CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of priority to U.S. Provisional Patent Application No. 63/375,518, filed September 13, 2022, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to recovering gold from a resin, and associated systems, devices, and methods. In particular embodiments, the present disclosure relates to utilizing a copper wash step in an elution process to remove copper from a loaded resin in order to produce a more purified gold bullion.

BACKGROUND

[0003] Gold can be extracted from a carbonaceous ore via leaching and using a high ion exchange resin as a soluble gold adsorbent, a process often referred to as Resin-in-Leach (RIL). Once extracted, the resin having the extracted gold is referred to as a loaded resin and includes other undesirable extracted metals such as silver, copper, iron, cobalt, nickel, and zinc. The loaded resin is further processed via multiple desorption steps including, e.g., surfactant wash, copper wash, acid wash and gold elution steps, to further enable the gold bullion to be produced. The subprocess for removing copper from the loaded resin before metals are removed via the acid washing step can be particularly difficult, and current methods for such processes often fail to remove sufficient amounts of copper. If a sufficient amount of the copper is not removed from the loaded resin, the resin activity decreases, and the copper can precipitate in a downstream process and plate on the elution circuit and also in other piping/pieces of equipment, thereby diminishing general efficiency of the facility and increasing operating costs. A difficulty associated with removing copper from the loaded resin is the associated expense incurred with the copper wash, and more particularly with only using the copper wash for a single use. For example, while various copper wash solutions can effectively remove copper from a loaded resin, the ability to regenerate these copper wash solutions, such that they can be reused, are limited. As a result, the use of such solutions is expensive and often economically unfeasible for gold producers. Accordingly, improved systems, devices, and methods for recovering gold from a resin are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Features, aspects, and advantages of the presently disclosed technology may be better understood with regard to the following drawings.

[0005] FIG. 1 is a flow diagram illustrating a method for separating copper from a loaded resin, in accordance with embodiments of the present technology.

[0006] FIG. 2 is a block diagram of a system for recovering gold from a loaded resin, in accordance with embodiments of the present technology.

[0007] FIG. 3 is a chart illustrating an elution profile of thiourea by bed volume, in accordance with embodiments of the present technology.

[0008] FIG. 4 is a chart illustrating elution efficiencies of thiourea by bed volume, in accordance with embodiments of the present technology.

[0009] FIG. 5 is a chart illustrating elution efficiencies of a copper wash solution by pH, in accordance with embodiments of the present technology.

[0010] FIG. 6 is a chart illustrating elution efficiencies of a copper wash solution by concentration of thiourea, in accordance with embodiments of the present technology.

[0011] FIG. 7 is a flow diagram illustrating a method for regenerating an eluate after a copper wash, in accordance with embodiments of the present technology.

[0012] FIG. 8 is a chart illustrating precipitating efficiencies of copper, in accordance with embodiments of the present technology.

[0013] FIG. 9 is a flow diagram illustrating a method for regenerating an eluate after a copper wash, in accordance with embodiments of the present technology.

[0014] FIG. 10 is a block diagram of a system for recovering gold from a loaded resin, in accordance with embodiments of the present technology. [0015] FIG. 11 is a diagram of a system for recovering cyanide, in accordance with embodiments of the present technology.

[0016] A person skilled in the relevant art will understand that the features shown in the drawings are for purposes of illustration, and variations, including different and/or additional features and arrangements thereof, are possible.

OVERVIEW

[0017] As noted above, removing copper from a loaded resin in an economic manner can be difficult due to the expenses incurred with the conventional copper wash process. This is largely due to the inability to regenerate copper wash solutions, such that they can be reused, in economically feasible ways. Embodiments of the present technology attempt to mitigate the above-described issues associated with recovering gold from a loaded resin, e.g., by utilizing copper wash steps and/or solutions that are more effective at removing copper from loaded resins, and/or that can be regenerated or reused multiple times. In some embodiments of the present technology, copper wash solutions comprise thiourea and a pH between 1.0-3.0, 1.5-2.0, or 1.55-1.80, e.g., at a temperature of at least 45 °C. As explained herein, this combination of thiourea and acidic pH can enable relatively high copper removal efficiencies. Moreover, this combination has shown that removal efficiencies decrease for pHs outside of the described ranges herein. For example, the copper removal efficiency has been shown to be higher for a pH within the 1.55-1.80 range, relative to a pH above or below this range. In addition to the relatively high removal efficiency of copper, this combination of thiourea and pH can also result in relatively minor gold losses. As also explained herein, such copper wash solutions can be regenerated or recovered, e.g., for reuse with multiple loaded resins, via thermal or chemical precipitation.

[0018] In some embodiments of the present technology, copper wash solutions include cyanide (e.g., sodium cyanide (NaCN)), which also has relatively high copper removal efficiencies. Such copper wash solutions can be regenerated or recovered by using cyanide recovery processes described herein, which include acidification of a solution comprising the cyanide, volatilization of the acidified solution, and absorption of the volatized solution via a hydroxide-containing compound. DETAILED DESCRIPTION

[0019] FIG. 1 is a flow diagram illustrating a method 100 for separating copper from a loaded resin, in accordance with embodiments of the present technology. The method 100 includes providing a copper wash solution comprising thiourea and a pH less than 3.0 (method portion 102). The copper wash solution can have a pH within a range of 1.0-3.0, 1.53-2.00, 1.53-1.90, 1.53-1.80, or any incremental value therebetween (e.g., 1.59, 1.60, 1.71, 1.80, etc.), and a temperature of at least 45°C, 50°C, 55°C, 60°C, or 65°C. In some embodiments, the desired pH of the copper wash solution comprising thiourea is based solely or at least predominantly on the corresponding expected copper removal efficiency, which as described herein can be highest within a range of 1.53-1.80. The concentration of thiourea for the copper wash solution can be within a range of 0.001-5.0 Mol/L, 0.01-2.0 Mol/L, or 0.1-1.0 Mol/L, 0.3-1.0 Mol/L, 0.4-1.0 Mol/L, 0.5-1.0 Mol/L, or any incremental value therebetween. In some embodiments, the copper wash solution comprises a strong acid, such as sulfuric acid (H2SO4). In such embodiments, the strong acid of the copper wash solution can include a concentration within a range of 0.001-1.0 Mol/L, 0.005-0.5 Mol/L, 0.01-0.04 Mol/L, or any incremental value therebetween.

