AU762872B2 - Apparatus for electrowinning metal - Google Patents

Description

1 APPARATUS FOR ELECTROWINNING METAL This application is a patent of addition to Australian patent application no.

58054/96 This invention relates to a cell assembly for electrowinning a metal from an electrolyte. This invention also extends to an apparatus comprising a bank of said cell assemblies.

This invention relates particularly, but not exclusively, to a cell assembly for electrowinning metals such as copper, nickel, gold and tin from solutions containing the corresponding metal cations and it will be convenient to hereinafter describe this invention with reference to this example application.

However, it is to be clearly understood that the invention is capable of broader application.

oooThe applicant has previously developed a cell for the electrowinning of metals from low grade metal ion containing streams. This cell is described in the applicant's earlier patent application, international patent application no.

PCT/AU96/00332 entitled MINERAL RECOVERY APPARATUS. The entire contents of this specification are hereby explicitly incorporated into the specification by cross-reference.

This document discloses a cylindrical housing having a cylindrical side 25 wall and end caps mounted on opposed ends of the side wall. A cathode in the ooooo S form of a split sleeve is received within the housing and is capable of being removed from the housing through the end cap. An anode which is rod-like projects axially through an end cap of the housing into the cell, i.e. the end cap which is removed to facilitate harvesting of metal. The anode is substantially coaxial with the cathode. Metal, e.g. in the form of plated copper or tin is harvested from the cell periodically by removing the cathode from the cell and 2 detaching the plated metal from the cathode.

The cell described in PCT/AU96100332 is very effective in electrowinning metal ions from solution, particularly low-grade solution. This is because the geometry of the cell constantly presents metal cations to the cathode surface to enable them to plate out on the cathode surface.

However, the cell does have some operational shortcomings, particularly when applied to a commercial industrial scale plant for the electrowinning of metals. For example, it is very unwieldy to remove the anode with the end cap each time copper has to be harvested from the cell. Accordingly, it would be advantageous if a cell assembly was provided which addressed these S. shortcomings.

According to one aspect of this invention, there is provided a cell assembly for electrowinning a metal from an electrolyte, the cell assembly o. including: l a housing having a substantially cylindrical side wall and two opposed end caps, the housing defining an inlet and an outlet axially spaced from the S 20 inlet, the inlet and the side wall being configured so as to induce the electrolyte to flow through the housing with a flow pattern in the form of a helical spiral; a removable cathode in the form of a sleeve which is split longitudinally, the cathode being snugly received within the side wall of the housing such that it is positioned adjacent the side wall of the housing, for harvesting metal deposited on the cathode, by removing one said end cap and lifting the cathode through the open end of the housing; an elongate anode projecting substantially axially through the other said end cap into the housing, said anode being substantially centrally positioned within the housing spaced radially inwardly from the cathode and defining an annular flow passage between the anode and the cathode; and releasable electrical connecting means for electrically connecting said cathode to an electrical circuit.

Thus, the anode is mounted to one end cap and the other end cap is removed for harvesting of the cathode. This is beneficial because it is considerably easier to remove an end cap on its own than an end cap having an anode attached and mounted thereto. This development is particularly 15 advantageous when applied to an industrial scale plant with over 100 cell assemblies wherein the harvesting of cells is an ongoing process for plant operators.

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Itllt: Preferably both the inlet and the outlet extend substantially perpendicularly to the longitudinal axis of the housing and tangentially relative to the side wall of the housing.

In one particularly advantageous application, the housing is substantially vertically extending and said one end cap through which the cathode is lifted is 25 positioned at the top of the housing, and said other end cap through which the 00 S" anode passes is positioned at the bottom of the housing.

Typically, the anode is also mounted to the end cap through which it passes. Typically the anode is also sealed to the end cap, e.g. by means of a sealing gland, sealing washer or the like.

Each end cap may be mounted to the housing by means of a quick release connection, e.g. a bayonet-type connection or the like.

