Metal recovery system and method

Abstract

A practical system and method for recovering a metal such as copper from a supply of metal sulfide are disclosed. In a first series of steps using a first circulation loop, a sodium hypochlorite solution is percolated through the supply whose pH is maintained to be greater than 4 to convert the sulfides therein to precipitated solids. The metal is then readily leached from these precipitated solids by percolating a leachant acid solution therethrough whose pH is maintained to be less than 2.5 after percolating in a second series of steps using a second circulation loop. The metal is then separated from the circulating leachant acid solution.

Description

[0001] METAL RECOVERY SYSTEM AND METHOD

[0002] Technical Field

[0003] The present invention pertains to improved methods and systems for recovery of metals from a supply comprising metal sulfides. In particular, it pertains to large scale methods and systems which involve the initial conversion of the sulfides to precipitates of metal oxides and / or hydroxides / basic complexes and then leaching the precipitates therefrom.

[0004] Background

[0005] Various important metals for industrial applications are obtained from primary sulfide minerals. For instance, the most abundant source of copper in nature is found in primary sulfides from which copper has typically been recovered therefrom using flotation and pyrometallurgical processes. Currently, global production of copper is about 20M tons / year and about 70% of global copper is from copper sulfide ores.

[0006] However, due to the depletion of high grade primary sulfide ores in recent years, the presence of toxic elements in concentrates such as arsenic (a carcinogen), and the increasing relevance of environmental, social and governance (ESG) regulation risk management, it is increasingly less feasible to treat primary sulfides using such processes. In their place, hydrometallurgical options (e.g. leaching) for processing primary sulfides have become more attractive because they represent more environmentally friendly processes. The most abundant copper containing primary sulfide is chalcopyrite but unfortunately it is also the most refractory (i.e. resistant) to conventional leaching processes at ambient conditions.

[0007] Numerous alternatives have therefore been used or have been proposed to address this difficulty. These include: pressure oxidation leaching (POX) which involves high pressure and temperature leaching of sulfides; bioleaching which uses bacteria to break down sulfide species, and various processes recently developed by industry.

[0008] One such process HydroCopper™ of METSO Corp, is disclosed in EP1834001 and relates to a method for the hydrometallurgical treatment of sulfide concentrate containing several valuable metals. This technology relates to a method, by means of which the valuable metals contained in a sulphidic, multicomponent concentrate are recovered using hydrometallurgical treatment. One constituent of the concentrate is copper sulphide, which is leached using an alkali chloride - copper (II) chloride solution. The sulphides of other valuable metals, such as zinc, nickel, cobalt and lead are leached before copper leaching and each is recovered as a separate product before copper recovery.

[0009] Another such process Hyperleach® of Metaleach is disclosed in WO2010135776 and relates to a method of oxidative leaching of sulfide ores and / or concentrates. This technology is for leaching one or more target

[0010] 1

[0011] #11273255.1 metals from a sulfide ore and / or concentrate containing such, the method comprising the steps of: (a) Exposing the ore and / or concentrate to an aqueous solution of chlorine -based oxidising species in which the hypochlorous acid comprises at least 10 mol% of the chlorine-based oxidising species; (b) Allowing and / or facilitating the oxidation of the target metals by the hypochlorous acid, thereby decreasing the pH such that the predominant chlorine-based oxidising species becomes chlorine; (c) Allowing and / or facilitating the oxidation of the target metals by the chlorine; (d) Allowing and / or facilitating the dissolution of the target metals by the solution species formed during the oxidation by hypochlorous acid and / or chlorine; and (e) Passing the pregnant solution produced thereby to a means for metal recovery.

[0012] Further examples of alternative processes include Galvanox™ of Incor Galvanox, the Intecprocess, the Albion Process ™ of Glencore technology, LixTRA™ of BASF, and the Jetti ™ technology of Jetti Resources.

[0013] A recent development in this regard is the broad process disclosed in WO2023 / 049967 of CSIRO which relates to a metal leaching process and apparatus. The technology here relates to a process for leaching metals from metal sulfide ore and / or concentrate, comprising: electrolytically generating a leach solution of oxidative halogen-based lixiviant; contacting the metal sulfide ore and / or concentrate with the leach solution of oxidative halogen-based lixiviant to produce a metal-bearing solution; and passing the metalbearing solution to metal separation. In the disclosed process, a distinction is made between the leach solution of the contacting step (i.e. the solution before contacting the ore and / or concentrate) and the metalbearing solution after leaching (i.e. the solution after contacting the ore and / or concentrate). Further an important distinction must be made between the pH ranges associated with these two solutions. The former may remain in a neutral or weakly acidic range which can be necessary or preferred depending on variability in the composition of ore bodies. The latter however must be in a pH range suitable for keeping the extracted metals in solution (i.e. acidic). In this regard, the disclosure was silent on a suitable upper range for the metal -bearing solution pH (although an exemplary value of at least 3 was mentioned). It should be noted that a metal-bearing solution with a pH of 4 or greater is unlikely to contain significant amount of copper.

[0014] Despite the numerous efforts in the field to date, there still remains a need for improved methods for recovering valuable metals such as copper from primary sulfide ores using hydrometallurgical techniques. In particular, copper demand continues to grow and so industry is targeting deposits with low copper concentrations (referred to as low copper grade) and is looking for ways to extract more at low cost from existing and / or old operations. The present invention addresses the need for improved recovery of copper and / or other transition metals from primary sulfide minerals, including those from low grade minerals, as well as providing other benefits as disclosed below.

[0015] 2

[0016] #11273255.1 Summary

[0017] Practical systems and methods for recovering metals such as copper from a supply comprising metal sulfides have been developed. The invention allows for a reasonably sized system to recover such metals using practical amounts of halogen containing solution in practical timeframes and thus represents an enabling improvement to the approaches and embodiments disclosed in the aforementioned WO2023 / 049967.

[0018] In the present invention, metal in a supply comprising metal sulfide is first reacted with an appropriate halogen containing solution provided by a suitable halogen generator. (Various generators can be considered in this regard. For instance, sodium hypochlorite solution can be provided using a modified sodium chlorate electrolyzer cellroom and / or a chloralkali-hypochlorite processor.) The halogen containing solution is circulated and percolated through the supply under appropriate pH conditions to convert the sulfides therein to precipitated solid oxides and solid hydroxide s / basic complexes. Because the converted sulfides remain as solids by way of this appropriate pH control, the circulating halogen containing solution remains essentially free of metal species. This allows for the partially depleted halogen containing solution to be regenerated in the generator / s employed without adversely affecting the operation thereof. Further, because the converted sulfides remain as solids, a strong acid leachant solution can be subsequently circulated and percolated therethrough to readily leach out the metal therefrom. And finally, the metal is separated from the circulating acid leachant solution using various conventional methods.

[0019] In a preferred embodiment, the halogen containing solution used is sodium hypochlorite and the circulating sodium hypochlorite solution is provided in part and regenerated using a suitable generator in the associated circulation loop. However, additional high strength sodium hypochlorite produced by a chloralkali- hypochlorite processor outside of, but connected to this circulation loop, is also added to the circulating sodium hypochlorite solution. This allows for higher concentrations of sodium hypochlorite solution to be obtained than could otherwise be generated by the typical inline generator.

