WO2019178051A1

WO2019178051A1 - Precious metals recovery processes

Info

Publication number: WO2019178051A1
Application number: PCT/US2019/021786
Authority: WO
Inventors: Jakub PEDZIWIATR; Ronald Todd GRAVES
Original assignee: Jabil Inc.
Priority date: 2018-03-12
Filing date: 2019-03-12
Publication date: 2019-09-19

Abstract

Materials and methods for precious metal recovery are disclosed. Usable leaching solutions may be aqueous based and include appropriate materials in sufficient quantities to solubilize and stabilize precious metals. Such materials typically include an oxidant. Additional materials included may be an amino acid. The leaching solution is typically contacted with a substrate having a target precious metal, thereby solubilizing precious metal to form a stable, pregnant solution. The precious metal can then be recovered from the pregnant solution. In some instances, components of the leaching solution can be regenerated and reused in subsequent leaching.

Description

PRECIOUS METALS RECOVERY PROCESSES

[0001] The present disclosure relates to processes for precious metal recovery, and, more particularly, to the preparation of leaching solutions and the use of leaching solutions in the recovery of precious metals from substrates, ore, concentrates, and other feedstock.

BACKGROUND

[0002] Processes to extract metals, such as precious metals, from waste products are known in the existing art. For example, Patent Cooperation Treaty Application No. WO2013090517, entitled,“Apparatus and Method for Stripping Solder Metals During the Recycling of Waste Electrical and Electronic Equipment”; United States Patent Application Publication No. 2013/0276284, entitled“Method for Recycling of Obsolete Printed Circuit Boards”, and United States Patent Application Publication No. 2017/0369967, entitled“Methods, Materials and Techniques for Precious Metal Recovery”, are directed to largely manual or otherwise less efficient methods of extracting precious metals from waste electrical and electronics equipment, such as from the printed circuit boards associated with such waste electronics equipment.

[0003] As detailed in the foregoing and like known references, waste products, such as waste electrical equipment, may include aspects, such as the

aforementioned printed circuit boards, that include precious metals in, for example, pins, connectors, contacts, and the like. Those aspects of the waste products which include precious metals may be subjected to extraction of the precious metals therefrom. To date, these extractions are understood to be complex chemical processes that have often been unsuitable for large-scale extractions, at least because these processes have provided lower yields, such as on the order of 80% or less, than is acceptable for large-scale precious metal extractions.

SUMMARY

[0004] Processes and materials disclosed relate to the extraction of precious metals from a substrate into solution, such as, for example, using a leaching solution. In addition, processes are disclosed for recovering precious metal from the leaching solutions. Processes disclosed herein also relate to methods for regenerating leaching solutions. [0005] The term substrate is intended to refer to ore, concentrates, jewelry, electronic scrap such as computers, computer monitors, televisions, cellular telephones, printed wire boards, and other precious metals containing feedstock or materials.

[0006] The term precious metal is intended to refer to gold (Au), silver (Ag), and the platinum group metals such as ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt).

[0007] According to disclosed aspects, an aqueous-based leaching solution for precious metal may include iodine containing compounds, such as triiodide, iodide compounds, and/or iodate compounds, and/or carboxylic acids, and/or amino acids. Carboxylic acids include water soluble carboxylic acids such as citric acid, acetic acid, and mixtures of citric acid and acetic acid. The amino acid may include amino acids, derivatives of amino acids such as amino acid salts and mixtures thereof. For example, the amino acid may include glycine, sodium glycinate, potassium glycinate, calcium glycinate and mixtures thereof.

[0008] In general, the aqueous-based leaching solution for precious metal may include the water-soluble carboxylic acid in an amount sufficient to enhance leaching, and the iodine containing compound in an amount effective to enhance leaching. The leaching solution may have a pH of no greater than 7, by way of example.

