WO2013095826A1

WO2013095826A1 - Cathode assembly including a barrier, system including the assembly and method for using same

Info

Publication number: WO2013095826A1
Application number: PCT/US2012/065555
Authority: WO
Inventors: Scot P. Sandoval; Gerald MOEN; Jason M. Morgan
Original assignee: Freeport-Mcmoran Corporation
Priority date: 2011-12-20
Filing date: 2012-11-16
Publication date: 2013-06-27
Also published as: US20130153437A1

Abstract

A cathode assembly for electrowinning metal in powder form, a system including the cathode assembly, and a method of using the assembly and system are disclosed. The cathode assembly includes a suspension element, a conductive element and a barrier element proximate the conductive element. The barrier element has a plurality of holes thereby reducing the effective active surface area of the cathode by shielding a portion of the cathode from participating in the electrowinning process. Metal is therefore deposited on or near the unshielded active surface in the form of metal powder. The assembly, system and method provide for improved metal powder formation. The system may be stationary or portable.

Description

CATHODE ASSEMBLY INCLUDING A BARRIER, SYSTEM INCLUDING THE ASSEMBLY AND METHOD FOR USING SAME

FIELD OF INVENTION

The invention relates generally to cathode assemblies, and more specifically, to cathode assemblies including a non-conducting barrier for use in metal recovery through eiectrowinning processes,

BACKGROUND OF THE INVENTION

Electrowmntng is often used in hydrometailurgieal processing of ore to recover metal, such as copper, silver, platinum group metals, molybdenum, zinc, nickel, cobalt, uranium, rhenium, rare earth metals, combinations thereof, and the like from ore. The recovery of metal from ore often includes exposing the ore to a leaching process (e.g., atmospheric leaching, pressure leaching, agitation leaching, heap leaching, stockpile leaching, thin-layer leaching, vat leaching, or the like) to obtain a pregnant leach solution including desired metal ions, optionally purifying and concentrating the pregnant leach solution, using, e.g., a solvent extraction process, and then recovering the metal using the eiectrowinning process.

A typical electrolytic cell for eiectrowinning includes an anode assembly, a cathode assembly that is spaced apart from the anode assembly, an electrolyte solution, and a tank to contain the electrolyte solution. Metal (e.g., copper) is recovered from the electrolyte solution by applying a bias across the cathode assembly and the anode assembly sufficient to cause the metal ions in solution to migrate towards and reduce onto an active area of the cathode assembly,

A typical cathode assembly often includes a starter sheet to produce a sheet of solid metal plated onto the starter sheet. Alternatively, metal, such as copper, may be produced as copper powder. Eiectrowinning metal in the form of powder may be desirable in some circumstances, because the metal powder may be easier to harvest and remove from an electrolytic cell than large, heavy solid metal sheets, in addition, metal powder can be produced and harvested in a semi-continuous or continuous process, which provides a more consistent supply of extracted and harvested metal, Also, metal powder may be electrowon from solutions containing lower concentrations of metal than solutions used in conventional eiectrowinning processes, Unfortunately, the metal powder formed during a typical electrowinning process tends to stick to the starter sheet, which inhibits the semi-continuous or continuous operation of the metal recovery. Accordingly, Improved cathode assemblies, systems including the assemblies, and methods of forming metal powder are desired.

In some cases it may be desirable to recover metal from poor-quality liquid streams, such as acid mine drainage, low grade PLS, bleed streams, and remediation streams. Traditional electrowinning cell systems for such recovery are large industrial scaie apparatus, which operate in permanent locations, such as full scale mining complexes. Many poor-quality metal sources, such as acid mine drainage and remediation streams, may require collection and transport to an industrial electrowinning facility. In certain circumstances, removal and transport of metal bearing liquid may create logistic difficulties and increased costs and time associated with recovering the metal. Accordingly, improved apparatus and methods tor recovering metal value from poor-quality supplies, as well as being capable of operation near the source of the supplies, are desired. SUMMARY OF THE INVENTION

The present invention relates generally to a cathode assembly for use in electrolytic metal recovery processes, to a system including the cathode assembly and to a method of using the cathode assembly and system. While the ways in which the present invention addresses the various drawbacks of the prior art are discussed in greater detail below, in general the cathode assembly, system and method in accordance with exemplary embodiments are used to recover metal in powder form from solution, and/or facilitate the recovery of metal value from poor-quality metal supplies and, in accordance with various aspects of these embodiments, allow for electrowinning of metal at or near the source of the metal.

in accordance with various exemplary embodiments, a cathode assembly includes a conductive element, a suspension element coupled to the conductive element, and a barrier element. In accordance with various aspects of these embodiments, the barrier element reduces an effective active surface area of the cathode assembly by shielding a portion of the cathode from participating in the electrowinning process, and metal deposits on or near the unshielded active surface of the cathode in the form of metal (e.g., copper) powder.