[0020] The present invention thus provides for improved systems and methods for recovering metals from metal sulfides. A specific embodiment of the invention is a system for recovering copper from copper sulfide comprising: a holder for the copper sulfide and two closeable circulation loops. The first closeable circulation loop is for percolating a sodium hypochlorite solution through the copper sulfide, is connected to the holder, and comprises a sodium hypochlorite generator, an inlet for a makeup sodium chloride (NaCl) and water solution or an additional sodium hypochlorite solution, an inlet for a pH controlling reagent, and a means for measuring the pH of the circulating sodium hypochlorite solution at a first measuring point downstream of the supply and before the inlet for the pH controlling reagent. The second closeable circulation loop is for percolating a leachant acid solution through the copper sulfide, is also connected to the holder and comprises a metal separation unit for separating copper from the leachant acid solution, an

[0021] 3

[0022] #11273255.1 inlet for makeup leachant acid and water, and a means for measuring the pH of the circulating leachant acid solution at a second measuring point downstream of the supply and before the inlet for the makeup leachant acid and water. In this embodiment, the inlet for makeup NaCl and water and the inlet for the pH controlling reagent can be upstream of the sodium hypochlorite generator, while the inlet for makeup leachant acid and water can be downstream of the metal separation unit. While this specific embodiment is for recovering copper from copper sulfide using sodium hypochlorite solution in a first series of steps, the invention may also be considered for use in recovering other metals from other metal sulfides. Further, halogen containing solutions other than sodium hypochlorite solution may be considered for use in the first series of steps.

[0023] In an exemplary embodiment, the first and second measuring points can be the same and the means for measuring the pH of the circulating sodium hypochlorite solution and for measuring the circulating leachant acid solution can be the same. Further, the means for measuring the pH can comprise a pH meter or a sampling port for obtaining a sample for pH measurement at the measuring point.

[0024] In certain embodiments, the sodium hypochlorite generator in the system can be a modified sodium chlorate electrolyzer. Further, the system may additionally comprise a chloralkali-hypochlorite processor connected to the first closeable circulation loop, for instance downstream of the sodium hypochlorite generator. Further still, the system may additionally comprise an inlet for wash water connected to the holder for percolating water through the metal sulfide.

[0025] In an embodiment in which the supply comprising copper sulfide is in the form of an ore, the system can be configured in a manner similar to those used for conventional heap leaching. For instance, the holder can be a pad (e.g. impermeable pad) and the ore can be held in the form of a heap on the pad. Optionally, the system can additionally comprise an agglomerator upstream of the holder for agglomerating crushed metal sulfide ore. The invention may also however be considered for use to recover metals from supplies that are in other forms, for instance in the form of a concentrate. In such a case, the holder may instead be a vessel, and the concentrate is held in the vessel.

[0026] Any relevant conventional type of metal separation unit can be considered for use in the second closeable circulation loop. For instance, the metal separation unit can be selected from the group consisting of a solvent extraction unit plus an electrowinning unit, an ion exchange unit plus an electrowinning unit, and a precipitation unit. In the first of these options, the metal separation unit can comprise a solvent extraction unit comprising an inlet for pregnant leachant acid solution, an inlet for stripping solution, an outlet for a copper loaded electrolyte solution, and an outlet for raffinate while the electrowinning unit can comprise an inlet fluidly connected to the outlet for the copper loaded electrolyte solution from the solvent extraction unit.

[0027] 4

[0028] #11273255.1 Another specific embodiment of the invention is a method for recovering copper from a supply of copper sulfide comprising the steps of: obtaining the aforementioned system; providing a supply comprising copper sulfide to the holder; in a first series of steps, opening the first closeable circulation loop and circulating a sodium hypochlorite solution having a pH greater than 4 therethrough; percolating the sodium hypochlorite solution through the supply thereby converting the copper sulfide to precipitated solid copper oxide and solid copper hydroxide s / basic complexes; measuring the pH of the circulating sodium hypochlorite solution at the first measuring point; providing sufficient pH controlling reagent to the first closeable circulation loop at the pH controlling reagent inlet to maintain the pH of the circulating sodium hypochlorite solution at the first measuring point to be greater than 4; providing a makeup NaCl and water solution or an additional sodium hypochlorite solution to the first closeable circulation loop; producing sodium hypochlorite in the sodium hypochlorite generator; and closing the first closeable circulation loop according to a first predetermined criterion; and in a second series of steps, opening the second closeable circulation loop and circulating a leachant acid solution therethrough; percolating the acid leachant solution through the precipitated solid copper oxide and solid copper hydroxide s / basic complexes thereby leaching the copper from the precipitated solid copper oxide and solid copper hydroxide s / basic complexes and forming a pregnant leachant acid solution; separating the copper from the pregnant leachant acid solution; measuring the pH of the circulating leachant acid solution at the second measuring point; providing sufficient supply of makeup leachant acid and water to the second closeable circulation loop at the inlet for makeup leachant acid and water to maintain the pH of the circulating leachant acid solution at the second measuring point to be less than 2.5; and closing the second closeable circulation loop according to a second predetermined criterion.

[0029] In the aforementioned method, the supply comprising metal sulfide can be chalcopyrite. To effect the desired precipitation, the pH can preferably be controlled to maintain the pH of the circulating sodium hypochlorite solution at the first measuring point to be about 7.

[0030] 5

[0031] #11273255.1 A suitable pH controlling reagent for use in the inventive method is a solution of calcium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate or ammonium hydroxide although other reagents can also be contemplated (e.g. sodium carbonate solution).

[0032] In an exemplary embodiment, sufficient supply of makeup leachant acid and water can be provided to maintain the pH of the circulating leachant acid solution at the second measuring point to be less than 2. Further, a suitable acid leachant is sulfuric acid.

[0033] In an embodiment of the method, the first predetermined criterion used to determine when to close the first closeable circulation loop and hence cease circulation of the solution therein can for example either be after a specified amount of the copper sulfide in the supply has been converted to precipitated solid copper oxide and solid copper hydroxides / basic complexes or after a specified time. In a like manner, the second predetermined criterion used to determine when to close the second closeable circulation loop and hence cease circulation of the solution therein can for example either be after a specified amount of copper has been leached from the precipitated solid copper oxide and solid copper hydroxides / basic complexes or after a specified time.

[0034] In embodiments in which the method comprises adding additional sodium hypochlorite to the first closeable circulation loop, for instance downstream of the sodium hypochlorite generator, the additional sodium hypochlorite can be provided by a chloralkali-hypochlorite processor. Further, the method may comprise a suitable pre-treating step in which the pre-treating achieves the removal of elements upstream of and detrimental to the operation of any halogen generators employed in the method.

[0035] Brief Description of the Drawings

[0036] Figure l is a simple illustration of prior art system and method for recovering copper from a copper bearing ore comprising chalcopyrite.

[0037] Figure 2 shows a schematic of a preferred embodiment of the system of the invention with optional chloralkali-hypochlorite processor and agglomerator for providing additional sodium hypochlorite to the first closeable circulation loop and for agglomerating crushed metal sulfide ore respectively.

[0038] Figure 3 shows a simplified flowchart of a method of the invention for recovering copper from a supply of copper sulfide.

[0039] 6

[0040] #11273255.1 Detailed Description

[0041] Unless the context requires otherwise, throughout this specification and claims, the words "comprise", “comprising” and the like are to be construed in an open, inclusive sense. The words “a”, “an”, and the like are to be considered as meaning at least one and not limited to just one.

[0042] In a numerical context, the word “about” is to be construed as meaning plus or minus 10%.

[0043] Herein, a “sodium chlorate electrolyzer” is an industrial generator designed and configured to produce sodium chlorate commercially. A “modified sodium chlorate electrolyzer” is such a generator that has been modestly modified either in structure or operating conditions in a manner so as to produce a different chemical product commercially (e.g. sodium hypochlorite and as such is called a sodium hypochlorite generator).

