WO2015107475A2

WO2015107475A2 - Electrodes for use in electrorefining and electrowinning

Info

Publication number: WO2015107475A2
Application number: PCT/IB2015/050304
Authority: WO
Inventors: Jan Petrus Human
Original assignee: Jan Petrus Human
Priority date: 2014-01-15
Filing date: 2015-01-15
Publication date: 2015-07-23
Also published as: WO2015107475A3

Abstract

A hanger bar (30) for use in electrowinning or electrorefining comprises two stainless steel strips (12) which are welded to a row of stainless steel blocks (34) so that the blocks are between the two strips. The blocks and strips are then sand blasted and a layer of copper is deposited onto the strip and blocks.

Description

ELECTRODES FOR USE IN ELECTROREFINING AND ELECTROWINNING FIELD OF THE INVENTION

THIS INVENTION relates to electrodes for use in electrorefining and electrowinning. BACKGROUND TO THE INVENTION

Electrodes in the form of cathodes and anodes are used in electrowinning and electrorefining.

Anodes comprise a hanger bar and an anode plate (also referred to as a blade) which is secured to the hanger bar and extends downwardly from it. In the electrowinning process the anode plate is of lead and the metal to be recovered is in the electrolyte. In the electrorefining process the anode plate is of the metal to be refined and it is eroded during the refining process.

Cathodes comprise a hanger bar and a metal starter sheet which is attached to the hanger bar and extends downwardly from it. The metal being recovered, in both electrowinning and electrorefining, is deposited onto the starter sheet.

Hanger bars can be of copper or copper alloy. The copper is lead covered, except at the bar's ends, to protect the bars from corrosion by the acid mist which rises from the surface of the acid in the cell. The ends of the bar cannot be covered as they must make contact with the electrical bus bars which extend along the top surfaces of the side walls of the cell. The electrodes are supported by the hanger bars.

In another form the hanger bars are of stainless steel and there is a copper layer which has been deposited onto the steel. The copper layer is provided as part of the electrical circuit in view of the poor electrical conductivity of stainless steel. The copper layer is lead covered to protect it from the acid mist.

There are two specific problems with electrodes as they are presently constructed.

The first problem is that there is significant electrical resistance where the electrode plate and the hanger bar are connected to one another. This resistance means that there are power losses and this consequently increases the cost of recovering or refining the metal.

The second problem is caused by the acid mist which rises from the cell during operation. Under some operating conditions oxygen is generated at the anode and as the oxygen bubbles break the surface of the acid in the cell, acid in the form of a mist is carried into the atmosphere. The exposed copper of the hanger bar is corroded by the acid mist which condenses on it.

The present invention provides an electrode which offers less resistance to the flow of electrical current between the hanger bar and the electrode plate than currently used electrodes.

The present invention also provides improved protection for the hanger bar against corrosion by the acid mist.

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect of the present invention there is provided an electrode for use in electrowinning or electrorefining and which comprises a hanger bar and an electrode plate depending from the hanger bar, the hanger bar having openings in it extending from the underside of the hanger bar to the top surface of the hanger bar and the electrode plate having portions which are in said openings. The electrode defined in the preceding paragraph can be produced by drilling holes in a hanger bar, the holes extending from the upper surface to the lower surface, placing the bar in a mould and feeding lead into the mould to encapsulate the bar, the lead entering said holes.

According to a second aspect of the present invention there is provided a hanger bar comprising two parallel strips of steel between which there are blocks of steel, the blocks and strips being welded together, there being slots through said hanger bar bounded by the strips and the blocks, and the surfaces of the blocks and strips having a layer of deposited copper thereon.

The strips and blocks can be of mild steel but stainless steel is preferred.

There can be three spaced apart blocks which, with the strips, define two slots separated by a centre one of the blocks.

According to a third aspect of the present invention there is provided an electrode comprising a hanger bar as defined in the preceding paragraph and a plate with tongues which are in said slots and a notch which receives said centre block.

According to a fourth aspect of the present invention there is provided a method of fabricating a hanger bar, the method comprising providing a number of steel blocks, providing two strips of steel, welding the strips to the blocks so that the blocks lie between the strips, there being slots extending through the hanger bar from its bottom surface to its top surface, and depositing a layer of copper onto the blocks and strips.

The blocks and the strip can be sandblasted before the copper layer is deposited.

The method can include the further steps of depositing a layer of tin onto the copper layer and depositing a second layer of copper on the tin. According to a fifth aspect of the present invention there is provided an anode for use in electrorefining or electrowinning which comprises a hanger bar and an anode blade extending downwardly from the hanger bar, there being a component attached to the blade below the hanger bar which component defines a downwardly open cavity into which acid mist evolved during electrorefinning or electrowinning rises and is trapped therein.

The component can be of inverted channel shape with a web thereof uppermost and two flanges thereof extending downwardly from the web.

One of said webs can be secured to the anode blade by an adhesive compound.

Holes can be provided in said component, the holes having in them plugs of a material which permits oxygen to permeate through but prevents liquid from passing through.

The anode plate can be a planar sheet and said component can be in the form of an elongate strip. Preferably there is a component on each side of the anode blade.

According to a sixth aspect of the present invention there is provided an electrode for use in electrorefining or electrowinning, the electrode comprising a hanger bar and a plate attached to and extending downwards from the hanger bar, the hanger bar, apart from the end portions thereof, being encapsulated by a lead sheath, there being sealing caps in the form of rectangular frames through which said end portions of the hanger bars pass and which sealing caps seal any gap between the adjacent end of the lead sheath and the hanger bar to inhibit ingress of acid between the sheath and the hanger bar.

