METHOD FOR RECOVERING PRECIOUS METALS FROM THIOSULFATE LEACH SOLUTIONS

Abstract

The present disclosure is directed to a process for thiosulfate leaching of a precious metal-containing material and recovering a precious metal from a pregnant leach solution using a resin extractant. The precious metal is eluted from the loaded resin optionally using an eluant comprising trithionate. Various process improvements include maintaining the thiosulfate-containing leach solution substantially free of thiols and amines, maintaining a concentration of a sulfide in the thiosulfate leach solution of no more than about 100 ppm, recycling the barren resin free of contact with a sulfide, bisulfide, and polysulfide, and/or maintaining a concentration of tetrathionates, trithionates, sulfur-oxygen anions, and/or combinations thereof within about 50% of a concentration level of the one or more of tetrathionates, trithionates, sulfur-oxygen anions, the combinations thereof in the precious metal-containing solution before contact with the recycled barren resin.

Claims

1. A method, comprising: leaching a precious metal-containing material with a thiosulfate-containing leach solution to form a precious metal-containing solution, wherein the thiosulfate-containing leach solution is substantially free of thiols and amines; loading a precious metal dissolved in the precious metal-containing solution onto a barren resin to form a precious metal-loaded resin and a precious metal barren solution; contacting the precious metal-loaded resin with a precious metal eluant to form a precious metal-rich eluant and the barren resin; and recovering the precious metal from the precious metal-rich eluant.

2. The method of claim 1, wherein the precious metal eluant comprises trithionate and a sulfite ion, and further comprising: contacting thiosulfate with an oxidant to convert at least a portion of the thiosulfate into a trithionate, wherein a sulfite ion concentration in the precious metal eluant is at least about 0.01 M, wherein a pH of the precious metal eluant is maintained within a range of from about pH 4.5 to about pH 14, and wherein a trithionate concentration in the precious metal eluant is at least about 0.01 M.

3. The method of claim 1, wherein the thiosulfate-containing leach solution comprises no more than about 180 ppb amines and thiols, collectively and wherein the thiosulfate-containing leach solution is substantially free of liquid and/or dissolved solids from a reclaim tank receiving at least a portion of the thiosulfate-containing solution after the leaching step.

4. The method of claim 1, wherein the thiosulfate-containing leach solution is substantially free of liquid and/or dissolved solids from a tailings storage facility storing previously leached precious metal-containing material.

5. The method of claim 1, wherein the barren resin is substantially free of sulfide ion, wherein the barren resin is recycled to the loading step, and wherein the recycled barren resin in the loading step comprises at least about 0.1 mole/L of tetrathionate.

6. The method of claim 1, wherein the precious metal-containing solution further comprises copper, wherein copper is loaded with the precious metal onto the precious metal-loaded resin, and wherein at least about 5 mole % of the Group 11 (IUPAC) metals loaded onto the resin comprises copper and more than about 50 mole % of the Group 11 metals loaded onto the resin comprise gold.

7. The method of claim 1, wherein the barren resin is recycled to the loading step and wherein a concentration of one or more of tetrathionates, trithionates, sulfur-oxygen anions, the combinations thereof is maintained within about 50% of a concentration level of the one or more of tetrathionates, trithionates, sulfur-oxygen anions, the combinations thereof in the precious metal-containing solution before contact with the recycled barren resin.

8. The method of claim 7, wherein, for a selected volume of barren resin, a number of loading and elution cycles within a 24-hour period is from about 1 to about 5.

9. The method of claim 6, wherein in the contacting of the precious metal-loaded resin with the precious metal eluant the precious metal-loaded resin is free of copper elution.

10. The method of claim 1, wherein in the leaching step the thiosulfate-containing leach solution is free of added copper and comprises no more than about 10,000 ppm thiosulfate.

11. A method, comprising: (a) contacting a precious metal-containing thiosulfate leach solution with a barren ion exchange resin to form a precious metal-loaded resin and a precious metal barren thiosulfate leach solution, wherein a concentration of one or more of an amine and thiol in the precious metal-containing thiosulfate leach solution is no more than about 100 ppm; (b) contacting the precious metal-loaded resin with a precious metal-barren eluant to form a precious metal-rich eluant and a barren resin; and (c) recovering the precious metal from the precious metal-rich eluant to form the precious metal-barren eluant for recycle to step (b).

12. The method of claim 11, wherein the concentration of one or more of an amine and thiol in the precious metal-containing thiosulfate leach solution is no more than about 180 ppb, wherein the precious metal-barren eluant comprises a trithionate, wherein the precious metal comprises gold, wherein the precious metal-barren eluant further comprises a sulfite ion, wherein a sulfite ion concentration in the precious metal-barren eluant is at least about 0.01 M, wherein a pH of the precious metal-barren eluant is maintained within a range of from about pH 4.5 to about pH 14, and wherein a trithionate concentration in the precious metal-barren eluant is at least about 0.01 M.