[0044] A “chloralkali-hypochlorite processor” is an industrial processor for producing sodium hypochlorite via the electrolysis of sodium chloride solutions and / or the reaction of caustic and chlorine.

[0045] “Ore” has the plain meaning of “a naturally occurring mineral containing a valuable constituent (such as metal) for which it is mined and worked.” (Merriam-Webster)

[0046] A “hydrometallurgical” process refers to various industrial processes involving chemical processing with aqueous and / or organic solutions. Hydrometallurgical processing involves the selective transfer of species in liquid / solid and liquid / liquid systems. In some circumstances gaseous reactants or products may also be present in the systems. “Leaching” is an example of a hydrometallurgical process in which a desired metal is extracted from a pile or “heap” of crushed metal-containing “ore” by percolating a suitable leachant solution therethrough, dissolving / leaching out the desired metal from the ore into the leachant solution (the metal laden solution being known as “pregnant leachant solution” in the industry), and thereafter recovering the metal from the pregnant leaching solution in some suitable manner. The solution remaining after recovering the metal in this way is known as “raffinate”.

[0047] “Solvent extraction” is an example of a conventional process for recovering metal from pregnant leaching solution which involves extracting metal into an organic solvent, then stripping the metal from the organic solution using highly acidic aqueous electrolyte in a “stripping unit”. Commonly, the metal is then recovered by “electrowinning” which involves plating the metal out from the metal laden electrolyte in an electrowinning unit. Typically, stripped organic solvent from the stripping unit is returned to the solvent extraction unit, and spent electrolyte from the electrowinning unit is returned to the stripping unit.

[0048] 7

[0049] #11273255.1 “Basic complexes” herein refer to complexes formed with one or more metal ions and a collection of anions including hydroxide ions such that they act as a base. They are basic sulfates, basic chlorides, or basic salts generally. The OH- anion substitutes for other anions because of a thermodynamic predominance of OH- over (SO4)2-, C1-, or even (CO3)2- thus for instance forming basic sulfates, basic chlorides, or basic carbonates. Examples include basic copper sulfate (copper hydroxide sulfate C’mH.OiuS). basic copper chloride (dicopper chloride trihydroxide CU2(OH)SC1), and basic copper carbonate (copper(II) carbonate hydroxide Q^OHECCE).

[0050] “Primary sulfide minerals” refer to those various naturally occurring sulfide minerals that have not been altered chemically since their crystallization from a cooling magma. (Secondary sulfide minerals on the other hand are formed during weathering of primary sulfide minerals.)

[0051] “Transition metals” in the present disclosure refers to those metallic elements defined as such by the IUPAC (International Union of Pure and Applied Chemistry).

[0052] A “refractory” ore is an “ore that resists the action of chemical reagents in the normal treatment processes and which may require pressure leaching or other means to effect the full recovery of the valuable minerals.” (as per US SEC.)

[0053] The phrase “available chlorine” is used herein and commonly in industry to describe chlorinated solutions because the chlorine may be present in the following forms: as sodium hypochlorite (OC1-), as hypochlorous acid (HOC!) and as dissolved gas (CE). Solution conditions are targeted to favor the sodium hypochlorite form and therefore the phrase sodium hypochlorite solution used throughout this document should be construed as such a solution.

[0054] The present invention provides practical systems and methods for recovering metals such as copper from a supply comprising metal sulfides. Suitable supplies in this regard include ores, concentrates, tailings, waste rock, and the like. The invention represents an enabling improvement to the approaches and embodiments disclosed in the WO2023 / 049967.

[0055] Figure 1 is a copy of Figure 16 from WO2023 / 049967 and illustrates a prior art system and method for recovering copper from a copper bearing ore comprising chalcopyrite. As disclosed therein, "leach environment 100 comprises a heap of crushed ore 102, for example a copper-hearing ore comprising chalcopyrite. Consistent with currently practiced heap leach methodologies, ore 102 is leached using sulfuric acid-based leach solution 104 to produce metal-hearing solution (pregnant leach solution; PLS) 106. Metal-hearing solution 106, recovered from the heap, is passed to metal separation to separate metals and produce a metal-depleted solution (raffinate) 110. Metal separation comprises solvent extraction via solvent extraction unit 108 and stripping unit 114. Thus, copper in PLS 106 is extracted into an organic

[0056] 8

[0057] #11273255.1 solvent in solvent extraction unit 108 to produce copper-loaded organic solution 112 and aqueous (metal- depleted) raffinate 110, with raffinate 110 typically being reacidified by exchange of protons with metal ions in the solvent exchange process. Copper- loaded organic solution 112 is then subjected to stripping of copper from the organic solution via contact with a highly acidic aqueous electrolyte in stripping unit 114, with the stripped organic solvent 116 recycled to solvent extraction unit 108. Pregnant electrolyte 118 is sent to electrowinning unit 120 for recovery of refined copper 122, with the spent electrolyte 124 recycled to stripping unit 114. Raffinate 110 is recycled via main recycle line 126 to become leach solution 104. ” It was determined though that, when using this approach, the halogen-based lixiviant employed would be too dilute to be feasible in practice. This is because technological limitations of known halogen generators is such that lixiviant can only be generated at very low concentrations. As a consequence, it was expected that hundreds of days of exposure would be required to extract metal from a supply of ore in this way. And, the volumes of lixiviant and resultant pregnant leach solution required would be enormous at commercial scale.

[0058] The present invention solves this problem and includes practical systems and methods for recovering metals such as copper from a supply comprising metal sulfides. The system is reasonably sized for commercial purposes and can recover metals using practical amounts of halogen containing solution in practical timeframes. This is achieved by first converting the metal sulfides to precipitated solid oxides and / or hydroxide s / basic complexes, thereafter leaching the metal out from these precipitated solids, and finally separating the metal out from the leachant solution.

[0059] Figure 2 shows a schematic of a preferred embodiment of a system of the invention for recovering copper from chalcopyrite ore. System 1 depicted in Figure 2 comprises optional chloralkali-hypochlorite processor 11 and optional agglomerator 3. As shown, crushed metal sulfide ore 2 (in this case chalcopyrite) is directed to agglomerator 3 which is used to agglomerate the crushed metal sulfide ore. The agglomerated ore forms supply 4 which is then is directed to holder 5. In this embodiment, holder 5 is a pad and supply 4 comprising agglomerated ore appears as a heap on pad / holder 5.

[0060] System 1 further comprises a pair of closeable circulation loops that are both connected to supply 4, namely first closeable circulation loop 6 for percolating a sodium hypochlorite solution through supply 4 and second closeable circulation loop 7 for percolating a leachant acid solution through supply 4. These loops can be closed off and isolated from supply 4 by respective sets of valves 6a and 7a.

[0061] First closeable circulation loop 6 comprises sodium hypochlorite generator 8, inlets 9a, 9b for makeup NaCl and water solution and additional sodium hypochlorite solution respectively, and inlet 10 for a pH controlling reagent (e.g. calcium carbonate solution). [Note that Figure 2 shows an embodiment with optional inlets 9a and 9b for both makeup NaCl and water solution and additional sodium hypochlorite solution. Other embodiments may employ just one or the other. Further, while Figure 2 shows inlet 9a being separate / distinct from inlet 10, in other embodiments they may be combined into a single inlet.] Also

[0062] 9

[0063] #11273255.1 appearing in the embodiment of Figure 2 is optional chloralkali-hypochlorite processor 11 which is connected to first closeable circulation loop 6 and can be used to produce and providing the additional sodium hypochlorite to first closeable circulation loop 6. As shown in Figure 2, an appropriate supply of NaCl and water solution can optionally be provided to chloralkali-hypochlorite processor 11 from the same source as that provided to inlet 9a.

