WO2017140723A1 - Hydrometallurgical processes for leaching or dissolving metal and enhancing electrorefinery and smelting operations - Google Patents

Hydrometallurgical processes for leaching or dissolving metal and enhancing electrorefinery and smelting operations Download PDF

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WO2017140723A1
WO2017140723A1 PCT/EP2017/053395 EP2017053395W WO2017140723A1 WO 2017140723 A1 WO2017140723 A1 WO 2017140723A1 EP 2017053395 W EP2017053395 W EP 2017053395W WO 2017140723 A1 WO2017140723 A1 WO 2017140723A1
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copper
leach
mechano
leaching
reactor
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PCT/EP2017/053395
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French (fr)
Inventor
Sara ROCKS (Sally)
David John CHAIKO
Paul Martin Keyser
Frank Baczek
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Flsmidth A/S
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Priority to US62/297,354 priority
Priority to US201662359124P priority
Priority to US62/359,124 priority
Application filed by Flsmidth A/S filed Critical Flsmidth A/S
Publication of WO2017140723A1 publication Critical patent/WO2017140723A1/en

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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22BPRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B15/00Obtaining copper
    • C22B15/0063Hydrometallurgy
    • C22B15/0065Leaching or slurrying
    • C22B15/0067Leaching or slurrying with acids or salts thereof
    • C22B15/0071Leaching or slurrying with acids or salts thereof containing sulfur
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22BPRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B11/00Obtaining noble metals
    • C22B11/04Obtaining noble metals by wet processes
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00Technologies related to metal processing
    • Y02P10/20Recycling

Abstract

This disclosure relates to systems and methods for the dissolution of metals, metallic compounds, metallic alloys, metallic solids, recyclable metal, semiconductors, and the like. Particularly disclosed, are exemplary systems, methods, and apparatus for leaching metallic solids such as blister copper, scrap copper anode, scrap copper cathode, and recycled/scrap copper. A hydrometallurgical leach process (130, 230, 730) may be provided in lieu of, or in addition to conventional electro-refining (914, 214) and fire-refining (911, 211) operations, in order to supplement and/or increase copper cathode production. Impure metallic solids are rapidly and selectively dissolved into solution via a mechano-chemical exothermic leach process, in a mechano-chemical (M-C) leach reactor. In some embodiments, impure metallic copper is rapidly and selectively dissolved into dilute sulfuric acid (e.g., 1-2 M H2SO4); wherein the mechano-chemical dissolution process is exothermic and produces a concentrated copper sulfate electrolyte that can be used to increase existing electrorefinery output, while simultaneously eliminating the need to recycle anode scrap back to a fire refinery (911). The disclosed processes may potentially eliminate fire refining (914, 214) steps altogether, for example, by processing blister copper directly, in order to produce a copper electrolyte (113, 222, 722) for cathode (116, 225, 725) production via electrowinning.

Description

HYDROMETALLURGICAL PROCESSES FOR LEACHING OR DISSOLVING METAL AND ENHANCING ELECTROREFINERY AND SMELTING OPERATIONS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application Serial
No. 62/157,386 filed on 19 February 2016 and titled "Systems and Methods for Leaching or Dissolving Metal". This application further claims the benefit of U.S. Provisional Patent Application Serial No. 62/359,124 filed on 6 July 2016 and titled "Hydrometallurgical Processes for Enhancing Electrorefinery and Smelter Operations". The aforementioned documents, and all others mentioned or referenced within this description, are hereby incorporated by reference in their entirety for any and/or all purposes as if fully set forth herein.
FIELD OF THE INVENTION
Embodiments of the invention relate to hydrometallurgical processing and more particularly, to leaching or dissolving metals. Embodiments also relate to enhancing electrorefining and/or smelting operations.
More precisely, this application pertains to novel systems and methods which may be employed for the rapid and complete dissolution of metals using a mechano- chemical/physico-chemical approach. The approach involves the application of mechanical energy which is sufficient to enable, facilitate, and/or promote metal dissolution in otherwise passivating systems, using a leaching agent (for example, oxygen-containing gas and an acid which may be selected from the group consisting of: sulfuric acid, hydrochloric acid, and a mixed acid which may comprise one or both of the former).
Some of the non-limiting embodiments disclosed herein pertain to systems and methods which may be employed for purposes of leaching blister copper (or metallic pieces substantially comprised of copper) using dilute sulfuric acid solutions (e.g., 1 -4M H2S04) and which may advantageously provide for the use of downstream direct copper electrowinning (D-EW) of resulting concentrated Cu(ll) sulfate solutions.
Some of the non-limiting embodiments disclosed herein pertain to systems and methods which may be employed for purposes of leaching blister copper (or metallic pieces substantially comprised of copper) using dilute hydrochloric acid solutions (e.g., 1 -4M HCI) and which may advantageously provide for the use of downstream direct copper electrowinning (D-EW) of resulting Cu(l) chloride solutions.
In some of the embodiments proposed, gold may be selectively recovered during a blister copper leaching process (or a leaching process involving the leaching of metallic solids substantially comprised of copper) as a solid residue. In still other embodiments, precious metals (e.g., silver and gold) may be recovered as their respective soluble chloro-complexes.
Some non-limiting embodiments disclosed herein further pertain to systems and methods which may be advantageously employed for leaching scrap portions of anodes used in electrorefining operations, as well as scrapped cathodes which do not meet London Metal Exchange (LME) grading requirements or need further refining.
Those skilled in the art will instantly recognize and appreciate that further embodiments of the technologies disclosed herein may present additional opportunities for leaching all types of metals, especially for recycling purposes. For example, embodiments may be configured for recycling components of batteries, printed electronic circuit boards (PCBs), and the like, without limitation. The processes described herein should not be limited in their use with only metallic copper, Rather, the leaching of metallic solids may be performed on a number of materials including, but not limited to, cobalt (Co), nickel (Ni), zinc (Zn), silver (Ag), gold (Au), lead (Pb), tin (Sn), iron (Fe), vanadium (V), rhodium (Rh), osmium (Os), rhenium (Re), platinum group metals (PGM's), other metals within the periodic table, and alloys thereof, without limitation.
BACKGROUND OF THE INVENTION
Traditionally, copper sulfides 901 are processed by first concentrating 902 copper-bearing minerals via crushing, grinding, and flotation. Gangue 903 is removed, and the produced concentrate 904 containing both copper and impurities is then smelted 905 to produce a copper-rich matte 907. Slag 906 is removed, and the copper-rich matte 907 is then converted 908 to blister copper 910 via the injection of oxygen within the melt, in order to remove impurities and sulfur dioxide (S02) 909. The blister copper 910 is then fire-refined 91 1 to still further remove impurities 912 such as sulfur (S) and oxygen (O). In the end, high purity copper (e.g., 99.7 - 99.99 % Cu) 916 may be produced via electrorefining 914. The aforementioned steps are schematically outlined in prior art process 900 shown in FIG. 1.
Conventional electrorefining 914 typically involves the melt-casting of copper anodes 913 which are to be used in the electrorefining step 914. Unfortunately, the various steps associated with electrorefining 914 generally involve significant amounts of energy and physical manipulation of copper intermediates. Additionally, metal impurities 915 such as iron (Fe), lead (Pb), selenium (Se), tellurium (Te), arsenic (As), and/or chrome (Cr), which may be present in the blister copper 910, are retained in the copper anodes 913 to be electro-refined 914. These impurities can eventually become captured in the "sludge" that forms at the bottom of electrorefining cells. The electrolyte flow through electrolytic cells is necessarily restricted to ensure that the impurity-containing sludge settles directly to the bottom of the cell(s) and does not come into contact with the high-purity cathode 916 surfaces. This restricted flow is a contributing factor in limiting cell throughput, and can be detrimental to the entire operation.
Selective leach processes (discussed herein) which would allow prior removal of impurities from the smelter product (ahead of cathode production), would advantageously enable the use of higher electrolyte flow and hence serve to increase cathode production.
Currently, very little information exists in literature regarding blister copper hydrometallurgy, the leaching of blister copper, or the acidic leaching of metallic solids. It is also well-known to those skilled in the art, that copper does not readily dissolve in dilute (e.g., 1 -2M) sulfuric or hydrochloric acids without the use of expensive oxidants such as hydrogen peroxide. While U.S. Patent Application Publication No. 2005/0130866 describes a process for the leaching of metallic copper via monoethanolamine and a carbonate salt the chemistry described in the publication is vastly different from the chemistry which is described herein.
Prior art methods related to the chemical-mechanical polishing of integrated circuits also rely on a variety of complexing agents (e.g., ammonium chloride (NH4CI)) and powerful oxidants (e.g., nitric acid (HN03), ferricyanide ([Fe(CN)6]3-), hydrogen peroxide (H202)) which are incompatible with a sulfuric acid system. A thermodynamic analysis of the effects of Cu(ll) concentration, pH, and redox potential shows that Cu(ll) is extremely insoluble in water under non-oxidizing conditions and that the Cu2+ stability field at low pH shrinks with increasing copper concentration (see, for example, K. Osseo- Asare, K. K. Mishra, Solution Chemical Constraints in the Chemical-Mechanical Polishing of Copper: Aqueous Stability Diagrams for the Cu-H20 and Cu-NH3-H20 Systems, Journal of Electronic Materials, Vol. 25, No. 10, 1996, pp. 1599-1607). Based on prior understandings regarding the limitations of Cu-H2S04-H20 systems, the dissolution of blister copper into a copper electrolyte for use in subsequent electrowinning operations would not be expected to be feasible. However, the inventors have established that the contrary is true (as will be further discussed herein).
To date, it has generally not been possible to dissolve a solid metal (such as blister copper) in an acid at or around atmospheric pressure, regardless of oxygen input or temperature. Dissolution into dilute sulfuric acid would, to date, require extremely high temperatures and high pressures - operating conditions such as those closely found in expensive pressure oxidation (POX) autoclaves. During electrorefining 914, most portions of metallic anodes 913 may be dissolved into solution, but typically up to around 10% of the anode mass is not dissolved into solution, and thus, the undissolved anodes (i.e., scrap anode) require recycling via recasting as new anodes.