13. The method of claim 11, wherein the concentration of one or more of an amine and thiol in the precious metal-containing thiosulfate leach solution is no more than about 100 ppb and wherein the precious metal-containing thiosulfate is free of liquid or solid recycled from tails generated in step (a).

14. The method of claim 13, wherein the method is free of gypsum precipitation from the tails.

15. The method of claim 11, wherein a concentration of one or more of an amine and thiol in the precious metal-containing thiosulfate leach solution is no more than about 50 ppb and wherein the barren resin is recycled to step (a) free of contact with a sulfide, bisulfide, and polysulfide.

16. The method of claim 11, wherein a concentration of thiosulfide in the precious metal-containing thiosulfate leach solution is no more than about 10,000 ppm, wherein the precious metal comprises gold, wherein the precious metal-containing thiosulfate leach solution is derived from thiosulfate leaching of a precious metal-containing feed material, wherein the precious metal-containing feed material comprises at least about 0.5 wt. % preg-robbing carbonaceous materials and wherein the precious metal-containing feed material comprises at least about 0.01 oz/ton gold.

17. The method of claim 11, wherein a concentration of one or more of an amine and thiol in the precious metal-containing thiosulfate leach solution is no more than about 10 ppb and wherein the precious metal-containing thiosulfate leach solution is substantially free of added copper.

18. A method, comprising: (a) contacting a precious metal-containing thiosulfate leach solution with a barren ion exchange resin to form a precious metal-loaded resin and a precious metal barren thiosulfate leach solution, wherein a concentration of a sulfide in the precious metal-containing thiosulfate leach solution is no more than about 100 ppm; (b) contacting the precious metal-loaded resin with a precious metal-barren eluant to form a precious metal-rich eluant and a barren resin; and (c) recovering the precious metal from the precious metal-rich eluant to form the precious metal-barren eluant for recycle to step (b).

19. The method of claim 18, wherein the barren resin is recycled to step (a) free of contact with a sulfide, bisulfide, and polysulfide.

20. The method of claim 18, wherein a concentration of thiosulfide in the precious metal-containing thiosulfate leach solution is no more than about 10,000 ppm, wherein the precious metal-containing thiosulfate leach solution is substantially free of added copper, wherein the precious metal comprises gold, wherein the precious metal-containing thiosulfate leach solution is derived from thiosulfate leaching of a precious metal-containing feed material, wherein the precious metal-containing feed material comprises at least about 0.5 wt. % pre-robbing carbonaceous materials and wherein the precious metal-containing feed material comprises no more than about 0.35 oz/ton gold.

21. The method of claim 18, wherein the precious metal-loaded resin in step (b) is free of prior elution of copper collected on the resin surface.

22. The method of claim 18, wherein the precious metal-loaded resin in step (b) is free of prior elution of copper collected on the resin surface.

23. A method, comprising: leaching a precious metal-containing material with a thiosulfate-containing leach solution to form a precious metal-containing solution; loading a precious metal dissolved in the precious metal-containing solution onto a barren resin to form a precious metal-loaded resin and a precious metal barren solution, wherein the precious metal-containing solution further comprises copper and wherein copper is loaded with the precious metal onto the precious metal-loaded resin; contacting the precious metal-loaded resin with a precious metal eluant to form a precious metal-rich eluant and the barren resin, wherein at least about 5 mole % of the Group 11 (IUPAC) metals loaded onto the precious metal-loaded resin immediately before the contacting step comprises copper and more than about 50 mole % of the Group 11 metals loaded onto the resin comprise gold; and recovering the precious metal from the precious metal eluant.

24. The method of claim 23, wherein the barren resin is recycled to the loading step and wherein the barren resin is recycled free of contact with a sulfide, bisulfide, and polysulfide.

25. A method, comprising: leaching a precious metal-containing material with a thiosulfate-containing leach solution to form a precious metal-containing solution; loading a precious metal dissolved in the precious metal-containing solution onto a barren resin to form a precious metal-loaded resin and a precious metal barren solution; contacting the precious metal-loaded resin with a precious metal eluant to form a precious metal-rich eluant and the barren resin; and recovering the precious metal from the precious metal eluant, wherein the barren resin is recycled to the loading step and wherein a concentration in the precious metal-containing solution of one or more of tetrathionates, trithionates, sulfur-oxygen anions, and combinations thereof after contact of the recycled barren resin is maintained within about 50% of a concentration in the precious metal-containing solution of the one or more of tetrathionates, trithionates, sulfur-oxygen anions, and combinations thereof before contact with the recycled barren resin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings are incorporated into and form a part of the specification to illustrate several examples of the present disclosure. These drawings, together with the description, explain the principles of the disclosure. The drawings simply illustrate preferred and alternative examples of how the disclosure can be made and used and are not to be construed as limiting the disclosure to only the illustrated and described examples. Further features and advantages will become apparent from the following, more detailed, description of the various aspects, embodiments, and configurations of the disclosure, as illustrated by the drawings referenced below.