[0064] System 1 further comprises common sampling port 16 for obtaining a pH measurement of the solutions circulating in either first and second closeable circulation loops 6, 7 at common measuring point 16a. That is, both the first and the second measuring points in first and second closeable circulation loops 6, 7 are the same point 16a. Sampling port 16 may also be used to obtain samples for purposes of testing for the presence of metal in the solution. As those skilled in the art will appreciate, there are alternative indirect means for measuring the pH of the circulating sodium hypochlorite solution at the first measuring point and for measuring the pH of the circulating leachant acid solution at the second measuring point. For instance, instead of directly measuring pH, the [metal] in the circulating solutions might be measured instead and the relevant pHs inferred from that. In the context of the present invention then, sampling and measuring the [metal] in these circulating solutions for purposes of controlling the pH would be equivalent to directly measuring the pH.

[0065] Second closeable circulation loop 7 comprises metal separation unit 12 and inlet 13 for makeup leachant acid and water. In the embodiment shown, metal separation unit 12 comprises solvent extraction unit 12a and electrowinning unit 12b. Solvent extraction unit 12a comprises inlet 12ai for pregnant acid leach solution, outlet 12aii for copper loaded electrolyte solution, outlet 12aiii for raffinate and inlet 12aiv for spent electrolyte. Electrowinning unit 12b comprises inlet 12bi which is fluidly connected to outlet 12aii for the copper loaded electrolyte solution and outlet 12bii which is fluidly connected to inlet 12aiv for spent electrolyte. In this embodiment, metal 15 that is recovered from metal separation unit 12 is obtained as plated copper from electro winning unit 12b.

[0066] As shown therefore, system 1 is configured so to allow for a solution of sodium hypochlorite to initially be percolated through supply 4 after which a distinct, separate solution of leachant acid (e.g. strong sulfuric acid) can be percolated therethrough. The percolating solution from one or the other of circulation loops 6, 7 is shown in Figure 2 as solution 14.

[0067] While the purpose of sodium hypochlorite generator 8 is of course to generate sufficient sodium hypochlorite for reacting with metal sulfides in supply 4, it can be advantageous to employ an arrangement comprising a suitably modified commercial-type sodium chlorate electrolyzer for processing recycling raffinate in the first closeable circulation loop (i.e. to serve as sodium hypochlorite generator 8) and an optional chloralkali-hypochlorite processor 11 (e.g. a commercial electrolyzer with the subsequent reaction of caustic and chlorine to sodium hypochlorite) for processing makeup salt (as is depicted in Figure 2).

[0068] 10

[0069] #11273255.1 With this arrangement, recycled raffinate is processed by the modified sodium chlorate electrolyzer which is then blended with fresh sodium hypochlorite produced using fresh makeup salt in the chloralkalihypochlorite processor. Such a blended solution would contain the desired sodium hypochlorite plus NaCl and possibly either hypochlorous acid and / or sodium hydroxide. As explained further below, the reason for considering such an arrangement is to obtain a desirably high concentration of sodium hypochlorite for converting the metal sulfides in supply 4 to metal oxides and hydroxides / basic complexes.

[0070] With regards to using a modified sodium chlorate electrolyzer to serve as sodium hypochlorite generator 8, sodium hypochlorite and hypochlorous acid are produced as intermediates in sodium chlorate production. To suitably modify a sodium chlorate electrolyzer, the electrolyzer need not change but rather the electrolyzer operating conditions such as temperature, pH and concentrations do and are altered to disfavor the subsequent reaction of sodium hypochlorite and hypochlorous acid such that they don't react to form sodium chlorate. More specifically, a typical sodium chlorate electrolyzer can be a multi-monopolar design, consisting of multiple open cell (i.e. no membrane separating the electrodes) in a back-to-back design to make an electrolyzer (or group of cells). The chemicals produced at the electrodes (namely Cfi, H2and NaOH which are the same chemicals produced in a chlor-alkali cell) are allowed to react. For sodium chlorate production, the operating parameters (pH and temperature) as well as reaction time are adjusted to allow these to form sodium hypochlorite and hypochlorous acid, which under favored operating parameters, further react to form sodium chlorate. For present purposes, the cell / electrolyzer design would remain essentially the same (although the anode catalytic coating may desirably be modified), but the balance of cellroom design and operating parameters would be adjusted so to form a stable solution of hypochlorous acid / sodium hypochlorite. At a target pH around 7, the predominant species would be hypochlorous acid with some sodium hypochlorite (based for instance on Figure VII.5 showing “Species resulting from reaction of chlorine in water”; Kirk-Othmer - Encyclopedia of Chemical Technology, 4thEdition, Vol. 9, pl34). The resultant solution from such a sodium chlorate electrolyzer modified in operation in this way would thus be a mix of NaOCl, H0C1, unreacted NaCl and traces of NaCICf. The chlorate cellroom design and operating parameters can thus be adjusted so as to minimize chlorate formation (via the reaction of hypochlorous acid and hypochlorite) via control of pH, temperature, reaction time, multiple passes of the recirculating liquor through the chlorate cells, and by minimizing side reactions. The overall process can be modified to involve a single pass of raffinate through the electrolysis cell / s, and by changing the balance of process parameters, a low strength hypochlorite solution (e.g. 2,000 to 2,500 ppm available chlorine) can be produced.

[0071] With regards to including optional chloralkali -hypochlorite processor 11, such a chlor-alkali electrolyzer produces chlorine gas, hydrogen gas and 32% caustic (NaOH). Subsequently, the chlorine and caustic can be reacted under controlled conditions to produce up to 30% sodium hypochlorite solution, a higher strength solution than can typically be provided by the aforementioned modified sodium chlorate electrolyzer. A yet further alternative that could be considered would be to provide additional sodium hypochlorite to the first

[0072] 11

[0073] #11273255.1 closeable circulation loop that was obtained from an external independent supply of high strength sodium hypochlorite. A yet further alternative that could be considered would be the production of sodium hypochlorite from chlorine gas and caustic and addition to the first closeable circulation loop. Still further alternatives that could be considered are the use of purchased sodium hypochlorite and / or the production of sodium hypochlorite from purchased chlorine and caustic soda.

[0074] In system 1 , wash water may be provided for percolating water through the supply of metal sulfide . In such a case, system 1 may optionally comprise an inlet for wash water connected to pad / holder 5 (not shown in Figure 2). Further, pre-treatment of the metal depleted solution upstream of sodium hypochlorite generator 8 may be required to adequately clean the solution first but this is also not shown in Figure 2.

[0075] The improved method of the invention involves two distinct percolation stages. In the first of these, circulating sodium hypochlorite solution is percolated through the supply being held in the holder to convert the sulfides therein to precipitated solids. The circulating solution dissolves and reacts with sulfide solids in the supply so as to convert them into oxides and / or hydroxides / basic complexes. Meanwhile, the pH of the circulating solution is measured and carefully controlled throughout such that these products deliberately precipitate as solids and remain in the holder. To accomplish this, the pH is maintained to greater than 4 downstream of the supply. Once the conversion to solids is considered adequate, the first percolation stage is ended and the second percolation stage is started. In this second percolation stage, circulating leachant acid is percolated through the supply so as to leach out these metal oxides and / or hydroxides / basic complexes into the leachant acid solution. The metal is separated out from the circulating leachant acid solution using an appropriate metal separation process. Again, the pH of the circulating solution is measured (in this second stage, the circulating solution is leachant solution) and carefully controlled such that it is maintained to be less than 2.5 just downstream of the supply. For both percolating stages, any conventional means known for applying the respective solutions to the supply may be considered, e.g. drip, subsurface injection, spray irrigation and the like.