In accordance with additional exemplary embodiments, a system for electrowinning metal includes a cathode assembly, an anode assembly, an electrolyte solution, and a tank. in accordance with various aspects of these exemplary embodiments, the components of the system may be configured to be portable, such that the system may be moved and operated at or near the source of the metal. A portable electrowinning ceil system may reduce time and costs associated with metal recovery by eliminating the need to transport the metal- containing liquid to an industrial eiectro winning iaciiity. in accordance with various aspects of these embodiments, the portable system is configured to remove metal (e.g., copper) from poor-quality metal-bearing solutions. In accordance with further aspects, the portable system produces electrowon metal in powder form, in accordance with yet further aspects, the cathode assembly includes a barrier element.

In accordance with additional exemplary embodiments, a method for recovering metal includes the steps of providing an electrolyte solution, electrowinning metal from the electrolyte solution using a cathode assembly, and harvesting the metal in the form of metal powder. In accordance with various aspects of these embodiments, the electrolyte solution is a poor-quality metal-bearing solution, such as a waste water or remediation solution, in accordance with other aspects, the electrolyte solution may be a low grade stream previously subjected to metallurgical processing, such as a low-grade PLS, recycle or bleed stream. In accordance with various aspects of these embodiments, the cathode assembly includes a barrier element (e.g., an insulative barrier) to facilitate recovery of metal in powder form.

These and other features and advantages of the present invention will become apparent upon a reading of the following detailed description when taken in conjunction with the drawing figures, wherein there is shown and described various illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the drawing figures, wherein like numerals denote like elements and wherein:

FIG. 1 illustrates a front-view of a cathode assembly in accordance with various exemplary embodiments; FIG. 2 illustrates a front-view of a cathode assembly in accordance with various additional exemplar}' embodiments;

FIG, 3 illustrates an electrolyte metal recovery system in accordance with various exem piary em hod i me nts ;

FIG. 4 illustrates a method of electro-winning metal in accordance with exemplary embodiments; and

FIG. 5 illustrates a method of electrowinning metal in accordance with additional exemplary embodiments.

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scaie. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of illustrated embodiments of the present invention.

DETAILED DESCRIPTION

The detailed description of various embodiments herein makes reference to the accompanying drawing figures, which show various embodiments and implementations thereof by way of illustration and best mode, and not of limitation. While these embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, it should be understood that other embodiments may be realized and that mechanical and other changes may be made without departing from the spirit and scope of the present disclosure. Other objects, advantages and novel features will become apparent from the following detailed description when considered in conjunction with the drawing figures.

The cathode assembly, system and method described herein can be used in a variety of applications, such as electrowinning various metals. The cathode assembly and system can be used to recover, for example, metals such as copper, gold, silver, zinc, platinum group metals, nickel, chromium, cobalt, manganese, molybdenum, rhenium, uranium, rare earth metals, alkali metals, alkaline metals, and the like. For example, the assembly and system of the present invention may be used in connection with recovery of copper from hydrometallurgical processing of copper sulfide ores and/or copper oxide ores. By way of particular example, the assembly, system and method can be used to recover copper from a solution, such as a pregnant leach solution, containing copper ions— without concentrating the leach solution (e.g., via treating the pregnant leach solution with a solvent extraction process). Other exemplary embodiments facilitate the removal of copper ions from low- quality copper supplies, such as waste water, recycled electrolyte, acid mine drainage, or other waste-type liquid streams,

To assist in understanding the context of the present disclosure, an exemplary cathode assembly for use in electrowinning metals in accordance with the present disclosure is illustrated in FIG, L Cathode assembly 100 includes a conductive element 102, suspension element 104 coupled to conductive element 102, barrier element 1 10, and attachment elements 106 and 108 coupled to suspension element 104 and barrier element 1 10.

n various aspects of the exemplary embodiment, a portion of conductive element 102 forms the active area of the cathode assembly. As used herein, "active area" of an electrode (such as a cathode assembly or an anode assembly) refers to the surface area of the respective assembly that is immersed in the electrolyte during an electrowinning process and is available to participate in the electrowinning process.

