OA12043A

OA12043A - Method and apparatus for electrowinning powder metal from solution.

Info

Publication number: OA12043A
Application number: OA1200200018A
Authority: OA
Inventors: Patrick Anthony Treasure; David Bruce Tarrant
Original assignee: Electrometals Technologies Ltd
Priority date: 1999-07-21
Filing date: 2000-07-21
Publication date: 2006-05-02
Also published as: KR100691080B1; AP1419A; WO2001007684A3; AUPQ176299A0; CA2416619C; ZA200201356B; JP4594573B2; CA2416619A1; AP2002002411A0; KR20020042620A; WO2001007684A2; EP1235950A2; JP2003505598A; EP1235950A4

Abstract

A cell (1) for electrowinning a metal in powder form from solution is disclosed. The cell (1) includes a housing (2) having an inlet (3) towards one end thereof and an outlet (4) towards an opposed end. The cell has a cylindrical anode (6) extending substantially axially through the housing (2) and a cathode (7) surrounding the anode (6) spaced outwardly away therefrom. The anode (6) and cathode (7) define a flow passage (8) therebetween having a gap of 5 to 25 millimetres. In use the cell has a substantially vertical orientation with the inlet (3) at the bottom and the outlet (4) at the top. During the flow of process solution through the cell (1) metal powder is deposited on the cathode (7). Periodically the flow process solution is interrupted and flush solution is passed in a reverse direction through the cell to remove powder metal from the cathode (7). A bank of cells in which the individual cells are connected in parallel to respectively an inlet main and an outlet main is also disclosed.

Description

12 0 4 3 1

METHOD AND APPARATUS FORELECTROWINNING POWDER METAL FROM SOLUTION

Field of the Invention5

This invention relates to a method and apparatus for electrowinningmetals from a solution containing metals. This invention is particuiariyconcemed with the production of particulate métal, eg in the form of powder, asdistinct from plated métal. 10

This invention relates particuiariy but not .exclusively to a method andapparatus for electrowinning copper in a powder form from a copper bearingsolution, eg a low grade copper solution such as is often found at mines andminerai Processing sites, and it will be convenient to hereinafter describe the 15 invention with reference to this example application. However it is to be clearly understood that the invention also applies to other metals, eg silver, nickel,cobalt and tin.

Background to the Invention 20

The applicant has previously designed an electrowinning cell forelectrowinning metals such as copper and tin from aqueous solutions. The cellis disclosed in the applicant’s international patent application numberPCT/AU96/00332 entitled minerai recovery apparatus. The entire contents of 25 this spécification are explicitly incorporated into this document by cross-reference.

The above application discloses a cell having a tangential iniet at thebottom of the housing and a tangential outlet at the top of the housing. The 30 orientation of the iniet which directs solution into the cell with a particularorientation in conjunction with the cylindrical housing induces a helical spiralflow through the cell. A rod-like anode extends axially the length of the housingcoaxial with the cell and a spiit sleeve cylindrical cathode bears against the wall of the housing and circumferentially surrounds the anode spaced outwardlytherefrom. In use a potential différence is applied across the flow passagebetween the cathode and the anode to drive the electrowinning métalproduction process. The helical flow through the cell from the inlet to the outletprésents copper ions to the cathode continuously to plate out the coppereconomically even in low grade solutions.

This process progessively plates out a copper tube on the inside of thesplit sleeve. When the copper plate is about 6 to 8 cm thick (2.4 to 3.14 inches)it is harvested. This is accomplished by removing a top end cap from the celland lifting the split sleeve out through the top of the cell. This is a laborintensive process and interfères with the otherwise continuous nature of theprocess.

As a commercial plant using the process contains banks of literallyhundreds of cells, the harvesting of the cells in the manner described above is alabor-intensive process. A further disadvantage of the production of coppertubes in the manner described above is that the tubes require spécifie handlingand transport procedures. It would therefore be advantageous if an easiermethod for harvesting the copper from the electrowinning cells could bedevised.

In addition the electrowinning cell described above may hâve less thanoptimum efficiency because of the large gap or distance between the cathodeand anode. As a resuit a relatively high voltage has to be applied across thecathode and anode and the applicable current density is relatively lower. As theamount of métal produced is directly proportional to the current density acrossthe cathode and anode it is désirable to hâve as high a current densify per unitamount of electrical power input as possible. PCT/AU00/00877

Received 06 August 2001

Summary of Invention T u

According to a first aspect of this invention there is provided a cell forelectrowinning a métal in powder form from solution, the cell including: a housing having an inlet towards one end thereof and an outlet towards anopposed end; an anode extending substantially axially through the housing;a cathode surrounding the anode spaced outwardly away from the anode todefine a flow passage between the cathode and anode, having a gap of 5 to25 millimétrés; and means for applying a potential différence between the anode and thecathode.