According to another aspect of this invention, there is provided a cell assembly for extracting a metal from an electrolyte, the cell assembly including: a housing having a substantially cylindrical side wall and two opposed end caps, the housing defining an inlet and an outlet axially spaced from the inlet, the inlet and the side wall being configured so as to induce the electrolyte to flow through the housing with a flow pattern in the form of a helical spiral; a removable cathode in the form of a sleeve which is split longitudinally, the cathode being snugly received within the side wall of the housing such that it is positioned adjacent the side wall of the housing, for harvesting metal 15 deposited on the cathode, by removing one of said end caps and lifting the cathode through the open end of the housing; an elongate anode projecting substantially axially through one of the end caps into the housing, said anode being substantially centrally positioned within 20 the housing spaced radially inwardly from the cathode and defining an annular flow passage between the anode and the cathode; *9 releasable electrical connecting means for electrically connecting said cathode to an electrical circuit; and means for accumulating gases generated by the electrolytic processes taking place within the cell assembly and directing said gases in a controlled manner out of the cell assembly.

Gases, particularly oxygen and hydrogen, but potentially also toxic gases such as hydrogen sulphide and arsine are a natural product of the electrolytic process. It is accordingly necessary to deal with these gases in a commercial plant. The gases need to be accumulated and then directed out of the cell assembly to a point at which they can be treated. According to prior art devices in this field, the gases evolved were vented from the cell assembly directly to atmosphere. This is highly undesirable particularly as toxic gases such as arsine and hydrogen sulphide are sometimes generated by the electrolytic process.

In a typical application, the inlet of the cell is positioned in a relatively 10 lower position and the outlet of the cell assembly is positioned in a relatively upper position whereby electrolyte solution flowing through the cell flows upwardly from the inlet to the outlet driving gases upwardly towards the top of the cell. In this application, the means for accumulating and exhausting gases generated with the housing includes a top or upper portion of the housing positioned above the outlet of the cell assembly and above the split sleeve which defines a head space within which gas may accumulate.

Thus by directing the flow of solvent upwardly through the cell assembly, gases are pushed towards the top of the cell assembly where they 2 o tend to accumulate, e.g. in the head space defined by the top portion.

Typically, the means for accumulating and exhausting gases further includes a vent mounted on the top portion of the housing and in fluid communication with the head space inside the housing and any gases accumulating therein.

In one form, the means for accumulating and exhausting gases further includes a gas manifold, e.g. operatively coupled to the vent, for exhausting gases away from the cells to a treatment point at which they can be effectively treated.

In another form, instead of a gas manifold, the means for accumulating and exhausting gases may further include a conduit that places the head 8 T space of the cell assembly in fluid communication with the top portion and enclosed portion of an adjacent cell assembly. This achieves the same effect as the o°o •go oo 6 manifold by conduiting the gas away from the cell assemblies to a treatment point. It does this by linking the cell assemblies with each other rather than a separate manifold.

With each of the above forms, the gases are conduited away from the cell assemblies to a treatment and/or disposal and/or venting point.

Preferably, the top portion of the housing has an axial extent or length which is not less than the diameter of the housing.

According to yet another aspect of this invention, there is provided a cell assembly for extracting a metal from an electrolyte, the cell assembly including: a housing having a substantially cylindrical side wall and two opposed S 15 end caps, the housing defining an inlet and an outlet axially spaced from the inlet, the inlet and the side wall being configured so as to induce the electrolyte to flow through the housing with a flow pattern in the form of a helical spiral; a removable cathode in the form of a sleeve which is split longitudinally, the cathode being snugly received within the side wall of the housing such that it is positioned adjacent the side wall of the housing, for harvesting metal deposited on the cathode, by removing one of said end caps and lifting the cathode through the open end of the housing; .25 an elongate anode projecting substantially axially through one of the end caps into the housing, said anode being substantially centrally positioned within the housing spaced radially inwardly from the cathode and defining an annular flow passage between the anode and the cathode; releasable electrical connecting means for electrically connecting said cathode to an electrical circuit; and means for masking the cathode, mounted over at least one end of the cathode for resisting plating of metal over said one end.

It has been found that in devices manufactured prior to the present invention, removing the plated copper from the sleeve can be troublesome.

The copper has a tendency to deposit over and around the edges of the sleeve making it difficult to urge the tubular split sleeve outwardly away from the plated copper tube. Advantageously, the invention according to another o10 embodiment of the present invention may further comprise masking means comprising removable masking elements mounted over each end of the cathode, which may prevent this type of deposit.