Cost-saving methods to more efficiently and economically handle impurities, as well as increase plant throughput and/or decrease energy consumption can be of great value to the market. For example, eliminating any one or more of the steps shown in FIG. 1 (i.e., fire refining 91 1 , recasting of copper anodes, or the recycling of anode residues) during the production of high grade copper cathodes 916 could reduce environmental impacts and operating costs associated with the production of high-grade copper metal.
The copper smelting process involves, sequentially, the production of a copper- bearing matte 907, and the production of blister copper 910having a purity of about 99%. Fire-refining 914 is performed to further increase purity of the blister copper 910 to about 99.5%, at which point the purified blister copper may be casted into copper anodes 913 for electrorefining 914. The copper anodes may then be elecro-refined to produce cathode copper 916 which is 99.95-99.99% pure (see, for example, M.E. Schlesinger, M.J. King, K.C. Sole, W. G. Davenport, Extractive Metallurgy of Copper, 5th Ed., Elsevier, Oxford, UK, 2011). Electrorefining 914 of copper typically produces recycle scrap in the form of anode ears and off-specification cathodes, the amount of which can range between 15- to 20-wt% of the anode casting production (see, for example, G. Cifuentes, J. Hernandez, N. Guajardo, "Recovering scrap anode copper using reactive electrodialysis", American Journal of Analytical Chemistry, Vol. 5, 2014, 1020-1027). The recycle scrap is returned to an appropriate process step, upstream in the smelter, where it is blended with blister copper 910 and then returned to anode casting for recycle back to the electrorefinery. If properly managed, the inventory of recycle scrap can be minimized; however, both recycling of scrap inventory and the accumulation of scrap inventory represents a huge process inefficiency.
Metal impurities, such as iron (Fe), arsenic (As), lead (Pb), bismuth (Bi), antimony (Sb), etc., as well as precious metal values, including gold (Au) and silver (Ag), may be eventually captured in the sludge that is collected at the bottom of electrorefining cells. The electrolyte flow through the electrolytic cells is necessarily restricted to ensure that the sludge settles directly to the bottom of the cell and that it does not come in contact with the high-purity cathode 916 surface. The restricted hydrodynamic characteristics of the electrorefining cells are a contributing factor in limiting cell throughput (see, for example, D. Pletcher, Industrial Electrochemistry, Springer-Verlag, Berlin, Germany, 1984). Electrowinning 1 14, 223, 723 according to proposed embodiments might be a potentially viable alternative to electrorefining 914 if it were possible to rapidly and selectively dissolve anode scraps or blister copper to produce a suitably concentrated copper electrolyte. However, because of its electrochemical potential, copper does not readily dissolve in dilute sulfuric acid (e.g., 1 -2 M) without the use of an oxidant such as oxygen (02). Low gas solubility and slow mass transfer of 02 into strong electrolyte solutions currently presents a huge technical challenge to achieving commercially-viable dissolution rates for metallic copper.
The inventors have explored the use of a mechano-chemical approach to enhance the dissolution and recovery of copper from refractory minerals like chalcopyrite (see, for example, C. Eyzaguirre, S. Rocks, R. Klepper, F. Baczek and D. Chaiko, "The FLSmidth Rapid Oxidative Leach (ROL) Process: A Mechano-Chemical Approach for Rapid Metal Sulfide Dissolution, " Hydroprocess, Antofagasta, Chile, 2015). The concept involves combining mechanical and chemical processes within a special purpose reactor. Mechanical interactions therein provide the activation energy necessary to drive chemical reactions as opposed to thermochemical processes, which require an adequate supply of heat to reach an activated transition state (see, for example, D.J. Chaiko, F. Baczek, S. Rocks, T. Walters, and R.P. Klepper, "The FLSmidth® Rapid Oxidation Leach (ROL) Process. Part I: Mechano-Chemical Process for Treating Chalcopyrite, " Conference of Metallurgists, Hydrometallurgical Processes & Technologies, Lucy Rosato Memorial Symposium, Toronto, Canada, August 23-26 2015).
The inventive concept of using mechanical activation, in the form of a combined mechano-chemical process, to facilitate and accelerate the dissolution of blister copper, anode scrap, off-specification cathode, and high-purity recycled copper is introduced herein. Because of its high-purity, the resulting acidic copper-sulfate electrolyte is deemed to be a suitable feed for direct electrowinning, and/or electrorefining, without limitation. Copper dissolution kinetics for blister copper, anode scrap, off-specification cathode, and high-purity recycled copper under atmospheric conditions, are also presented.
The following additional references to literature within the field of the invention and being made herewith are as follows:
P. Balaz, Mechanochemistry in Nanoscience and Minerals Engineering, Springer-Verlag, Berlin, Germany, 2008.
S.L. James, C.J. Adams, C. Bolm, D. Braga, P. Collier, T. Friscic, F. Grepioni,
K.D.M. Harris, G. Hyett, W. Jones, A. Krebs, J. Mack, L. Maini, A. G. Orpen, I. P. Parkin, 1/1/. C. Shearouse, J. W. Steed and D. C. Waddell, "Mechanochemistry: opportunities for new and cleaner synthesis", Chem. Soc. Rev., Vol. 41, 2012, 413-447.
E. Mattisson and J. O'M. Bockris, "Galvanostatic studies of the kinetics of deposition and dissolution in the copper/ copper sulphate system", Trans. Faraday Soc, Vol. 55, 1959, 1586-1601.
P. Marcus, Corrosion Mechanisms in Theory and Practice, CRC Press, Boca Raton, FL, USA, 2012.
P. Balaz and M. Achimovicova, "Mechano-chemical leaching in hydrometallurgy of complex sulphides, " Hydrometallurgy, Vol. 84, 2006, 60-68.
J.R. Cobble, C.E. Jordan, and D. A. Rice, "Hydrometallurgical production of copper from flotation concentrates", USBM Rl 9472, 1993.
EKATO Handbook of Mixing Technology, EKATO Ruhr- und Mischtechnik GmbH, Schopfheim, Germany, p. 15, 2002.
N. de Nevers, Fluid Mechanics for Chemical Engineers, 3rd ed., McGraw Hill, New York, NY, USA, 2005, p. 567.
Z.D. Stankovic, V. Svetkovski and M. Vukovic, "The effect of antimony in anodic copper on kinetics and mechanism of anodic dissolution and cathodic deposition of copper, " Journal of Mining and Metallurgy, Vol. 44, 2008, 107-114.
All of the above-mentioned references are hereby incorporated by reference in their entirety for any and all purposes as if fully set forth herein.
OBJECTS OF THE INVENTION
It is, therefore, an object of some embodiments of the present invention, to provide a more efficient way to produce a metal cathode.
It is also an object of some embodiments of the present invention, to provide a manner in which to produce metal cathodes via leaching and electrowinning, rather than via fire refining/electrorefining steps.
It is also an object of some embodiments of the present invention, to provide a manner in which to produce metal cathodes via leaching and electrowinning, in addition to fire refining/electrorefining steps.
It is also an object of some embodiments of the present invention, to provide a manner in which to produce metal cathodes by direct electrowinning (D-EW) of dissolved blister copper, rather than by electrorefining.
It is yet another object of some embodiments of the present invention, to reduce the amount of S02 and CO produced during cathode production. Moreover, it is an object of some embodiments of the present invention, to provide a system and method for rapidly, efficiently, and economically dissolving a metallic solid into solution (i.e., acidic metallic dissolution) at or substantially near atmospheric conditions.
These and other objects of the present invention will be apparent from the drawings and description herein. Although every object of the invention is believed to be attained by at least one embodiment of the invention, there is not necessarily any one embodiment of the invention that achieves all of the objects of the invention. BRIEF SUMMARY OF THE INVENTION
A method of dissolving impure metallic copper (Cu°) is disclosed. The method may comprise the step of providing a leach reactor. The leach reactor is preferably configured to mechano-chemically dissolve impure metallic copper. The method may further comprise the step of providing impure metallic copper to the leach reactor in the presence of (i) sulfuric acid, and (ii) oxygen or air. In preferred methods, mechano- chemical leaching of the metallic solids takes place in the leach reactor. Moreover, preferred methods involve an exothermic dissolution of the impure metallic copper. For example, the impure metallic copper in the leach reactor may be exothermically and mechano-chemically leached at a temperature above 50°C, according to one of the following equations:
2Cu° + 02 + 2H2S04→ 2CuS04 + 2H20
(1 )
2Cu2+ + S03 2" + H20→ 2Cu+ + H2S04
(2)
Figure imgf000008_0001
Cu°+ Cu2+
without limitation. During exothermically and mechano-chemically leaching, the leach reactor may consume between approximately 50 and 1000 kWh per ton of copper recovered from the impure metallic copper, without limitation. More preferably, the leach reactor may consume between approximately 50 and 500 kWh per ton of copper recovered from the impure metallic copper, without limitation. For example, as shown in the accompanying example and Table 3 herein, approximately 91 -236 kWh per ton of copper recovered may be consumed by a leach reactor, without limitation. Moreover, the method is preferably capable of reaching dissolved copper concentration levels which are (i) equal to or greater than a solution saturation level, (ii) saturated, or (iii) super-saturated, without limitation (See FIG. 8).
In some embodiments, the method may comprise a size reduction step, wherein the impure metallic copper may be divided into smaller pieces or otherwise reduced in size before exothermic mechano-chemical leaching takes place, without limitation. It should be understood that size reduction of the impure metallic copper may also occur during mechano-chemical leaching. In some embodiments, the step of exothermically and mechano-chemically leaching may be performed under oxygen (02) partial pressure conditions between approximately 0.1 bar and 10 bar, without limitation. In some embodiments, the impure metallic copper may comprise material selected from one or more of the group consisting of: blister copper, copper cathode, copper anode, recycled copper, and scrap copper, without limitation.