The cell therefore has a substantially narrower gap between the cathode andanode then either electrowinning plate cells or cylindrical cells for producing coppertubes. This -assists in increasing the current density between the cathode and theanode, particularly for low conductivity solutions.

Typically the housing is devoid of mechanical means within the housing fordisplacing the solution through the housing and the housing is also devoid ofmechanical stripping means for mechanically stripping plated métal from the cathodeafter it has been deposited.

More preferably the gap is 5 to 20 millimétrés, even more preferably 10 to 15millimétrés, most preferably 12 to 13 millimétrés.

Typically both the anode and the cathode are substantially cylindrical. Thecathode may be formed by the wall of the housing or by a sleeve positioned adjacentthe wall of the housing. Preferably the cathode is formed bythe wall of the housingwhich is metallic.

Typically one end of the cell has a relatively upper orientation and anopposed end of the cell has a relatively lower orientation in use, and the inlet is

AMENDED SHEE1IPEA/AU PCT/AU00/00877

Received 06 August 2001 4 12 0 4 3 positioned at or adjacent the lower end and the outlet is positioned at or adjacent theupper end.

Thus in use process solution containing métal ions to be electrowon travelsupwardly through the cell from the inlet to the outlet and métal is deposited on thecathode as a powder. Periodically a flush solution is pumped in a reverse directionthrough the cell to remove deposited métal from the cell for harvesting. It is preferredthat the process solution travels up through the cells so that gas generated by theelectrowinning process can be vented through a vent associated with an upperrégion of the cell. It is particularly preferred that flush solution travels downwardlythrough the cell so that gravity assists with the flushing process. Typically flushingwould be assisted by other factors such as increased pressure of flush solution andpassing air bubbles or other means over the cathode to assist in loosening the métalpowder.

Preferably the inlet directs solution into the cell in substantially an axialdirection.

Preferably the outlet is oriented such that flushing fluid which is passedthrough the cell in a reverse direction is directed axially into the cell through theoutlet.

In a preferred form said inlet is defined in said one end of the cell and saidoutlet is defined in said opposed end of the cell.

The orientation of the inlet and gap of the flow passage facilitâtes processsolution flowing through the flow passage with a turbulent flow. This is quite differentfrom the tangential inlet in the prior art cell which induces a helically spirally plug flowthrough the cell from inlet to outlet. Plug flow is fundamentally different fromturbulent flow.

It is similarly advantageous that the flush solution which flows in a reversedirection through the outlet of the cell is directed axially into the cell to promote amendeosheet

IPEA/AU PCT/AU00/00877

Received 06 August 2001 12 0 4 3 turbulent flow. this turbulent flow of flush solution assists in dislodging the métalpowder from the cathode.

Preferably the cell further includes means for guiding powder which is washedoff the cathode during a flush cycle towards the inlet through which it is drained fromthe cell. The guiding means may be formed by the internai surface of the housingwhich slopes inwardly downwardly towards the inlet.

This reduces the likelihood of métal powder collecting in dead spaces in thebottom of the cell and assists in fully draining métal powder from the cell.

Preferably the cell further includes mechanical cleaning means for breakingany dendrites of métal that may hâve formed in the flow passage between the anodeand the cathode. Optionally the mechanical cleaning means may comprise amechanical cleaner which is physically moved along the flow passage although othercleaning means may also be used.

Naturally the process flow parameters are set so as to reduce the likelihood ofsolid métal eg dendrites of métal from depositing on the cathode. While the applicantbelieves that it is highly unlikely that métal plate obstructions such as dendrites willform in the flow passage it is still necessary to provide a means for checking for andremoving blockages of métal should they occur to provide a reliable pièce of processequipment for use in a commercial plant.

Preferably the ends of the anode are closed to direct fluid around the anodeand through the annular flow passage. One end has a flow formation having abroadly conical configuration for directing flush solution passing through the outlettowards the flow passage. The closèd ends ensure that solution flows around theanode and through the flow passage.