[0009] Accordingly, a stable, aqueous-based, precious metal-containing leachate results from leaching precious metals oxidizable with an aqueous-based leach solution. Various leaching methods are contemplated, such as continuous or batch stirred tank agitation, vat leaching, or in situ techniques, by way of non-limiting example.

[0010] A process for recovering a precious metal from the precious metal- containing pregnant leach solution may include recovery by any of various methods, such as electrowinning, precipitation, cementation, ion exchange, and/or adsorption onto activated carbon, by way of non-limiting example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings are included to provide a further

understanding of the disclosure, and are incorporated into and thus constitute a part of this specification. The drawings illustrate disclosed embodiments and/or aspects and, together with the description, serve to explain the principles of the disclosure. In the drawings:

[0012] Figure 1 is a flow diagram indicating steps in a process for precious metal recovery;

[0013] Figure 2 is a flow diagram indicating exemplary steps in a precious metal recovery;

[0014] Figure 3 is a flow diagram illustrating a precious metal recovery process including a pre-leach; and

[0015] Figure 4 is a flow diagram illustrating a precious metal recovery process including a feedstock classification.

DESCRIPTION

[0016] The figures and descriptions provided herein may be simplified to illustrate aspects of the described embodiments that are relevant for a clear understanding of the herein disclosed processes, machines, manufactures, and/or compositions of matter, while eliminating for the purpose of clarity other aspects that may be found in typical similar devices, systems, compositions and methods. Those of ordinary skill may thus recognize that other elements and/or steps may be desirable or necessary to implement the devices, systems, compositions and methods described herein. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the disclosed embodiments, a discussion of such elements and steps may not be provided herein. However, the present disclosure is deemed to inherently include all such elements, variations, and modifications to the described aspects that would be known to those of ordinary skill in the pertinent art in light of the discussion herein.

[0017] Embodiments are provided throughout so that this disclosure is sufficiently thorough and fully conveys the scope of the disclosed embodiments to those who are skilled in the art. Numerous specific details are set forth, such as examples of specific aspects, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. Nevertheless, it will be apparent to those skilled in the art that certain specific disclosed details need not be employed, and that embodiments may be embodied in different forms. As such, the exemplary embodiments set forth should not be construed to limit the scope of the disclosure. [0018] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. For example, as used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises,"

"comprising," "including," and "having," are inclusive and therefore specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

[0019] The steps, processes, and operations described herein are thus not to be construed as necessarily requiring their respective performance in the particular order discussed or illustrated, unless specifically identified as a preferred or required order of performance. It is also to be understood that additional or alternative steps may be employed, in place of or in conjunction with the disclosed aspects.

[0020] Yet further, although the terms first, second, third, etc. may be used herein to describe various elements, steps or aspects, these elements, steps or aspects should not be limited by these terms. These terms may be only used to distinguish one element or aspect from another. Thus, terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, step, component, region, layer or section discussed below could be termed a second element, step, component, region, layer or section without departing from the teachings of the disclosure.

[0021] Precious metal recovery generally involves separation of the precious metal, such as gold, from a substrate such as ore and/or waste feedstock, such as electronic waste. The treatment of the precious metal containing substrate with a leach solution produces a“pregnant solution”. That is, a“pregnant solution” includes a depleted leach solution that contains the leached precious metal.

[0022] Leaching solutions may be aqueous solutions that, when in contact with substrate, solubilize at least a portion of the precious metal in the substrate by oxidizing the precious metal. Typical aqueous leaching solutions may be effective under a wide pH range, such as between a pH of about 3 to about 10. Moreover, typical aqueous-based solutions may have at or near-neutral pH, such as, for example, pH in the range of pH about 4 to a pH about 7.

[0023] Leaching solutions that avoid the use or production of soluble, inorganic cyanide compounds (such as cyanide salts) are desired. Cyanide compounds are at least substantially avoided in the disclosed leaching solutions, at least because they are hazardous and subject to stringent environmental regulations.

[0024] The described leaching solutions may be aqueous, and may include iodine containing compounds and one or more acids.