Conductive element 102 may include various forms, such as a metal sheet. Exemplary materials suitable for conductive element 102 include copper, copper alloy, copper aluminum alloys, stainless steel, titanium, aluminum, combinations thereof, or other suitably conductive material, in a, preferred aspect, conductive element 102 comprises a sheet of copper, commonly referred to as a copper starter sheet. However, conductive element 102 may include any suitably conductive material.

With continued reference to FIG. 1 , suspension element 104 is coupled to conductive element 102. Suspension element 104 is designed to provide current from a current source to conductive element 102 during an electrowinning operation and may further provide suspension support to conductive element 102. In an aspect of the exemplary embodiment, conductive element 102 is removably secured to suspension element 104 by using fasteners, such as bolts 103. In another aspect, conductive element 102 may be permanently attached - e.g., element 102 may be welded to suspension element 104. Any method of sufficiently ecuring conductive element 102 to suspension element 104 is in accordance with the present disclosure.

In accordance with various aspects of the exemplary embodiment, suspension element 104 may be any suitable configuration, such as a metal rod. n a preferred aspect of the exemplary embodiment, suspension element 104 is a metal bar used in an electrowinning process - e.g., a hanger bar. Exemplary materials suitable for suspension element 104 include copper, copper alloy, copper aluminum alloys, stainless steel, titanium, aluminum and combinations thereof. However, any suitably conductive material which is capable of providing sufficient current and support to conductive element 102 is in accordance with the present disclosure.

With continued reference to FIG, 1 , in the exemplary embodiment, cathode assembly 100 includes a barrier element 110. Barrier element 1 10 is designed to inhibit the flow of ions to shielded portions of element 102 during an electrowinning process, such that reduction of the metal ions takes place primarily on or near an exposed or unshielded active area of conductive element 102. and little or no deposition takes place on the portion of conductive element 102 shielded by barrier element 1 10. n various aspects of the exemplary embodiment barrier element 1 10 is formed of an insulating material, having holes 1 12 formed therein. In these embodiments, the effective active area of conductive element 102 is the portion which is aligned with holes 112, such that electrodeposition or powder formation takes place primarily at regions of conductive eienient 102 that are exposed to a solution of metal ions. In other words, barrier element 1 10 shields a portion of conductive element 102 from metal ion flow, such that the electrowinning takes place primarily on or near the exposed or unshielded regions of conductive element 102.

In accordance with aspects of the exemplary embodiment, the active area of conductive element 102 is between about 20% and about 80% of the surface area of conductive element 102. In a preferred aspect, the active area of conductive element 102 is between about 40% and 60%.

in accordance with aspects of the exemplary embodiment, barrier element 1 10 is a sheet of insulating material proximate the surface of conductive element 102 and having a plurality of holes 1 12. The insulating material may include a polymer, such as polyvinyl chloride, polyethylene, polystyrene or polytetratluoroethylene. In a preferred embodiment, barrier element 1 10 is a sheet of polyvinyl chloride having a plurality of holes approximately 0.5 inches in diameter, the sheet covering substantially the entire surface of conductive element 102.

In accordance with other aspects of the exemplary embodiment, barrier element 1 10 may include an insulating material applied directly to the surface of barrier element 1 1 0. This insuiaiing material may include a film, overlay or laminate which includes a plurality of holes 1 12. In this configuration, the film, overlay or laminate of barrier element 1 10 directs the flow of electrolyte ions to the surface area of conductive element 102 that is exposed to the electrolyte by holes 1 12,

in accordance with aspects of the exemplary embodiment, cathode 100 may include multiple barrier elements 1 10. For example, barrier element 1 10 may be proximate both the front and rear faces of conductive element 102.