The cell may also include a support for supporting the anode in the form of asupport member mounted to an end of the housing and projecting substantiallyaxially into the housing. The support member mechanically supports the anode in

AMENDEDSHEET

IPEA/AU PCT/AU00/00877Received 06 August 2001 6 1 2 0 4 3 the appropriate position vertically aiigned with the cathode and also electricallyconnects the anode to the electrical circuit.

In a particularly preferred form the housing comprises a cyiindrical body ofstainless Steel and end caps of non-conductive material on each end of thecyiindrical body, each of the end caps defining a chamber positioned axiallyoutwardly of the cathode and anode. One of the end chambers may form the slopinginternai surface described above for guiding powder métal through the inlet.

This way the cyiindrical body which forms the cathode is electrically isolatedfrom the support member and electrical connection to the anode which passesthrough one of the end caps.

The anode and flow formations ensure that solution flows around the anodeand through the flow passage. The support member mechanically supports theanode in the appropriate position vertically aiigned with the cathode and alsoelectrically connects the anode to the electrical circuit. A particularly preferred form of the cell has a cathode with a diameter of 7½ to8½ inches, preferably about 8 inches, and the anode has a diameter of 6½ to 7½inches, preferably about 7 inches, with the gap between the anode and cathodebeing 0.5 to î.5 inches, preferably about 1 inch. Further in the most preferred formthe housing is substantially vertically extending and the inlet is defined in the end ofthe lower end cap and the outlet is defined in the end of the upper end cap.

According to another aspect of this invention there is provided a bank of cellsincluding: a plurality of cells as defined ih claim 1 arranged in parallel; an inlet main coupled directly to the inlet of each of the cells in the bank for directing process solution through the cells in parallel; an outlet main coupled directly to the outlets of each of the cells for directingprocess solution away from the cells; and

AMENDED SHEET ipbvau 12 0 A 3 7 means for interrupting a flow of process solution through the bank ofcells when required and then passing a flush solution in a reverse directionthrough the outlet main, then through each of the cells in the bank, and then outthrough the inlet main.

In use therefore process solution is passed in parallel through each ofthe cells of the bank and flush solution in tum is periodically or intermittentlypassed in a reverse direction in parallel through the cells to flush the powdermétal out of the cells.

Preferably the flow reversai means includes a process solution inletvalve means for opening and shutting off the flow of process solution into theinlet main, and process solution outlet valve means for opening and shutting offthe flow of process solution out of the outlet main in a downstream direction andalso flush solution inlet valve means for opening and shutting off the flow ofprocess solution into the outlet main, and flush solution outlet valve means foropening and shutting off the flow of flush solution out of the inlet main.

Thus control of respectively process and flush solution flow through thebank of cells can be accomplished by an inlet and outlet main and single sets ofvalves associated with each of the process and flush solutions. This is a fairlysimple réticulation and valve arrangement fôr a bank having a number of cells.It is far simpler than having a separate valve arrangement for each cell.

The bank may further include control means for controlling the valveseg to permit only flush solution or process solution to flow through the bank atone time. Many different control means may be used but a PLC controller isparticularly useful.

The control of the valve means can be accomplished in a variety ofways including by manual control. The PLC controller is a proven piece of off-the-shelf equipment that can be used to reliabiy control the process. 12 0 4 3 δ

Typically the bank will also include means for venting gas generated bythe electrowinning process from the cells in the bank. Typically the ventingmeans comprises a vent operatively coupled to the outlet main.

The vent is important for removing gas generated by the electrowinningprocess in a commercial plant. By having the outlet main operatively coupled tothe outlets of each of the cells a single vent can be used to vent ail the cells in abank. It is considerably simpler and cheaper than having a vent for each cell.

Preferably the inlet main is adjacent a lower end of each of the cells andthe outlet main is adjacent an upper end of the cells. Naturally the inlet andoutlet main will be positioned so as to minimise the length of piping required.

According to yet another aspect of this invention there is provided amethod of operating an electrowinning cell for electrowinning a métal fromsolution, the cell having a spaced inlet and outlet and a substantially cylindricalcathode surrounding an anode defining a flow passage therebetween, themethod including: passing a métal containing process solution through the flow passagefrom the inlet to the outlet while a voltage is applied across the cathode andanode so as to deposit particulate métal from the solution on the cathode; periodically interrupting the flow of solution through the cell and passinga flush solution in a reverse direction through the cell, the flush solutiondislodging métal powder from the cathode and washing it out of the cell and intoa metals recovery section of the plant.