[0055] FIG. 1 is a schematic diagram of a thiosulfate resin-in-pulp process;

[0056] FIG. 2 plots solids grade (opt) (vertical axis) against date (horizontal axis) for an experiment using 1B alkaline solids;

[0057] FIG. 3 plots solids grade (opt) (vertical axis) against date (horizontal axis) for an experiment using 1B acid solids;

[0058] FIG. 4 plots solids grade (opt) (vertical axis) against date (horizontal axis) for an experiment using 0A acid solids;

[0059] FIG. 5 is a bar graph of tails grade (opt) (vertical axis) against batch tails, plant tails, and lab tails (horizontal axis) comparing batch, plant and lab tails;

[0060] FIG. 6 tri/tetrathionates on resin (%) (vertical axis) against date (horizontal axis) for an experiment using 1B resin;

[0061] FIG. 7 tri/tetrathionates on resin (%) (vertical axis) against date (horizontal axis) for an experiment using 0A resin;

[0062] FIG. 8 tri/tetrathionates on resin (%) (vertical axis) against date (horizontal axis) for an experiment using 0A resin;

[0063] FIG. 9 is a copper pre-elution curve demonstrating pre-elution of copper from an anion exchange resin by 0.5 M sodium thiosulfate with and without hydrogen peroxide addition; and

[0064] FIG. 10 is an elution curve demonstrating elution of gold from an anion exchange resin by 0.2M trithionate in admixture with 0.2 M sodium sulfite following copper pre-elution by 0.5 M sodium thiosulfate with and without hydrogen peroxide addition.

DETAILED DESCRIPTION

[0065] The present disclosure is directed to thiosulfate leaching of precious metal-containing materials. The materials can be any refractory or double refractory preg-robbing precious metal-containing material. The precious metal-containing material includes ore, concentrates, tailings, recycled industrial matter, spoil, or waste and mixtures thereof. The process of this disclosure is particularly effective for recovering precious metals, particularly gold, from refractory carbonaceous material. The refractory or double refractory alkaline or acidic (e.g., sulfidic) precious metal (e.g., gold and/or silver)-containing material is typically subjected to pressure oxidation, such as in an autoclave, to form an oxidized output slurry, that includes a precious metal-containing residue. Thiosulfate has also been shown to be effective in recovering precious metals from such pretreated refractory preg-robbing carbonaceous ores and sulfidic ores. As used herein, preg-robbing is any material that interacts with (e.g., adsorbs or binds) precious metals after dissolution by a lixiviant, thereby interfering with precious metal extraction, and carbonaceous material is any material that includes one or more carbon-containing compounds, such as humic acid, graphite, bitumens and asphaltic compounds. The precious metal(s) can be associated with nonprecious metals, such as base metals, e.g., copper, nickel, and cobalt.

[0066] In one application, the feed includes at least about 0.5 wt. %, more typically at least about 1 wt. %, and more typically at least about 1.5 wt. % but typically no more than about 7.5 wt. % and more typically no more than about 5 wt. % total carbonaceous material.

[0067] In one application, the gold content of the feed is at least about 0.01 oz/ton gold and more typically at least about 0.05 oz/ton.

[0068] In a preferred embodiment of the disclosure, gold and other precious and metals in a feed are recovered into solution at a metal recovery plant by a thiosulfate leaching process 100 followed by ion exchange to recover gold thiosulfate complex present in pregnant leach liquor, or precious metal-containing solution, from the leach step via a resin-in-pulp (RIP) or resin-in-leach (RIL) process, as shown schematically in FIG. 1. Leaching 100 is normally performed by heap or tank leaching techniques. The tails 112 are sent to a tails tank 116, then optionally to a tail thickener 120, and then to a tailing storage facility 124.

[0069] In one leach circuit configuration, the gold-containing solution in the leach step 100 includes thiosulfate as a leaching agent. The thiosulfate concentration in the solution commonly ranges from about 0.005 to about 5 M, more commonly from about 0.01 to about 2.5 M, and more commonly from about 0.02 to about 2 M. In some applications, it has been discovered that relatively low thiosulfate concentration levels can be employed in the lixiviant without compromising gold recovery. The thiosulfate concentration in the lixiviant commonly is no more than about 10,000 ppm, more commonly no more than about 8,500 ppm, more commonly no more than about 7,500 ppm, more commonly less than about 5,000 ppm, more commonly no more than about 3,500 ppm, and even more commonly no more than about 2,500 ppm.

