Formula II(a) wherein M comprises a precious metal e.g. Au; and Y and R.sup.2-R.sup.5 are as defined herein). .sup.44 Moradi, L. Salimi, H. Piltan, M. Yavari, I. United States Patent. Pub. No. US 2012/0228151 A1. Sep. 13, 2012.

(124) ##STR00021##

(125) In addition, based on the resonance contributors depicted in Scheme 3, the nitrogen atoms will increase the Lewis basicity at the sulfur atoms, making the sulfur electrons more available to donate to the metal center (further resonance contributors exist when Y=N or S rather than C).

(126) ##STR00022##

(127) Ligands wherein X=O and R.sup.1=aryl behave similarly but were found to take longer to dissolve the gold; e.g. six hours to completely dissolve gold compared to four hours for the dithiobiuret ligands (X=S) studied.

(128) In a typical known solvent extraction process, the desired metal would first be dissolved into water using large amounts of acid in the presence of an oxidant such as hydrogen peroxide or HNO.sub.3. In a second step, the metal would then be extracted into an organic phase. Subsequent processing would then usually be required to remove other metal impurities that were also extracted in the process. The solvents would then be removed and the desired metal would be reduced back to its base metal form.

(129) Hydrochloric acid in combination with strong oxidants like HNO.sub.3, H.sub.2O.sub.2 and Cl.sub.2 is a well-known leaching media for gold and other transition metals, but high efficiency is only achieved when high concentrations of acid and oxidant are used. By decreasing the hydrochloric acid concentration in known processes, the leaching kinetic decreases dramatically. However, by keeping the oxidant and HCl concentrations high, their consumption will not be economical and produces a highly corrosive media. In addition, in the case of gold ores, the temperature also is typically increased to obtain an effective leaching. Addition of compounds of Formula I of the application to the leaching media advantageously allows for lower concentrations of acid and oxidant and lower temperatures to be used. Plus, leaching and extraction occur in a single step.

(130) The derivative of dithiobiuret shown in Scheme 4 has been disclosed as a ligand for selective extraction of gold from hydrochloric acid media.sup.44.

(131) ##STR00023##

(132) In the present studies, both leaching and extraction steps are done simultaneously under mild conditions which increased the overall efficiencies of the process. As shown in Scheme 1, above, this is accomplished by forcing the reaction equilibrium to the right by withdrawing the dissolved gold from aqueous solution containing small amounts of acid and oxidant into the organic phase containing the ligand. In such a process, highly efficient ligands are used which are able to extract even very small amounts of dissolved gold. .sup.44 Moradi, L. Salimi, H. Piltan, M. Yavari, I. United States Patent. Pub. No. US 2012/0228151 A1. Sep. 13, 2012.

(133) In known processes, solvent extraction is usually applied after the leaching step. As far as the inventors are aware, performing both steps at the same time to improve the leaching step (as well as overall extraction rates) has never been reported before.

Example 2: Simultaneous Leaching and Solvent Extraction of Palladium

(134) 5.0 mg palladium powder (0.047 mmol) was added to a vial containing 5 ml water containing HCl (1M) and HNO.sub.3 (0.22 M). Then, 64.95 mg (0.184 mmol) of ligand I(a)(i) was dissolved in 5 ml dichloromethane and added to the previous solution. After 2 hours, the palladium was completely dissolved. The two phases were separated and the organic phase (dark brown) was stripped with 5 ml H.sub.2SO.sub.4 (1 M) containing 0.7 M thiourea for 15 minutes. Then, the yellow precipitate was filtered off and heated up in a furnace to 700° C. to produce a fine black palladium powder (99.3% of palladium was recovered).

Example 3: Reduction of Leached Gold in Different Organic Solvents

(135) For each test, 5 ml of organic solvent (which contained 0.5 grams of 37% HCl; i.e. the molarity of the HCl in the organic solvent was 1 M) containing different amounts of gold as shown in Table 6 was treated with the indicated reducing reagent for 10 minutes. In the case of Fe powder, the stirring time was 2 hours. The concentration of gold solutions was measured by AAS.