The method may include the further step of recovering the particulatemétal from the flush solution, eg in a métal recovery section of the plant.

Advantageously the method further includes the step of interrupting theflow of flush solution when the particulate or powder métal has been removedfrom the cells and restoring the normal flow of solution through the cell to plateout further copper. 12 0 4 3 9

The method may include flushing the cells after 1 to 6 hours of pumpingprocess solution through the cells, typically 2½ to 4½ hours of passing processsolution through the cells. Typically the flush solution is passed through the cellfor 15 to 30 seconds, preferably 20 to 25 seconds.

Preferably the process solution is passed through the cell at flow rate of1,000 to 3,500 litres per hour, preferably 2,000 to 3,000 litres per hour, and theflush solution is pumped through the cell at a flow rate of 6,000 to 10,000 litresper hour, preferably 7,000 to 9,000 litres per hour.

Typically the flush solution is pumped through the cell at a higherpressure than the process solution. This higher pressure assists in dislodgingmétal powder from the cathode.

In a typical cell during normal operation the métal containing processsolution travels up the cell from the iniet to the outlet and the flush solutiontravels In a reverse direction down the cell from outlet to iniet. This way gravityassists in dislodging the powder métal from the cathode and in washing it out ofthe cell.

The method may also include periodically passing a mechanical cleanerthrough the flow passage to remove any plate or other solid dendrites or the likewhich may hâve plated out on the cathode.

The method may also include passing bubbles, eg air bubbles, upthrough the flow passage of the cell, eg after the flow of process solution hasbeen interrupted and before the flow.of flush solution has been started, to assistin dislodging powder métal from the cathode.

According to yet another aspect of this invention there is provided anelectrowinning plant comprising a plurality of banks of cells as described abovewith reference to the second aspect of the invention, the banks being 12 0 4 3 10 operatively connected together such that process solution containing métal tobe electrowon can be passed through each of the banks in sériés.

Typically flush solution is passed in a reverse direction through thebanks of cells.

Typically the flush solution is only passed through a single bank of cellsat any one time. It is not passed through ail the banks in sériés in a reversedirection.

The plant may comprise at least three banks of cells in sériés. Theexact number of banks for any particular application- will dépend on the initialgrade of process solution and the target grade of the product solution as well asthe current density in the cells.

Typically only one bank of cells has the flow of process solutiontherethrough interrupted for flushing at any one time. That way the flow ofprocess solution through the plant can be continuous, only one bank of cellsbeing taken out of production for flushing at any one time.

Detailed Description

An apparatus and a method in accordance with this invention maymanifest itself in a variety of forms. It will be convenient to hereinafter describein detail several preferred embodiments of the invention with reference theaccompanying drawings. The purpose of providing these drawings is to instructpersons having an interest in the subject matter of the invention how to carrythe invention into practical effect. It is to be clearly understood however that thespécifie nature of this description does not supersede the generality of thepreceding broad description. In the drawings:

Fig. 1 is a sectional front view of a cell in accordance with the inventionin a normal process flow condition; 12 0 4 3 11

Fig. 2 is a sectional front view of the cell of Fig. 1 in a flush flowcondition;

Fig. 3 is a front view of a bank of the cells of Fig. 1 operatively coupledto each other; and

Fig. 4 is a process flow sheet of a plurality of banks of cells of Fig. 3.

In Figs. 1 and 2 reference numéral I refers generally to a cell inaccordance with the invention. . The cell 1 comprises broadly a housing 2 having an inlet 3 at the lowerend thereof and an outlet 4 at the upper end thereof. The cell 1 further includesan axially extending anode 6 and a cathode 7 spaced radially away from theanode 6. The anode 6 and cathode 7 define a flow passage 8 therebetweenthrough which process solution is passed from the inlet 3 to the outlet 4. Thecell aiso includes electrical power and an electrical circuit for applying apotential différence across the cell between the anode 6 and the cathode 7. Inuse the cell alternâtes between a process flow condition illustrated in Fig. 1 anda flush flow condition illustrated in Fig. 2.

The housing 2 comprises broadly an elongate circular cylindrical body10, eg made of stainless Steel, and end caps 11 and 12, eg made ofengineering plastics material, mounted on each end of the cylindrical body 10.Typically the end caps 11 and 12 are permanently mounted to the body 10although this is not necessary. In the illustrated embodiment the· ends of thebody are flanged and the end caps .are mounted to the body by bolts passingthrough the flanges and the end caps.