[0070] As will be appreciated, in thiosulfate-based gold leaching systems copper is believed to catalytically oxidize gold. In many applications, the gold-containing solution in the leach step 100 is maintained at a leach copper solution concentration in the range of from about 0.1 to about 100 ppm, more commonly in the range of about 0.1 to about 50 ppm, more commonly in the range of about 0.1 to about 25 ppm, more commonly in the range of about 0.1 to about 15 ppm, and more commonly in the range of about 0.1 to about 5 ppm. In some applications, it has been discovered that copper does not need to be added in the leach step 100 and therefore that the leach step 100 can be substantially, or completely, free of added copper. The copper present in the feed is typically at a high enough level to enable high gold recovery while maintaining thiosulfate conversion to polythionates to acceptable levels.

[0071] In many applications, the gold-containing solution, or lixiviant, in the leach step 100 is maintained at a leach copper solution concentration commonly of no more than about 100 ppm, more commonly of no more than about 75 ppm, more commonly of no more than about 50 ppm, and more commonly no more than about 25 ppm and commonly at least about 0.1 ppm and more commonly at least about 5 ppm and has a gold solution concentration commonly of no more than about 0.010 ounces/tonne (opt), more commonly of no more than about 0.0075 opt, more commonly of no more than about 0.0050 opt, more commonly of no more than about 0.0025 opt, and more commonly of no more than about 0.001 opt.

[0072] In the ion exchange step (which is typically performed in the leach step 100), a strong base anion exchange resin 104 is used to adsorb the gold thiosulfate complex from the gold-containing solution to form a gold-loaded resin 108. There are a number of commercially available strong base ion exchange resins which have an affinity to gold and which are useful for the ion exchange process. The functional group of most strong base resins is quaternary ammonium, R4N+. Such a resin may be in sulfate or chloride form. Any other anion exchange resin may, however, be used. The typical capacity of the strong base resins is from about 1 to about 1.3 eq/L, and, for the purposes of demonstrating some aspects of the process, the discussion below is based on a resin having a capacity of about 1.2 eq/L. A typical concentration of resin ranges from about 5 to about 250 ml/L, more typically from about 10 to about 150 ml/L, and more typically from about 15 to about 100 ml/L, and even more typically from about 15 to about 75 ml/L. As will be appreciated, such resins can load not only gold but also copper from the pregnant leach liquor. Typically, at least about 2.5 mole %, more typically at least about 5 mole %, more typically at least about 10 mole %, and even more from about 15 to about 45 mole % of the Group IB (CAS) (or Group 11 (IUPAC)) metals of the Periodic Table of the Elements loaded onto the loaded resin is copper, with the remainder being primarily gold, though a small amount can be silver.

[0073] Following loading or adsorption of the thiosulfate complex onto the resin 104, the gold is recovered from the loaded resin 108 by elution; that is, desorption. A simplified elution flowsheet is shown in FIG. 1. In this flowsheet, any washing or draining stages have been omitted for simplicity, as they do not materially change the nature of the elution system.

[0074] The optional first stage is copper pre-elution (step 128 of FIG. 1), which is conducted using a copper eluant solution 133 containing thiosulfate and, optionally, trithionate to precondition the resin 140 (FIG. 1) for precious metal elution. The main purpose of this stage is to strip the copper from the resin before elution, and hence reduce the quantity of copper that reports to the gold product. Surprisingly and unexpectedly, copper pre-elution is optional in many applications and not required to obtain acceptable levels of gold recovery. In other process configurations, it may be performed to avoid complications posed by the presence of copper in the recovered gold product.

[0075] When copper elution is performed, the thiosulfate in the copper eluant solution can be any source of thiosulfate, such as an alkali metal thiosulfate (e.g., sodium or potassium thiosulfate), an alkaline earth metal thiosulfate (e.g., calcium thiosulfate), or ammonium thiosulfate. The latter is not preferred, unless the leaching circuit also utilizes ammonium thiosulfate. The thiosulfate concentration in the pre-elution copper eluant and product 15 typically ranges from about 30 to about 200 g/L, and the desorbed copper concentration in the copper-rich eluant ranges from about 100 to about 1,500 ppm.

[0076] When present, the concentration of trithionate in the copper eluant solution 133 typically ranges from about 0.01 to about 0.1 M. The trithionate may be generated by contacting an oxidant, commonly a peroxide, with the copper eluant solution 133, which converts thiosulfate into trithionate per equation (2) below. The copper pre-elution product 136 can be used as a thiosulfate feed stream for leaching, and hence can be recycled. In one process configuration, the barren electrowinning solution 300 is contacted with the resin 140 to elute thiosulfate, which can then be recycled to the leach step 100.