[0025] The iodine containing compounds are selected from iodide compounds, iodate compounds, triiodine ions, and mixtures thereof. Suitable iodide compounds include, but are not limited to, alkali metal iodides and alkaline earth metal iodides such as lithium iodide, sodium iodide, potassium iodide, ammonium iodide, calcium iodide, magnesium iodide, covalent iodides such as phosphorus triiodide and ammonium iodide, tetraalkylammonium iodides, wherein the alkyl groups may be the same as or different from one another and are selected from the group consisting of straight-chained CrC₆ alkyls (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl) and branched CrC₆ alkyls, and mixtures thereof.

[0026] When an iodide compound is included in the leach solution, the concentration of the iodide compound is about 5 g/L to about 300 g/L, and in some embodiments is about 10 g/L to about 200 g/L, or about 20 g/L to about 100 g/L, or about 30 g/L to about 80 g/L, or about 40 g/L to about 60 g/L, and in some embodiments is about 50 g/L.

[0027] Generally, iodate compounds are those compounds that, when present in an aqueous environment provide the iodate anion (I0₃ ). Suitable iodate compounds include, but are not limited to, ammonium iodate, calcium iodate, iodic acid, lithium iodate, potassium iodate, sodium iodate, and mixtures thereof.

[0028] When an iodate compound is included in the leach solution, the concentration of the iodate compound is 1 g/L to about 200 g/L, and in some embodiments is from about 2 g/L to about 100 g/L, or from about 5 g/L to about 50 g/L, or about 7 g/L to about 20 g/L, or about 8 g/L to about 15 g/L, and in some embodiments is about 10 g/L.

[0029] The triiodide ion can be formed by any known method including, but not limited to, the reaction of iodine in an aqueous solution of iodides (e.g., Kl, Nal,

NH₄I) or hydroiodic acid, or the reaction of an iodide with an iodate in acidic media.

[0030] The triiodide ion may also be formed by oxidation of iodide

electrochemically on electrochemical cell anode and/or optionally by addition of a chemical oxidant such as hypochlorite, hydrogen peroxide, persulfate (e.g., potassium monopersulfate, potassium persulfate, and sodium persulfate), ozone, or other materials capable of oxidizing iodide to iodine. Alternatively, triiodide can be generated using iodate compounds with addition of acid (i.e., mixing an iodate compound with an acid).

[0031] In one embodiment, the triiodide is generated in-situ through

electrochemical approaches from relatively inexpensive, safe and easy to use sources, such as iodide compounds and iodate compounds. An exemplary pathway using hydrogen peroxide as a starting material iodine with iodide to form triiodide ion is shown below:

H₂0₂ + 2G + 2H⁺ l₂ + 2H₂0 (1 ) l₂ + G Is (2)

[0032] Another exemplary pathway uses persulfate followed by iodine with iodide to form triiodide ion.

S₂0₈ ² + 2G l₂ + 2S0₄ ² (3) l₂ + G Is (4)

[0033] Given the foregoing concentrations and reaction environment (further described below), and using gold as the exemplary leached precious metal, gold leaching with iodine/iodide may take place via the following reactions:

2Au + G + I₃- 2Aul₂

2Au + 3I₃ 2Aul₄ +

[0034] The acids useful in the leaching solution are typically weak acids and their salts such as the weak mineral acids (e.g., hydrofluoric acid, boric acid,

phosphorous acid), weak mineral acid salts, carboxylic acids and derivatives of carboxylic acids such as salts of carboxylic acids and may include, but are not limited to water soluble carboxylic acids. Suitable carboxylic acids include but are not limited to lower alkyl (C1 -C5) carboxylic acids such as carbonic acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, tricarboxylic acids such as citric acid, alpha hydroxy acids such as glycolic and lactic acid, their salts, and mixtures thereof. Suitable salts may include, but are not limited to alkali metal salts and alkaline earth metal salts such as sodium citrate.