In preferred forms the body 10 has a diameter of 6 inches (152.4millimétrés) or 8 inches (203.2 millimétrés). The inlet 3 which is axiallyextending is defined in the bottom end cap 12 of the housing 2 which directs 12 0 4 3 12 process solution axially into the housing 2. In the illustrated embodiment theinlet 3 is positioned off centre although the précisé position of the inlet is notessehtial. The inlet is positioned off centre to accommodate a centrallypositioned support member which is described in more detail below.

The inlet 3 and outlet 4 will typically hâve a diameter of 35 to 40millimétrés. This is to facilitate a flow rate of about 1000 to 3500 litres per hourthrough the cells during the normal process flow conditions and 6000 to 10,000litres per hour during the flush flow condition.

The outlet 4 extends axially away from the upper end cap 11 of thehousing in a similar fashion to the inlet 3. The outlet 4 is however centrallypositioned as illustrated. When powder métal is flushed from the cell the outlet4 acts as an inlet for the flush solution and the inlet 3 acts as an outlet for theflush solution as will be described in more detail below.

The cathode 7 is formed by the wall of the body 10 which is made ofelectrically conductive material as described above.

The anode 6 is similarly cylindrical being sized to leave a relativelysmall gap and flow passage 8 between the anode 6 and the cathode 7.Typically the width of the flow passage is of the order of 10 to 15 millimétrés.Consequently the différence in diameter between cathode and anode istypically about 1 inch (25.4 millimétrés). In the illustrated embodiment theanode 6 has a diameter of 7 inches and the cathode 7 has a diameter of 8inches.

The anode 6 is supported by a support 15 projecting through the lowerend cap 12 of the housing 2. The member 15 is subsfantially centrallypositioned which is why the inlet 3 is off centre. The member 15 is positivelyattached to both the end cap 12 and the anode 6 to support the anode in theappropriate vertical position aligned with the cathode. 1 2 0 4 3 13

Naturally the upper and lower ends 18 and 19 of the anode 6 are closedso as to direct solution around the anode 7 into the flow passage 8. The upperend of the anode 6 comprises a conical flow formation 20 for directing flushsolution entering the housing 2 around the anode 6 and through the flowpassage 8.

The end caps 11 and 12 space the inlet 3 and outlet 4 axially away fromthe ends of the cathode 7 and anode 6. This defines chambers 21 and 22adjacent the inlet 3 and outlet 4. In the illustrated embodiment the chamber 22has a flow surface 23 which slopes inwardly from the sïdes of the end cap 12towards the inlet 3. This assiste in guiding or directing powder métal towardsthe inlet 3 when it is flushed off the cathode 7.

In the process flow condition, process solution containing métal ions forelectrowinning, eg Cu ions, is passed upwardly through the cell from the inlet 3to the outlet 4 as shown in Fig. 1. While the process solution is being passedthrough the flow passage 8 a voltage is applied across the flow passage fromthe cathode 7 to the anode 6. This causes deposited métal, eg in the form ofmétal particles or métal powder, to deposit on the cathode 7. After some timewhen the solid copper has at least partially occluded the flow passage 8, theflow of process solution through the cell 1 is interrupted.

The cell induces powder métal to deposit on the cathode. Theformation of powder as distinct from plate métal is promoted by: turbulent flowin the flow passage, reducing the flow rate of process solution and thereby thevelocity of the solution over the cathode when compared with applicant’s priorart cell, reducing the current density and treating a relatively low grade solution.Certain process parameters will yield the formation of powder métal dependingon the grade of process solution.

The lower the grade of métal in solution the more likely the métal is toproduce powder. Further the lower the velocity of fluid through the cell and thecurrent density the more likely the solution is to produce powder métal as 12 0 4 3 14 distinct from plate métal. Further turbulent flow through the cell as distinct fromplug flow also promûtes the formation of powder.

Thereafter a flow of flush solution is commissioned in a reverse ordownward direction from the outlet 4 to the inlet 3. The flush solution, assistedby gravity, dislodges the powder métal deposited on the cathode 7 anddisplaces it down the cathode 7 towards the inlet 3. The inlet 3 acts as anoutlet in the flush flow condition.

The tapered walls of the chamber defined by the end cap 12 assists inguiding the powder métal towards and through the outlet 3. The pressure of theflush solution is typically higher than the process solution to assist the flushingprocess.

From the inlet 3 the powder métal is typically conveyed, eg by means ofthe flush solution in a gravity drain, to a downstream collection or furtherProcessing point.