In some embodiments, the leach reactor may be configured to stir the impure metallic copper via a driven shaft. The driven shaft may be provided with an impeller, one or more stirring arms extending radially from the driven shaft, or at least one cantilevered arm extending from the driven shaft at an angle which is not parallel to the axis of the driven shaft, without limitation. As suggested in FIG. 5, a plurality of substantially orthogonally-extending arms 403 which are configured as stirring bars may be employed by a leach reactor, without limitation. Various types of stirring devices may be provided to the driven shaft, including, but not limited to: a flat paddle agitator, a finger paddle agitator, a gate paddle agitator, a counter-rotating a paddle agitator, a disk and cone agitator, a impeller, a straight blade turbine agitator, a pitched blade turbine agitator, a vaned disk turbine agitator, a curved blade turbine agitator, a slotted rotary or rotating disk agitator, a helical screw agitator, a ribbon helix agitator, a gate agitator, an anchor agitator, a round anchor agitator, a flame-type agitator, a combined anchor and gate agitator, a propeller agitator, an oar-type agitator, a turbine-type agitator, or the like, without limitation.
In some embodiments, as suggested in FIGS. 6 and 7, the leach reactor may be configured to tumble the impure metallic copper in order to enhance chemical reactivity, without limitation. Tumbling may occur via a leach reactor configured with a horizontally- arranged rotating drum chamber. In some embodiments, the leach reactor may agitate the impure metallic copper in order to enhance chemical reactivity, by intermittently alternating the direction of drum rotation (e.g., from counter-clockwise, to clockwise, and back to counter-clockwise); or, by intermittently reversing the direction of shaft rotation (e.g., from counter-clockwise, to clockwise, and back to counter-clockwise), without limitation. In some embodiments, the leach reactor may vibrate the impure metallic copper in order to enhance chemical reactivity, without limitation. In some embodiments, the leach reactor may tumble the impure metallic copper via a rotating horizontally- arranged drum, in order to enhance chemical reactivity. While not explicitly shown in the figures, in some embodiments, the leach reactor may vibrate the impure metallic copper via a chamber configured with a vibratory or shake mechanism, in order to enhance chemical reactivity.
In some embodiments, the method may further comprise the step of producing leach residue during the step of exothermically and mechano-chemically leaching. The leach residue may be processed to remove or recover precious metals, impurities, or insoluble metals contained within the leach residue, without limitation. Steps of producing electrolyte, electrowinning the electrolyte, producing spent electrolyte, and processing the spent electrolyte to remove or recover impurities contained therein may also be practiced in accordance with some embodiments.
Also disclosed, is a method of dissolving impure metallic solids into solution. The method may comprise the step of providing a leach reactor configured to mechano- chemically dissolve said impure metallic solids. The method may further comprise the step of providing impure metallic solids to the leach reactor in the presence of (i) oxygen or air, and (ii) one or more leaching agents which are configured to facilitate the dissolution of the impure metallic solids. The impure metallic solids may, according to some preferred embodiments, comprise a metal selected from the group consisting of: copper, nickel, zinc, gold, silver, lead, tin, cobalt, iron, vanadium, rhodium, osmium, rhenium, a platinum group metal, and a combination thereof, without limitation. The impure metallic solids may be exothermically and mechano-chemically leached in the leach reactor at a temperature above 50°C. During exothermically and mechano- chemically leaching, the leach reactor may consume between approximately 50 and 1000 kWh per ton of metal recovered from the impure metallic solids. For example, between approximately 50 and 500 kWh per ton of metal recovered from the impure metallic solids may be consumed, without limitation. In most preferred embodiments, the method is capable of reaching dissolved metal concentration levels which are (i) equal to or greater than a solution saturation level, (ii) saturated, or (iii) super-saturated, without limitation. In some embodiments, the impure metallic solids may comprise precipitate. In some embodiments, a size reduction step may be employed, wherein the impure metallic solids may be divided into smaller solids or otherwise reduced in size before exothermically and mechano-chemically leaching them, without limitation. The step of exothermically and mechano-chemically leaching may be performed under oxygen (02) partial pressure conditions between approximately 0.1 bar and 10 bar, however, oxygen (02) partial pressure conditions during exothermic mechano-chemical leaching may lie between approximately 0.1 bar and 5 bar, for example, between approximately 0.1 and 2 bar, without limitation.
In some embodiments, the leach reactor may stir the impure metallic solids via a driven shaft which may be provided with an impeller, one or more stirring arms extending radially from the driven shaft, or at least one cantilevered arm extending from the driven shaft at an angle which is not parallel to the axis of the driven shaft, without limitation. In some embodiments, the leach reactor may tumble the impure metallic solids, in order to enhance chemical reactivity, without limitation. In some embodiments, the leach reactor may agitate the impure metallic solids, in order to enhance chemical reactivity, without limitation. In some embodiments, the leach reactor may vibrate the impure metallic solids, in order to enhance chemical reactivity, without limitation. In order to make the impure metallic solids more conducive for leaching in a leach reactor, they may be cut, sheared, shredded, machined, forged, cast, formed, drawn, rolled, stamped, punched, ground, comminuted, crushed, chemically-treated, melt-screened, or shaped in the form of strips, rods, bars, elongated members, beads, or shot, prior to exothermic and mechano-chemical leaching within the leach reactor, without limitation. In some embodiments, tumbling may be utilized to leach larger metallic solids such as strips, rods, bars, and elongated metallic members. In some embodiments, high energy stirring may be utilized to leach smaller metallic solids such as beads and shot.
According to some embodiments, the method may further comprise the step of producing a leach residue from leaching. The leach residue may be processed for the treatment of, removal of, and/or recovery of precious metals, impurities, or insoluble metals contained within the leach residue, without limitation.
A cathode product may be formed via any of the embodiments shown and described herein - in particular, through the use of exothermic mechano-chemical leaching techniques involving impure metallic solids (e.g., impure metallic copper) as both a feed material (to be leached), and as an autogenous grinding media catalyst for driving exothermic mechano-chemical reactions, without limitation.
Further details may be appreciated from the below detailed description, appended drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS
To complement the description which is being made, and for the purpose of aiding to better understand the features of the invention, a set of drawings illustrating various methods and systems according to certain embodiments has been added to the present specification as an integral part thereof, in which the following has been depicted with an illustrative and non-limiting character. It should be understood that like reference numbers used in the drawings (if any are used) may identify like components. In the drawings:
FIG. 1 suggests a pyrometallurgical copper refining circuit and process according to the prior art.
FIG. 2 suggests a modified pyrometallurgical copper refining circuit and process according to some embodiments, which incorporates the hydrometallurgical leaching of blister copper and subsequent electrowinning of the formed electrolyte, in lieu of the traditional fire refining and subsequent electrorefining steps shown in prior art FIG. 1.
FIG. 3 suggests a modified pyrometallurgical copper refining circuit and process according to some embodiments, which incorporates the hydrometallurgical leaching of scrap copper anodes (or other metallic solids substantially comprising copper, such as scrap copper cathode), and subsequent electrowinning of the electrolyte formed therefrom.
FIG. 4 suggests a method of leaching a metal, such as metallic copper, in an acid, such as a dilute sulfuric acid, according to some non-limiting embodiments.
FIG. 5 suggests stirring apparatus for subjecting metallic solids to autogenous contact and mechano-chemical/physico-chemical processing, while in the presence of a leaching agent, according to some non-limiting embodiments.
FIG. 6 suggests tumbling apparatus for subjecting metallic solids to autogenous contact and mechano-chemical/physico-chemical processing, while in the presence of a leaching agent, according to some non-limiting embodiments.
FIG. 7 suggests tumbling apparatus for subjecting metallic solids to autogenous contact and mechano-chemical/physico-chemical processing, while in the presence of a leaching agent, according to some non-limiting embodiments.
FIG. 8 compares prior art performance with results achieved by mechano- chemical/physico-chemical leaching of metallic copper in a dilute sulfuric acid according to some non-limiting embodiments.
FIG. 9 shows a scanning electron microscopy (SEM) image of a polished cross section of a metallic copper particle which was partially-leached according to prior art methods. The passivating layer shown may be primarily composed of copper oxides as determined by energy dispersive X-ray spectroscopy (EDS), without limitation. The passivating layer shown may be primarily responsible for poor leach performance (See bottom of FIG. 8, "prior art methods").
FIG. 10 suggests that in the absence of mechanical activation (i.e., surface scrubbing during the leach process), the dissolution rate of anode scrap in 180 g L"1 H2S04 may be linear with respect to the square root of time, without limitation. This correlation may be indicative of a metal corrosion process with the continuous buildup of a surface passivation layer, without limitation.
FIG. 1 1 shows increasing copper tenor versus time with the mechano-chemical leaching of blister copper using a solution of 155 g L"1 H2S04 and 15 g L"1 initial Cu, at 1 atmosphere 02, according to some embodiments.
FIG. 12 illustrates an effect of antimony (Sb) impurity concentration on the mechano-chemical leaching of metallic copper, according to some non-limiting embodiments.
FIG. 13 shows the mass balance of copper (Cu), oxygen (02), sulfuric acid
(H2SO4), and water for a leach-electrowinning circuit (assuming no losses through bleed streams), according to some embodiments.
FIG. 14 suggests a flowsheet for processing anode scrap via leach and direct electrowinning, according to some non-limiting embodiments.
In the following, the invention will be described in more detail with reference to drawings in conjunction with exemplary embodiments.
DETAILED DESCRIPTION OF THE INVENTION The following description of the non-limiting embodiments shown in the drawings is merely exemplary in nature and is in no way intended to limit the inventions disclosed herein, their applications, or their uses.
Disclosed herein are processes 100, 200, 300, 700 for the rapid leaching of solid metal (e.g., blister copper). Preferred embodiments of the processes 100, 200, 300, 700 aim to improve upon traditional copper recovery processes 900 (FIG. 1 ), by enabling commercially-viable leaching of solid copper metals. Some preferred embodiments may advantageously replace traditional fire refining operations 91 1 with novel leaching techniques 1 1 1 that allow pure copper 1 16 to be manufactured from lesser grade copper 1 10 via electrowinning 1 14, as opposed to electrorefining 914. As suggested by FIGS. 3 and 14, some preferred embodiments might supply supplemental processing routes through the provision of one or more hydrometallurgical process islands 230, 730, which can serve to "upgrade" existing refineries. For example, according to some embodiments, a method 100 of rapidly leaching a metal might include the steps of: i) identifying a plant having a fire refining operation 91 1 and an electrorefining operation 914, ii) replacing the fire refining operation 91 1 with a leach operation 1 1 1 as suggested by FIG. 2, and iii) replacing the electrorefining operation 914 with an electrowinning operation 1 14 to form an improved process 100 as suggested in FIG. 2, without limitation.