[0077] As noted, in some process configurations copper pre-elution is not performed. It has been discovered that copper collected on the surface of the gold-rich resin does not need to be removed in a copper elution step 128 prior to gold elution. In other words, the copper can be present on the gold-rich resin surface at levels in excess of those following the copper elution step 128. In such applications, typically, at least about 2.5 mole %, more typically at least about 5 mole %, more typically at least about 10 mole %, and even more from about 15 to about 45 mole % of the Group IB (CAS) (or Group 11 (IUPAC)) metals of the Periodic Table of the Elements loaded onto the loaded resin is copper, with the remainder (typically more than about 50 mole % and more typically at least about 60 mole %) being gold, though a small amount (e.g., typically less than about 25 mole %) can be silver.

[0078] Precious metal elution is then conducted from the resin 144 using a mixture of trithionate and sulfite ion as an eluant 148. Commonly, a concentration of trithionate in the precious metal eluant 148 is at least about 0.01 M, more commonly is at least about 0.05 M, more commonly ranges from about 0.1 to about 5 M, and even more commonly ranges from about 0.2 to about 2 M. The concentration of sulfite ion in the precious metal eluant 148 commonly is at least about 0.01 M, more commonly is at least about 0.1 M, and even more commonly ranges from about 0.1 to about 2 M. The concentration of dissolved gold in the gold-rich eluant 152 typically ranges from about 100 to about 500 ppm. The pH of the precious metal eluant 148 is typically maintained within a range of from about pH 4.5 to about pH 14.

[0079] This elution mixture is generated by mixing peroxide in a trithionate reactor with the sodium thiosulfate, as per reaction 2.

2Na.sub.2S.sub.2O.sub.3+4H.sub.2O.sub.2.fwdarw.Na.sub.2S.sub.3O.sub.6+Na.sub.2SO.sub.4+4H.sub.2O(2)

[0080] This reaction also generates heat, and therefore the preferred embodiment of the flowsheet utilizes either a cooled or chilled reactor to remove heat. The reaction temperature is preferably in the range of about 10 C. to about 60 C. At higher reaction temperatures, some loss of trithionate becomes evident. The addition of peroxide is commonly between about 75% and about 110%, and more commonly between about 75% and about 97%, of the stoichiometric amount to react with the thiosulfate contained in the spent regeneration solution 156 (reaction 2).

[0081] One method of generating additional trithionate is to add extra thiosulfate to the trithionate synthesis stage. When running an ammonium thiosulfate-based leach system, the addition of ammonium thiosulfate to trithionate synthesis is ideal. However, if the generation of ammonium sulfate in the process is not desired, another approach is required. Sodium thiosulfate can be used, but it is an expensive reagent. Alternatively, sodium thiosulfate can be generated from the cheaper calcium thiosulfate feed material by precipitation of calcium. The precipitation of calcium can be conducted using a source of either sodium sulfate and/or sodium carbonate.

[0082] After elution, the resin 104 is almost completely loaded with trithionate, Based on the prior art, a skilled artisan would understand trithionate to reduce the equilibrium gold loading in the adsorption circuit, and therefore recycle of a resin without the regeneration (and hence fully loaded with trithionate) would be problematic. Surprisingly and unexpectedly, it has been discovered that resin regeneration can be omitted without compromising gold recovery so that the trithionate-loaded resin can be returned to the leach step 100. The chemical equilibria in the leach and gold elution steps enables the resin to load gold in preference to trithionate in the leach step 100 and (unload gold and) load trithionate in preference to gold in the gold elution step. While the leaching and gold eluting steps commonly have similar pH levels, the equilibria are understood to be driven by concentration of trithionate. At higher trithionate levels (e.g., at least about 25,000 ppm and more commonly at least about 50,000 ppm trithionate) in the gold elution step, the resin loads trithionate in preference to dissolved gold and at the lower trithionate levels (no more than about 5,000 ppm, more commonly no more than about 2,500 ppm, more commonly no more than about 1,000 ppm, and more commonly no more than about 500 ppm trithionate) in the leaching step 100, the resin loads dissolved gold in preference to trithionate.

[0083] The amount of trithionate loaded onto the barren resin can vary depending on the application. For a resin capacity of 1.2 eq/L, the maximum loading of trithionate, which is a 2-charge, is 0.6 mole/L of resin. The resin, is typically, close to being saturated with trithionate after elution, a condition which is commonly required to ensure optimal gold elution; that is, a loading of 0.6 moles of trithionate per L of resin is required in such applications. In most applications, the barren resin, after elution, comprises typically at least about 0.1 mole/L of trithionate, more typically at least about 0.25 mole/L of trithionate, and even more typically from about 0.3 to about 0.6 mole/L of trithionate.