The flush flow condition is usually carried out for 20 to 25 secondsalthough this spécifie time is not critical. After the métal has been flushed fromthe cell the flow of flush solution is interrupted and the flow of process solutionis restored.

In Fig. 3 référencé numéral 30 refers generally to a bank of cells. Eachof the cells is as described above with référencé to Figs.1 and 2. Accordinglythe same référencé numerals will be used to refer to the components of thecells as in Figs. 1 and 2.

Each bank of cells 30 comprises a plurality of cells 1, typically 5 to 20,connected in parallel. An inlet main 32 is operatively coupled to the inlets 3 ofeach of the cells 1 and an outlet main 34 is operatively coupled to the outlets 4of each of the cells 1. 12 0 4 3 15 A process solution inlet conduit 36 is operatively coupled to the inletmain 32. Similarly a process solution outlet conduit 38 is also operativelycoupled to the outlet main 34. Process solution inlet and outlet valves 40 and41 are provided for opening and shutting off the flow of process solution throughthe mains 32 and 34.

Correspondingly the outlet main 34 is coupled to a flush solution inletconduit 42 and the inlet main 32 is coupled to a flush solution outlet conduit 43.This typically is a gravity drain leading to a settling cône. These conduits alsohâve associated therewith valves 44 and 45 similar to valves 40 and 41.

The bank 30 also includes gas vent means in the form of a riser 46inciuding a pneumatic valve projecting out from an upper région of the outletmanifold 34. This enables the gases generated by the electrowinning processto be vented from the process as is necessary. Further it enables this to beefficientfy accomplished by having a single vent for the entire bank 30 of cells.

Typically the valves 40, 41, 44 and 45 are pneumatic valves althoughother valves may also be used.

The bank 30 also includes control means in the form of a PLC controllerfor opening and closing the valves to change the bank between process flowcondition and flush flow condition. Each process flow cycle lasts one to threehours, eg two hours and each flush flow cycle lasts 20 to 25 seconds.

In use, process solution is passed through the conduit 36 through thevalve 40 into the inlet main 32. It then flows through each of the cells 1 inparallel. During the passage through the cells métal is electrowon from solutionas is described above with référencé to Figs. 1 and 2. The solution then exitsthe cells 1 through the outlets 4 and passes into the outlet main 34 and fromthere out from the conduit 38. From there it passes to the next bank of cells. 120 A 3 16

When the bank is changed from process flow condition to flush flowcondition, valves 40 and 41 are closed and valves 44 and 45 are opened. Thisshuts off process solution and permits flush solution to flow through the cells ina reverse direction.

An advantage of the bank of cells described above is that it has arelatively simple valve System. The entire bank of cells has only four valves forreversing flow through the individual cells. This makes the process morereliable and maintenance free. It is also cheaper. In addition a single gas ventis used for the entire bank of cells.

Fig. 4 illustrâtes a flow sheet of a plant comprising a plurality of banks ofcells. Each bank is as described above with référencé to Fig. 3. Accordinglythe same référencé numerals will be used to refer to the same components asin Figs. 1 to 3.

The individual cells in each bank 30 are connected in parallel, the inlets3 and outlets 4 of each 1 being directly connected to respectively the inlet main32 and outlet 34 main. The banks of cells in turn are connected in sériés. Thusa process solution containing métal ions is passed through each of the banks inturn. Métal ions are progressively stripped from the solution as it passesthrough each of the banks of cells. Thus the total number of banks of cellsused in any plant will dépend on the Initial grade of the feed solution, theamount of métal desired to be removed, and the target grade of the end productsolution.

Only one bank of cells is flushed at a time. This enables a continuousflow of process solution through the plant with the solution merèly bypassing thebank of cells which is being flushed. The bank is flushed by passing flushsolution in a reverse direction through the cells in parallel. The flush solutionand entrained métal powder is coliected in the inlet main and then directed bygravity to a settling tank. 12 0 4 3 17 A key advantage of the cell described above is that it produces métalpowder which is easy to handle as distinct from copper tubes. It also permitsthe métal powder to be automatically harvested by means of a processarrangement rather than manual handling. With prior art cells it is necessary to 5 periodically open up the cell and physically remove a bulky tube of copper andthen close up the cell to recommence the process. . The process describedabove is the only non-invasive automatic electrowinning cell of which theapplicant is aware. As a resuit of these properties it is practical and applicableto industrial scale plants. 10

An advantage of the cell described above is that it is able to producepowder métal relatively efficiently. Because the cathode anode gap is relativelynarrow the current density is higher for a given voltage which leads to a higheryield of métal product. 15

Another advantage of the plant described above is that a single inletmain and outlet main and a single set of valves can be used to control theflushing of the cells to harvest powder métal. 20 It will of course be realised that the above has been given only way of illustrated example of the invention and that ail such modifications andvariations thereto as would be apparent to persons skilled in the art are deemedto fall within the broad scope and ambit of the invention as is herein said forth.