[0020] The method 100 can further comprise combining the copper wash solution with a loaded resin comprising gold and copper to form a copper-reduced resin and an eluate comprising copper and thiourea (process portion 104). The loaded resin can be an adsorbent or other composition for extracting gold from the ore. Combining the copper wash solution with the loaded resin can remove a vast majority of the copper (e.g., at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% of the copper) from the resin, with limited gold losses. For example, as explained in more detail elsewhere herein (e.g., with reference to FIG. 5), the amount of gold separated or lost from the loaded resin during process portion 104 can be less than 0.10 grams (g) / ton (t) of resin, 0.09 g/t, 0.08 g/t, 0.07 g/t, 0.06 g/t, 0.05 g/t, 0.04 g/t, 0.03 g/t, 0.02 g/t, or 0.01 g/t. The copper wash solution can also effectively remove other metals from the resin (e.g., silver, nickel and zinc, iron, and cobalt). The ability for the copper wash solution to remove significant amounts of copper, while not removing the target metal(s) (e.g., gold and silver), provides functional and economic benefits over existing copper wash solutions, and reduces incurred losses from undesirable gold extraction from the loaded resin during the elution process downstream. [0021] The copper wash solution and resin can be combined in a reaction vessel (e.g., an elution column), which can be a medium or large-scale chamber for industrial-scale production, e.g., dependent on the loading concentration. The reaction vessel is part of a larger system, such as the system 200 (FIG. 2) described herein. The copper wash process can occur once the copper wash solution and the loaded resin are combined, in which the copper wash solution, at a predetermined temperature (e.g., 45-65°C), acts as a copper eluent (e.g., a solvent) to (i) penetrate the loaded resin, (ii) chemically bind with (e.g., adsorb) elements of the loaded resin, and (iii) suspend the bound elements within the copper wash solution, thereby forming an eluate and an element-reduced or depleted resin. The copper wash solution can also bind with one or more precious metals in the loaded resin to form the eluate. In such embodiments, those metals are also reduced or depleted from the resin.

[0022] The method 100 can further comprise separating the eluate from the copper-reduced resin (process portion 106). Once the eluant is near or reaches its carrying capacity for copper and the loaded resin is copper-reduced (e.g., the copper wash process is complete), the eluate and the copper- reduced resin can be separated by draining or syphoning the eluate from the reaction vessel or by removing or filtering the copper-reduced resin from the reaction vessel. The eluate may then be prepared for disposal or regeneration and the copper-reduced resin may be prepared for further element removal processing and gold elution.

[0023] FIG. 2 is a block diagram of a system 200 for recovering gold from a loaded resin, and can incorporate aspects of the method 100 described with respect to FIG. 1. Referring to FIG. 2, the system 200 can include (i) a surfactant wash subsystem 210 configured to receive a loaded resin 205 that includes a target metal (e.g., gold or silver) and non-target metals (e.g., copper, iron, cobalt, nickel, and zinc), and (ii) a copper wash subsystem 220 for removing a vast majority of copper from the loaded resin 205. As such, the copper wash subsystem 220 can be configured to receive a copper wash solution 222 and the loaded resin 205, and produce an eluate 224 and a copper-washed resin 234. The copper wash solution 222 can correspond to the copper wash solution described with reference to FIG. 1. That is, the copper wash solution 222 can comprise thiourea, a pH within a range of 1.0- 3.0 (e.g., 1.5-2.0, 1.53-1.9, or 1.53-1.80), and optionally a strong acid (e.g., sulfuric acid). The copper wash solution 222 can be at a temperature of at least 45 °C, 50°C, 55 °C, 60°C, or 65 °C, or within a range of 45-65°C. In such embodiments, the eluate 224 comprises thiourea and copper (i.e., the copper removed from the loaded resin 205). As described herein, the eluate 224 can undergo further processing to separate the copper from the solvent (e.g., the thiourea), such that the solvent can be reused in a copper wash solution. The copper-reduced resin 234 produced via the copper wash subsystem 220 can comprise gold, non-target materials, and less or preferably minimal amounts of copper.

[0024] The system 200 further comprises an acid wash subsystem 230, e.g., for cleaning kerosene (if any) from the cupper-washed resin 234. The acid wash subsystem 230 is configured to receive and combine the copper- washed resin 234 and an acid solution 232, and, via an acid washing process, produce an eluate 236 and an acid-reduced resin 244. During the acid washing process, the acid solution 232 acts as an eluent to (i) penetrate the copper-washed resin 234, (ii) chemically bind with elements of the copper-washed resin 234, and (iii) suspend the bound elements within the acid solution 232, thereby forming the eluate 236 and the acid-washed resin 244. The acid solution 232 may bind with one or more precious metals to form the eluate 236. When the acid solution 232 binds with one or more precious metals, those metals are reduced or depleted from the copper-washed resin 234. The acid solution 232 can comprise one or more strong acids (e.g., sulfuric acid), and can have a concentration within the ranges of 0.1-3.0 Mol/L, 0.4-2.0 Mol/L, or 0.7-1.5 Mol/L, or any incremental value therebetween. The eluate 236 can comprise the strong acid from the acid solution and one or more of the non-target materials from the copper-washed resin 234. In some embodiments, the acid wash subsystem 230 represents one of multiple acid washes, each of which corresponds to removing one of the non-target metals from the copper-washed resin 234 and/or loaded resin 205. For example, the acid wash subsystem can comprise a first acid wash subsystem to remove nickel and a second acid wash subsystem to remove cobalt, zinc and/or iron. The acid-washed resin 244 can comprise gold or the target metal and one or more of the non-target metals, with quantities of the non- target metals being less than the respective quantities of the copper-washed resin 234.

[0025] The system 200 can further comprise an elution/electrowinning subsystem 240 (“elution subsystem 240”) for removing the target metal(s) from the acid-reduced resin 244, and can include an electrolytic process or circuit (e.g., electro winning). The elution subsystem 240 can be configured to receive and combine the acid-reduced resin 244 and an elution solution 242, and produce a residual resin 250 and a pregnant solution that is further processed to produce the bullion 246 comprising the target metal(s) (e.g., at least 90%, 95%, 96%, 97%, 98% of the target metal(s)). The bullion 246 can undergo further processing, e.g., via smelting in an induction furnace, and the residual resin 250 may be further processed for reuse or disposal. The elution solution 242 may comprise thiourea and/or a strong acid (e.g., sulfuric acid), which can each have a concentration within the ranges of 0.01-5.0 Mol/L, 0.1-2.0 Mol/L, 0.5- 1.5 Mol/L, or any incremental value therebetween.