As another example, in some embodiments, rather than blister copper 910 entering a fire refining 91 1 step to produce copper anode 913 which can be elecro- refined 914 to produce pure copper cathode 916 (FIG. 1 ), an upgraded plant 100 may, instead, leach 1 1 1 blister copper 1 10 and then electrowin 1 14 the electrolyte 1 13 formed during the leach operation 1 1 1 , without limitation.
Moreover, in some embodiments (FIG. 3), scraps of copper anode 217 recovered after elecro-refining 214 may be leached 220 to produce copper cathode 225 via an electrowinning operation 223. As shown, leaching 220 and electrowinning 223 may be performed in a downstream hydrometallurgical process island 230. Upstream from the process island 230, plant operations 200 may continue to fire refine 212 blister copper 210 and electro-refine 214 resulting copper anodes 213, as conventionally done, without limitation. In any embodiment discussed herein, scraps of copper anode 217 recovered from elecro-refining 214 may be optionally recycled to a fire-refining operation 21 1 (if present), in any amount(s), for anode re-cast, without limitation.
FIG. 2 illustrates a system and method 100 according to some embodiments of the invention, wherein some process steps (e.g., operations 91 1 -915 shown in prior art FIG. 1 ) may be replaced with other process steps (e.g., operations 1 1 1 -1 15 shown in FIG. 2), without limitation. For example, FIG. 2 suggests how the fire refining 91 1 and electrorefining 914 operations of FIG. 1 may be bypassed completely by employing inventive mechano-chemical/physico-chemical hydrometallurgical leaching 1 1 1 and electrowinning operations 1 14 in their place. Leaching 1 1 1 may be performed under atmospheric or substantially atmospheric pressure conditions, as well as above atmospheric conditions, without limitation.
Copper sulfides 101 containing copper-bearing minerals are concentrated 102 via crushing, grinding, and flotation as conventionally done in a sulfide concentrator. Gangue 103 may be removed, and the produced copper-rich concentrate 104 may be smelted 105 to remove impurities 106 (e.g., slag, S02), producing a copper-rich matte 107. The copper-rich matte 107 may be converted 108 to blister copper 1 10 via the injection of oxygen within the melt, in order to remove impurities 109 and sulfur dioxide (S02), without limitation. The blister copper 1 10 may then be leached 1 1 1 to further remove impurities 1 12 such as gold (Au), selenium (Se), sulfur (S), and/or antimony (Sb), without limitation. The leaching operation 1 1 1 preferably employs mechano- chemical, physico-chemical, and electrochemical interactions between the blister copper 1 10 being leached. Electrolyte 1 13 may be formed during the leaching process 1 1 1 may move to an electrowinning step 1 14 as shown, wherein additional impurities 1 15 (e.g., silver (Ag), tellurium (Te), lead (Pb), bismuth (Bi), and/or arsenic (As), without limitation) can be removed from the spent electrolyte. In the end, high purity copper (e.g., 99.7 - 99.99 % Cu) 1 16 may be produced via electrowinning 1 14. The aforementioned steps are schematically outlined in the process 100 embodiment shown in FIG. 2, without limitation.
FIG. 3 suggests how electrorefining 914 operations of FIG. 1 may be bypassed- in-part, through the provision of a downstream hydrometallurgical process island 230 which may comprise an optional size reduction operation 218, a specialized mechano- chemical/physico-chemical leach operation 220, and an electrowinning operation 223, without limitation. The process island 230 may, as shown, operate in parallel to a conventional flowsheet 900 similar to that shown in prior art FIG. 1 . Inventive mechano- chemical/physico-chemical hydrometallurgical leaching techniques 220 may be employed to leach copper anode scraps 217 obtained from electrorefining operations 214. Dissolution of the metallic solids may occur under atmospheric or substantially atmospheric pressure conditions within the leach operation 220; however, it should be understood that slightly above atmospheric pressure conditions (e.g., between 1 and 5 bar) and/or oxygen partial pressures between about 0.1 bar and 10 bar) are envisaged, without limitation. The figure illustrates a system and method 200 according to some embodiments of the invention, wherein process islands 230, 240 and their respective process steps or operations 217-225 may be added to the circuit 100 depicted in prior art FIG. 1. For example, existing fire refining 21 1 and electrorefining 214 operations may be upgraded with an "add-on" or "retrofittable" hydrometallurgical circuit 230, for example, to make copper cathode 225 from anode scraps 217 which are formed during electrorefining operations 214, as a more economical means for producing high grade cathode products.
In some embodiments, it may be desirable to send some or all pieces of scrap anodes 217 to the hydrometallurgical circuit 230, rather than recycle 226 them 217 to an upstream fire-refining operation 21 1 via a recycle process island 240, depending on economic considerations or circumstances which can vary over time. In some embodiments, some of the scrapped anodes 217 or pieces thereof may be recycled 226 to a fire refining process 21 1 via recycle process island 240, while some of the scrapped anodes 217 or pieces thereof may be hydrometallurgically processed in the hydromet circuit 230. It will be readily understood by those having an ordinary skill in the art, that scrap copper anodes 217 produced during an electrorefining step 214 may contain impurities 215. Some or all of the scrap copper anodes 217 may be sent to a downstream exothermic mechano-chemical leach operation 220 to remove a first number of the impurities 221 (e.g., gold, selenium, sulfur, antimony, etc., without limitation). Electrolyte 222 from the leach operation 220, in the form of a pregnant leach solution (PLS), may be sent to an electrowinning operation 223 downstream of the leach operation 220, in order to remove a second number of the impurities 224 (e.g., silver, tellurium, lead, bismuth, arsenic, etc.), without limitation. As suggested in FIG. 3 and 14, any portion of the scrap copper anodes 217 sent to the leach operation 220 from the electrorefining operation 214 may first be broken up 218, 718 into smaller pieces, in order to improve mechano-chemical, physico-chemical, and electrochemical interactions within the leaching 220, 720 portion of the circuit 230, 730 without limitation. As suggested in FIG. 14, screening operations 731 may be employed to remove liquids 720 (e.g., process water) after metallic solids have been reduced in size. Screening operations 731 may also be used to ensure a uniform size density for optimum leaching.
Regarding FIG. 2, copper sulfides 201 containing copper-bearing minerals may be concentrated 202 via crushing, grinding, and flotation. Gangue 203 may be removed, and the copper-rich concentrate 204 produced may be smelted 205 to remove impurities 206 (e.g., slag, S02) and produce a copper-rich matte 207. The copper-rich matte 207 may be converted 208 to blister copper 210 via the injection of oxygen within the melt, in order to remove impurities 209 and sulfur dioxide (S02), without limitation. The blister copper 210 may then be fire-refined 21 1 to further remove impurities 212 in the form of slag and sulfur dioxide (S02). Copper anodes 213 produced during the fire-refining step 21 1 may then be electro-refined 214 to form high-grade copper cathode 216 and sludge 215 comprising impurities like gold (Au), silver (Ag), selenium (Se), tellurium (Te), lead (Pb), bismuth (Bi), antimony (Sb), arsenic (As), etc., without limitation. Portions of copper anodes 213 which are typically left over from electro-refining processes 214 (i.e., scrap anodes 217) may be recycled back to the fire refining operation 21 1 via a process island 240 which includes the optional step 226 of recycling such scrap pieces 217 of copper anodes.
Downstream of the electro-refining operation 214, a hydrometallurgical process island 230 may comprise a size reduction step 218, wherein incoming pieces of scrapped copper anode 217 may optionally be reduced in size and/or number in any practical or feasible way known in the arts. For example, saw blade cutting, water jet cutting, plasma cutting, torching, scoring/breaking, shearing, or other method known in the art may be used to reduce the size of the scrap copper anodes 217 and increase the number of metallic solids, without limitation. In some preferred embodiments, (see FIG. 7), the scrap copper anodes may be provided as thin strips or bars, without limitation. After size reduction has occurred (if applicable) the anode scraps 217, 219 may be fed to a leaching operation 220 within the hydrometallurgical process island 230. Preferably, the leaching operation 220 employs means for encouraging mechano-chemical, physico- chemical, and electrochemical interactions between the blister copper solids 220 in the presence of a leaching agent (e.g., dilute sulfuric acid, spent electrolyte) and oxygen or air, without requiring nitric acid, peroxide, or external heating to drive dissolution.
Electrolyte 222 formed during the leaching process 220 may be moved to an electrowinning step 223, wherein additional impurities 224 (e.g., silver (Ag), tellurium (Te), lead (Pb), bismuth (Bi), arsenic (As), without limitation) can be removed and/or processed further. In the end, high purity copper cathode 225 (e.g., 99.7 - 99.99 % Cu) may be produced via electrowinning 223. The aforementioned steps are schematically outlined in the process 200 shown in FIG. 3.
Preferably, embodiments of the leach step 1 1 1 , 220, 720 shown in FIGS. 2, 3, or
14 may comprise the use of a specialized mechano-chemical leach reactor, such as a shear-tank reactor that is robust to wear and abrasion, and which may be pressurizable, and may withstand pH levels below 3, without limitation. The shear-tank reactor preferably comprises means for ingress of metallic solids, so that the metallic solids may autogenously be used as both i) grinding media, as well as ii) the "material to be leached" (see co-pending related application PCT/US 15/66003 which is hereby incorporated by reference in its entirety for any and all purposes as if fully set forth herein). For example, a leach step 1 1 1 , 220, 720, according to some embodiments, may comprise a stirred media reactor (SMRt); wherein the media provided to the stirred media reactor comprises blister copper 1 10 entering the leach step 1 1 1 , and wherein the blister copper simultaneously serves as autogenous grinding media, as well as the leach feed material to be dissolved into solution. According to some embodiments, additional media (e.g., ceramic beads) may be added to supplement mechano-chemical activation and provide a semi-autogenous application to the leach 1 1 1 , 220, 720, without limitation.