Claims

HC1/AUUU/UU8 ! Z Received 06 August 2001 18 120 4 3 CLAIMS

1. A cell for electrowinning a métal in powder form from solution, the cellincluding: a housing having an inlet towards one end thereof and an outlet towards anopposed end; an anode extending substantially axially through the housing;a cathode surrounding the anode spaced outwardly away from the anode todefine a flow passage between the cathode and anode having a gap of 5 to25 millimétrés; and means for applying a potential différence between the anode and thecathode.
2. A cell according to claim 1, further including means for passing a hydraulicflush solution _in a reverse direction through the flow passage between theanode and cathode to detach métal plated on the cathode from the cathodeand flush it out of the housing.
3. A cell according to claim 2, wherein the flush solution means comprises theoutlet at said opposed end of the housing through which flush solution isdirected into the flow passage, and the inlet at said one end of the housingthrough which flush solution and detached métal are discharged from thecell.
4. A cell according to claim 3, wherein said outlet is oriented such that flushingfluid which is passed into the cell in a reverse direction is directed axially intothe cell.
5. A cell according to claim 3 or claim 4, wherein the ends of the anode areclosed to direct solution around the anode and then through the flowpassage. AMENDED SHEET IPEA/AU PCT/AU00/00877 Received 06 August 2001 19 1 2 0 4 3
6. A cell according to any one of daims 1 to 5, wherein one end of the cell has arelatively upper orientation and an opposed end of the cell has a relativelylower orientation in use, and the inlet is positioned at or adjacent the lowerend and the outlet is positioned at or adjacent the upper end so that métalcontaining solution flows upwardly through the cell and flush solution flowsdownwardly through the cell.
7. A cell according to any one of daims 1 to 6, wherein the housing is devoid ofmechanical means within the housing for displacing the solution through thehousing and the housing is devoid of mechanical stripping means formechanically stripping plated métal from the cathode after it has beendeposited.
8. A cell according to any one of daims 1 to 7, wherein the cathode issubstantially cylindrical and the anode is also cylindrical but with a diameterless than that of the cathode.
9. A cell according to any one of daims 1 to 8, wherein the gap between theanode and the cathode is 10 to 15 millimétrés.
10. A cëll according to any one of daims to 3 to 5, further including a flowformation having broadly a conical configuration for directing flush solutionentering the cell through the outlet towards the flow passage between thecathode and the anode.
11. A cell according to claim 8, wherein the cell further includes means forguiding powder which is washed off the cathode during a flush cycle towardsthe inlet.
12. A cell according to claim 11, wherein the guiding means is formed by theinternai surface of the housing which slopes inwardly downwardly towardsthe inlet. AMENDEDùr— IPEA/AU PCT/AU00/00877Received 06 August 2001 20 12 0 4 3
13. A cell according to any one of daims 1 to 12, further including mechanicalcleaning means for breaking any dendrites of métal that may hâve formed inthe flow passage between the anode and cathode.
14. A cell according to claim 13, further including a support for supporting theanode in the housing.
15. A cell according to claim 14, wherein the support includes a support membermounted to an end of the housing and projecting substantially axially into thehousing where it supports the anode, and wherein the inlet is off-set from acentral position to accommodate the support.
16. A cell according to any one of daims 1 to 15, wherein the housing comprisesa cylindrical body of stainless Steel and end caps of non-conductive materialand each of the end caps defines a chamber axially outwardly of the cathodeand the anode.
17. A cell according to claim 16, wherein the cathode has a diameter of 7½ to 8½inches and the anode has a diameter of 6½ to 7½ inches, and the différencein diameter between the anode and the cathode is 0.5 inches to 1.5 inches.
18. A cell according to any one of daims 1 to 17, further including means forbubbling gas upwardly through the flow passage between the cathode andthe anode for assisting in dislodging métal powder from the cathode.
19. A cell according to any one of daims 1 to 18, wherein the housing issubstantially vertically extending and wherein the inlet is defined in thebottom end of the cell and the outlet is defined in the top end of the cell, andthe cathode and anode define a gap of 10 to 15 millimétrés therebetween.