[0026] As described herein, embodiments of the present technology can include copper wash solutions comprising thiourea that are used to remove copper from a loaded resin. FIGS. 3 and 4 are charts illustrating the elution profile and elution efficiency profile, respectively, of thiourea in a thiourea-resin mixture. The profiles of FIG. 3 (the "Elution Profile") and of FIG. 4 (the "Efficiency Profile") identify the bonding properties between thiourea and gold, silver, and copper (amongst other metals). These profiles also identify the difficulties associated with extracting only copper (i.e., not gold or silver) from a loaded resin, and the functional benefits that a copper wash solution comprising thiourea and a desired pH can provide.

[0027] The Elution Profile of FIG. 3 illustrates the amount (mg/L) of nickel, zinc, gold, silver, and copper stripped by a thiourea solution from the mixture of thiourea and a set amount of loaded resin, as more thiourea is added to the mixture (i.e., as BV increases). The left vertical axis is a scale for the amount of nickel, zinc, gold, and silver stripped by the thiourea in mg/L, the right vertical axis is a scale for the amount of copper absorbed by the thiourea in mg/L, and the horizontal axis is a scale for the volume (e.g., bed volume in relation to resin volume inside the column) of thiourea solution added to the mixture. The Elution Profile identifies that the highest amount of silver and copper stripped within the thiourea solution both occur at -0.75 BV, and the highest stripped amount of gold occurs at -1.2 BV. This means the greatest stripping of gold, silver, and copper by the thiourea is understood to occur relatively simultaneously from 0.0- 1.2 BV.

[0028] The Efficiency Profile of FIG. 4 illustrates the percentage of gold, silver, and copper removed from the mixture of thiourea solution with the set amount of loaded resin by thiourea as more thiourea is added to the mixture (i.e., as BV increases). The vertical axis is a scale for the percentage of gold, silver, and copper removed from the loaded resin, and the horizontal axis is a scale for the volume (e.g., bed volume) of thiourea solution added to the mixture. The Efficiency Profile identifies that thiourea solution strips from the loaded resin (i) -98% of gold by -3.2 BV, (ii) 100% of silver by -1.2 BV, and (iii) 100% of copper by -2.2 BV. Further, the Efficiency Profile identifies that, by -0.75 BV and -1.2 BV, respectively, thiourea solution strips from the loaded resin (i) -12% and -60% of the gold, (ii) -60% and -100% of the silver, and (iii) -50% and -80% of the copper. The Efficiency Profile compliments the Elution Profile to suggest that the greatest desorption of gold, silver, and copper by thiourea solution occurs simultaneously from 0.0-1.2 BV. Moreover, the Efficiency Profile and the Elution profile substantiates the difficulty when using thiourea solution to efficiently extract less than all three of gold, silver, and copper.

[0029] As described herein, embodiments of the present technology can include copper wash solutions comprising thiourea that are used to remove copper from a loaded resin, e.g., as an additional step to a normal elution process. FIGS. 5 and 6 are charts illustrating the results of using a copper wash solution comprising thiourea with a loaded resin, with FIG. 5 illustrating the copper removal efficiency and FIG. 6 illustrating the associated gold losses. The results illustrated in FIGS. 5 and 6 show the effectiveness of a copper wash solution comprising thiourea and the appropriate pH for separating copper from the loaded resin, while also removing a minimal amount of gold from the loaded resin.

[0030] The combined copper wash solution and loaded resin can correspond to the combined copper wash solution 222 and loaded resin 224 described with respect to FIG. 2, as well as the eluate described with respect to FIG. 1. As such, the copper wash solution shown and described with reference to FIGS. 5 and 6 comprises thiourea and in some embodiments a strong acid (e.g., sulfuric acid). The charts of FIGS. 5 and 6 illustrate the percentage of copper removed and the amount (grams / ton) of gold removed from the loaded resin, with FIG. 5 based on pH and FIG. 6 based on concentration of thiourea.

[0031] Referring first to FIG. 5, the left vertical axis is a scale for the percentage of copper removed from the loaded resin by the copper wash solution, the right vertical axis is a scale for the amount of gold removed from the loaded resin by the copper wash solution in g/ton, and the horizontal axis is a scale for the pH of the copper wash solution at a 0.2 Mol/E concentration of Thiourea. As shown in FIG. 5, the copper removal efficiency generally decreases as pH increases, as the percentage of copper removed is approximately 99% at or below a pH of 1.52, and decreases to 43% at a pH of 2.04. Specifically, the percentage of copper removed (i) decreases from 99% to 94% as pH is raised from 1.52 to 1.78, and (ii) decreases from 94% to 43% as pH is raised from 1.78 to 2.04. [0032] As shown in FIG. 5, the gold loss experienced an initial increase as pH was raised from 1.00 to 1.34, followed by a subsequent decrease as pH was raised further from 1.34 to 1.78, and then another increase as pH was raised from 1.78 to 2.04. It is noted that the subsequent increase in gold loss experienced as pH was raised from 1.78 to 2.04 was slight (i.e., from 0.0 to 0.02), however despite the slight increase, a desirable pH range based in part on the increase is identified at which gold losses are minimized. The gold loss experienced as the pH rises are unexpected and represent surprising results. That is, while a person of ordinary skill in the art may expect the gold loss to generally decrease as pH is increased, a person of ordinary skill in the art would not expect the gold losses to initially increase after an initial pH increase and then decrease after a subsequent pH increase. Moreover, a person of ordinary skill in the art would not expect the gold losses to then increase again after another pH increase.

[0033] Considering the effect of pH on the copper removal efficiency and the gold loss together, and more specifically the pH range that optimizes both copper removal efficiency (i.e., maximizing copper removal efficiency) and gold loss (i.e., minimizing gold loss), embodiments of the present technology comprise copper wash solutions (or compositions generally) that include thiourea and a pH within a range of 1.53-2.00, 1.53-1.90, 1.53-1.80, 1.53-1.78, or any incremental value therebetween. By focusing on this pH range, copper wash solutions can effectively and/or optimally be used to recover copper from a loaded resin, and more generally to recover gold from a loaded resin.

[0034] Copper wash solutions can be further optimized by increasing the concentration of thiourea, as illustrated by FIG. 6, which is a chart illustrating the elution efficiencies the copper wash solution by concentration of thiourea, or more specifically the percentage of copper removed and the amount (g/ton) of gold removed from the loaded resin as concentration of thiourea increases and the pH remains at 1.7. As shown in FIG. 6, the left vertical axis is a scale for the percentage of copper removed from the loaded resin by the copper wash solution, the right vertical axis is a scale for the amount of gold removed from the loaded resin by the copper wash solution in g/ton, and the horizontal axis is a scale for the concentration thiourea of the copper wash solution in Mol/L.