[0076] In a specific example, the method of the invention can be used to recover copper from a supply of copper sulfide. This is shown in the simplified flowchart of Figure 3 comprising broad steps 31-33 in which: step 30 comprises obtaining a system comprising a holder and first and second closeable circulation loops suitable for performing the two aforementioned distinct percolation stages, step 31 comprises providing a supply comprising copper sulfide to the holder, step 32 comprises converting the copper sulfide to precipitated solid copper oxide and solid copper hydroxides / basic complexes in a first series of steps; and step 33 comprises leaching the copper from the precipitated solid copper oxide and solid copper hydroxides / basic complexes and separating the copper from the leachant acid solution in a second series of steps.

[0077] 12

[0078] #11273255.1 Further, the first series comprises opening first closeable circulation loop 6 and circulating a sodium hypochlorite solution having a pH greater than 4 therethrough; percolating the sodium hypochlorite solution through supply 4 thereby accomplishing the converting; measuring the pH of the circulating sodium hypochlorite solution at the first measuring point; providing sufficient pH controlling reagent to the circulating sodium hypochlorite solution to maintain the pH at the first measuring point to be greater than 4; providing a supply of makeup NaCl and water solution or an additional sodium hypochlorite solution to first closeable circulation loop 6; producing sodium hypochlorite in the sodium hypochlorite generator; and closing the first closeable circulation loop according to a first predetermined criterion. In an exemplary embodiment (see Examples below), sufficient pH controlling reagent may be provided to the circulating sodium hypochlorite solution to maintain the pH at the first measuring point to be about 7.

[0079] The second series of steps comprises opening second closeable circulation loop 7 and circulating a leachant acid solution therethrough; percolating acid leachant solution through the precipitated solid copper oxide and solid copper hydroxide s / basic complexes thereby accomplishing the leaching; separating the leached copper from the leachant acid solution; measuring the pH of the circulating leachant solution at the second measuring point; providing sufficient supply of makeup leachant acid and water to second closeable circulation loop 7 to maintain the pH of the circulating leachant solution at the second measuring point to be less than 2.5; and closing second closeable circulation loop 7 according to a second predetermined criterion. In a preferred embodiment, sufficient supply of makeup leachant acid and water is provided to second closeable circulation loop 7 to maintain the pH of the circulating leachant solution at the second measuring point to be less than 2 and more preferably between 0.8 and 2.

[0080] In this embodiment, supply 4 can be chalcopyrite. Suitable pH controlling reagents can for instance include solutions of calcium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium hydroxide and the like. A suitable acid leachant solution can be sulfuric acid. (The acid could be supplied as purchased in acid or be supplied from an integral on-site acid production unit.) The reactions taking place during the method consume sodium hypochlorite and thus additional sodium hypochlorite is required in first closeable circulation loop 6. This additional sodium hypochlorite can be obtained by adding NaCl at inlet 9a from which sodium hypochlorite is generated using sodium hypochlorite generator 8. In the preferred embodiment shown in Figure 2, additional supplemental sodium hypochlorite is also provided to first closeable circulation loop 6 from chloralkali-hypochlorite processor 11. Here, NaCl and water is also provided to and processed by chloralkali-hypochlorite processor 11 to initially produce Ch and NaOH (and by-product H2), which is then subsequently reacted to produce NaOCl. Further still, additional sodium hypochlorite (preferably high strength) may be provided from an external supply.

[0081] In the first stage, the circulating sodium hypochlorite solution dissolves and reacts with sulfide solids in the supply so as to convert them into metal oxides and / or hydroxide s / basic complexes. An important aspect in the method relates to maintaining conditions such that these oxides and / or hydroxides / basic complexes

[0082] 13

[0083] #11273255.1 immediately precipitate out from the circulating solution as solids and thus remain in holder 5. Aside from keeping the desired metal in holder 5 for the second subsequent percolation or leaching stage, these metal species do not get directed to sodium hypochlorite generator 8 where they could otherwise contaminate it and interfere with its operation. The appropriate precipitation conditions in this regard involve controlling the pH of the circulating sodium hypochlorite solution to be greater than 4. Without being bound by theory, it is believed that hypochlorous acid, which is also present in the sodium hypochlorite solution, is a favored species in the pH range between 4 and 5 and it is this species which primarily reacts with the copper sulfide to form the copper oxides and solid copper hydroxides / basic complexes.

[0084] In the inventive method, the selection of first and second predetermined criteria would be expected to be based on economic considerations. Trade-offs would be made between operation times and associated costs versus efficiency of metal recovery. Those of ordinary skill would readily be able to make appropriate decisions in this regard. In exemplary embodiments, the first predetermined criterion could therefore be after a specified amount of the copper sulfide in the supply comprising copper sulfide has been converted to precipitated solid copper oxide and solid copper hydroxides / basic complexes. Or alternatively it might instead be simply after a specified time. In a like manner, the second predetermined criterion could be after a specified amount of copper has been leached from the precipitated solid copper oxide and solid copper hydroxides / basic complexes or alternatively after a specified time.

[0085] In the preferred embodiment shown in Figure 2, both sodium hypochlorite generator 8 and chloralkalihypochlorite processor 11 are used to electrolyze salt and thus produce sodium hypochlorite in two parallel processes because of the desired available chlorine concentration required to convert the metal sulfides in the ore in a practical timeframe and using practical volumes of solution. Typical devices which may be used as sodium hypochlorite generator 8 can only produce available chlorine concentrations at about 2,500 ppm (similar to that produced in commercial seawater hypochlorite generators). But at these low concentrations, the conversion stage of sulfides to oxides and / or hydroxides / basic complexes can become undesirably long. Additionally, adding makeup NaCl upstream thereof would increase the size of the system substantially. Instead then, much makeup salt can be instead processed via chloralkali-hypochlorite processor 11 (e.g. a commercial chlor-alkali electrolyzer) to make much more concentrated NaOCl. This concentrated NaOCl is then blended with product from sodium hypochlorite generator 8 (e.g. in about a 40% / 60% ratio), resulting in a circulating solution with much higher available chlorine thereby reducing the conversion time to a more practical level. Further advantages of this approach may include the chloralkali-hypochlorite processor being well established in the art and that the strong product it produces can be more practically stored. Further, impurities in the recycle raffinate may result in more frequent stoppage of sodium hypochlorite generator 8 to acid-wash the electrodes to remove harmful deposits from the raffinate that plate out on the electrodes, if the product was solely obtained from therefrom.)

[0086] 14

[0087] #11273255.1 With regards to the selection of operating parameters and particularly the desired target pH for the circulating solution in the first percolation stage, the differences in the compositions of the supply used will be the main determining factor. That is because that along with the target sulfide mineral in the supply (i.e. the sulfide mineral from which the metal is to be recovered), there are generally numerous other gangue minerals in the supply (i.e. minerals present that do not contain the desired metal to be recovered). The types and amounts of such gangue minerals can affect the chemistry and resultant pH of the circulating sodium hypochlorite solution during the first percolation stage. Generally, for instance, when recovering copper from copper sulfide minerals, as sodium hypochlorite reacts with the target copper sulfides, sulfuric acid is generated which lowers the pH. If the pH drops too much however then the extracted copper won’t precipitate as required. At a minimum, there is a need to maintain the solution pH to be greater than 4 in order to prevent the copper from staying in solution. For a given supply, the actual minimum pH actual and the preferred operating pH values will be influenced to a certain extent by the type and amount of gangue minerals present and whether or not they consume or generate acid under specific operating conditions. As an example, the presence of calcium carbonate in a supply of ore can help buffer the circulating solution and thereby stop the solution pH from dropping too low and thus help maintain a desired pH. Those skilled in the art will recognize that the pH of the circulating solution can be adjusted by addition of a variety of pH controlling reagents (such as H2SO4, HC1, lime or NaOH) to the circulating solution at a convenient location in the system.