[0084] While not wishing to be bound by any theory, it is believed that gold recovery in the leach step 100 is decreased by sulfide ion carried by resin beads 104 that are recirculated to the leach step 100. The recirculated sulfide ion can cause dissolved gold to precipitate as gold sulfide during the leach step 100, thereby preventing it from loading onto the resin surface. To avoid this detrimental outcome, the recirculated resin 104 and thiosulfate lixiviant in the leach step 100 commonly have no more than about 100 ppm, more commonly no more than about 75 ppm, more commonly no more than about 50 ppm, more commonly no more than about 25 ppm, more commonly no more than about 10 ppm, more commonly no more than about 5 ppm, more commonly no more than about 1 ppm, more commonly no more than about 25 ppb, more commonly no more than about 10 ppb, more commonly no more than about 5 ppb, more commonly no more than about 1 ppb, and even more commonly is free of sulfide ion.

[0085] It has further been discovered that the number of elution and regeneration cycles completed is often related inversely to gold recovery and that the gold recovery is inversely proportional to the gold content of the feed. While not wishing to be bound by any theory, these effects result from the need to reduce as much as possible the frequency of resin bead recycle to the leach step 100 from the gold elution step. This is so because it is believed that maintaining optimal gold recovery requires the maintenance of a constant thermodynamic state or environment in the leach step 100. Recycling resin beads to the leach step 100 can disrupt, or change, the thermodynamic state, thereby decreasing gold recovery due to the presence in the leach step of deleterious chemical species that are absorbed by strong-base resins (such as tetrathionate, trithionate, sulfur-oxygen anions, and metal (e.g., lead, copper, and zinc) thiosulfate complexes) generated in or otherwise recirculated from the gold elution step. These species can compete with gold for absorption sites on the resin. The number of elution cycles within a 24-hour period typically ranges from about 1 to 5, with the fewer elution cycles being preferred. This can maintain the levels of the deleterious chemical species at levels low enough that they do not compete strongly with gold for absorption sites on the resin. Stated differently, the concentration levels of each of the deleterious chemical species in the leach step 100 are typically maintained within about 50%, more typically within about 25%, more typically within about 20%, more typically within about 15%, more typically within about 10%, and even more typically within about 5% of the concentration level present before contact of the recycled resin with the leach solution. Maintaining a substantially constant thermodynamic state in the leach step can enable the process to a lower residence time of the feed in the leach step without compromising gold recovery. Typically, the residence time of the feed in the leach step is no more than about 15 hours and more typically no more than about 10 hours.

[0086] The gold can be recovered from the trithionate product solution 152 by a number of technologies, including but not limited to, electrowinning 168, cementation by metals such as copper and zinc, and precipitation by sulfide-containing solutions. Each one of these technologies has been demonstrated to successfully recover the gold to very low concentrations (>99% removal of gold). In the preferred embodiment, standard gold electrowinning cells 168 are adopted, and the integrated elution/electrowinning flowsheet is shown in FIG. 3. The barren electrowinning solution 300 can be recycled back to the trithionate synthesis step 164 and/or after optional copper preelution. By adding the barren electrowinning solution 300 to the trithionate synthesis, some additional thiosulfate that is stripped off the resin during gold elution is recycled. Alternatively, when adding the barren electrowinning solution 300 as a step after pre-elution, the sulfite present in this stream reacts with any adsorbed tetrathionate on the resin, which is an effective conditioning step to ensure optimum gold elution performance. The same benefit is achieved when recycling the barren electrowinning solution either before the copper pre-elution, or by mixing the barren electrowinning with the copper pre-eluant. For all these options, trithionate is recycled back to the elution system, and to maintain the water balance, there is an additional volume of copper pre-eluate, which mainly contains copper, sulfate and thiosulfate, since this product is taken before trithionate and gold break through, as discussed below.

[0087] A similar principle applies for the recovery of gold using cementation of precipitation, whereby the barren solution is recycled back to the elution system to recover trithionate.

[0088] As can be seen from FIG. 1, the supernatant of the tailings storage facility 124 is not recycled to the reclaim tank 182 (as shown in FIG. 1) as it has been surprisingly and unexpectedly discovered that treatment of the supernatant, such as by reverse osmosis 172, and/or reuse of the resulting permeate or liquid from the reclaim tank 182 can negatively impact gold recovery. Stated differently, the reclaim tank is at least substantially free (e.g., typically containing no more than about 10 vol. % and more typically containing no more than about 5 vol. % supernatant from the tailings storage facility 124,

[0089] Additionally neither the permeate nor concentrate of reverse osmosis 172 is recirculated for use in generating the thiosulfate lixiviant 176. It has been discovered that recirculating one or both of these streams can reduce gold recovery in the leach step 100. While not wishing to be bound by any theory, it is believed that thiols and/or amines in the recycled stream(s) act as gold chelators or otherwise sequester dissolved gold, thereby preventing the dissolved gold from being collected by the resin beads (particularly when the resin beads comprise a quaternary ammonium). For this reason, the thiosulfate-containing stream 180 is typically substantially free e.g., typically containing no more than about 10 vol. % and even more typically no more than about 5 vol. %), or completely free, of liquid and/or dissolved solids from the reclaim tank 182.