Exemplary cathode assembly 100 may further include one or more attachment elements. For example, attachment elements 106 and ! 08 may couple barrier element 1 10 to suspension element 104. Attachment elements 106 and 108 may be formed of a variety of materials. Irs accordance with various aspects of the exemplary embodiment, attachment elements 106 and 108 are formed of non-conductive material, such as polyethylene, polystyrene, polyvinyl chloride and/or polytetrafluoroethylene (PTFE). In a preferred aspect, attachment elements 106 and 108 are formed of polyvinyl chloride. However, any material which is capable of securing barrier element 1 10 to suspension element 1 04 is in accordance with the present disclosure.

in one aspect of the exemplary embodiment, holes 1 12 are substantially circular. However, any shape of hole, including the use of multiple different shapes together, that provides access by the electrolyte to the surface of conductive element 102 is in accordance with the present disclosure,

As set forth in more detail below, use of barrier element 1 10 as part of cathode assembly 100 was surprisingly and unexpectedly found to, among other things, enhance metal powder formation from poor-quality solutions and to facilitate semi-continuous or continuous recovery of metal powder from systems including such assemblies. Poor-quality solutions may include, for example, solutions with low concentrations of metal ions. Poor- quality solutions may also include significant concentrations of impurities. Such solutions include, for example, previously processed solutions (e.g., recycle and bleed streams), waste water solutions, remediation solutions, and acid-mine drainage.

With initial reference to FIG. 2, a cathode assembly 200 is illustrated in accordance with additional exemplary embodiments. Cathode assembly 200 includes a conductive element 102. Cathode assembly 200 further includes a suspension element 104, which is coupled to conductive element 102. In accordance with various aspects of the exemplary embodiment, cathode assembly 200 further includes a barrier element 210, which, similar to barrier element 1 10, is designed to reduce the surface area of the conductive element 102 which participates in an electrowinning operation and to increase the current density applied to the active surface. In accordance with exemplary aspects of the embodiment, barrier element 210 is positioned on and in contact with one or more surfaces of conductive element 102, In a preferred aspect, barrier element 210 is applied to the surface of conductive element 102 in order to reduce the effective active area of both sides of conductive element 102. However, barrier element 210 may be applied only to one side of conductive element 102.

In accordance with various aspects of exemplary embodiments barrier element 21 0 is non-conductive film applied, for example, by coating material directly onto the surface of conductive element 102, or by attaching non-conductive material to conductive element 102 using adhesives. Barrier element 210 may include non-conductive films, overlays, mechanical attachments, and laminates, in a preferred aspect, barrier element 210 comprises a polyvinyl chloride film. However, any coating able to sufficiently inhibit eiectrodeposiiion of metal onto conductive element 102 is in accordance with the present disclosure.

In accordance with other aspects of the exemplary embodiment, cathode assembly 200 may include multiple barrier elements 1 10. For example, barrier element 1 10 may be attached to the front and rear faces of conductive element 102.

Holes 1 12 may be formed using a variety of techniques. For example, holes 1 12 may he formed by removing portions of barrier element 210 be tore it is applied to the surface of conductive element Ϊ 02. For example, barrier element 210 may be formed from a fiat, rectangular film, in which hole-shaped sections of the film are stamped, cut or scored. The hole-shaped sections may then be removed from the film, leaving a segment of film with a plurality of holes 1 12. Alternatively, holes 1 12 may be formed after barrier element 210 is applied to conductive element 102 using the techniques noted above, using patterned deposition and removal techniques, or using other patterned deposition techniques.

With initial reference to FIG. 3, an exemplary system 300 for electrowinning metal from solution is illustrated. System 300 includes a cathode assembly 302, an anode assembly 304, a tank 306, and an electrolyte solution 308, System 300 also includes power supplies coupled to the cathode assemblies and/or anode assemblies to provide a bias between cathode assembly 302 and anode assembly 304 sufficient to eause metal to deposit on or near the active area of cathode assembly 302 - i.e., the area of conductive element 102. exposed to electrolyte solution 308 and near open areas of a barrier element, such as barrier element 1 10 or 210, Although illustrated with a single cell, including one cathode assembly 302 and one anode assembly 304, eiectrowtrsmng systems in accordance with the present disclosure may include multiple cells, having anode assemblies and/or cathode assemblies coupled together in series and/or in parallel.