[0035] The carboxylic acids are typically present in the leach solution at a concentration from about 1 g/L to about 250 g/L, and in some embodiments is from about 2 g/L to about 100 g/L, or from about 5 g/L to about 50 g/L, or about 10 g/L to about 20 g/L, and in some embodiments is about 15 g/L. [0036] During typical leaching operations, electrochemical cell(s) may be used to maintain the oxidation reduction potential (ORP) of the leaching solutions. In some cases, additives may be provided to a barren solution ( i.e ., the solution resulting after removing precious metal from a leaching solution) to at least partially regenerate the barren solution. Electrochemical cells may additionally be used to regenerate the leaching solution.

[0037] The addition of carboxylic acid, for example, has been shown to accelerate the leaching rate and stabilize gold in solution. Further, the addition of iodate and an acid to the leaching solution may result in a rapid increase in ORP via the following reaction:

I0_3- + 2I- + 6H⁺ l_3- + 3H₂0

[0038] The leaching solution may or may not also include bromine or chlorine compounds. The bromine and chlorine compounds may include, but are not limited alkali metal salts, alkaline earth metal salts, and mixtures thereof. For example, the bromine and chlorine compounds may include sodium bromide, sodium chloride, potassium bromide, potassium chloride, and mixtures thereof.

[0039] In the described improved leaching solution embodiments, an additional acid, such as an amino acid, may be added to the leaching solution above.

[0040] The amino acid includes those compounds that contain both a carboxyl (- COOH) and an amino (-NH₂) functional group. The term amino acid is intended to include derivatives of amino acids such as amino acid salts such as alkali metal salts, for example, a sodium or potassium glycinate, or alkaline earth salts, for example a calcium salt.

[0041] In many instances, the amino acid contains a -CHR or CH₂ group and the amino (-NH₂) group and the carboxyl (-COOH) group connects to the same -CHR or CH₂ group and are referred to as primary a-amino acids. The“R” group in the CHR connecting group may be any organic structure, such as aliphatic hydrocarbon groups to complex organic structures including aromatic groups, heterocyclic groups, and poly-nuclear groups or other organic groups. In its simplest form R is hydrogen (H) in which case the amino acid is glycine. Other suitable amino acids include, but are not limited to, glycine, proline, leucine, histidine, valine, alanine, phenylalanine, cysteine, asparagine, aspartic acid, glutamine, glutamic acid, lysine, methione, serine, threonine, tyrosine and mixtures thereof. [0042] The concentration of the amino acid in the leach solution is typically from about 1 g/L to about 250 g/L, and in some embodiments is from about 2 g/L to about 100 g/L, or from about 5 g/L to about 50 g/L, or about 10 g/L to about 20 g/L, and in some embodiments is about 15 g/L.

[0043] An exemplary leach solution is shown in Table 1

Table 1

[0044] Upon contact with a precious metal containing substrate, the leaching solution solubilizes the precious metal. Contact time between the disclosed leaching solution and the substrate can be selected to achieve desired recovery targets and processing goals. In some embodiments, the contact time is between about 5 minutes and about 120 minutes, or from about 5 minutes to about 60 minutes, or from about 10 minutes to about 30 minutes.

[0045] Turning now to Fig. 1 , an embodiment of a method 10 of recovering precious metal using the leaching solution described above. The method 10 includes providing the leaching solution 20, leaching 30, and recovering the precious metals 40. Fig. 2 shows a more detailed method 100 for recovering precious metal using leaching solutions.

[0046] The exemplary method 10 includes providing a leaching solution 20. The leaching solution can be pre-made, obtained from a third party, or prepared on-site. Generating the leaching solution may include preparing an aqueous based solution as disclosed throughout, and may include raising the oxidation-reduction potential (ORP) of the solution. As part of preparing the aqueous-based leaching solution, one or more additives may be added.