A schematic representation of mechano-chemical/physico-chemical hydrometallurgical leaching techniques according to some embodiments is shown in FIG. 4. Some or all of the process steps 301 -310 shown in the illustrated method 300 may be advantageously employed, in any combination, with the operations shown in FIGS. 2, 3, and/or 7, as well as in other conceived embodiments which may not be illustrated. For example, according to some non-limiting embodiments of a process 300, metallic solids may be provided 301 and optionally divided 302 into smaller pieces. For example, cutting (e.g., water jet, plasma cutting, etc.), shearing, shredding, machining, forging, casting, forming, drawing, rolling, stamping, punching, grinding, comminuting, crushing, chemically treating, melt-screening, shaping, or other methods known in the art may be used alone or in various combinations to form smaller pieces from metallic solids, without limitation. The metallic solids may then subjected to mechano- chemical/physico-chemical leaching in the presence of acid and an oxidant 303, without limitation. In some preferred embodiments, the metallic solids may comprise copper and may be provided in the form of blister copper, portions of scrapped copper anode tongues, pieces of scrapped cathodes which do not meet London Metal Exchange (LME) grade requirements, and/or recycle copper without limitation.
By virtue of chemical heating and/or friction between metallic solids being vigorously stirred, agitated, tumbled, or vibrated in a leaching vessel 400, 500, 600, a chamber of the leach reactor used in the leaching step 1 1 1 , 220, 720 may be exothermically heated. Accordingly, embodiments may comprise a leach reactor having a chamber which is optionally cooled 305 via the provision of means for cooling (e.g., a heat exchanger, a fluid-cooled jacket, a convection cooler, a conduction cooler, a fan, an evaporative cooler, a combination thereof, etc.), without limitation. The metallic solids within the leach reactor may be dissolved 306 into one or more leaching agents to form an electrolyte 1 13, 222, 722. Sludge (e.g., in the form of leach residue) may be optionally removed 307 from the respective leaching operation 1 1 1 , 220, 720, and processed or treated to remove or recover one or more impurities selected from a first set of impurities associated with the metallic solids leached, without limitation. The electrolyte 1 13, 222, 722 may be electrowon 308 to form a copper cathode 1 16, 225, 725 which is purer than the metallic solids leached (by grade or composition wt%). Spent electrolyte 1 15, 224, 724 may be removed 309 from the electrowinning operations 1 14, 223, 723, and may be processed 310 or treated to remove or recover one or more impurities selected from a second set of impurities associated with the metallic solids leached, without limitation. Spent electrolyte 1 15, 224, 724 may be recycled to the mechano-chemical leaching operation 1 1 1 , 220, 720 after impurity removal/recovery, without limitation.
For example, blister copper may be provided within a mechano-chemical leach reactor comprising an oxygen-containing gas and a dilute sulfuric acid, in some non- limiting embodiments. The leach reactor may be preferably configured to impart high energy mechanical stirring, agitation, tumbling, and/or vibration so as to promote autogenous contact between, and promote electrochemical reactions between blister copper solids in the presence of one or more leaching agents (e.g., dilute acid and 02), accelerate leach rates, and achieve dissolution to saturated or supersaturated dissolved copper concentration levels. The leach reactor may be configured to impart increased shear forces between the blister copper and reactor walls; wherein highly-energetic collisions taking place therein accelerate electrochemical reactivity between solids and improve copper dissolution kinematics (evidenced by FIGS. 8 and 10-12), without limitation. Mechano-chemical leaching may increase the number of collision sites, increase particle contact probability, increase the frequency and/or intensity of inter- particle surface contacts, and/or increase the surface area of contact zones between solids at a given time.
The leach reactor may comprise a specialized reactor such as a high-energy shear-tank reactor configured with a robust chamber which is resistant to oxidation, abrasion, impact, and/or excessive wear, without limitation. The leach reactor may comprise a specialized reactor such as a shear-tank reactor discussed in related copending applications, without limitation.
The schematic illustrations depicted in FIGS. 5-7 suggest various non-limiting systems and apparatus which may be employed within the hydrometallurgical leach component of the flowsheets shown in FIGS. 2, 3, and 7 without limitation. As depicted, various forms of rotational motion, agitation, tumbling, and vibration may be used to promote mechano-chemical leaching in a leach reactor. For example, vigorous stirring may be performed by rotationally driving a shaft that is provided with an impeller, one or more stirring arms extending radially from the shaft, or at least one cantilevered arm extending from the shaft at an angle which is not parallel to the axis of the shaft, without limitation. The driven shaft may (i) be rotated along its axis in one rotational direction (e.g., clockwise or counter-clockwise), or, the driven shaft may (ii) be agitated between clockwise and counter-clockwise rotational directions, without limitation. Tumbling may be accomplished by continuously rotating a horizontally-arranged drum (e.g., a drum reactor or a tumbling mill reactor) such that metallic solids therein may continuously rise and fall (by gravity), thereby creating autogenous high-energy mechanical collisions between the metallic solids in the presence of one or more leaching agents (e.g., air or oxygen and sulfuric acid), without limitation. Agitation may be accomplished by intermittently rotating a horizontally-arranged or a vertically-arranged drum reactor in a first rotational direction (e.g., clockwise), and then changing its rotational direction to the opposite rotational direction (e.g., counter-clockwise), without limitation. Vibration may be accomplished by providing a leach reactor with means for imparting vibration to the leach feed. The means for vibration may include, for example, a vibration mechanism (e.g., a rotating eccentric weight applied to a damped or un-damped spring-supported chamber or other spring and mass vibratory system), which is capable of receiving mechanical inputs. The vibration means may, upon mechanical input, shake or vibrate metallic solids within the leach reactor and promote exothermic and mechano-chemical leaching, without limitation.
As suggested in FIG. 5, the leach reactor may comprise an open- or closed- chamber having a driven stirring shaft provided therein, for vigorous stirring of metallic solids, without limitation. As suggested in FIGS. 6 and 7, the leach reactor may comprise a tumbling mill reactor configured with a rotating drum which forms a leaching chamber therein. The rotating drum of the leach reactor may be horizontally-arranged and may be supported below by rollers. In some embodiments, it may be supported by an axial, horizontally-disposed shaft spindle and accompanying shaft bearings provided along a horizontal axis 502 of rotation, without limitation. While not explicitly shown, the rotating drum may be driven by friction or torque via one or more peripherally-arranged driven rollers along its circumference, gearing, a chain and sprocket mechanism, a magnetic drive, a driven shaft, or the like, without limitation. For example, while not explicitly shown, the drum may be driven about its horizontal axis 502 via a drive shaft motor which is configured to impart a torque to the drum, without limitation. The drive shaft motor may be geared or provided with a transmission, without limitation. In some embodiments, a tumbling mill reactor may be agitated back and forth about axis 502 by changing rotational direction of the drum, or may it may be purely rotary in design (i.e., continuous clockwise or counter-clockwise rotation about axis 502). In some embodiments, a tumbling mill reactor may resemble a mini semi-autogenous grinding (SAG) mill, a mini ball mill, or a mini rod mill, without limitation. In preferred embodiments, a tumbling mill reactor may be adequately configured to hold one or more leaching agents (including dilute acids), adequately configured to resist corrosion and wear, adequately configured to handle impact forces, and/or configured to consume less power per unit of metal cathode produced than a traditional grinding mill, without limitation. In some embodiments, mechano-chemical leaching may occur in a modified pug mill apparatus, without limitation.
In preferred embodiments, autogenous contact occurs between metallic solids within the leach reactor. The leach reactor may be provided with means for introducing metallic solids such as blister copper, and may be open to ambient environments or pressurized/pressurizable to above atmospheric conditions (i.e., sealed), without limitation. For example, in some non-limiting embodiments, the leach reactor may resemble one or more of the reactors taught in related application PCT/US2015/066003 (published as WO2016/100453 and incorporated by reference herein, in its entirety, for any and all purposes as if fully set forth herein), without limitation.
As suggested in FIG. 6, metallic solids (e.g., blister copper) may be employed and provided to a rotating drum reactor (i.e., tumbling mill reactor) in the presence of one or more leaching agents, in order to impart energetic collisions therebetween and to encourage exothermic mechano-chemical/physico-chemical leaching therein. According to some embodiments, such a reactor may be provided to leach operations shown in FIGS. 2, 3, or 14, wherein the metallic solids comprise blister copper or pieces of scrap anodes, without limitation. The blister copper 1 10 may be provided to the leach operation 1 1 1 shown in FIG. 2 in the form of asymmetrical copper beads, without limitation. Metallic copper may be provided to the leach operation 220 shown in FIG. 2 in the form of cut up scrap copper anodes 219, without limitation.
As suggested in FIG. 7, strips of copper metal, copper metal bars, elongated pieces of undissolved copper anodes, and/or pieces of off-spec or scrapped copper cathodes not meeting LME-grade criteria may also be employed and provided to a rotating drum reactor/tumbling mill reactor, (with or without blister copper or other ceramic media), in order to impart energetic collisions therebetween and encourage exothermic mechano-chemical/physico-chemical leaching. While not shown, combinations of smaller and larger blister copper particles may be provided within the same chamber of a mechano-chemical/physico-chemical leach reactor, without limitation.
It should be duly noted that the disclosed technology may advantageously be applied to many other types, forms, and compositions of metallic solids. Accordingly, metallic solids comprising metals other than copper, or forms other than blister copper 1 10, 210 and/or scrap anodes 217, 717 may be applicable with the systems and methods 100, 200, 300, 730 disclosed herein. Such metallic solids may be similarly employed to leach operations 1 1 1 , 220, 720 as shown for impure metallic copper, without limitation. For example, the inventors contemplate that the processes disclosed herein, and various steps thereof, could advantageously be practiced with zinc, lead, gold, silver, aluminum, chromium, cobalt, manganese, rare earths, alkali metals, nickel, cadmium, and other metals which are able to be leached and electrowon, without limitation. According to some embodiments, metallic solids may comprise precipitated solids (i.e., "precipitate"), without limitation.
The inventors have discovered that increasing the frequency, probability, and/or intensity of dynamic inter-particle contacts between the metallic solids in the presence of one or more leaching agents (e.g., an oxygen-containing gas and an acid such as sulfuric acid for dissolving into solution, blister copper, scrap metals, and/or copper anodes) unexpectedly appears to greatly improve both dissolution kinetics and the extent of reaction for materials that are otherwise refractory.