[0090] To realize higher gold recoveries, the thiosulfate lixiviant 176 in the leach step 100 has commonly no more than about 100 ppm, more commonly no more than about 180 ppb, more commonly no more than about 100 ppb, more commonly no more than about 75 ppb, more commonly no more than about 50 ppb, more commonly no more than about 25 ppb, more commonly no more than about 10 ppb, more commonly no more than about 5 ppb, more commonly no more than about 1 ppb, and even more commonly is free of amines (e.g., a compound or functional group that contains a basic nitrogen atom with a lone pair; amines are typically derivates of ammonia in which one or hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group) and/or thiols (e.g., an organic compound containing the group SH, i.e. a sulfur-containing analog of an alcohol).

[0091] Because no liquid or solid component of the concentrate and optionally the permeate is recirculated to thiosulfate lixiviant generation or present in the leach step 100, there is no need to precipitate gypsum and gypsum precipitation is not performed. Stated differently, the thiosulfate lixiviant used in the leach step 100 is free of liquid and solid components of the concentrate 174.

EXPERIMENTAL

[0092] The following examples are provided to illustrate certain aspects, embodiments, and configurations of the disclosure and are not to be construed as limitations on the disclosure, as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.

Example 1

[0093] There has been a 10-20% gap between plant and lab recoveries based on the process of U.S. Pat. No. 9,051,625. To understand the cause(s) of the gap, multiple batch leach tests were conducted using resin-in-leach as taught by U.S. Pat. No. 9,051,625. Test parameters are outlined in the table below. Copper was added for all tests at a concentration of 20 ppm. Resin addition was approximately 30 m.sup.3.

TABLE-US-00001 Test # Date Tank Ore Dilution Resin 1 11/29-12/9 1B Alk Permeate Barren/Fresh 2 12/15-12/28 1B Acid TS Discharge Barren 3 12/16-12/29 0A Acid Permeate Barren

[0094] The daily solids and solution leach profile for each test are shown in the Figures. Across all three tests, leach kinetics seemed to be hindered and required upwards of a week before the solids profile leveled out. It should be noted that tank temperatures dropped at a rate of 5 F./day due to cooling of the tanks. Additionally, solution samples indicate the absence of copper in solution despite adding in sufficient copper to reach 20 ppm. In the 1B alkaline test, an additional 80 ppm of copper was added, however, copper was still not detected in solution.

[0095] The test results are shown in FIGS. 2-4. With reference to FIG. 2, soluble gold in the 1B alkaline test remained low (<0.002 opt) which may be explained by the utilization of a half barren and half fresh resin mix. With reference to FIGS. 3-4, solution gold in the other two tests remained low initially in the test, but climbed when the solids started to leach substantially. Solution gold remained at 0.0008 opt until the end of the test which aligns HARIL data using barren resin.

[0096] For consideration and with reference to FIG. 5, the batch leach recoveries were compared to the respective plant and lab recoveries as shown below. In all tests, the batch leach outperformed the plant significantly, however, a 5-10% recovery gap still exists compared to the lab. It should be noted that fresh resin was used in the lab test work. Nonetheless, the batch data bridges a large portion of the gap between plant and lab data.

[0097] Surprisingly, polythionate (e.g., trithionates and tetrathionates) remained relatively stable during the duration of the tests as seen in FIGS. 6-8. Polythionate concentrates on resin and in solution remained largely unchanged which contrasts past data where polythionate generation was uncontrollable once a tank was taken offline. However, it is not certain whether the lack of solubilized copper contributed to the stability of polythionates. It is surmised that the low polythionate concentrations contributed to low solution gold losses.

[0098] There were additional interesting observations from the batch tests. The first is that there was 7% recovery difference between the 0A and 1B acid leach test where the only difference in operating parameter was that permeate was used for 0A dilution while thiosulfate discharge and regenerated thiosulfate was used for 1B dilution. This suggests that thiosulfate discharge and/or regenerated thiosulfate may have an adverse effect on recovery.

[0099] Secondly, the batch leach test for 0A acid was tested at 400 ppm thiosulfate. Small amounts of thiosulfate discharge and/or regenerated thiosulfate was inadvertently introduced to 0A. Calcium thiosulfate was not added to 0A due to plugged lines. With a recovery of 67.4% achieved, this indicates low thiosulfate concentrations still allow for sufficient leaching. Additionally, polythionate stability remained largely unaffected at this lower concentration.