[0047] Thereafter, precious metal containing substrate may be contacted with the leaching solution. The leaching 30 strips the precious metal from the substrate and the precious metal forms complexes such that the precious metal is in solution, thereby creating a pregnant solution. Once the precious metal is in solution, any solid(s) may be separated from the pregnant solution and the precious metal can be recovered 40 from the solution. [0048] Recovery 40 of the precious metal may include one or more operations. Precious metal recovery operations 40 may include methods such as

electrowinning, precipitation, cementation or loading onto activated carbon, and/or ion exchange resins, or any combination thereof, by way of non-limiting example.

[0049] Recovery 40 may also include recovering one or more additives, such as by electrolysis, and/or reactivating/regenerating the leaching solution. Upon regeneration, the leaching solution may be reused for subsequent leaching.

[0050] Figure 2 is an embodiment of a method 100 for generating and using an aqueous-based leaching solution. The method 100 shown includes mixing the leaching solution in a tank 102, passing the solution through electrochemical (EC) cell(s) 104, receiving precious metal containing substrate 108, optionally, reducing the particle size of the precious metal containing substrate as needed 1 10, mixing reduced-in-size or non-reduced precious metal containing substrate with the leaching solution 1 12, leaching 1 14, removing solids 1 16, recovering precious metals 1 18, optionally recovering secondary materials 120, and leach solution regeneration 122.

[0051] Method 100 may include providing the leaching solution 20. Specifically, providing the leaching solution 20 may include combining ingredients (iodine containing compound, carboxylic acid and optionally, amino acid) in an aqueous solution in a tank 102 and then passing the leaching solution through an

electrochemical cell 104. The tank's contents may be agitated or stirred to promote mixing of tank contents, by way of example.

[0052] After the ingredients are mixed, the solution may be directed to the electrochemical cell 104. The electrochemical cell may be divided or undivided. Additionally, more than one electrochemical cell can be used, wherein the cells may be arranged in series and/or in parallel.

[0053] While passing the solution through the electrochemical cell 104, the ORP of the solution may be monitored. The solution may be electrified until the ORP is raised to a predetermined level. The predetermined level is may be at a minimum of about 350 mV (vs SHE (standard hydrogen electrode)), or about 380 mV (vs SHE), and may be from about 540 mV to about 750 mV (vs SHE), or from about 560 mV (vs SHE) to about 700 (vs SHE), or about 570 (vs SHE) to about 690 (vs SHE) or about 580 (vs SHE). Without being bound by any particular theory, it is believed that a leach solution with a standard reduction potential within the above ranges will promote effective precious metal complexes, for example gold complexes such as Aul₂ . The resulting mixture may be used as the leaching solution.

[0054] The precious metal containing substrate and/or other precious metal containing material may be received 108. The precious metal containing substrate or material carrier may be further reduced 1 10 in size as needed. This may include milling or other suitable size reduction step.

[0055] The precious metal containing substrate, reduced in size as needed, is combined with the leaching solution 1 12 in leach step 1 14. The leach step may be a batch process or a continuous process.

[0056] Leaching may be performed at a predetermined temperature, as discussed herein, such as from about 30° C to about 80° C or from about 40° C to about 70° C, or from about 50° C to about 60° C. In some instances, the leaching may be performed at room temperature (between about 20° C to about 25° C), and may be performed for a predetermined time, such as discussed throughout.

[0057] The application of heat in the instant processes may increase the leach efficiency and kinetics of the disclosed embodiments, particularly when compared to leaching 1 14 at room temperature. More particularly, the foregoing method of leaching (using the above-described leach solution) at a temperature of about 50° C, may extract about 15 ppm more gold on known feed materials, which is about a 20% improvement in gold extraction efficiency over the known art. Additionally, the foregoing method of leaching (using the above-described leach solution) extracts about four (4) times more silver than in other known processes. Yet further, the formula referenced above also provides for the dissolution of palladium, which is not extracted in other known processes.

[0058] During leaching 1 14, the precious metal goes into solution, resulting in a pregnant leach solution. The pregnant leach solution may include solids and/or substrates that may be removed before the precious metal recovery operation(s).