20. A bank of cells including: a plurality of cells as defined in claim 1 arranged in parallel; AMENDED IPE/VAU PCT/AU00/00877 Received 06 August 2001 21 12 0 4 3 an inlet main coupled directly to the inlet of each of the cells in the bank fordirecting process solution through the cells in parallel;an outlet main coupled directly to the outlets of each of the cells for directingprocess solution away from the cells; and means for interrupting a flow of process solution through the bank of cellswhen required and then passing a flush solution in a reverse directionthrough the outlet main, then through each of the cells in the bank, and thenout through the inlet main.
21. A bank of cells according to claim 20, wherein said flow reversai meansincludes a process solution inlet valve means for opening and shutting off theflow of process solution into the inlet main, and process solution outlet valvemeans for opening and shutting off the flow of process solution out of theoutlet main in a downstream direction.
22. A bank of cells according to claim 21, wherein the flow reversai meansfurther includes flush solution inlet valve means for opening and shutting offthe flow of process solution into the outlet main, and flush solution outletvalve means for opening and shutting off the flow of flush solution out of theinlet main.
23. A bank of cells according to claim 22, further including control means forcontrolling respectively opening and shutting of the process solution inletvalve means and outlet valve means and the flush solution inlet valve meansand outlet valve means.
24. A bank of cells according to claim 23, wherein the control means only permitsthe flush solution inlet and outlet valve means to open when the process solution inlet and outlet valve means are closed.
25. A bank of cells according to claim 24, wherein the control means only permitsthe process solution inlet and outlet valve means to open when the flushsolution inlet and outlet valve means are closed. AMENDED Sric_ IPEA/AU PCT/AU00/00877 Received 06 August 2001
26. A bank of cells according to any one of daims 23 to 25, wherein the controlmeans is a PLC controller.
27. A bank of cells according to any one of daims 20 to 27, further includingmeans for venting gas from each of the cells in the bank.
28. A bank of cells according to daim 27, wherein the gas venting meanscomprises a vent operatively coupled to the inlet main.
29. A bank of cells according to any one of daims 20 to 28, wherein the inletmain is adjacent to or proximate to a lower end of each of the cells.
30. A bank of cells according to daim 29, wherein the outlet main is adjacent toor proximate to an upper end of the cells.
31. A bank of cells according to daim 30, wherein the inlet main is spaced ashort distance substantially directly below the lower ends of the cells and theoutlet main is spaced a short distance directly above the upper ends of eachof the cells.
32. A method of operating an'electrowinning cell for electrowinning a métal froma métal ion containing solution, the cell having an inlet and an outlet spacedfrom the inlet and a substantially cylindrical cathode surrounding an anodedefining a flow passage therebetween, the method including: passing a métal containing process solution through the flow passagefrom the inlet to the outlet while a voltage is applied acrôss the cathode andanode so as to cause métal ions in the solution to plate on the cathode asmétal; periodically interrupting the flow of métal ion containing solution throughthe cell and passing a flush solution in a reverse direction through the cell,the flush solution dislodging plated métal from the cathode and washing it outof the cell where it can be collected. AMENDEO SHEEt IPEA/AU PCT/AU00/00877 Received 06 August 2001 12 0 4 3
33. A method according to claim 32, wherein the flush solution is passed into thecell through the outlet for the métal ion containing solution and the flushsolution is passed out of the cell through the inlet for the métal ion containingsolution.
34. A method according to claim 33, wherein the outlet is towards a top of thecell and the inlet is towards a bottom of the cell.
35. A method according to claim 34, further including the step of interrupting theflow of flush solution when the métal has been removed from the cell andthen restoring the flow of métal ion containing solution through the cell torésumé plating of métal.
36. A method according to claim 35, including flushing the cells after 1 to 6 hoursof passing métal ion containing solution through the cells by passing flushsolution through the cell for 15 to 30 seconds.
37. A method according to claim 36, wherein the flush solution is pumpedthrough the cell at a higher pressure than the métal ion containing solutionand the higher pressure assists in dislodging métal powder from the cathode.
38. A method according to any one of daims 32 to 37, further including collectingthe particulate métal and flush solution in a conduit and then conduiting it to ametais recovery plant. AMENDED SHtu IPEA/AU