While wishing not to be held to any one particular theory, the inventors believe that a possible mechanism for the greatly improved dissolution and leach kinetics may be attributed to special mechano-chemical/physico-chemical interactions (i.e., bond strain and lattice deformation(s)) which occur especially between anodic and cathodic sites along surfaces of metallic pieces during energetic physical contact. In some preferred embodiments, the energetic physical contact takes place within any combination of one or more mechano-chemical reactors selected from the group consisting of: a shear-tank reactor, a stirred media reactor, a rotating drum reactor, a tumbling mill reactor, and a vibratory reactor, without limitation. Metallic solids such as metal beads (e.g., blister copper beads), pieces of spent anodes (e.g., spent copper anode pieces), and/or pieces of scrap/off-spec cathodes (e.g., pieces of scrap/off-spec copper cathodes), may simultaneously serve as both grinding media and leach feed material.
Regardless of the actual mechanism(s) being employed, the unexpected dissolution results for otherwise refractory solid blister copper (shown in FIG. 8-1 1 ) indicate that some phenomenon occurs which greatly outperforms the less dynamic, electrochemical dissolution techniques found within the prior art. It is suspected that special mechano-chemical/physico-chemical interactions and energetic contacts/collisions between metallic solids in the presence of oxygen or air, and one or more leaching agents may be responsible for the increased performance. EXAMPLE 1
Attempted dissolution of blister copper in a dilute sulfuric acid electrolyte (i.e., 200 g H2S04 per L) with conventional solution agitation and in the presence of an oxygen gas purge failed to produce any appreciable dissolution of metallic copper. This result is fully consistent with prior art experience. However, according to some preferred embodiments, a feed of blister copper may be added to an intensely mixed stirred-media reactor filled with liquor containing the same components (i.e., dilute sulfuric acid, and oxygen) with much better and unanticipated results. For example, by employing the stirred-media reactor and aforementioned leach liquor, it has been demonstrated that it is possible for blister copper to be leached to completion and to reach solution saturation with respect to copper sulfate within only 40 minutes or less, as shown in FIG. 5. It is preferred that the copper beads being leached vigorously rub against one another and/or against various metallic reactor surfaces. During testing, the copper beads being leached underwent vigorous particle-particle collisions together with vigorous impact against the stainless steel reactor walls.
Interestingly, when practicing the above preferred blister copper leaching method, a black, hydrophobic solid forms during the leach reaction. Analysis of this black, hydrophobic solid proved that it contained less than 1 % of the copper feed to the reactor, but contained significant fractions of the contaminating elements present in the blister copper leached (e.g., sulfur, silver, gold, bismuth, selenium, arsenic). Within error of the analytical method (ICP-AES), the inventors noted that selenium, lead, gold, and silver were quantitatively recovered within the insoluble leach residue. Additional elements which were only poorly solubilized within the copper sulfate electrolyte included iron, chrome, antimony, bismuth, arsenic, and manganese.
The blister copper leach reaction was highly exothermic and appeared quite capable of autogenously heating the electrolyte solution to at least near its boiling temperature. The dissolution reaction also proceeds with highly unexpected speed. Due to the isolated and hydrophobic nature of the leach residue, it may be separated from the electrolyte solution by any number of processes known to those skilled in the art, such as filtration, centrifugation, or flotation (without limitation), and separately processed.
Accordingly, in some embodiments, precious metals and other insoluble metals contained within leach residue 1 12, 221 , 721 may be sent to another step for further processing or treatment in order to separate, and remove or recover metal values. Advantageously, without having to collect tank house slimes as traditionally done, more intense mixing within the electrolytic cells can be used to increase cathode production via electrowinning.
Applying the inventive concepts associated with the systems and methods disclosed herein, it is envisaged that portions of scrap metallic anodes 217 which might be recycled back into the fire-refining step 21 1 may be optionally divided 218, 718 into smaller pieces 219, 719 (e.g., via waterjet or sawblade cutting or the like), and then leached 220, 720 within a shear-tank reactor (e.g., a stirred-media reactor), wherein the metal scraps constitute both "media" and the "material to be leached". In some preferred embodiments, energy imparted within the shear-tank reactor (e.g., in the form of aggressive agitation, stirring, tumbling, vibrating, or a combination thereof) is sufficient to quickly dissolve metallic anode segments within the electrolyte solution. Using the inventive systems and methods disclosed herein, it is further envisaged that rejected cathodes which do not meet quality specifications (e.g., which are not LME grade, or, are less than 99.95% pure) or are to be scrapped or recycled, may be optionally divided into smaller pieces, and then leached within a mechano-chemical leach reactor in the presence of one or more leaching agents. In some preferred embodiments, energy imparted to metallic solids within the mechano-chemical leach reactor (e.g., in the form of agitation, stirring, tumbling, vibrating, or a combination thereof) is sufficient to quickly dissolve scrapped cathode.
In some envisaged embodiments, reject cathodes may be cut into long strips or bars, as suggested in FIG. 7. A rod mill configured as a tumbled media leach reactor which is able to contain one or more leaching agents (e.g., an oxygen-containing gas, and dilute sulfuric acid) may receive the reject metal for dissolution. The tumbled media leach reactor may be run in the presence of the one or more leaching agents, without limitation.
Autogenous grinding of the reject metal pieces and the increased probability of impacts therebetween, in the presence of one or more leaching agents, may substantially expedite leaching (FIGS 8, 10-1 1 ). Energetic collisions between the pieces of reject metal may also expedite leaching. In order to address exothermic heating, a leach reactor conducting the leach reactions may be optionally configured with cooling means, to compensate for increases in chamber temperatures due to friction and reactions taking place. As suggested in step 305 of FIG. 4, cooling means may include such apparatus as one or more heat exchangers, one or more fluid-cooled jackets, one or more convection coolers, one or more conduction coolers, one or more fans, one or more evaporative coolers, one or more cooling baths, one or more radiators, one or more leaching agent coolers with recycle stream, one or more spray coolers, one or more air conditioning units, one or more air-cooling blowers, a combination thereof, or the like, without limitation. Any cooling means known in the art may be employed to regulate temperatures and exothermic heating of leach reactors described herein. Moreover, such leach reactors may be configured to hold or release pressure, without limitation. In this regard, boiling acid and/or buildup of acid vapor pressure during dissolution operations 1 1 1 , 220, 303, 720 may be handled and managed appropriately.
EXAMPLE 2
The following portion of this example employs experimental data, as well as data pertaining to prepared samples used for the leach studies described herein. General Considerations
Leaching of metallic copper was conducted using a mechano-chemical (M-C) reactor and a reservoir of solution (1 1 L volume) with an initial sulfuric acid concentration of 1 .8 M (180 g L"1). Details of the reactor used have been published (see, for example, D.J. Chaiko, F. Baczek, S. Rocks, T. Walters, and R.P. Klepper, "The FLSmidth® 20 Rapid Oxidation Leach (ROL) Process. Part I: Mechano-Chemical Process for Treating Chalcopyrite, " Conference of Metallurgists, Hydrometallurgical Processes & Technologies, Lucy Rosato Memorial Symposium, Toronto, Canada, August 23-26 2015). Leach tests were conducted at a constant temperature of 80°C. During the leach tests, the metallic copper samples, in the form of copper shot, were retained within the M-C reactor while H2S04 electrolyte was recirculated through the system. Pure oxygen gas was injected in-line and upstream of the bench top M-C reactor, and return copper- bearing electrolyte solution and excess oxygen gas, if any, were collected in the liquid reservoir for recycle.
Feed Characteristics
Three sources of copper were used in the leach tests: 1 ) recycle copper shot, 2) blister copper, and 3) anode scrap. Elemental analyses of the copper feeds are provided in Table 1 . The recycle copper and blister copper were processed in their native form. The anode scrap was melted and cast through a ceramic screen (Belmont Metals, Brooklyn, NY) to produce a granulated product amenable to leaching in the M-C reactor. Size distributions of the metallic copper feeds are provided in Table 2. Table 1 - Abbreviated elemental analysis of copper test samples
Anode Scrap Blister Copper Recycle Copper
Element Unit Concentration
Cu wt% 97.4 97.4 98.1
Fe wt% 0.016 0.109 0.007
As ppm 1460 653.6 1 1.9
Bi wt% 0.042 0.044 <0.001
Sb ppm 61.6 53.4 2.4
Co ppm <2.0 5.27 <2.0
Pb wt% 0.179 0.195 0.061
Se ppm 467 423 12.3
Zn wt% 0.159 0.305 0.305
W wt% <0.0004 0.012 0.01 1
Cr ppm 6.34 1 1.08 6.75
Ni wt% 0.022 0.018 0.0035 To investigate the efficacy of the M-C metallic leach on smelter products, blister copper and anode scrap were used as feed materials. Because this leach technology also applies to metal recycling, mechano-chemical leach tests were performed using recycled copper in addition to smelter products. Additionally, recycled copper could be expected to yield leach results similar to off-specification cathodes. Since the composition of an ore body will directly impact the impurity content of smelter products, blister copper and anode scrap samples would contain a wider range of impurity concentrations compared to recycled copper. We should note that these three particular samples are not related to one another by process, hence the higher-than-expected impurities in the anode scrap relative to the blister copper sample. The three different feed types afforded an opportunity to examine the impact of impurities on the copper leach rate with arsenic, antimony, selenium and bismuth contents varying greater than an order of magnitude between samples. Table 2 - Particle size distributions of the three metallic copper samples
Anode Scrap Blister Copper Recycle Copper
Mesh Size % Passing
1/4" 98.1 100 100
4 M 69.8 94.6 100
10 M 24.1 72.8 80.2
14 M 1 1.6 53.7 30.5
20 M 5.9 31.8 1 1.5
28 M 2.9 14.8 3.4
35 M 1 .6 1 .9 1 .2
48 M 0.9 1 .3 0.4
65 M 0.5 0.9 0.1
The following portion of this example employs results. Effect of Mechanical Activation on Cu Dissolution
Unlike the metals that occupy positions higher in the electrochemical series and which are capable of reducing H+ to H2 (e.g., Zn and Fe), copper is not capable of reacting directly with dilute sulfuric acid solutions (i.e., 1 -2 M H2S04) (see, for example, E. Mattisson and J. O'M. Bockris, "Galvanostatic studies of the kinetics of deposition and dissolution in the copper/ copper sulphate system", Trans. Faraday Soc, Vol. 55, 1959, 1586-1601). Instead, an oxidant must be supplied to drive the anodic dissolution of copper in H2S04. If sufficient oxygen and acid are supplied, the dissolution reaction will proceed according to:
2Cu° + 02 + 2H2S04→ 2CuS04 + 2H20 (1 )
The rate of copper dissolution will depend, in part, upon oxygen and H+ ion concentrations at the reacting surface. However, the accompanying formation of a passivation layer during oxygen-catalyzed dissolution further contributes to the difficulty of dissolving copper in dilute sulfuric acid (see FIGS. 8 and 9). The leach data in FIG. 10 are consistent with the classic kinetics profile of a metal corrosion process coincident with the production of a passivation layer (see, for example, P. Marcus, Corrosion Mechanisms in Theory and Practice, CRC Press, Boca Raton, FL, USA, 2012).