[0059] Once any necessary solids above a predetermined size are removed from the pregnant solution, the precious metals may be recovered 1 18. The precious metals may be recovered 1 18 in any suitable process including

electroplating/electrowinning, precipitation, cementation, ion-exchange, and/or adsorption onto activated carbon, to extract the precious metal out of solution, by way of non-limiting example. [0060] The disclosed method 100 may optionally include one or more secondary recovery operations 120. Secondary recovery operations 120 may take advantage of other properties of the precious metal or other materials to remove the precious metal or other materials from solution.

[0061] The used/barren solution from the recovery 1 18 (and, optionally, the secondary recovery operation 120) may be subjected to a leach solution recycle 122. The leach solution recycle 122 may include passing the solution through one or more electrochemical cells. The leach solution recycle 122 may also include adding or replenishing one or more of the chemical compounds (iodine containing compounds, carboxylic acid, and/or amino acid) added during operation 102, as shown in Fig. 3. The regenerated solution may then be re-used as detailed above.

[0062] The replenishing (top off) may include adding one or more of the iodine containing compounds, carboxylic acid, and amino acid so that the concentration of the iodine compounds, the carboxylic acid and the amino acid is substantially similar to the concentration of the iodine compounds, the carboxylic acid and the amino acid in the leach solution.

[0063] According to the method 100 using the described leach solution, improved precious metal recovery may be obtained, such as the recovery of 90+% or more gold yield in approximately 10 minutes, such as in the range of 10 to 20 or 30 minutes, as compared to the approximate 80% yield in a 1 hour or longer process provided by the known art. Further, the addition of an amino acid, such as glycine, may greatly enhance the yield and speed of precious metal (e.g. gold) recovery 1 18 in the disclosed embodiments.

[0064] Turning now to Fig. 3, a method to recover precious metals is shown with an optional pre-leach 201 step to remove iron that may be present in the precious metal containing substrate.

[0065] The known art encounters difficulty in handling low grade substrates (i.e., cable box boards, PCI cards, motherboards or any other type of feedstock that have a high iron content). In general, these low grade boards, such as those with a high iron content, may thus go through pre-leach step 201 , wherein the ground up board powder (such as 35 US Mesh or finer) may be soaked in a 40% Sulfuric acid bath for about 2 hours, by way of non-limiting example. During this pre-leach, at least 50% of the iron may be dissolved (tin, zinc and other base metals may go into solution as well). [0066] After the pre-leach 201 , the board powder may be separated from the base metal rich liquid 203. After the solid liquid separation is completed, this powder may enter the main leach process(es) 1 14. Of note, high grade material with a low iron content (i.e., memory chips, cell phone boards etc.) may enter the main leach process(es) 1 14 without being subjected to the pre-leach step 201 referenced above.

[0067] Figure 4 illustrates an exemplary differential process based on the need for, or absence of a need for, a pre-leach 201 . According to the process shown in Fig. 4, high grade feed stock 301 a is differentiated from low grade feedstock 301 b (e.g., printed circuit board assembly that may contain iron, base metals, and other non-precious metals) at classification step 301 , such as based on the disclosed feedstock characteristics. The low grade feedstock 301 b is then treated at pre-leach step 201 , while the high grade feedstock 301 a is not. Thereafter, the two processes may share common characteristics, such as discussed with respect to Fig. 2.

[0068] In the main leaching 1 14, once the ORP reaches a value of at least 380 mV, the aforementioned board powder may be added. The optimal loading ratio may preferably be between 10 and 20 wt.% (10-20% pulp), depending on the precious metal containing substrate, by way of non-limiting example. Typically, higher grade feedstock may be loaded at higher quantities.