[0035] As shown in FIG. 6, the copper removal efficiency increases and the gold losses remain at zero as thiourea concentration increases. Specifically, when the copper wash solution had a concentration of 0.1 Mol/L, 0.2 Mol/L, 0.3 Mol/L, and 0.4 Mol/L, the copper wash solution removed 64%, 88%, 94%, and 96% of copper, respectively. There were no gold losses registered for any of the varying concentrations. Based on these results, at a pH of 1.7 the copper wash solution experiences a greater copper removal efficiency as the concentration of thiourea increases, while gold removal remains unchanged. In view of these results, embodiments of the present technology comprise a thiourea concentration of at least 0.4 Mol/L, or as noted elsewhere herein within a range of 0.3-1.0 Mol/L, 0.4-1.0 Mol/L, 0.5-1.0 Mol/L, or any incremental value therein.

[0036] As noted elsewhere herein, the expense associated with using copper wash solutions only a single time can be significant, and thus there is a need to process the corresponding eluate compositions to regenerate the copper wash solutions and enable their reuse to extract copper from additional loaded resins. As such, for those embodiments in which the eluate comprises thiourea, there is a desire to separate the extracted copper from the thiourea and use the thiourea to generate copper wash solutions for further use. Similarly, for those embodiments in which the eluate comprises cyanide, there is a desire to separate the extracted copper from the eluate and reuse the cyanide for future use. FIG. 7, which is a flow diagram illustrating a method 700 for regenerating an eluate after a copper wash, is one such method. The method 700 includes process portions 102, 104, and 106 described with reference to FIG. 1, which include providing a copper wash solution comprising thiourea and a pH less than 3.0 (process portion 102), combining the copper wash solution with a loaded resin comprising gold and copper to form a copper-reduced resin and an eluate comprising copper and thiourea (process portion 104), and separating the eluate from the copper-reduced resin (process portion 706).

[0037] The method 700 further comprises processing the eluate to regenerate the copper wash solution (process portion 708). Processing the eluate to regenerate the copper wash solution can comprise thermal precipitation, chemical precipitation via a precipitant (e.g., sodium hydrosulfide, ammonium hydroxide, sodium hydroxide, and/or calcium hydroxide), copper absorption, electrowinning, or another process for separating the copper from the thiourea (i.e., the eluant) and/or the eluate. Once the copper is removed from the eluant or eluate, the copper wash solution is regenerated and may be reused with method portion 702 and the extracted copper otherwise utilized. When using chemical precipitation, the precipitant is combined with the eluate and agitated in a reaction vessel. As the mixture is agitated, copper suspended within the eluate binds with the precipitant and precipitates, settling to the bottom of the vessel. [0038] FIG. 8 is a chart illustrating the precipitating efficiencies of copper, or more specifically the percentage of copper removed from the eluate by chemical precipitation via sodium hydroxide relative to the amount (mg/L) of copper in the eluate. The left vertical axis of the chart is a scale for the amount of copper in the eluate in mg/L, the right vertical axis is a scale for the percentage of copper removed by chemical precipitation via sodium hydroxide, and the horizontal axis identifies the different trials performed producing these results. As shown in FIG. 8, the copper removed from the eluate using chemical precipitation via sodium hydroxide varied between approximately 60-90%, and on average was approximately 75%. During precipitation, approximately 25% of the thiourea in the eluate was consumed, thereby indicating that a majority of copper can be removed from an eluate while only consuming 25% of the eluant during the chemical precipitation process. As such, chemical precipitation can be an economically viable option to reuse or recycle thiourea for multiple uses in copper wash solutions, e.g., as described with respect to FIGS. 1 and 2 herein.

[0039] The need to process eluate compositions to regenerate the copper wash solutions and enable their reuse to extract copper from additional loaded resins also applies to eluates that include cyanide. FIG. 9 is a flow diagram illustrating a method 900 for regenerating an eluate after a copper wash. The method 900 comprises process portions generally similar to those described for the method 700 with respect to FIG. 7. For example, the method 900 can comprise providing a copper wash solution comprising cyanide and sodium hydroxide (process portion 902), and combining the copper wash solution with a loaded resin comprising gold and copper to form a copper-reduced resin and an eluate comprising copper and cyanide (process portion 904). In some embodiments, the copper wash solution comprises sodium cyanide and sodium hydroxide, and is supplied from a storage tank (e.g., on a continuous basis) to a mixer where the copper wash solution and loaded resin are combined. In such embodiments, the copper wash solution can have a sodium cyanide concentration within a range of 0.5-3.0 Mol/L, 0.5-2.0 Mol/L, or 1.0-2.0 Mol/L, 1.5-2.0 Mol/L, or any incremental value therebetween, and a sodium hydroxide concentration within a range of 0.01-2.0 Mol/L, 0.01-1.0 Mol/L, or 0.05-1.0 Mol/L, 0.05-0.5 Mol/L, or any incremental value therebetween. Mixing of the copper wash solution and the loaded resin can occur for a predetermined minimum time (e.g., 60 minutes 90 minutes, or 120 minutes) and at a predetermined minimum temperature (e.g., ambient temperature or 60°C). [0040] Combining the copper wash solution with the loaded resin can remove all or a vast majority of the copper (e.g., at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% of the copper) from the resin, while also removing very little amounts of the gold from the loaded resin. For example, the amount of gold separated from the loaded resin during process portion 904 can be less than 0.10 g/t of resin, 0.09 g/t, 0.08 g/t, 0.07 g/t, 0.06 g/t, 0.05 g/t, 0.04 g/t, 0.03 g/t, 0.02 g/t, or 0.01 g/t. Further, the copper wash solution also removes minimal amounts of other metals of the resin (e.g., silver, nickel, zinc, iron, and cobalt). The ability for the copper wash solution to remove significant amounts of copper while not removing other precious metals provides functional and economic benefits over existing copper wash solutions, and reduces incurred losses from premature gold extraction from the loaded resin.

[0041] The mixer in which the copper wash solution and the loaded resin are combined can be part of a more general system for recovering, similar to the system 200 (FIG. 2). An elution process can occur once the copper wash solution and the loaded resin are combined, in which the copper wash solution acts as an eluent (e.g., a solvent) to (i) penetrate the loaded resin (e.g., an absorbent, raw material, slurry, etc.), (ii) chemically bind with (e.g., absorb) elements of the loaded resin, and (iii) suspend the bound elements within the copper wash solution, forming an eluate and an element- reduced or -depleted resin. The copper wash solution may bind with one or more precious metals in the loaded resin to form the eluate. When the copper wash solution binds with one or more precious metals, those metals are reduced or depleted from the resin.