In turn, each masking element may comprise a base member mounted over the end of the cathode and having a depending skirt which extends inwardly into the interior of the sleeve adjacent to the wall of the sleeve to "inhibit plating of metal on that portion of the cathode.

An apparatus and cell assembly (cell) for electrowinning metal, e.g.

20 copper from low grade copper solution, may manifest itself in a variety of forms. It will be convenient to hereinafter describe in detail one preferred embodiment of the invention with reference to the accompanying drawings.

The purpose of providing this specific description is to enable persons having an interest in the subject matter of the invention how to carry the invention into practical effect. It is to be clearly understood however that the specific nature of this description does not supersede the generality of the preceding broad description. In the drawings: FIG. 1 is a part sectional front view of a cell in accordance with one embodiment of the invention; FIG. 2 is a three dimensional view of the bottom cap of the cell of FIG.

1; FIG. 3 is a part sectional front view showing detail of an upper region of A 11 7a the cell of FIG. 1; FIG. 4 is a part sectional front view showing detail of a lower region of the cell of FIG. 1; FIG. 5 is a three dimensional view of a top cathode mask for the cell of FIG. 1; o* o° a.

0@ a a 8 FIG. 6 is a three dimensional view of a bottom cathode mask for the cell of FIG. 1; FIG. 7 is a three dimensional view of a split sleeve cathode showing a copper tube plated to the inner surface thereof; FIGS. 8 and 9 are sectional front views showing the use of a tool to insert the split sleeve cathode back into the housing; FIGS. 10 and 11 are sectional front views showing a harvesting tool for lifting the split sleeve cathode from the housing; FIG. 12 is a top plan view of a bank of cells of the type shown in FIG. 1; FIG. 13 is a front view of the bank of cells of FIG. 12; and FIG. 14 is an end view of the bank of cells of FIG. 12.

In FIGS. 1 to 4 the cell is indicated generally by numeral 1. While the cell is described with reference to the electrowinning of copper it can also be used to recover other metals.

The cell 1 comprises broadly an elongate housing 2 having two end caps 3 and 4. An inlet 7 is defined in the housing 2 towards the lower end cap 4 and an outlet 8 is defined in the housing 2 towards the upper end cap 3.

An elongate rod-like anode 10 extends longitudinally through the housing 2 concentrically with the housing 2. The anode 10 is basically supported by a packing gland 12 defining an opening 11 in the cap 4. The free end 13 of the anode 10 is received in a guide recess 14 defined by the end cap 3.

The cell 1 includes a cathode 15 in the form of a removable split sleeve.

The split sleeve 15 has a cylindrical configuration and extends around the inner wall of the housing 2 when mounted therein. The sleeve 15 is in a spring loaded condition when received within the housing 2.

Electrical connections 18 and 19 that are coupled to an electrical power 9 supply, are connected to respectively the anode 10 and the cathode 15. The connection 19 is not positively attached to the cathode 15, e.g. by clamping or the like because the cathode 15 is periodically removed from the cell. Rather, the electrical connection is achieved by having the cathode 15 in abutting contact with a conductive surface associated with the electrical connection 19.

The illustrated housing 2 is formed from a six inch diameter (approx 152mm) cylindrical pipe 20 of plastic with a head pipe 21 mounted on an upper end 22 of the pipe 20 forming a top portion of the housing and defining a head space. The end cap 3 is in turn mounted on an open end of the head pipe 21.

Gases generated by the electrowinning process can be accumulated in the head space and then directed out of the cell in a manner which will be described in more detail below.

The end cap 3 is mounted to the housing 2 by means of complementary retaining formations 25 and 26 on respectively the end cap 3 and the housing 2.

S Typically a rotation of 45o-900 will be sufficient to rotate the engagement formations 25 and 26 on the end cap 3 out of register with those on the housing 2 permitting the end cap 3 to be lifted off the housing 2. The end cap 3 has a hex configuration 23 when viewed in plan view which makes it easy to rotate to detach the cap 3 from the housing 2. FIG. 2 shows the end cap 4 which has the i: same basic configuration as the end cap 3.