[0069] The precious metal leaching process 1 14 according to the disclosed embodiments may take place over 10 to 30 minutes, by way of example and as referenced throughout. After a leach time of 10 to 30 minutes, there is a solid liquid separation step where the spent/depleted powder (i.e., powder from which the precious metals have been extracted) may be separated from the precious and base metal impregnated solution. Following the solid liquid separation, the spent/depleted PCBA powder may be subjected to a rinse and backwash step in order to recover lost chemical solution, by way of example, before regeneration 122.

[0070] Thereafter, the pregnant leach solution is directed to a recovery step 1 18, which is exemplified in Fig. 4 as an electrowinning process to electrolytically reduce iodine and reduction and precipitation of the precious metal (gold) at a cathode with the concomitant reoxidation of iodide to iodine at the anode.

[0071] Yet further, the reaction on the anode in the electrochemical cell generates a triiodide species that may be suitable for leaching according to the following reaction: 3 l_3- + 2e

[0072] The reaction at the cathode in the electrochemical cell is:

2H₂0 + 2e H₂ + 20H

[0073] The electrowinning may be conducted in one or more electrowinning (EW) units. The EW units may be operated in a window of 6 to 9 volts with a variable amperage, by way of non-limiting example. During the EW process, the precious metals are reduced from their ionic state to a neutral solid state. The reduced neutral precious metals are deposited and collected on the cathodes of the EW units, leading to the formation of a precious metal (e.g., gold) concentrate. This

concentrate is removed from the cathodes and collected as the final product of the process. The cathodes are put back into use after the precious metal concentrate is removed.

[0074] The EW process also functions as an electrochemical charging step, wherein the solution is being charged as evidenced by an increase in ORP. While the EW process usually takes between about 100 and about 120 minutes, the time can vary based on the copper concentration. The EW process is conducted until all the gold is being out of solution and until the copper concentration reaches at least a level of 1000 to 1500 ppm (or lower).

[0075] Of note, the amino acid, such as glycine, in step 1 14, above, may provide an additional advantage. By way of example, the amino acid may provide an EW efficiency aid, and as such may additionally serve as a metals-recovery improving agent.

[0076] As discussed throughout, at step 1 18, precious metals to be extracted may be plated on to one or more cathodes, by way of non-limiting example. Sensors may monitor this plating at step 1 18 and, as is the case throughout, the data from these sensors may be used to modify, or may provide data for variables within, or changes to the leach solution at step 1 14. The modification may include a

modification in the amounts of ingredients forming the leach solution in light of sensor output, for example.

[0077] Once the precipitated precious metals (e.g. gold) are removed, the resulting solution is referred to as a“barren solution”. The barren solution, including the iodide and iodate, may then be treated to a regeneration process (at step 122) as follows:

10 g/L of KI03 (or Nal03)

15 g/L of Glycine

[0078] Exemplary runs of the foregoing exemplary embodiments for the disclosed leaching solution and leaching process 1 14, such as including a pre-leach 202, are summarized in Tables 2 and 3 below.

Table 2

Table 3

[0079] Although the invention has been described and illustrated in exemplary forms with a certain degree of particularity, it is noted that the description and illustrations have been made by way of example only. Numerous changes in the details of construction, combination, and arrangement of parts and steps may be made. Accordingly, such changes are intended to be included within the scope of the disclosure.

Claims

Claims:

1. An aqueous-based leaching solution for precious metal, the leaching solution comprising:

an iodine containing compound

carboxylic acid; and

amino acid;

the leaching solution being made by a process including the step of passing the foregoing mixture through an electrochemical cell until a predetermined measured oxidation reduction potential (ORP) is reached.

2. The leaching solution of claim 1 , wherein the iodine containing compound is selected from iodide compounds, iodate compounds, triiodine ions, and mixtures thereof.

3. The leaching solution of claim 2 wherein the iodide compound is an alkali metal iodide, an alkaline earth metal iodide, or mixtures thereof.

4. The leaching solution of claim 3 wherein the iodide compound is present in a concentration of about 5 g/L to about 300 g/L.

5. The leaching solution of claim 2 wherein the iodate compound is an alkali metal iodate, an alkaline earth metal iodate, or mixtures thereof.