[0042] The method 900 can further comprise separating the eluate from the copper-reduced resin (process portion 906). Once the eluant is near or reaches its carrying capacity for copper and the loaded resin is copper-reduced (e.g., elution is complete), the eluate and the copper-reduced resin may be separated by draining or syphoning the eluate from the reaction vessel or by removing or filtering the copper-reduced resin from the reaction vessel. The eluate may then be prepared for disposal or further processing (e.g., regeneration).

[0043] The method 900 can further comprise processing the eluate to regenerate the copper wash solution (process portion 908). As described with reference to FIG. 10, processing the eluate to regenerate the copper wash solution can comprise acidification, volatilization, and reabsorption. Once the copper is removed from the eluant or eluate, the copper wash solution can be regenerated and may be reused (e.g., for process portion 902), and the extracted copper may be otherwise utilized. [0044] FIG. 10 is a block diagram of a system 1000 for recovering gold from a loaded resin using a copper wash solution that includes cyanide, and can incorporate aspects of the method 900 described with respect to FIG. 9. Referring to FIG. 10, the system 1000 can include a surfactant wash subsystem 210 configured to receive the loaded resin 205 that includes a target metal (e.g., gold or silver) and non-target metals (e.g., copper, iron, cobalt, nickel, and zinc), and a copper wash subsystem 1020 for removing a vast majority of copper from the loaded resin 205. As such, the copper wash subsystem 1020 can be configured to receive a copper wash solution 1018 and the loaded resin 205, and produce an eluate 1021 and the copper-reduced resin 244. The copper wash solution 1018 can correspond to the copper wash solution described with reference to FIG. 9. That is, the copper wash solution 1018 can comprise sodium cyanide and caustic soda. The copper wash solution 1018 can be at ambient temperature. In such embodiments, the eluate 1021 comprises cyanide, caustic soda and copper (i.e., the copper removed from the loaded resin 224), e.g., at ambient temperature. The copper-reduced resin 244 produced via the copper wash subsystem 220 can comprise gold and the non-target metals, with less or preferably minimal amounts of copper.

[0045] The eluate 1021 can undergo further processing to recover the cyanide and also to separate the copper from the solution, such that the solution can be reused in the leaching and/or copper wash solution and copper could be used as copper sulfate in the Detox process. As shown in FIG. 10, the eluate 1021 can be directed to a regeneration subsystem 1022 configured to separate at least a portion of the cyanide 1023 from the eluate 1021. The separated cyanide 1023 can be directed to a copper wash solution source 1016 configured to provide the copper wash solution 1018. The residual solution portion 1025 of the eluate 1021 containing copper (e.g., copper sulphate) can be directed elsewhere, e.g., a detoxification unit. The regeneration subsystem 1022 can include equipment and chemical compositions for acidification, volatilization, and reabsorption of cyanide, and can generally correspond to the system 1100 of FIG. 11.

[0046] The system 1000 can further comprise additional subsystems described elsewhere herein (e.g., with reference to the system 200 of FIG. 2). For example, the system 1000 can include the acid wash subsystem 230 for removing one or more of the non-target metals from the copper- reduced resin 244. In some embodiments, the copper-washed resin 234 is rinsed with water prior to being received by the acid wash subsystem 230. The acid wash subsystem 230 is configured to receive and combine the copper-washed resin 234 and the acid solution 232, and, via an elution process, produce the eluate 236 and the acid-reduced resin 244. During the elution process, the acid solution 232 acts as an eluent to (i) penetrate the copper- washed resin 234, (ii) chemically bind with elements of the copper-washed resin 234, and (iii) suspend the bound elements within the acid solution 232, thereby forming the eluate 236 and the acid-reduced resin 244. The acid solution 232 may bind with one or more precious metals in the copper-washed resin 234 to form the eluate 236. When the acid solution 232 binds with one or more precious metals, those metals are reduced or depleted from the acid-reduced resin 244. The acid solution 222 can comprise one or more strong acids (e.g., sulfuric acid), and can have a concentration within the ranges of 0.1-3.0 Mol/L, 0.4-2.0 Mol/L, or 0.7-1.5 Mol/L, or any incremental value therebetween. The eluate 236 can comprise the strong acid from the acid solution and one or more of the non-target metals from the copper-washed resin 234. In some embodiments, the acid wash subsystem 230 represents one of multiple acid washes, each of which corresponds to removing one of the non-target metals from the copper-washed resin 234. For example, the acid wash subsystem 230 can comprise a first acid wash subsystem to remove nickel and a second acid wash subsystem to remove cobalt, zinc and/or iron. The acid-reduced resin 244 can comprise gold or the target metal and one or more of the non-target metals, with quantities of the non- target metals being less than the respective quantities of the copper-washed resin 234.

[0047] The system 1000 can further comprise the elution subsystem 240 for removing the target metal(s) from the acid-reduced resin 244, and can include an electrolytic process or circuit (e.g., electro winning). The elution subsystem 240 can be configured to receive and combine the acid- reduced resin 244 and an elution solution 242, and produce the residual resin 250 and a pregnant solution that is further processed to form the bullion 246 comprising the target metal(s) (e.g., at least 90%, 95%, 96%, 97%, 98% of the target metal(s)). The bullion 246 can undergo further processing, e.g., via smelting in an induction furnace, and the residual resin 250 may be further processed for reuse or disposal. The residual resin 250 can be further processed (e.g., rinsed with water) and be reused to extract additional target metals from ore. The elution solution 242 may comprise thiourea and/or a strong acid (e.g., sulfuric acid), which can each have a concentration within the ranges of 0.01-5.0 Mol/L, 0.1-2.0 Mol/L, 0.5-1.5 Mol/L, or any incremental value therebetween.

[0048] FIG. 11 illustrates a system 1100 for separating cyanide from a copper wash solution, in accordance with embodiments of the present technology. Features of the system 1100 are generally described with reference to the system 1000 of FIG. 10. The system 1100 can process a loaded copper wash solution 1102 (e.g., the eluate 226; FIG. 2) comprising one or more target metals (e.g., copper) through one or more processes including acidification, volatilization, and reabsorption to separate cyanide from the loaded copper wash solution 1102, and output a concentrated aqueous cyanide solution 1114 and a low-cyanide loaded copper wash solution 1124. The aqueous cyanide solution 1114 can be further processed to generate a recharged copper wash solution for use in a copper wash and/or gold recovery process (e.g., as described for the methods 100, 700, 900).