Anode assembly 304, tank 306 and electrolyte solution 308 may include any anode configuration, tank and electrolyte used to recover metal from solution. Cathode assembly 302 may include, among various exemplary embodiments, any of the exemplary cathodes assemblies described herein. System 300 may be configured for use in conventional electrowinning of metal (e.g., electrowmning of copper from solution including copper sulfate). Alternatively, system 300 may be configured for electrowinning metal (e.g., copper) powder from an electrolyte solution, using, for example, a ferrous/ferric anode reaction.

In various exemplary embodiments, anode assembly 304 includes a plate-type (i.e.. non-flow-through) or a flow-through active area. As used herein, "flow-through anode" refers to any anode that allows solution to flow through the active area of the anode— e.g., during the electrowinning process.

in the case when anode assembly 304 is a flow-through configuration, the active area of the anode may be configured as a porous metal sheet, metal wool, metal fabric, porous non-metallic materials, expanded porous metal, metal mesh (e.g., 80x80 strands per square inch or 30x30 strands per square inch), expanded metal mesh, corrugated metal mesh, a plurality of metal strips, multiple metal wires or rods, woven wire cloth, perforated metal sheets, the like, or combinations thereof, Anode assembly 304 may include a substantially planer or a three-dimensional surface,

The active surface of anode assembly 304 may include lead or a lead alloy, such as a iead-tin-caicium alloy, a valve metal, such as titanium, tantalum, zirconium, or niobium, other metals, such as nickel, stainless steel, or metal alloys, such as a nickel-chrome alloy, intermetailie mixtures, or a ceramic or cermet containing one or more valve metals. By way of example, the active surface includes titanium, which may be alloyed with nickel, cobalt, manganese, or copper to form the active surface. The active area may also include any electrochemically active coating, including platinum, ruthenium, iridium, or other Group VI II metals, Group VIII metal oxides, or compounds comprising Groisp VIII metals, and oxides and compounds of titanium, molybdenum, tantalum, and/or mixtures and combinations thereof. Alternatively, the coating may include carbon, graphite, mixtures thereof, a precious metal oxide, a spinel-type material, a carbon composite, or a metal (e.g., titanium)~graphiie sintered material.

Tank 306 is configured to retain electrolyte 308 and to facilitate flow of electrolyte 308 between and adjacent to cathode assembly 302 and anode assembly 304. in accordance with various embodiments, tank 306 includes a tapered bottom section to facilitate collection of eiectrowon metal powder,

In various exemplary embodiments, tank 306 comprises an industrial-sized tank. For example, tank 306 may have a volume of between about 10 nr' and about 20m³. However, any size tank which is capable of operating at least one pair of cathode assembly 302 and anode assembly 304 is in accordance with the present disclosure.

As noted above, in various alternative exemplary embodiments, system 300 is configured to be operational at or near a source of metal-bearing solution to be eiectrowon, in these cases, tank 306 preferably comprises a portable tank formed of non-conductive materials such as fiberglass, polyethylene, or polypropylene Portable tank 306 is generally smaller than industrial-sized tank that may be used in conjunction with smaller scaled cathode assemblies 302 and anode assemblies 304. For example, portable tank 306 may have a volume of between about 5 nr' and about 10 m³,

Whether system 300 is portable or stationary, system 300 may be designed such that cathode assembly 302 and anode assembly 304 are placed as close together as possible without causing a direct electrical short between assemblies 302 and 304, In cases where either assembly includes a non-conductive frame, container or barrier element, as described above in connection with exemplary assemblies illustrated in FIGS. 1 and 2, assemblies 302 and 304 may be in direct contact, or may be spaced apart, for example having a spacing of less than about 2 inches, or between about 0.25 inches and about 1.5 inches,

Electrolyte 308 may include any suitable solution containing metal ions to be recovered, By way of particular examples, system 300 may be used for direct electrowirming of copper metal from a high-quality solution, such as a pregnant leach solution (e.g., a solution that has not been treated with conventional concentrating or solvent extraction processes). The pregnant leach solution may be obtained from a leaching process

(e.g., a heap leach, a vat. leach, a tank leach, a pad leach, a leach vessel or any other leaching technology useful for leaching a metal value from processed metal-bearing material). Jn accordance with some exemplary embodiments of the invention, the leach solution may be conditioned using, for example, a solid-liquid phase separation step, an additional leach step, a pH adjustment step, a dilution step, a concentration step, a metal precipitation step, a filtering step, a settling step, as well as any combinations thereof.