(136) While the present application has been described with reference to examples, it is to be understood that the scope of the claims should not be limited by the embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

(137) All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Where a term in the present application is found to be defined differently in a document incorporated herein by reference, the definition provided herein is to serve as the definition for the term.

FULL CITATIONS FOR DOCUMENTS REFERRED TO IN THE APPLICATION

(138) TABLE-US-00001 TABLE 1 Simultaneous leaching and extraction of gold powder in different HCl concentrations. Entry HCl (M) Time (h) Au Recovery (%) 1 0.1 4 5.3 2 0.5 4 20.7 3 1 4 4.6* 4 1 4 99.2 5 1.5 3 99.1 6 2 2.5 99.3 *Conventional leaching by HCl/HNO.sub.3.

(139) TABLE-US-00002 TABLE 2 Simultaneous leaching and extraction of gold powder with different ligand:Au ratios. Entry Ligand:Au Au Recovery % 1 1:1 42.7 2 2:1 72.4 3 3:1 99.5 4 4:1 99.4

(140) TABLE-US-00003 TABLE 3 Simultaneous leaching and extraction of gold powder with different ligands. Entry Ligand Au Recovery % 1 I(a)(i) 99.7 2 I(a)(ii) 72.4 3 I(a)(iii) 96.5 4 I(a)(iv) 70.4 5 L.sub.1 3.3 6 DBC 5.1* *Pure DBC was used as the organic phase.

(141) TABLE-US-00004 TABLE 4 Effect of other impurities on simultaneous leaching and extraction of gold (113 ppm of gold was extracted in the presence of large excesses of Fe, Cu and Zn impurities). Fe Cu Zn Au Aq phase (ppm) 991.8 2140.3 542.8 0.3 Stripping solution (ppm) 0.4 0.1 0.1 112.3

(142) TABLE-US-00005 TABLE 5 Simultaneous leaching and extraction of gold powder in different water-immiscible organic solvents. Entry Solvent Au Recovery % 1 DCM 99.9 2 Chloroform 97.4 3 Dichloroethane 68.4 4 Chlorobenzene 98.8 5 Dichlorobenzene 61.3 6 Toluene 56.1

(143) TABLE-US-00006 TABLE 6 Reduction of leached gold in different organic solvents. Au Au concen- concen- tration tration Reducing before after agent reduction reduction Reduction Entry Solvent (mg) (ppm) (ppm) % 1 Ethyl Zn powder 1000 5 99.5 acetate (20) 2 Ethyl Zn powder 10 0 100 acetate (10) 3 Ethyl NaBH.sub.4 1000 5 99.5 acetate (10) 4 Ethyl NaBH.sub.4 10 0 100 acetate (5) 5 Ethyl Fe powder 1000 8 99.2 acetate (20) 6 Ethyl Fe powder 10 0 100 acetate (10) 7 MeCN Zn powder 1000 2 99.8 (20) 8 MeCN Zn powder 10 0 100 (10) 9 MeCN NaBH.sub.4 1000 6 99.4 (10) 10 MeCN NaBH.sub.4 10 0.3 97.0 (5) 11 MeCN Fe powder 1000 12 98.8 (20) 12 MeCN Fe powder 10 0.1 99.0 (10) 13 CH.sub.3COOH Zn powder 1000 1 99.9 (20) 14 CH.sub.3COOH Zn powder 10 0 100 (10) 15 CH.sub.3COOH NaBH.sub.4 1000 9 99.1 (10) 16 CH.sub.3COOH NaBH.sub.4 10 0 100 (5) 17 CH.sub.3COOH Fe powder 1000 8 99.2 (20) 18 CH.sub.3COOH Fe powder 10 0.5 95.0 (10)