[0088] Those skilled in the art will further be expected to be able to determine approximate desirable pH ranges in this regard based on a knowledge of the composition of the provided supply (i.e. the amounts of target and gangue minerals present) and relevant Pourbaix diagrams which show the thermodynamically stable phases of various aqueous electrochemical systems (e.g. conditions for solubility of Cu and Fe in chalcopyrite) as a function of pH, EH, temperature, pressure, and concentration (see for instance: Barton, IF, Hiskey, JB 2022, “Chalcopyrite leaching in novel lixiviants”, Hydrometallurgy, vol 207, pp 2, fig 1 ; or Havlik, T 2008, “Hydrometallurgy Principles and applications”, Woodhead Publishing Limited, pp 165, fig. 5.20). As those in the art are aware, the relative stabilities of the various phases can be changed dramatically by the introduction of other elements into a system. In some situations, acid may be generated as copper sulfides in the supply are oxidized during the first percolation stage. If so, in order to maintain the pH above 4 as the circulating solution exits the supply (i.e. at the first measuring point), the pH of the solution being applied to the supply may need to exceed 7 in practice.

[0089] As illustrated in the following Examples, the present invention solves problems relating to the practicality of certain prior art approaches. Here, metal recovery can be achieved in commercially reasonable timeframes, using reasonable volumes of processing solutions and reasonably sized equipment. The precipitation of the metal solids aspect in the first percolation stage desirably keeps metal species out of the first closeable circulation loop. This prevents contamination of the sodium hypochlorite generator therein or at least minimizes any need for removal of contaminants. Further, by using two separated closeable

[0090] 15

[0091] #11273255.1 circulation loops, chlorides involved in the first percolation stage are desirably kept away from the metal separation unit. In turn, this also allows for the second leaching percolation stage to be performed with higher acid concentrations thereby making the volumes going to the metal separation more manageable. It should be noted that the processing time is constrained by the irrigation rate, the amount of sodium hypochlorite required, and the concentration of sodium hypochlorite. The amount of sodium hypochlorite required is fixed for a given supply (i.e. is that amount stoichiometrically needed to react with the copper present). The irrigation rate is also generally fixed, as it is a function of the state of the supply.

[0092] While the preceding describes preferred embodiments of the invention, it is expected that the invention may be suitable for the recovery of other metals from other metal sulfides in other forms. Other alternative system components and modifications to the method may also be contemplated. For instance, recovering transition metals (e.g. copper, nickel, cobalt, gold, silver) from low grade primary metal sulfides. Such materials may be processed in the form of a concentrate rather than an ore. (“Concentrate” here refers to an ore that has already been beneficiated to increase the concentration of metal minerals therein. Typically, beneficiation is achieved via a flotation process.) Also for instance, alternative metal separation units may be considered, including for instance a combination of an ion exchange unit and an electrowinning unit or alternatively a precipitation unit.

[0093] The following Examples have been included to illustrate certain aspects of the invention but should not be construed as limiting in any way.

[0094] INVENTIVE EXAMPLE

[0095] Modelling, using METSIM® process simulation software, was done on a representative commercial scale copper recovery system that was designed and configured in accordance with the invention. Specifically, the commercial scale system was configured as shown in Figure 2. The system was modelled to treat 20 million tonnes per annum of copper ore at 0.7% copper. The first percolation stage employing circulating sodium hypochlorite solution was assumed to be configured as a conventional heap leach with 6.5m lifts and an irrigation rate of 10L / h / m2. An evaporative loss from the heap during the percolation was modelled at 4 mm / d. The sodium hypochlorite solution was added to the heap at 13,291 m3 / h containing 50.5 t / h of available chlorine.

[0096] The sodium hypochlorite generator was assumed to be a modified sodium chlorate electrolyzer configured to produce a solution with 0. 19% w / w available chlorine. The sodium chlorate electrolyzer would generate sodium hypochlorite from the residual sodium chloride in the circulating solution collected from the heap, with the production modelled at 30.0 t / h of available chlorine.

[0097] 16

[0098] #11273255.1 As shown in Figure 2, an optional chloralkali-hypochlorite processor was employed which consisted of a commercially available chloralkali plant and caustic chlorine reactor modelled to produce 21.5 t / h available chlorine at an available chlorine concentration of 14.39% w / w which was added to the product from the sodium hypochlorite generator. This high strength sodium hypochlorite obtained from the chloralkali- hypochlorite process was used to make up for any chloride lost from the system as residue moisture left in the heap after percolating. (Those skilled in the art will recognize that the concentration of NaCl contained in the hypochlorite solution can be reduced by increasing the NaOCl concentration and thus the ratio of NaCl to NaOCl can be controlled to the desired value.)

[0099] The copper ore would be contacted with the sodium hypochlorite solution and the following reactions were modelled:

[0100] Cu2O + NaOCl -> 2CuO + NaCl

[0101] CuS + 4NaOCl — > C11SO4 + 4NaCl

[0102] Cu2S + BNaClO -> CuSO4+ CuO + BNaCl

[0103] 2CuFeS2+ UNaClO -> Fe2O2+ 2CuS04+ UNaCl + 2S CuSO4+ 2H2O -> CU(OH)2+ H2SO4

[0104] The pH in the solution collected from the heap was assumed to be maintained via the addition of hydrated lime slurry to a target of 7 pH at the measuring point. (Note that some pretreatment of the solution collected from the heap may be required if lime is employed.)

[0105] The second percolation stage employing leachant acid solution was assumed to use the same configuration used in the first percolation stage. A solvent extraction unit was used as the metal separation unit. And the heap was irrigated with raffinate returning from the solvent extraction unit.

[0106] Sulfuric acid was added to the raffinate to maintain 25 g / L of free acid in the raffinate. The heap was irrigated at a rate of 10 L / h / m2(the percolation duration was set to 50 days resulting in a raffinate flowrate of 2479 m3 / h). The precipitated solid copper oxides and hydroxide s / basic complexes in the heap were contacted with the raffinate solution and the following reactions were modelled:

[0107] CuO + H2SO4-> CuS04+ H2O

[0108] CU(OH)2+ H2SO4 C11SO4 + 2H2O

[0109] The pregnant leachant acid solution drained from the heap was sent to the solvent extraction unit. Following the second percolation stage, the heap was considered to be irrigated with fresh water to displace any residual copper bearing solution which was then added to the pregnant leachant acid solution reporting to the solvent extraction unit. A residual moisture content of 12% w / w was modelled in the heap.

[0110] The solvent extraction unit was assumed to be a typical commercial copper solvent extraction plant consisting of extract, scrub and strip stages using commercially available extractant and organic. The 17

[0111] #11273255.1 solvent extraction unit was modelled to have an overall copper recovery of 98%, consistent with the performance of commercially available solvent extraction plants. The electrowinning subsystem assumed a commercially available electrowinning plant that plates copper cathode. The system was modelled to produce 13 t / h of copper cathode.

[0112] In summary in the preceding Example, the amount of ore processed in the model per annum was 20 million tons. The copper content in the ore was 0.7 % Cu by weight, with a 78.3% total recovery, and therefore 114 kilotons of copper was recovered therefrom per annum.