In various other exemplary embodiments, electrolyte 308 comprises a poor-quality solution, such as those recovered from previous physical or chemical processes. For example, electrolyte 308 may comprise a recycle stream from previous electrowinning processes, such as a lean electrolyte. Other sources of electrolyte 308 include acid mine drainage streams, remediation solution, and other polluted water supplies. However, any electrolyte 308 which contains a suitable amount of metal to be recovered by system 300 is in accordance with the present disclosure.

In accordance with particular embodiments, electrolyte 308 includes a copper ion concentration of about 0.1 g/1 to about 2.5 g/i copper ion. The electrolyte may also include about 1 to about 10 g/i acid.

in accordance with various embodiments of the invention, electrolyte 308 includes

Iron ions (ferrous and ferric iron ions) which are co-extracted with copper in the leaching step, in accordance with various aspects of these embodiments, electrolyte 308 includes about 0.5 g/1 to about 3.5 g/1 total iron ion concentration, in accordance with additional aspects, the ferric ion concentration is about 0, 1 g/i to about 1 g/1.

To maintain desired operating efficiency, defined as the actual amount of metal plated divided by the theoretical amount of metal that could be plated for a set of conditions, electrolyte 308 includes a relatively high Cu/ Fe ^÷ ratio (e.g., about 2 to about 6) and relatively high Fe Fe³ ratio (e.g., about 2 to about 8),

During the electrowinning process, when electrolyte 308 includes iron ions, the ferrous ions may be oxidized to ferric ions at the anode, and thus the concentration of ferrous ions is depleted during the process, while the concentration of ferric ions is increased. An amount of ferrous ions in the electrolyte may be controlled by, for example, addition of ferrous sulfate to electrolyte 308 and the amount of ferric ions can be controlled through, for example, solution extraction of the ferric ions. Ferrous/ferric ions can also be leached from ore or any iron source to generate additional iron, preferably in the form of ferrous ions. Additionally and/or alternatively, sulfur dioxide or other suitable reducing agent, alone or in the presence of a catalyst, may be added to electrolyte 308 (e.g., as part, of a regeneration process) to reduce the ferric ion concentration to desired levels. Also, pH may be adjusted to cause ferric ion precipitation in order to reduce ferric ion concentration to desired levels.

System 300 may also include electrolyte pumping, circulation, and/or agitation .systems (not illustrated) to maintain desired flow and circulation of electrolyte 308 between the active area of cathode assembly 302 and anode assembly 304 and adjacent the acttve areas of the respective assemblies. In accordance with various embodiments of the invention, an electrolyte flow rate is between about 0.05 gpm/fP of active cathode area to about 5 gpm/ft² of active cathode area.

FIG, 4 illustrates a method 400 for recovering metal in accordance with further exemplary embodiments. Method 400 includes the steps of providing a solution including metal ions (step 402), optionally conditioning the solution (step 404), electrowinning metal (step 406), and harvesting the metal (step 408).

During step 402, an electrolyte solution suitable for electrowinning metal ions from the solution is provided. The solution may include, for example, any of the solutions described above in connection with electrolyte 308 and may suitably be provided in a tank, such as tank 306.

If desired, the solution containing metal ions may be conditioned during step 404. Conditioning step 404 may include, for example, filtration to remove particles from the solution. When the solution includes a pregnant leach solution, conditioning step 404 may additionally or alternatively include, for example, adding ferrous ions and/or removing ferric ions. This conditioning process may be used to manipulate (e.g., increase) an efficiency of an electrowinning system, such as system 300. For example, when system 300 is used for direct electrowinning of copper using a ferrous/ferric anode reaction, an efficiency of system 300 can be increased by increasing Cu/Fe^''^"" and Fe'7 Fe^31" ratios.