Example 2

[0100] An alternative method for generating additional trithionate is to make use of some of the thiosulfate in the optional copper pre-elution feed. By adding peroxide to this stream, a larger volume (for instance 5BV) of lower concentration trithionate can be generated. This is advantageous, since the heat of reaction is taken up by the large solution volume, and, hence, an additional cooling system or cooling capacity is not necessary.

[0101] FIG. 9 shows the profile for copper pre-elution for a 0.5 M sodium thiosulfate solution, compared to a solution for which sodium thiosulfate and peroxide were mixed to give a composition of 0.5 M sodium thiosulfate+0.05 M sodium trithionate, as per reaction 2. The presence of trithionate in the thiosulfate pre-eluant results in a higher quantity of copper being stripped from the resin during 30 copper pre-elution. This is beneficial to the gold elution process, as increasing the stripping of copper during pre-elution results in less copper in the final gold product. Another significant advantage of adding peroxide to the copper pre-elution stream is an improvement in the gold elution performance in terms of required breakthrough volume. FIG. 10 shows the gold elution profiles obtained for a mixture of 0.2 M trithionate+0.2 M sulfite. The resin which had been pre-eluted in the presence of the trithionate undergoes elution earlier than the other sample resin, with the gold elution peak being after 1.3 bed volumes of solution, compared to 2.6 bed volumes, respectively. In addition, the peak gold concentration is higher for the resin which had been pre-eluted in the presence of trithionate. This is also advantageous, as more concentrated gold electrowinning product may be generated. For the data in FIGS. 9 and 10, the resin had the same loading of all species, including copper and gold.

[0102] Without wishing to be bound by theory, it appears that the role of peroxide addition to the copper pre-elution is to generate a low concentration of trithionate, which does not strip the gold during the copper pre-elution stage, but conditions the resin by adsorbing trithionate prior to the gold elution stage. This results in a significantly better performance during the elution step. Preferably, the addition of peroxide to the copper pre-elution should be between about 0.1 and 2.0 moles of hydrogen peroxide per L of resin to be eluted to produce a concentration of trithionate in pre-elution ranging from about 0.025 to about 0.5 moles/L resin. For the data in FIG. 9, 5 BV of solution containing 0.05 M trithionate was utilized, for which the peroxide addition was 1 mole per L of resin, and the quantity of trithionate was 0.25 moles per L of resin. Tests were also conducted with 5 BV of copper pre-eluant containing 0.025 M trithionate (i.e. 0.5 moles of peroxide per L of resin), and good results were also obtained. It should be apparent that, when the loaded resin contains a higher concentration of polythionates, less conditioning, i.e., 0.1 moles of peroxide per L of resin, may be preferred. However if the loaded resin contains a very low loading of polythionates, more conditioning may be required. Therefore, this is a robust process that can treat a wide range of resin feeds. Various sources of thiosulfate can be adopted for pre-elution, and since the product is recycled to leach, the thiosulfate salt needs to be compatible with the leach system. When adopting an ammonium thiosulfate leach, the preferred reagent for elution would be ammonium thiosulfate. However, for non-ammonium based leach systems, alternative reagents such as calcium thiosulfate can be adopted. However, as discussed above, a calcium removal step may be required. For instance, the system described in Example 2 can also be adopted here, whereby the reverse osmosis concentrate is combined with calcium thiosulfate, followed by gypsum removal. Ideally, the peroxide is added prior to gypsum removal, since reaction 2 generates sulfate.

[0103] A number of variations and modifications of the disclosure can be used. It would be possible to provide for some features of the disclosure without providing others.

[0104] The present disclosure, in various aspects, embodiments, and configurations, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various aspects, embodiments, configurations, subcombinations, and subsets thereof. Those of skill in the art will understand how to make and use the various aspects, aspects, embodiments, and configurations, after understanding the present disclosure. The present disclosure, in various aspects, embodiments, and configurations, includes providing devices and processes in the absence of items not depicted and/or described herein or in various aspects, embodiments, and configurations hereof, including in the absence of such items as may have been used in previous devices or processes, e.g., for improving performance, achieving ease and or reducing cost of implementation.

[0105] The foregoing discussion of the disclosure has been presented for purposes of illustration and description. The foregoing is not intended to limit the disclosure to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the disclosure are grouped together in one or more, aspects, embodiments, and configurations for the purpose of streamlining the disclosure. The features of the aspects, embodiments, and configurations of the disclosure may be combined in alternate aspects, embodiments, and configurations other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed aspects, embodiments, and configurations. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the disclosure.

[0106] Moreover, though the description of the disclosure has included description of one or more aspects, embodiments, or configurations and certain variations and modifications, other variations, combinations, and modifications are within the scope of the disclosure, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative aspects, embodiments, and configurations to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.