••"Gas vents 31 and 32 are defined in the housing 2 towards the top of the 25 head space. The vents 31 and 32 are connected by means of conduits to the vents of adjacent cells in a manner which will be described in more detail below with reference to FIGS. 13 and 14. The vents enable oxygen, hydrogen, hydrogen sulphide, arsine and any other gases evolved during the electrowinning process to be vented and conduited away from the cells. The gases can then be collected at a point, e.g. adjacent the end of the bank of cells and treated before either using the gas or discharging it to atmosphere.

An upper cathode mask 40 is mounted on the upper end 41 of the split sleeve cathode 15. This stops metal, eg copper, plating over and around the end 41 of the split sleeve 15. Dendrites of deposited metal would otherwise tend to grow at the ends of the sleeve because the charge is at the highest at the end of the sleeve. This metal deposition at the ends would cause a problem during harvesting as it would make it difficult to detach the sleeve from the plated copper.

FIG. 5 shows the structural details of the cathode mask 40. The mask has an upper end 42 which is supported on a shoulder 43 in the housing 2 and a depending skirt 45. The skirt 45 extends into the upper end 41 of the split sleeve 15 around the circumference of the sleeve thereby to physically stop copper from plating in these regions.

A bottom cathode mask 50 shown in FIG. 6 is of similar construction and works in a similar fashion. It has a skirt or flange which acts to physically block Sthe plating of copper in the bottom end region of the sleeve. One difference though is that the bottom cathode mask 50 is permanently fixed to the sleeve 15, eg by adhesive, unlike the upper mask 40 which is removed each time the copper is harvested.

Sipe* When an appropriate amount of copper has been plated on the cathode sleeve 15, eg 20 40 kilograms of copper, then the copper has to be harvested.

25 The flow of solution to the cell 1 is shut off, and the end cap 3 is removed. FIG.

7 shows the copper 51 plated to the inner surface of the split sleeve 15. FIGS.

and 11 show a harvesting tool 70 for use in harvesting plated copper tubes from the cell 1.

The tool 70 comprises a handle 72, a shaft 73 and a gripping element remote from the handle 72. The tool 70 also has an inner passage 76 to receive 11 the anode 10 which remains fixed in position along the axis of the housing 2 during the harvesting operation. The tool 70 is lowered into the housing 2 and used to lift the sleeve 15 and plated copper tube out of the housing 2.

An example mechanism for the gripping element 75 is shown in FIGS. and 11. Such a mechanism would be well known to persons skilled in the art and accordingly will not be described in further detail in the specification.

FIGS. 8 and 9 show a tool 60 which is used to insert the sleeve 15 into the housing 2.

The tool 60 comprises a circular collar 61 of a diameter which can be received within the housing 2 and a transverse handle formation 62 which is passed through the collar 61 and which is used to manually handle the tool The sleeve 15 is manually rolled up and the collar 61 of the tool 60 is mounted over the end 41 thereof. The sleeve 15 is then lowered into the open top of the housing 2 and the tool 60 is detached from the end 41 of the sleeve The sleeve 15 then bears, under spring action, against the wall of the housing 2.

use, the cell 1 plates out metal from a stream containing metal ions in solution, e.g. copper sulphate, which is pumped through the cell. A potential difference is applied across the cathode 15 and anode 10. This causes the copper ions in solution to plate out as copper metal on the cathode 15. Over time the copper builds up to form a copper tube 51 on the radially inward surface of the cathode 15 as shown in FIG. 7. When the plated copper has reached a mass of about 30 to 40 kilograms and a thickness of about 50 to millimetres, it is harvested from the cell 1.

When this occurs, the flow of solution to the cell 1 is shut off and the end cap 3 is removed from the housing 2. The cathode 15 and plated copper tube 51 are then lifted out through the open upper end of the housing 2.

The cathode masks 40 and 50 on each end of the sleeve 15 resist copper plating over and around the ends of the sleeve 15 which would otherwise occur as described above. This enables the sleeve 15 to spring open to some extent due to the spring bias in the sleeve 15 when the sleeve 15 is freed from the constraint of the housing 2. This serves to detach the sleeve from the plated copper tube 51. If it does not spring open of its own accord it can be manually prised away from the copper. The top cathode mask 40 is removed from the sleeve 15 during harvesting. However the bottom cathode mask 50 usually remains mounted to the bottom end of the sleeve.