During step 406, metal is recovered from the solution, using, e.g. system 300, by applying a sufficient bias across a cathode assembly (e.g., cathode assembly 302) and an anode assembly (e.g., anode assembly 304) to cause metal ions in solution (e.g., electrolyte 308) to deposit onto an active area of the cathode assembly. Step 406 may be performed under constant current or constant voltage operating conditions. In accordance with exemplary embodiments of the invention, step 406 is performed using a constant voltage source with a voltage of about 1.0 V to about 2.5 V. In this case, exemplary current densities applied to the active cathode surface range from about 5 amp/if of active cathode area to about 25 amp/ft^ of active cathode area.

Metal is harvested during step 408, in a preferred aspect, the metal is recovered in powder form, in the case of powder recovery, while in situ harvesting techniques may be desirable to minimize movement of cathodes and to facilitate the removal of copper powder from an e!ectrowinning system (e.g., system 300) on a continuous basis, any number of mechanisms ma be utilized to harvest the metal (e.g., copper) powder product from the cathode assembly in accordance with various aspects of the present disclosure. Any device now known or hereafter devised that functions to facilitate the release of copper powder from the surface of the cathode to, e.g., a base portion of the electrowinning apparatus, enabling collection and further processing of the copper powder may be used. The optimal harvesting method and apparatus for a particular embodiment will depend largely on a number of interrelated factors, primarily current density, copper concentration in the electrolyte, electrolyte flow rate, and electrolyte temperature. Other contributing factors include the level of mixing within the electrowinning apparatus, the frequency and duration of the harvesting method, and the presence and amount of any process additives (such as, for example, fiocculant, surfactants, and the like).

In accordance with embodiments of the invention, in situ harvesting, using either self-harvesting (described below) or other in situ devices, is used ibr the removal of metal (e.g., copper) powder from the electrowinning cell. Examples of harvesting techniques for use with various embodiments include vibration (e.g., one or more vibration and/or impact devices affixed to one or more cathodes to displace copper powder from the cathode surface at predetermined time intervals), a pulse flow system (e.g., electrolyte flow rate increased dramatically for a short time to displace copper powder from the cathode surface), use of a pulsed power supply to the ceil, use of ultrasonic waves, and use of other mechanical displacement means to remove copper powder from the cathode surface, such as intermittent or continuous air bubbles. Alternatively, under some conditions, '"self-harvest" or "dynamic harvest" may be achievable, when the growth of copper powder from the cathode surface is such that it will fall away as it is formed, or shortly after deposition and crystal growth occurs. The copper powder thai is carried through the cell with the electrolyte may he removed via a suitable filtration, sedimentation, or other fmes removal/recovery system,

As noted above, use of a barrier element 1 10 or 210 facilitates formation of metal powder that will fall away from the cathode assembly. It is thought that barrier element 1 10 or 210 directs electrical current to form separate micro-ceils formed by the holes 1 12 or 212 of barrier elements 1 10 or 210, which in turn directs the growth of copper powder in each micro-cell The separate micro-cells produce copper powder that is independent from the copper powder formed in adjacent micro-ceils. In addition, the density of the copper powder growth may be controlled so that the copper will snore easily fall away from the starter sheet as growth continues.

FIG. 5 illustrates a method 500 for recovering metal from a remediation site in accordance with exemplary embodiments of the invention. Method 500 includes the steps of selecting a remediation site (step 502), providing a remediation solution including metal ions (step 504), optionally conditioning the solution (step 506), eleetrowinning metal in powder form using a cathode assembly (step 508), and harvesting the metal powder (step 510),

During step 502, a location is selected to perform an eleetrowinning process. In various exemplary embodiments, the location may include a site in which raining operations were previously performed and a supply of solution containing metal and/or metal ions is present, n one embodiment, the location includes a remediation site, and eleetrowinning is used to recover metal value from a waste water supply and/or remediation solution.

During step 504, a remediation solution suitable for eleetrowinning metal ions is provided. The remediation solution may include any of the solutions described above in connection with electrolyte 308. In a preferred embodiment the remediation solution is a solution recovered from previous industrial and/or mining processes.

If desired, the remediation solution including metal ions may be conditioned during step 506. Optional conditioning step 506 may include, for example, filtration to remove particles from the solution. However, any conditioning step which facilitates the removal of metal ions from the remediation solution is in accordance with the present disclosure.