[0049] As shown in FIG. 11, The system 1100 can include an acidification tank 1105, a stripping column 1115 fluidically coupled to the acidification tank 1105, a neutralization tank 1125 fluidically coupled to the stripping column 1115, and an absorption column 1135 fluidically coupled to the stripping column 1115. The system 1100 can combine the loaded copper wash solution 1102 with a strong acid (e.g., sulfuric acid) 1104 in the acidification tank 1105 to form an acidified solution 1106. As shown in Reaction 1, the cyanide of the loaded copper wash solution 1102 and sulfuric acid 1104 react to hydrogen cyanide and sulfate. Reaction 1

The pH of the acidification tank 1105 can be within a range of 2.0-7.0, 2.0-5.0, 2.0-4.0, or any incremental value therebetween.

[0050] The acidified solution 1106 can be transferred or pumped to the stripping column 1115, which receives (i) the aqueous acidified solution 1106 at an upper portion of the stripping column 1115 and (ii) a low-pressure air fluid 1110 at a lower portion of the stripping column 1115. As the low-pressure air fluid 1110 progresses upward through the stripping column 1115 and the acidified solution 1106 falls downward through the stripping column 1115 due to gravity, the cyanide is stripped from the acidified solution 1106 to produce a gaseous stream 1108 comprising hydrogen cyanide and air. Stated differently, the hydrogen cyanide from the acidified solution 1106 is volatilized and transitions from an aqueous to gaseous fluid. The sulfate or remaining portions (e.g., cyanide) of the acidified solution 1106 falls to the bottom of the stripping column 1115 to form a stripped solution 1112 that is directed to a neutralization tank 1125.

[0051] The gaseous stream 1108 comprising hydrogen cyanide and air exits a top portion of the stripping column 1115 and is directed to an intermediate or lower portion of the absorption column 1135. The absorption column 1135 also receives, at a lower portion of the absorption column 1135, an absorption stream 1116 comprising sodium hydroxide and/or milk of lime (e.g., calcium hydroxide). For absorption streams 1116 comprising sodium hydroxide, the sodium hydroxide reacts with the hydrogen cyanide of the gaseous stream 1108 to form sodium, water, and concentrated cyanide, as shown in Reaction 2. Relatedly, for absorption streams 1116 comprising calcium hydroxide, the calcium hydroxide reacts with the hydrogen cyanide of the gaseous stream to form calcium, water, and concentrated cyanide, as shown in Reaction 3.

NaOH + HCN(g) -» Na ⁺ + CN- + H ₂ 0 Reaction 2

Ca(0H) ₂ + 2HCN _(g) Ca ⁺² + 2CN“ + 2H ₂ O Reaction 3

[0052] The concentrated cyanide can be captured from the bottom of the absorption column 1135 as an aqueous cyanide solution 1114. The cyanide solution 1114 can be transferred or pumped to other areas for further processing, such as to generate the copper wash solutions described elsewhere herein. As shown in FIG. 11 , a portion of the aqueous solution 1114 is pumped and recycled to an upper portion of the absorption column 1135 as a recycle stream 1118, which can help maintain the system 1100 under a slight vacuum. Once the cyanide has been absorbed from the gaseous stream 1108, the remaining portion of the gaseous stream 1108 progresses upward through the absorption column 1135 and exits a top portion as low-pressure air fluid 1110 directed to the stripping column 1115 for further cyanide absorption.

[0053] The stripped solution 1112 from the stripping column 1115 that is directed to the neutralization tank 1125 can be combined with an absorption stream 1116 comprising milk of lime. The absorption stream 1116 can originate from the same source as the absorption stream 1116. The cyanide from the stripped solution 1112 can react with the calcium hydroxide of the absorption stream 1116 to form calcium, water, and cyanide, as shown in Reaction 4. The calcium and water products formed via Reaction 4 can react with the sulfate from the stripped solution 1112 to form a leach solution 1124 comprising calcium sulfate, as shown in Reaction 5.

Ca(0H) ₂ + 2HCN _(g) Ca ⁺² + 2CN“ + 2H ₂ O Reaction 4

Ca ⁺² + S0 ₄ ^-2 + 2H ₂ O -» CaS0 ₄ -H ₂ 0 Reaction 5

[0054] The system 1100 enables cyanide (e.g., from loaded copper wash solutions) to be separated therefrom, therein further enabling the reuse of cyanide for additional copper wash solutions. In practice, the percentage of cyanide recovered via the system 1100 has exceeded 90%. At such high levels of cyanide recovery, the system 1100 and embodiments of the present technology improve the economic feasibility of utilizing cyanide as a copper wash solution and generally decrease costs traditionally associated with discarding cyanide after single use. As such, embodiments of the present technology improve the ability to reuse copper wash solutions, and therein improve the recovery of gold.

CONCLUSION

[0055] It will be apparent to those having skill in the art that changes may be made to the details of the above-described embodiments without departing from the underlying principles of the present disclosure. In some cases, well known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the present technology. Although steps of methods may be presented herein in a particular order, alternative embodiments may perform the steps in a different order. Similarly, certain aspects of the present technology disclosed in the context of particular embodiments can be combined or eliminated in other embodiments. Furthermore, while advantages associated with certain embodiments of the present technology may have been disclosed in the context of those embodiments, other embodiments can also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages or other advantages disclosed herein to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein, and the invention is not limited except as by the appended claims.

[0056] Throughout this disclosure, the singular terms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. The term “and/or” when used in reference to a list of two or more item is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term “comprising,” “including,” and “having” should be interpreted to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional types of other features are not precluded.

[0057] Reference herein to “one embodiment,” “an embodiment,” “some embodiments” or similar formulations means that a particular feature, structure, operation, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present technology. Thus, the appearances of such phrases or formulations herein are not necessarily all referring to the same embodiment. Furthermore, various particular features, structures, operations, or characteristics may be combined in any suitable manner in one or more embodiments.

[0058] Unless otherwise indicated, all numbers expressing numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about” or “approximately.” The terms “about” or “approximately” when used in reference to a value are to be interpreted to mean within 10% of the stated value. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present technology. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Additionally, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a range of “1 to 10” includes any and all subranges between (and including) the minimum value of 1 and the maximum value of 10, i.e., any and all subranges having a minimum value of equal to or greater than 1 and a maximum value of equal to or less than 10, e.g., 5.5 to 10.

[0059] The disclosure set forth above is not to be interpreted as reflecting an intention that any claim requires more features than those expressly recited in that claim. Rather, as the following claims reflect, inventive aspects lie in a combination of fewer than all features of any single foregoing disclosed embodiment. Thus, the claims following this Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment. This disclosure includes all permutations of the independent claims with their dependent claims.