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The harvesting tool 70 shown in FIGS. 10 and 11 is used to grip the plated copper and lift it out of the housing. By appropriate manipulation, the gripping element 75 is displaced radially outwardly into tight frictional engagement with the copper.

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Once detached from the copper, the sleeve 15 has to be returned to the housing. This is accomplished by the use of the tool 60 which is mounted over the upper end of the sleeve 15. This reduces the diameter of the sleeve 15 to the extent that it can be dropped into the open top of the housing 2. The tool is then detached from the sleeve 15 and the cathode mask element 40 placed over the upper end of the cathode. The cycle can then be repeated.

FIGS. 12 to 14 show a bank of cell assemblies. In the drawings the bank is indicated generally by the numeral 90 and the individual cells by the numeral 1. Unless otherwise illustrated the same reference numerals will be used to refer to the same components as in FIGS. 1 to 11.

The individual cells 1 are connected in series by means of pipes 92 13 which connect the outlet of any given cell 1 to the inlet of the next succeeding cell 1. As the copper containing solution is pumped through the cell assemblies it is progressively depleted of copper which is plated out on the cathode. The solution exiting the downstream end of the bank of cell assemblies 90 may be substantially depleted of copper and have reduced ability to harm the environment. The air vents 31 and 32 of each cell 1 are interconnected as described above. At the end of each bank 90 of cells 1, the air vents lead into a common manifold 95 which enables the gases to be conduited to a treatment point. At the treatment point, the gases can be appropriately treated or released to atmosphere, e.g. through a stack.

Naturally the bank of cells is supported by a support structure 98 which spaces the cells above the ground. Further a working platform (not shown) is typically provided spaced below the top of the cells to provide operator access 15 to the end cap 3 to enable the harvesting procedures to occur.

An advantage of the cell assembly described above is that it lends itself readily to commercial scale process plants. The features of the invention enable the plated copper to be harvested easily and economically on a regular basis from banks of literally hundreds of cells.

Further the cell is engineered to collect gases produced by the electrowinning process and direct them to a treatment plant where they can be appropriately treated. By directing solution upwardly through the cell and 25 providing a head space, means is provided for accumulating the gases and then they can be conduited out of the cell.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as is herein set forth.

Claims (5)

1. A cell assembly for electrowinning a metal from an electrolyte, the cell assembly including: a housing having a substantially cylindrical side wall and two opposed end caps, each end cap closing an opening at an end of the housing, the housing defining an inlet and an outlet axially spaced from the inlet, the inlet and the side wall being configured so as to induce the electrolyte to flow through the housing with a flow pattern in the form of a helical spiral; said two opposed end caps including a first removable end cap closing a first opening at one end of the housing, the cathode removable through the first opening, and a second removable end cap closing a second opening at a second end of the housing; a removable cathode in the form of a sleeve which is split longitudinally, the cathode being snugly received within the side wall of the housing such that it is positioned adjacent the side wall of the housing in use and removable for harvesting metal deposited on the cathode, by removing said first removable end cap and lifting the cathode through the thus open S. end of the housing; an elongate anode projecting substantially axially through the second end cap into the housing and removably mounted thereto, said anode 25 being substantially centrally positioned within the housing spaced radially inwardly from the cathode and defining an annular flow passage between the anode and the cathode; and releasable electrical connecting means for electrically connecting said cathode to an electrical circuit.

2. A cell assembly according to claim 1, wherein both the inlet and the outlet extend substantially perpendicularly to the longitudinal axis of the housing and tangentially relative to the side wall of the housing.

3. A cell assembly according to claim 1 or claim 2, wherein the housing is substantially vertically extending and said one end cap through which the cathode is lifted is positioned at the top of the housing, and said other end cap through which the anode passes is positioned at the bottom of the housing.

4. A cell assembly according to claim 3, wherein the anode is mounted to said other end cap through which it passes and wherein the end cap is sealed to the anode. A cell assembly according to claim 3 or claim 4, wherein each end cap is mounted to the housing by means of a quick release connection. DATED this 13 th day of May 2003 ELECTROMETALS MINING LIMITED o By their patent attorneys CULLEN CO.

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