The concept of combining mechanical and chemical processes has been shown to offer potentially significant benefits in a variety of hydrometallurgical applications (see, for example, P. Balaz and M. Achimovicova, "Mechano-chemical leaching in hydrometallurgy of complex sulphides, " Hydrometallurgy, Vol. 84, 2006, 60-68.; See also, J.R. Cobble, C.E. Jordan, and D. A. Rice, "Hydrometallurgical production of copper from flotation concentrates", USBM Rl 9472, 1993). This is a technology area in which the inventors of the present invention have been active, and have developed a patent- pending mechano-chemical process for treating highly refractory minerals, such as chalcopyrite (see, for example, C. Eyzaguirre, S. Rocks, R. Klepper, F. Baczek and D. Chaiko, "The FLSmidth Rapid Oxidative Leach (ROL) Process: A Mechano-Chemical Approach for Rapid Metal Sulfide Dissolution, " Hydroprocess, Antofagasta, Chile, 2015:, See also, D.J. Chaiko, F. Baczek, S. Rocks, T. Walters, and R.P. Klepper, "The FLSmidth® 20 Rapid Oxidation Leach (ROL) Process. Part I: Mechano-Chemical Process for Treating Chalcopyrite, " Conference of Metallurgists, Hydrometallurgical Processes & Technologies, Lucy Rosato Memorial Symposium, Toronto, Canada, August 23-26 2015). This new approach takes advantage of the enhanced chemical reactivity of transitory, surface-defect structures generated under applied mechanical energy, and it has been highly effective at increasing both leach rates and copper recoveries. The inventors of the present invention are also exploring the application of mechano-chemical leaching to a variety of other process systems - including, but not limited to, metal recycling.
As shown in FIG. 1 1 , the application of mechano-chemical processing during metallic copper leaching, results in a dramatic increase in leach kinetics and in dissolved metal recovery. The leach rate may be pseudo-zero order, as evidenced by the linear relationship between dissolved copper concentration and time. The mechanical forces acting upon the particle surfaces appear to eliminate the build-up of surface passivation films. Accordingly, mechano-chemical processing during leaching operations discussed herein may include periodically removing or hampering the formation of passivation layers, without limitation. The leach data in FIG. 1 1 , show that the electrolyte rapidly reached a copper tenor of 68 g L"1 - a concentration that we were unable to reach with a conventional fluidized bed reactor. Simultaneously, the redox potential of the electrolyte dropped gradually during the leach test, indicating that the leach rate would eventually become limited by oxygen mass transfer. This is not unexpected as 02 solubility necessarily decreases with increasing electrolyte concentration. Comparing the data from FIGS. 10 & 1 1 , it is evident that mechano-chemical processing can significantly accelerate the leach rate of metallic copper.
Influence of M-C Reactor Specific Power
As shown in Table 3, increasing applied mechanical power to the M-C reactor resulted in significantly increased copper dissolution rates. Energy consumption, in terms of kWh/t of Cu leached, and the stoichiometric amount of oxygen which is required to support the measured leach rates, is also reported in Table 3. Table 3 - Effect of applied power on Cu leach rates and O? Mass Transfer at 80°C
Applied Energy Consumption Relative Theoretical 02 Mass
Mechanical (kWh/t Cu leached) Leach Transfer
Power Rate (L 02/ Lelectrolyte h @1 atm)
(kW/t Cu feed)
0 0 1 0.5 (0.55 kg 02 m"3 h"1)
1 .98 91 9.8 4.4 (4.6 kg 02 m"3 h"1)
9.2 214 19.4 8.8 (9.2 kg 02 rrf3 h"1)
15.9 236 30.2 14 (14.6 kg 02 rrf3 h"1)
25.2 * >30.2 *
*At this power input, the 02 transfer rate was no longer sufficient to maintain an oxidative solution potential.
To derive estimated energy input, the applied mechanical power to the mixing shaft (P) in the M-C reactor at various mixing intensities was estimated from the power equation for mixing processes (see, for example, EKATO Handbook of Mixing Technology, EKATO Ruhr- und Mischtechnik GmbH, Schopfheim, Germany, p. 15, 2002.; See also, N. de Nevers, Fluid Mechanics for Chemical Engineers, 3rd ed., McGraw Hill, New York, NY, USA, 2005, p. 567.):
P = Ne p n3 d5 (2) Where Ne is the power number for the specific shaft & impeller combination (the inventors used a value of 7, as determined from torque measurements), p is the slurry density, n is rotational speed (s"1), and d is the impeller diameter (m).
For the series of leach tests summarized in Table 3, increasing applied mechanical power to the M-C reactor by 16-fold increased the relative copper leach rate 30-fold. Increasing applied mechanical power to the M-C reactor by 2-fold increased the relative copper leach rate 10-fold. In other words, increasing mechanical power unexpectedly yields a disproportionate increase in leach rates. In Table 3, we also report the minimum theoretical oxygen mass transfer, according to the stoichiometry of Equation 1 , which is needed to support the observed copper dissolution rates. In this particular series of tests, the theoretical minimum gas transfer eventually reached 14-15 kg 02 m"3 h"1. The inventors have previously observed similar gas transfer rates in the acidic ferric sulfate leaching of chalcopyrite. In that system, the inventors obtained effective oxygen mass transfer rates as high as 5 kg 02 m"3 h"1 at 50-150 kWh/t Cu leached (see, for example, C. Eyzaguirre, S. Rocks, R. Klepper, F. Baczek and D. Chaiko, "The FLSmidth Rapid Oxidative Leach (ROL) Process: A Mechano-Chemical Approach for Rapid Metal Sulfide Dissolution," Hydroprocess, Antofagasta, Chile, 2015.).
Because of the high mass density of the leached particles, energy consumption relative to the amount of copper leached is actually quite low, ranging from 91 - to 236- kWh/t Cu leached in this particular example. With an assumed electrical energy cost of 0.14 USD/kWh, the energy costs for the M-C reactor may range between approximately 0.0058- to 0.015- USD/lb. Cu leached. To put this in perspective, the reported cost estimate for anode scrap recycling (i.e., scrap washing, melting, recasting, and delivery to the tank house) is comparatively approximately 0.0136 USD/lb. Cu. See, for example, M.E. Schlesinger, M.J. King, K.C. Sole, W. G. Davenport, Extractive Metallurgy of Copper, 5th Ed., Elsevier, Oxford, UK, 2011.
According to Equation 1 , copper dissolution should continue as long as the concentrations of hydrogen ions and dissolved oxygen are sufficient to meet stoichiometric requirements. The activation energy for the metallic copper leach reaction taking place within the M-C reactor was found to be 26 kJ/mol, thereby confirming that a diffusion process plays a dominant role in the rate-determining step. Additionally, the leach process appears to be highly exothermic and the leach rates appear to be fast enough to produce an autogenously heated process. In a bench-scale test reactor, the system became self-heating at applied mechanical power levels between 2-9 kW/t Cu feed. At these power levels, electrolyte temperatures can readily exceed the atmospheric boiling point if oxygen transfer rates are sufficient to meet stoichiometric needs.
Cu Dissolution Pathways
The oxidation of Cu° in dilute sulfuric acid is known to be a two-step process, with the rapid generation of a Cu(l) intermediate followed by a slower second oxidation step, to produce Cu(ll) (see, for example, E. Mattisson and J. O'M. Bockris, "Galvanostatic studies of the kinetics of deposition and dissolution in the copper/ copper sulphate system", Trans. Faraday Soc, Vol. 55, 1959, 1586-1601.). In the absence of enough oxidant (i.e. dissolved oxygen), the unstable Cu(l) intermediate will preferentially follow a disproportionation pathway to regenerate metallic copper:
Figure imgf000030_0001
At the highest applied mechanical power input studied (i.e., 25 kW/t Cu feed), the gas transfer rate was no longer able to keep up with the stoichiometric demand. Consequently, the redox potential of the system became dominated by the production of Cu(l) which, in turn, led to Cu(l) disproportion (i.e., 2Cu(l) → Cu° + Cu(ll)) and precipitation of metallic copper as depicted in Equation 3. Increasing oxygen pressure within the M-C reactor, above atmospheric levels, might allow still further increases in leach rates and avoid over production of the Cu(l) reaction intermediate.
Alternatively, the disproportionation may be driven to completion with S02 to produce copper metal directly from the Cu(l) intermediate, summarized by Equations 3 & 4. By producing copper metal in situ without electricity, electrical costs associated with EW/ER could be virtually eliminated.