[0060] Aspects of the present technology are described below, and various examples of the present technology are described as numbered clauses (1, 2, 3, etc.) for convenience. These clauses are provided as examples and do not limit the present technology. It is noted that any of the dependent clauses may be combined in any combination, and placed into a respective independent clause. The other clauses can be presented in a similar manner. 1. A method for recovering gold from a loaded resin, comprising: providing a copper wash solution comprising thiourea and a pH less than 3.0; combining the copper wash solution with a loaded resin comprising gold and copper to form a copper-reduced resin and an eluate comprising copper and thiourea; and separating the eluate from the copper-reduced resin.

2. The method of any one of the clauses herein, wherein the pH of the copper wash solution is within a range of 1.0-3.0.

3. The method of any one of the clauses herein, wherein the pH of the copper wash solution is within a range of 1.53-2.0.

4. The method of any one of the clauses herein, wherein the pH of the copper wash solution is within a range of 1.55-1.80.

5. The method of any one of the clauses herein, wherein the pH of the copper wash solution is within a range of 1.55-1.80, and wherein, within the pH range, the copper wash solution has a copper removal efficiency from the loaded resin of at least 80%, 85%, 90%, 91%, 92%, 93%, or 94%.

6. The method of any one of the clauses herein, wherein the pH of the copper wash solution is within a range of 1.55-1.80, and wherein, within the pH range, the copper wash solution has a copper removal efficiency from the loaded resin within a range of 90-94%.

7. The method of any one of the clauses herein, wherein the copper removal efficiency of the copper wash solution from the loaded resin decreases as pH of the copper wash solution increases.

8. The method of any one of the clauses herein, wherein a first amount of gold loss occurs when the pH of the copper wash solution is below 1.5, and a second amount of gold loss, less than the first amount, occurs when the pH of the copper wash solution is greater than 1.5. 9. The method of any one of the clauses herein, wherein a first amount of gold loss occurs when the pH of the copper wash solution is below 1.5, and a second amount of gold loss, less than the first amount, occurs when the pH of the copper wash solution is within a range from 1.5-2.0.

10. The method of any one of the clauses herein, wherein (i) a first amount of gold loss occurs when the pH of the copper wash solution is below 1.5, (ii) a second amount of gold loss occurs when the pH of the copper wash solution is within a range from 1.5-2.0, and (iii) a third amount of gold loss occurs when the pH of the copper wash solution is greater than 2.04, wherein the second amount is less than the first amount and the third amount.

11. The method of any one of the clauses herein, wherein the thiourea concentration of the copper wash solution is less than 1.0 Mol/L, less than 0.9 Mol/L, less than 0.8 Mol/L, less than 0.7 Mol/L, less than 0.6 Mol/L, less than 0.5 Mol/L, less than 0.4 Mol/L, less than 0.3 Mol/L, less than 0.2 Mol/L, or less than 0.1 Mol/L.

12. The method of any one of the clauses herein, wherein the thiourea concentration of the copper wash solution is within a range of 0.2-0.6 Mol/L.

13. The method of any one of the clauses herein, wherein the copper wash solution further comprises a strong acid.

14. The method of any one of the clauses herein, wherein the copper wash solution further comprises sulfuric acid.

15. The method of any one of the clauses herein, wherein the copper wash solution further comprises a strong acid including a concentration less than 0.1 Mol/L.

16. The method of any one of the clauses herein, wherein the copper wash solution further comprises a strong acid including a concentration within a range of 0.01-0.04 Mol/L.

17. The method of any one of the clauses herein, further comprising processing the eluate to separate the thiourea of the eluate from the copper of the eluate. 18. The method of any one of the clauses herein, further comprising processing the eluate to regenerate the copper wash solution.

19. The method of any one of the clauses herein, wherein the eluate is a first eluate, the method further comprising: combining an acid solution comprising a strong acid with the copper-reduced resin to

(i) separate at least one of nickel, zinc, or iron from the copper-reduced resin, and

(ii) produce an acid- washed resin; and eluting the acid-washed resin to separate gold from the acid-washed resin.

20. The method of any one of the clauses herein, further comprising processing the eluate to separate the copper therefrom and/or regenerate the copper wash solution, wherein processing the eluate is done via at least one of thermal precipitation, chemical precipitation via sodium hydroxide, chemical precipitation via calcium hydroxide, copper adsorption, or electrowinning.

21. A composition for removing copper from a loaded resin, comprising: a strong acid; and thiourea, wherein the composition has a pH less than 3.0.

22. The composition of any one of the clauses herein, wherein the pH of the composition is within a range of 1.0-3.0.

23. The composition of any one of the clauses herein, wherein the pH of the composition is within a range of 1.5-2.0.

24. The composition of any one of the clauses herein, wherein the pH of the composition is within a range of 1.55-1.80.

25. The composition of any one of the clauses herein, wherein the pH of the composition is within a range of 1.55-1.80, and wherein, within the pH range, the composition has a copper removal efficiency from the loaded resin of at least 80%, 85%, 90%, 91%, 92%, 93%, or 94%. 26. The composition of any one of the clauses herein, wherein the pH of the composition is within a range of 1.55-1.80, and wherein, within the pH range, the composition has a copper removal efficiency from the loaded resin within a range of 90-94%.

27. The composition of any one of the clauses herein, wherein a copper removal efficiency of the composition from a loaded resin decreases as pH of the composition increases.

28. The composition of any one of the clauses herein, wherein a first amount of gold loss occurs when the pH of the composition is below 1.5, and a second amount of gold loss, less than the first amount, occurs when the pH of the composition is greater than 1.5.

29. The composition of any one of the clauses herein, wherein a first amount of gold loss occurs when the pH of the composition is below 1.5, and a second amount of gold loss, less than the first amount, occurs when the pH of the composition is within a range from 1.5-2.0.

30. The composition of any one of the clauses herein, wherein (i) a first amount of gold loss occurs when the pH of the composition is below 1.5, (ii) a second amount of gold loss occurs when the pH of the composition is within a range from 1.5-2.0, and (iii) a third amount of gold loss occurs when the pH of the composition is greater than 2.04, wherein the second amount is less than the first amount and the second amount.

31. The composition of any one of the clauses herein, wherein a thiourea concentration of the composition is less than 1.0 Mol/L, less than 0.9 Mol/L, less than 0.8 Mol/L, less than 0.7 Mol/L, less than 0.6 Mol/L, less than 0.5 Mol/L, less than 0.4 Mol/L, less than 0.3 Mol/L, less than 0.2 Mol/L, or less than 0.1 Mol/L.

32. The composition of any one of the clauses herein, wherein a thiourea concentration of the composition is within a range of 0.2-0.6 Mol/L.