[0113] In the first percolation stage, the flowrate of the circulating sodium hypochlorite solution applied to the ore heap was 13,291 m3 / h. In the second percolation stage, the leachant acid solution applied to the ore heap was 2479 m3 / h, following losses to evaporation and residual moisture in the heap plus the application of wash water the resultant pregnant leachant solution directed to the solvent extraction unit was 2554 m3 / h. The copper concentration in g / L in the circulating leachant acid solution going to the solvent extraction unit was 5.2 g / L Cu.

[0114] The first percolation stage lasted 265 days and the second percolation stage lasted 50 days. With 2 additional days taken for a wash water step, the total time required for extraction and recovery was 317 days.

[0115] COMPARATIVE EXAMPLE

[0116] The aforementioned prior art WO2023 / 049967 contemplates the recovery of copper from copper sulfide minerals using a single closed circulation loop with an inline halogen generator to regenerate the oxidative halogen based lixiviant from the metal depleted solution coming from metal separation.

[0117] In this example, modelling was done on a system configured as shown in the prior art Figure 1 shown herein (i.e. also Fig. 16 from WO2023 / 0499672). Again, it was assumed that 20 million tonne per annum of copper ore at 0.73% copper would be processed, achieving a comparative 78.3% recovery of copper. The oxidative halogen based lixiviant used was hypochlorous acid which is the predominant species at the pH values required to produce a metal bearing solution described in the prior art WO2023 / 049967.

[0118] The sole halogen based lixiviant leaching and the acid leaching step were modelled as described in the prior art WO2023 / 049967. The leaching stage was again assumed to be configured as a conventional heap leach with 6.5m lifts and an irrigation rate of 10L / h / m2.

[0119] An evaporative loss from the heap during the percolation was modelled at 4 mm / d. The hypochlorous acid solution was added to the heap at 23,416 m3 / h containing 50 t / h of available chlorine and 62 t / h of sulfuric acid.

[0120] 18

[0121] #11273255.1 The halogen generator was again assumed to be a modified sodium chlorate electrolyzer configured to produce a solution with 0.19% w / w available chlorine. The sodium chlorate electrolyzer would generate sodium hypochlorite from the residual sodium chloride in the raffinate solution from the metal recovery solvent extraction unit, with the production modelled at 50 t / h of available chlorine. Additional sodium chloride is added to the raffinate to account for any loss of chlorine from the system. The pH of the raffinate is increased through the addition of hydrated lime slurry prior to entering the modified sodium chlorate electrolyzer. Any metal ions present in the raffinate are removed using chemical precipitation or ion exchange.

[0122] In order to leach the copper species into solution, acid is added to the sodium hypochlorite solution, converting the sodium hypochlorite to hypochlorous acid and lowering the lixiviant solution pH. An additional 62 t / h of sulfuric acid is added to the lixiviant solution to leach any oxides generated or naturally present in the ore. Including additional make up water, a total of 23,754 m3 / h of hypochlorous acid and sulfuric acid lixiviant solution is applied to the heap.

[0123] The copper ore would be contacted with the hypochlorous acid and sulfuric acid lixiviant solution and the following reactions were modelled:

[0124] Cu20 + HOCl -> 2CuO + HCl

[0125] CuS + 4HOCI -^ CuSO4+ HCl

[0126] Cu2S + 5HCIO -> CuS04+ CuO + 5HCI

[0127] 2CuFeS2+ 11HCIO -► Fe2O2+ 2CuSO4+ 11HCI + 2S

[0128] CuO + H2SO4-> CuS04+ H2O CuO + 2HCI — * CuCl2T H2O

[0129] The pregnant leach acid solution drained from the heap, totaling 23,128 m3 / h, was sent to the solvent extraction unit. The copper concentration of the combined pregnant leach solution is modeled at 0.6 g / L of copper. A residual moisture content of 12% w / w was modelled in the heap.

[0130] The solvent extraction unit was assumed to be a typical commercial copper solvent extraction plant consisting of extraction, wash, scrubbing and stripping stages using commercially available extractant and organic. A wash stage was included following the extraction stage to remove or reduce chloride species carried over into the electrolyte. Again, the solvent extraction unit was modelled to have an overall copper recovery of 98%, consistent with the performance of commercially available solvent extraction plants. The electrowinning subsystem assumed a commercially available electrowinning plant that plates copper cathode. The system was modelled to produce 13 t / h of copper cathode.

[0131] 19

[0132] #11273255.1 Based on the lixiviant volumetric flowrates, the heap geometry and the irrigation rates, the time required to deliver the require stoichiometric mass of lixiviants to achieve the target recovery was 476 days.

[0133] As is evident from the preceding examples, use of the system of the prior art results in large volumes of pregnant leach solution at low copper concentrations needing to be treated and further requires longer times to accomplish the desired recovery. Here, the Inventive Example employs a pregnant leach solution of 2554 m3 / h, a 89% reduction in the volumes of pregnant leach solution treated when compared with 23,128 m3 / h resulting from the prior art configuration of the Comparative Example. The pregnant leach solution in the Inventive Example has a higher concentration of copper, 5.2 g / L, compared with the 0.6 g / L in the Comparative Example. Both the lower volumetric flowrate and the higher concentration of copper in the pregnant leach solution represent a significant improvement on the prior art and can significantly reduce the capital and operating costs of the metal separation unit. Further, the use of high strength sodium hypochlorite make-up and subsequent higher strength lixiviant solution in the Inventive Example allows for more active reagent to be applied to the heap in a shorter duration than in the Comparative Example. Specifically, the Inventive Example involved a total leach time of 317 days, which is a 33% reduction in leach time compared with the 476 days of the Comparative Example. Again, this represents a significant improvement over the prior art and can significantly increase the throughput when operating in this configuration. Advantageously, a large portion of the hypochlorite is made in a normal, “clean” chloralkali plant and this can significantly reduce the amount of any pretreatment required for the “in-line” modified chlorate electrolyzer which has to handle an impure feed stream. The invention thus provides for an economically feasible system for extracting copper sulfides.

[0134] ILLUSTRATIVE EXAMPLE

[0135] The following example is provided to illustrate the conversion of chalcopyrite to oxides using sodium hypochlorite. It demonstrates on copper ore how free chlorine at suitable pHs can be used to convert solid copper sulfides into acid soluble solid copper oxides and hydroxides / basic complexes without mobilizing significant amounts of copper or gangue material into solution.

[0136] The conversion of copper sulfides to solid oxides and solid hydroxides / basic complexes using different sodium hypochlorite strengths was investigated. The ore sample (sample A) used was a copper ore with the following composition: Cu (0.7%), Fe (5.1%), S (0.6%), Si (33.5%), Mg (1.0%), Al (4.6%). Acid digestion tests were performed to estimate the copper species present in the copper ore sample, including Hot Acid Soluble (HAS) sulfuric, cyanide soluble (CN), and a 4-acid digestion test (HC1, HNOs, HF, HCICh) resulting in the following distribution of copper species: oxides (7%), secondary sulfides (8%) and primary sulfides (85%). Quantitative X-Ray Diffraction (QXRD) mineralogical analysis identified chalcopyrite as the primary sulfide species.

[0137] 20

[0138] #11273255.1 Samples of the copper ore were crushed to sub 35mm then pulverised to sub 75pm. The copper ore samples ranging from 150-300g were combined with 0.17-0.93 molar NaOCl prepared from stock commercial grade ~93 g / L stock by mixing with deionised water resulting in slurries weighing ~2,000g each that were placed in a sealed stirred beaker and agitated at ambient temperature and stirred between 200 and 550 rpm for 24 hours.