2Cu2+ + S03 2" + H20→ 2Cu+ + H2S04 (4) Mechano-Chemical Leach Selectivity & Recovery
In addition to rapid leach rates, another benefit of the mechano-chemical leaching of either anode scrap or blister copper might include the ability to selectively leach copper to very high tenors. Furthermore, the majority of the metal impurities (i.e., selenium, tellurium and lead) report as a hydrophobic residue that is very similar in chemical and physical properties to anode slimes produced in an electrorefinery. A comparison of leach resides with anode slimes is given in Table 4. Due to the hydrophobic nature of the leach residue, separating the residue from electrolyte could be done via flotation, sedimentation, or filtration, without limitation. While the concentration of copper within the leach residue is relatively high, less than 1 % of the total feed copper reports to the final leach residue. Copper within the leach residue could be recovered by existing processes used to treat anode slimes. Furthermore, recovery of precious metals could follow existing state-of-the-art processes (i.e. Dore smelting) after solid liquid separation.
Table 4 - Abbreviated elemental analysis of blister copper leach residues compared to anode slimes produced from primary smelters[1 ]
99% Cu Leached Residue Typical Anode Slime Composition
Element Composition, wt%
Cu 50.4 1 -30
Fe 1 .5 0.04-2
As 0.051 0.3-9
Bi 0.016 0.04-2.8
Sb 0.002 0.3-19
Pb 2.3 1 -50
Se 5.3 1 -20
Effect of Impurities on Leach Rates
The three copper samples, representing a wide range in impurity levels, yielded significantly different leach rates. Recycled copper produced the highest leach rate, followed by blister copper and anode scrap. Interestingly, antimony (Sb) concentrations within the metal had a depressing effect on the mechano-chemical leach rate. The data in FIG. 12 show the inverse linear relationship between Sb concentration in the copper sample and relative copper dissolution rate. The inventors found that the leach data also displayed an inverse logarithmic correlation between copper leach rate and arsenic (As) concentration. However, given the limited amount of data and variance in particle size, it is not possible to independently assess the influence of these two impurities on Cu leach rates. Contrary to these findings and observations, Sb has been found to enhance the anodic dissolution of binary Cu-Sb alloys (see, for example, ZD. Stankovic, V. Svetkovski and M. Vukovic, "The effect of antimony in anodic copper on kinetics and mechanism of anodic dissolution and cathodic deposition of copper, " Journal of Mining and Metallurgy, Vol. 44, 2008, 107-114.). Nevertheless, the mechano-chemical leach data in FIG. 12 follow the trends observed with the mechano-chemical leaching of copper sulfide minerals, where leach rates appear to follow the order: Cu-sulfides > Cu,As sulfosalts > Cu,Sb sulfosalts.
Flowsheet Options If cathode is a desired final product for the recovery of copper from anode scrap, electrowinning (EW) may be considered as a process option, since the consumption of acid and oxygen within the leach process may be balanced by equivalent acid and oxygen production within the EW process. An example of the overall Leach-EW process chemistry is given below:
Leach: Cu° + 0.5 02 + H2S04 → CuS04 + H20 (5) Electrowinning Cathode: CuS04 + 2e" → Cu° + S04 2" (6) Electrowinning Anode: H20 → 2 H+ + 0.5 02 + 2e" (7) Electrowinning Overall: CuS04 + H20 → Cu° + H2S04 + 0.5 02 (8)
A theoretical mass balance based on the overall chemistry (assuming no copper losses through bleed streams), for processing 1 kg of copper contained in anode scrap, is given in FIG. 13.
An example process for converting scrap metal to LME Grade A cathode, shown in FIG. 14, may comprise feeding copper scrap 717to a shredder 718 to make copper feed 719 more amenable to leaching in an M-C reactor 720. Copper-rich electrolyte 722 from the reactor 720 may be sent directly to electrowinning 723 through a solution filter to remove any suspended solids. Spent electrolyte 724 may be returned to the reactor 720 to increase the copper concentration. As shown in the mass balance, the sulfuric acid produced in the electrowinning circuit 723 should be adequate to meet the demand for the leach, with makeup acid 744 being provided as required. Oxygen off-gas 734 from electrowinning 723 can be captured and recycled to further reduce oxygen costs in the leach process, with make-up oxygen 746 being provided as required. A periodic purge or backflush of the reactor 720 may be used to remove leach residues 721 containing precious metals and other potential, salable by-products, without limitation. Liquor purged in this process will serve as a bleed stream to control impurity accumulation in the electrolyte. Accordingly, make up process fluid 742 may be provided back to the M-C reactor 720, as required.
Thus, by eliminating the circulating load on the anode furnace, a 15-20% increase in copper cathode production could be realized by treating anode scrap 217, 219, 717through leach/EW processes. Alternatively, a process which drives the disproportionation reaction (Equations 3 and 4) could be used to treat blister copper 910, 1 10, 210 by producing high purity metallic copper directly within the leach. Electrowinning/electrorefining power would be significantly reduced because of direct formation of pure metallic copper within the leach process. Conclusions may be drawn from the aforementioned experimental data, results, and discussion. Laboratory investigations have shown the potential benefit of atmospheric, mechano-chemical processing for the production of a copper sulfate- sulfuric acid electrolyte from either refinery scrap anodes or smelter blister copper. With an assumed cost of 0.14 USD/kWh, the anticipated energy costs for the mechano- chemical portion of the leach process ranges between approximately 0.0058 - 0.015 USD/lb. Cu leached. Precious metals and other elements typical of refinery anode slimes report to the leach residue and can be recovered by conventional methods.
Where used herein, the words "copper" or "blister copper" may be substituted with "metal" or "metallic solids" or "alloy" or "pieces" or "material which can be leached and electrowon", without limitation. Also, where used herein, certain terms sharing the same reference numeral, or sharing a like reference numeral may be used interchangeably with each other, without limitation.
Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.

Claims

1 . A method of dissolving impure metallic copper (Cu°), comprising:
providing a leach reactor configured to mechano-chemically dissolve the impure metallic copper;
providing the impure metallic copper to the leach reactor in the presence of (i) sulfuric acid, and (ii) oxygen or air; and,
exothermically and mechano-chemically leaching the impure metallic copper in the leach reactor at a temperature above 50°C according to one of the following equations:
2Cu° + 02 + 2H2S04→ 2CuS04 + 2H20
(1 )
2Cu2+ + S03 2" + H20→ 2Cu+ + H2S04
(2)
Figure imgf000034_0001
Cu° + Cu2
wherein during exothermically and mechano-chemically leaching, the leach reactor consumes between 50 and 1000 kWh per ton of copper recovered from the impure metallic copper; and
wherein the method is capable of reaching dissolved copper concentration levels which are equal to or greater than a solution saturation level.
2. The method of claim 1 , further comprising a size reduction step, wherein the impure metallic copper is divided into smaller solids or reduced in size before exothermically and mechano-chemically leaching.
3. The method of claim 1 , wherein the step of exothermically and mechano- chemically is performed under oxygen (02) partial pressure conditions that are between 0.1 bar and 10 bar.
4. The method according to claim 1 , wherein the impure metallic copper comprises material selected from one or more of the group consisting of: blister copper, copper cathode, copper anode, recycled copper, and scrap copper.
5. The method according to claim 1 , wherein the leach reactor stirs the impure metallic copper via a driven shaft that is provided with: an impeller, one or more stirring arms extending radially from the driven shaft, or at least one cantilevered arm extending from the driven shaft at an angle which is not parallel to the axis of the driven shaft.
6. The method according to claim 1 , wherein the leach reactor tumbles the impure metallic copper via a rotating horizontally-arranged drum, in order to enhance chemical reactivity; or, wherein the leach reactor vibrates the impure metallic copper via a chamber configured with a vibratory or shake mechanism, in order to enhance chemical reactivity.
7. The method according to claim 1 , further comprising the steps of:
producing a leach residue while exothermically and mechano-chemically leaching; and,
processing the leach residue to remove or recover precious metals, impurities, or insoluble metals contained within the leach residue.
8. The method according to claim 1 or 7, further comprising the steps of:
producing electrolyte;
electrowinning the electrolyte;
producing spent electrolyte; and,
processing the spent electrolyte to remove or recover impurities contained therein.
9. A method of dissolving impure metallic solids into solution, comprising:
providing a leach reactor configured to mechano-chemically dissolve the impure metallic solids;
providing impure metallic solids to the leach reactor in the presence of (i) oxygen or air, and (ii) one or more leaching agents configured to facilitate dissolution of the impure metallic solids; the impure metallic solids comprising a metal selected from the group consisting of: copper, nickel, zinc, gold, silver, lead, tin, cobalt, iron, vanadium, rhodium, osmium, rhenium, a platinum group metal, and a combination thereof. exothermically and mechano-chemically leaching the impure metallic solids in the leach reactor at a temperature above 50°C;
wherein during exothermically and mechano-chemically leaching, the leach reactor consumes between 50 and 1000 kWh per ton of metal recovered from the impure metallic solids; and
wherein the method is capable of reaching dissolved metal concentration levels which are equal to or greater than a solution saturation level.
10. The method according to claim 9 wherein the impure metallic solids comprise precipitate.
1 1 . The method according to claim 9, further comprising a size reduction step, wherein the impure metallic solids are divided into smaller solids or reduced in size before exothermically and mechano-chemically leaching.
12. The method according to claim 9, wherein exothermically and mechano- chemically leaching is performed under oxygen (02) partial pressure conditions between 0.1 bar and 10 bar.
13. The method according to claim 9, wherein the leach reactor stirs the impure metallic solids via a driven shaft that is provided with: an impeller, one or more stirring arms extending radially from the driven shaft, or at least one cantilevered arm extending from the driven shaft at an angle which is not parallel to the axis of the driven shaft.
14. The method according to claim 9, wherein the leach reactor tumbles the impure metallic solids via a rotating horizontally-arranged drum, in order to enhance chemical reactivity; or, wherein the leach reactor vibrates the impure metallic solids via a chamber configured with a vibratory or shake mechanism, in order to enhance chemical reactivity.
15. The method according to claim 9, wherein the impure metallic solids are cut, forged, cast, formed, drawn, rolled, melt-screened, or shaped in the form of strips, rods, bars, elongated members, beads, or shot.
16. The method according to 9, further comprising the steps of:
producing a leach residue during exothermically and mechano-chemically leaching; and, processing the leach residue to remove or recover precious metals, impurities, or insoluble metals contained within the leach residue.
17. The process of exothermically and mechano-chemically leaching impure metallic solids as substantially shown and/or described.
18. A cathode product made by the process of claim 17.
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