33. The composition of any one of the clauses herein, wherein the composition further comprises sulfuric acid.

34. The composition of any one of the clauses herein, wherein the composition further comprises a strong acid including a concentration less than 0.1 Mol/L. 35. The composition of any one of the clauses herein, wherein the composition further comprises a strong acid including a concentration within a range of 0.01-0.04 Mol/L.

36. The composition of any one of the clauses herein, further comprising a regenerated composition.

37. A system for recovering gold from a resin, comprising: a copper wash subsystem configured to receive (i) a loaded resin and (ii) a copper wash solution comprising thiourea and a pH less than 3.0, the copper wash subsystem being configured to produce a copper-reduced resin and an eluate comprising copper and thiourea.

38. The system of any one of the clauses herein, wherein the pH of the copper wash solution to be received by the copper wash subsystem is within a range of 1.0-3.0.

39. The system of any one of the clauses herein, wherein the pH of the copper wash solution to be received by the copper wash subsystem is within a range of 1.5-2.0.

40. The system of any one of the clauses herein, wherein the pH of the copper wash solution to be received by the copper wash subsystem is within a range of 1.55-1.80.

41. The system of any one of the clauses herein, wherein the pH of the copper wash solution to be received by the copper wash subsystem is within a range of 1.55-1.80, and wherein, within the pH range, the copper wash solution has a copper removal efficiency from the loaded resin of at least 80%, 85%, 90%, 91%, 92%, 93%, or 94%.

42. The system of any one of the clauses herein, wherein the pH of the copper wash solution to be received by the copper wash subsystem is within a range of 1.55-1.80, and wherein, within the pH range, the copper wash solution has a copper removal efficiency from the loaded resin within a range of 90-94%.

43. The system of any one of the clauses herein, wherein a first amount of gold loss occurs when the pH of the copper wash solution to be received by the copper wash subsystem is below 1.5, and a second amount of gold loss, less than the first amount, occurs when the pH of the copper wash to be received by the copper wash subsystem solution is greater than 1.5.

44. The system of any one of the clauses herein, wherein a first amount of gold loss occurs when the pH of the copper wash solution to be received by the copper wash subsystem is below 1.5, and a second amount of gold loss, less than the first amount, occurs when the pH of the copper wash solution to be received by the copper wash subsystem is within a range from 1.5-2.0.

45. The system of any one of the clauses herein, wherein (i) a first amount of gold loss occurs when the pH of the copper wash solution to be received by the copper wash subsystem is below 1.5, (ii) a second amount of gold loss occurs when the pH of the copper wash solution to be received by the copper wash subsystem is within a range from 1.5-2.0, and (iii) a third amount of gold loss occurs when the pH of the copper wash solution to be received by the copper wash subsystem is greater than 2.04, wherein the second amount is less than the first amount and the second amount.

46. The system of any one of the clauses herein, wherein the thiourea concentration of the copper wash solution to be received by the copper wash subsystem is less than 1.0 Mol/L, less than 0.9 Mol/L, less than 0.8 Mol/L, less than 0.7 Mol/L, less than 0.6 Mol/L, less than 0.5 Mol/L, less than 0.4 Mol/L, less than 0.3 Mol/L, less than 0.2 Mol/L, or less than 0.1 Mol/L.

47. The system of any one of the clauses herein, wherein the thiourea concentration of the copper wash solution to be received by the copper wash subsystem is within a range of 0.2-0.6 Mol/L.

48. The system of any one of the clauses herein, wherein the copper wash solution to be received by the copper wash subsystem further comprises a strong acid.

49. The system of any one of the clauses herein, wherein the copper wash solution to be received by the copper wash subsystem further comprises sulfuric acid.

50. The system of any one of the clauses herein, wherein the copper wash solution to be received by the copper wash subsystem further comprises a strong acid including a concentration less than 0.1 Mol/L. 51. The system of any one of the clauses herein, wherein the copper wash solution to be received by the copper wash subsystem further comprises a strong acid including a concentration within a range of 0.01-0.04 Mol/L.

52. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid wash subsystem being configured to produce an acid-washed resin and an eluate comprising copper.

53. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid wash subsystem being configured to produce an acid-washed resin and an eluate comprising iron.

54. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid wash subsystem being configured to produce an acid-washed resin and an eluate comprising cobalt.

55. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid wash subsystem being configured to produce an acid-washed resin and an eluate comprising nickel.

56. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid wash subsystem being configured to produce an acid-washed resin and an eluate comprising zinc.

57. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid solution comprising a strong acid.

58. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid solution comprising a sulfuric acid.

59. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid solution comprising a concentration of sulfuric acid less than 2.0 Mol/L, less than 1.9 Mol/L, less than 1.8 Mol/L, less than 1.7 Mol/L, less than 1.6 Mol/L, less than 1.5 Mol/L, less than 1.4 Mol/L, less than 1.3 Mol/L, less than 1.2 Mol/L, less than 1.1 Mol/L, or less than 1.0 Mol/L.

60. The system of any one of the clauses herein, further comprising an acid wash subsystem positioned to receive the copper-reduced resin and an acid solution, the acid solution comprising a concentration of sulfuric acid within a range of 0.5-1.5 Mol/L.

61. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution subsystem being configured to produce a residual resin and a bullion comprising gold.

62. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution subsystem being configured to produce a residual resin and a bullion comprising silver.

63. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution solution comprising thiourea.

64. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution solution comprising a strong acid.

65. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution solution comprising a sulfuric acid.

66. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution solution comprising a concentration of thiourea less than 1.0 Mol/L, less than 0.9 Mol/L, less than 0.8 Mol/L, less than 0.7 Mol/L, less than 0.6 Mol/L, less than 0.5 Mol/L, less than 0.4 Mol/L, less than 0.3 Mol/L, less than 0.2 Mol/L, or less than 0.1 Mol/L. 67. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution solution comprising a concentration of thiourea within a range of 0.2-0.6 Mol/L.

68. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution solution comprising a concentration of sulfuric acid less than 2.0 Mol/L, less than 1.9 Mol/L, less than 1.8 Mol/L, less than 1.7 Mol/L, less than 1.6 Mol/L, less than 1.5 Mol/L, less than 1.4 Mol/L, less than 1.3 Mol/L, less than 1.2 Mol/L, less than 1.1 Mol/L, or less than 1.0 Mol/L.

69. The system of any one of the clauses herein, further comprising an elution subsystem positioned to receive an acid-washed resin and an elution solution, the elution solution comprising a concentration of sulfuric acid within a range of 0.5-1.5 Mol/L.