6. The leaching solution of claim 5 wherein the iodate compound is present in a concentration of about 1 g/L to about 200 g/L.

7. The leaching solution of claim 1 or 2, wherein the carboxylic acid is a water soluble carboxylic acid.

8. The leaching solution of claim 1 or 2 wherein the carboxylic acid is a C1 -C5 alkyl carboxylic acid or a mixture thereof.

9. The leaching solution of claim 7 wherein the carboxylic acid is present in a concentration of about 1 g/L to about 250 g/L.

10. The leaching solution of any preceding claim, wherein the amino acid is selected from the group consisting of glycine, proline, leucine, histidine, valine, alanine, phenylalanine, cysteine, asparagine, aspartic acid, glutamine, glutamic acid, lysine, methione, serine, threonine, tyrosine and mixtures thereof.

1 1 . The leaching solution of claim 10 wherein the amino acid is present in a concentration of about 1 g/L to about 250 g/L.

12. A method of recovering a precious metal, the method including the steps of: providing an aqueous-based leaching solution that includes an iodine compound, a carboxylic acid; and an amino acid;

contacting a substrate including the precious metal with the aqueous-based leaching solution to produce a pregnant leach solution;

recovering precious metal from the pregnant leach solution, thereby generating a barren aqueous-based leaching solution.

13. The method of claim 12 wherein the iodine containing compound is selected from iodide compounds, iodate compounds, triiodine ions, and mixtures thereof.

14. The method of claim 13 wherein the iodide compound is an alkali metal iodide, an alkaline earth metal iodide, or mixtures thereof.

15. The method of claim 14 wherein the iodide compound is present in a concentration of about 5 g/L to about 300 g/L.

16. The method of claim 13 wherein the iodate compound is an alkali metal iodate, an alkaline earth metal iodate, or mixtures thereof.

17. The method of claim 16 wherein the iodate compound is present in a concentration of about 1 g/L to about 200 g/L.

18. The method of claims 12 to 17 wherein the carboxylic acid is a water soluble carboxylic acid.

19. The method of claim 18 wherein the carboxylic acid is a C1 -C5 alkyl carboxylic acid or a mixture thereof.

20. The method of claim 18 wherein the carboxylic acid is present in a

concentration of about 1 g/L to about 250 g/L.

21 . The method of claims 12 to 20 wherein the amino acid is selected from the group consisting of glycine, proline, leucine, histidine, valine, alanine, phenylalanine, cysteine, asparagine, aspartic acid, glutamine, glutamic acid, lysine, methione, serine, threonine, tyrosine and mixtures thereof.

22. The method of claim 21 wherein the amino acid is present in a concentration of about 1 g/L to about 250 g/L.

23. The method of claims 12 to 22 wherein the recovery comprises

electrowinning.

24. The method of claim 23 wherein the electrowinning is performed in a range of 6-9 Volts.

25. The method of claims 23 or 24 wherein the electrowinning is performed for a time in a range of about 100 to about 120 minutes.

26. The method of claims 12 to 25, wherein the contacting occurs for about 10 to about 30 minutes.

27. The method of claims 12 to 26 wherein the contacting is performed at about 50° C.

28. The method of claims 12 to 27 wherein the recovering comprises recovering of at least 90% of the precious metal.

29. The method of claims 12 to 28, further comprising regenerating the barren aqueous-based leaching solution to form a regenerated solution.

30. The method of claim 29, wherein the regenerating comprises passing current through the barren aqueous-based solution to increase an oxidation reduction potential (ORP) of the barren aqueous-based solution.

31 . The method of claim 29, further comprising contacting the regenerated solution with a substrate including the precious metal.

32. The method of claim 29 to 31 , wherein the regenerating comprises adding one or more of the iodine compound, carboxylic acid; and amino acid.

33. The method of claim 32, comprising adding 10 g/L of KI0₃ or Nal0₃ and 15 g/L of glycine.