[0139] During the experiments, the pH was adjusted with sodium hydroxide solution at concentrations between 50 and 70 g / L to maintain a solution pH of around 8. Samples at regular intervals were taken to identify any solubilised material in the liquor. The liquor samples were analysed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) which demonstrated that, although there was a trace of soluble copper (<= 4 ppm) detected soon after one of the experiments was started, there was no soluble copper measured (below the detection limit of 0.01 ppm) in any of the experiments at hour 6 or later. The results demonstrate that copper will not readily solubilize into solution at the pH levels investigated in these tests. These same patterns are seen for potentially problematic elements including aluminum and iron. These results highlight the specific benefit of the process, namely keeping copper and problematic cations and metal species out of solution via manipulation of pH to enable the efficient electrochemical regeneration of NaOCl using the leachate, while ensuring the converted copper species remain in the heap available for subsequent recovery using more standard sulfuric acid leaching.

[0140] Table 1- pH-controlled suppression of soluble metal species at hour 6

[0141] ND = Not Detected (below 0.01 ppm detection limit)

[0142] At the completion of the tests, the same acid digestion assays used to estimate the copper species present in the copper ore sample were performed to determine the copper species present in the residue solids. Table 2 below shows the shifting of copper sulfides in the sample to acid leachable species (oxides) for Sample A across four tests, alongside the starting concentration of sodium hypochlorite, demonstrating the positive relationship between it and copper species conversion.

[0143] 21

[0144] #11273255.1 Table 2 - Sample A Leach Tests (LT) 1-4

[0145] The conversion of chalcopyrite to oxides and hydroxide s / basic complexes is influenced strongly by the concentration of NaOCl. To more clearly demonstrate this relationship, Table 3 lists the specific proportion of chalcopyrite converted to other leachable species plotted alongside the starting concentration of NaOCl (mol / L).

[0146] Table 3 - Relationship between primary sulfide conversion and NaOCl concentration

[0147] All of the above U.S. patents, U.S. patent applications, foreign patents, foreign patent applications and nonpatent publications referred to in this specification, are incorporated herein by reference in their entirety, including U.S. Provisional Patent Application No. 63 / 716,169 filed November 4, 2024, unless otherwise stated. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications, and publications to provide yet further embodiments.

[0148] While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since further modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings. Such modifications are to be considered within the purview and scope of the claims appended hereto.

[0149] 22

[0150] #11273255.1

Claims

Claims1. A system for recovering copper from a supply comprising copper sulfide comprising: a holder for the copper sulfide; a first closeable circulation loop connected to the holder for percolating a sodium hypochlorite solution through the copper sulfide comprising: a sodium hypochlorite generator; an inlet for a makeup NaCl and water solution or an additional sodium hypochlorite solution; an inlet for a pH controlling reagent; and a means for measuring the pH of the circulating sodium hypochlorite solution at a first measuring point downstream of the supply and before the inlet for the pH controlling reagent; a second closeable circulation loop connected to the holder for percolating a leachant acid solution through the supply comprising: a metal separation unit for separating copper from the leachant acid solution; an inlet for makeup leachant acid and water; and a means for measuring the pH of the circulating leachant acid solution at a second measuring point downstream of the supply and before the inlet for the makeup leachant acid and water.

2. The system of claim 1 wherein the first and second measuring points are the same and the means for measuring the pH of the circulating sodium hypochlorite solution and for measuring the circulating leachant acid solution are the same.

3. The system of claim 2 wherein the means for measuring the pH comprises a pH meter or a sampling port for obtaining a sample for pH measurement at the measuring point.

4. The system of claim 1 wherein the sodium hypochlorite generator is a modified sodium chlorate electrolyzer.

5. The system of claim 1 additionally comprising a chloralkali-hypochlorite processor connected to the first closeable circulation loop.

6. The system of claim 1 comprising an inlet for wash water connected to the holder for percolating water through the metal sulfide.23#11273255.

17. The system of claim 1 wherein the supply is in the form of an ore, the holder is a pad, and the ore is held in the form of a heap on the pad.

8. The system of claim 7 additionally comprising an agglomerator upstream of the holder for agglomerating crushed metal sulfide ore.

9. The system of claim 1 wherein the metal separation unit is selected from the group consisting of a solvent extraction unit plus an electrowinning unit, an ion exchange unit plus an electrowinning unit, and a precipitation unit.

10. The system of claim 9 wherein the metal separation unit comprises: a solvent extraction unit comprising an inlet for pregnant leachant acid solution, an inlet for stripping solution, an outlet for a copper loaded electrolyte solution, and an outlet for raffinate; and an electrowinning unit comprising an inlet fluidly connected to the outlet for the copper loaded electrolyte solution from the solvent extraction unit.

11. A method for recovering copper from a supply of copper sulfide comprising the steps of: obtaining the system of claim 1; providing a supply comprising copper sulfide to the holder; in a first series of steps, opening the first closeable circulation loop and circulating a sodium hypochlorite solution having a pH greater than 4 therethrough; percolating the sodium hypochlorite solution through the supply thereby converting the copper sulfide to precipitated solid copper oxide and solid copper hydroxide s / basic complexes; measuring the pH of the circulating sodium hypochlorite solution at the first measuring point; providing sufficient pH controlling reagent to the first closeable circulation loop at the pH controlling reagent inlet to maintain the pH of the circulating sodium hypochlorite solution at the first measuring point to be greater than 4; providing a makeup NaCl and water solution or an additional sodium hypochlorite solution to the first closeable circulation loop; producing sodium hypochlorite in the sodium hypochlorite generator; and closing the first closeable circulation loop according to a first predetermined criterion; and in a second series of steps, opening the second closeable circulation loop and circulating a leachant acid solution therethrough;24#11273255.1percolating the leachant acid solution through the precipitated solid copper oxide and solid copper hydroxide s / basic complexes thereby leaching the copper from the precipitated solid copper oxide and solid copper hydroxide s / basic complexes and forming a pregnant leachant acid solution; separating the copper from the pregnant leachant acid solution; measuring the pH of the circulating leachant acid solution at the second measuring point; providing sufficient supply of makeup leachant acid and water to the second closeable circulation loop at the inlet for makeup leachant acid and water to maintain the pH of the circulating leachant acid solution at the second measuring point to be less than 2.5; and closing the second closeable circulation loop according to a second predetermined criterion.

12. The method of claim 11 wherein the supply comprising metal sulfide is chalcopyrite.

13. The method of claim 11 comprising providing sufficient pH controlling reagent to the circulating sodium hypochlorite solution at the pH controlling reagent inlet to maintain the pH of the circulating sodium hypochlorite solution at the first measuring point to be about 7.

14. The method of claim 11 wherein the pH controlling reagent is a solution of calcium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate or ammonium hydroxide.

15. The method of claim 11 wherein sufficient supply of makeup leachant acid and water is provided to maintain the pH of the circulating leachant acid solution at the second measuring point to be less than 2.

16. The method of claim 11 wherein the leachant acid is sulfuric acid.

17. The method of claim 11 wherein the first predetermined criterion comprises after a specified amount of the copper sulfide in the supply comprising copper sulfide has been converted to precipitated solid copper oxide and solid copper hydroxides / basic complexes or after a specified time.

18. The method of claim 11 wherein the second predetermined criterion comprises after a specified amount of copper has been leached from the precipitated solid copper oxide and solid copper hydroxides / basic complexes or after a specified time.

19. The method of claim 11 wherein an additional sodium hypochlorite solution is provided to the first closeable circulation loop and the additional sodium hypochlorite is provided by a chloralkali-hypochlorite processor.25#11273255.1

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