During step 508, metal is recovered from the solution, using, e.g. system 300, by applying a sufficient bias across a cathode assembly (e.g., cathode assembly 302) and an anode assembly (e.g., anode assembly 304). Step 508 may be performed under constant current or constant voltage operating conditions. In accordance with exemplary embodiments of the invention, step 406 is performed using a constant voltage source with a voltage of about L0 V to about 2.5 V. As current is applied to the anode and cathode assemblies, metal ions in solution (e.g., electrolyte 308) deposit onto or near the active area of the cathode assembly.

During step 510, the metal recovered in step 508 is harvested. In various exemplary embodiments, in situ harvesting, using either self-harvesting or other in situ devices, is used for the removal of copper powder from the electrowinning cell Any of the above-discussed harvesting techniques are in accordance with the present disclosure. The copper powder that is carried through the cell with the remediation solution may be removed via a suitable filtration, sedimentation, or other fines removal/recovery system.

Although this disclosure has been described above with reference to a number of exemplary embodiments, it should be appreciated that the particular embodiments shown and described herein are illustrative of the invention and its best mode and are not intended to limit in any way the scope as set forth in the claims. Those skilled in the art having read this disclosure will recognize that changes and modifications may be made to the exemplary embodiments without departing from the scope. For example, various aspects and embodiments may be applied to electrolytic recovery of metals other than copper, such as nickel, zinc, cobalt, and others. Although certain preferred aspects are described herein in terms of exemplary embodiments, such aspects may be achieved through any number of suitable means now known or hereafter devised. Accordingly, these and other changes or modifications are intended to be included within the scope of the present disclosure.

Claims

What is claimed is:

1. A cathode assembly for eieetrowinning metal comprising:

a suspension element:

a conductive element coupled to the suspension element; and

a barrier element having a plurality of holes.

2. The cathode assembly of claim I, further comprising at least one attachment element coupled to the suspension element and the barrier element.

3. The cathode assembly of claim 1 , wherein the barrier element comprises a material selected from the group of polyethylene, polystyrene, polyvinyl chloride, and po 1 y tetrafluoroethy 1 ene ,

4. The cathode assembly of claim 1 , wherein the barrier element comprises one of a film, laminate or overlay,

5. The cathode assembly of claim 1, wherein the conductive element comprises a metal starter sheet.

6. The cathode assembly of claim 5, wherein the metal starter sheet comprises copper.

7. The cathode assembly of claim 1, wherein the suspension element comprises material selected from the group consisting of copper, copper alloy, copper aluminum alloys, aluminum, stainless steel, titanium, gold, and combinations thereof.

8. A system for eieetrowinnmg metal comprising:

a cathode assembly comprising a suspension element, a conductive element coupled to the suspension element, and a barrier element having a plurality of holes;

an anode assembly;

an electrolyte solution between the anode assembly and the cathode assembly; and a tank containing the electrolyte solution.

9. The system of claim 8, wherein the electrolyte solution comprises one of a recycled solution, bleed solution, remediation solution, waste water solution, or acid mine drainage stream. 1 0, The system of claim 8, wherein the barrier element comprises a materia! selected from the group of polyethylene, polystyrene, polyvinyl chloride, and polyteirafliioroethyiene.

1 1. ^'The system of claim 8, wherein the barrier element comprises a film, laminate or overlay,

12. The system of claim 8, wherein the electrolyte solution contains between 0.1 g/l and 2.5 g/l of metal ions. 13. The system of claim 8, wherein the tank comprises a portable tank.

1 . A method of electrolytic reco very of metal comprising the steps of:

providing an electrolyte solution;

electrowinning a metal from the electrolyte solution using a cathode assembly, the cathode assembly comprising a conductive element and a barrier element proximate a surface of the conductive element, the barrier element having a plurality of holes: and

harvesting the metal in the form of a metal powder,

15. The method of claim 14, wherein the metal is copper,

16. The method of claim 14, further comprising the step of recovering the electrolyte solution from a remediation site.

17. The method of claim 14, wherein the barrier element comprises a material selected from the group of polyethylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene.

18. The method of claim 14, wherein the barrier element comprises a film, laminate or overlay,

19. The meihod of claim 14, wherein the concentration of ferrous iron ions in the electrolyte solution is controlled by the addition of a reducing agent.

20. The method of claim 14, wherein the concentration of ferrous iron ions in the electrolyte solution is controlled by adjusting the pll of the electrolyte solution.