The ends of the sheath can be coated with an acid resistant sealing compound and the sealing caps can be in contact with sealing compound. BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which;-

Figure 1 is an "exploded" pictorial view of a component, and two end caps for attachment to an electrode;

Figure 2 is a pictorial view of a hanger bar fabricated from steel;

Figure 3 is a view of the hanger bar of Figure 2 after being coated with copper;

Figure 4 is a sequence drawing illustrating a method of manufacturing an electrode;

Figure 5 is a pictorial view of an electrode having two of the components of Figure 1 fitted to it;

Figure 6 and 7 are pictorial views of the opposed faces of an end cap;

Figure 8 is a pictorial view illustrating the use of the end cap of Figures 6 and 7;

Figure 9 is a pictorial view from above of a further hanger bar; and

Figure 10 is a view of the hanger bar of Figure 9 from below.

DETAILED DESCRIPTION OF THE DRAWINGS The component 10 illustrated in Figure 1 comprises a strip 12 which is of inverted channel shape. The web 14 of the strip 12 is horizontal and the flanges 6 of the strip 12 depend from the web 14. The strip 12 is of an acid resistant synthetic plastics material such as polypropylene.

The web 14 has holes 18 in it. These holes receive plugs of a synthetic plastic material which allows gaseous oxygen to permeate through it but forms a barrier to liquids. Polyethylene is a suitable material for the plugs.

End caps 20 are provided which are a force fit in the ends of the strip 12. A downwardly open elongate cavity is bounded by the strip 12 and the end caps 20.

Turning now to Figure 2, the hanger bar 30 which is illustrated is fabricated by welding two stainless steel strips 32 to opposite sides of three stainless steel blocks 34. The blocks 34 are spaced apart along the strips 32, this construction resulting in there being two slots 36 which pass through the hanger bar from the top surface to the bottom surface.

The fabricated hanger bar 30 is then copper plated by making it the cathode of an electrodeposition cell. As can be seen from Figure 3 every surface of the bar is copper plated. This ensures that the electrical flow path from the bus bars to the anode plate (or blade) has the maximum cross-sectional area. The hanger bar can be used either as part of a cathode or as part of an anode.

The preferred method, after the hanger bar has been fabricated, is to sandblast all surfaces of the bar and then electrodeposit a copper layer onto the steel. A layer of tin is electrodeposited onto the previously deposited copper layer and finally a further copper layer is deposited onto the tin layer. ln the upper drawing of Figure 4 the hanger bar 30 and an anode plate 38 are shown. The anode plate 38 can be cast or rolled.

A rolled anode plate 38 is produced by rolling a thick cast lead block to produce a number of anode plates of the requisite thickness. The rolled plate is trimmed to shape and its upper edge is cut to form a notch 40 between two tongues 42 as shown in the second drawing from the top of Figure 4.

The tongues 42 are pushed into the slots 36 (see the third drawing of Figure 4) so that the centre block 34 enters the notch 40. The plate 38 and the hanger bar 30 are lead burned together where the plate 38 emerges from the hanger bar 30 and where the tongues 42 are visible at the upper ends of the slots 36.

The hanger bar 30 and the adjacent part of the plate 38 are then dipped in a tin bath so that the entire hanger bar and the immediately adjacent part of the plate 36 are tinned. This improves the electrical connection between the hanger bar 30 and the plate 38.

The part of the anode plate 38 immediately adjacent the hanger bar, and the hanger bar apart from its ends, are encapsulated in lead which is designated 44 in the lower drawing of Figure 4.

If the anode plate is to be produced by casting, as opposed to being produces by rolling, then the copper coated hanger bar 30 is dipped in a tin bath and then placed in the mould in conventional manner. During casting lead enters the slots 36 and encapsulates the entire hanger bar except for its ends.

If the hanger bar is to be part of a cathode the fabricated bar 30 is as a first step copper plated. A steel starter plate having the same edge configuration as is shown in Figure 4 is used. The tongues of the starter plate enter the slots 36 and the centre block 34 enters the notch in the edge of the starter plate. The starter plate and the hanger bar are welded where the starter plate emerges from the hanger bar and also where the free edges of the tongues 42 are visible through the upper ends of the slots 36.

The hanger bar, and the immediately adjacent strips of the steel plate on both sides of the steel plate, then have a copper layer deposited onto them. This layer covers the welds and also enhances the electrical connection between the hanger bar and the starter sheet.

Figure 5 illustrates an anode, produced as described above, with one of the components 10 on each side of the plate 38 thereof. The web 16 of each component 10 which is adjacent the plate is secured to the plate by a bonding compound such as "Sikaflex".

In use, the current flowing through the cell between the anodes and the cathodes causes gaseous oxygen to be evolved on both surfaces of the anode plate 38.

The oxygen bubbles up through the acid in the cell and the oxygen bubbles burst at the surface of the acid in the cell. The bursting bubbles agitate the surface of the acid and an acid mist composed of fine droplets of the acid rise with the oxygen.

The position of the components 10 is such that the rising gaseous oxygen and the acid mist enter the downwardly open cavities defined by the strip 12 and end caps 20. The oxygen permeates through the plugs in the holes 18. The droplets constituting the mist accumulate in the cavities and eventually the liquid acid drops back into the cell. In this way the quantity of acid mist that can reach the hanger bars and erode them is significantly reduced.

The sealing cap 46 shown in Figures 6 and 7 is injection moulded using an acid resistant synthetic plastic material, The cap 46 is in the form of a rectangular frame. All four of the inside surfaces of the cap are stepped, as shown in Figure 6, to form an abutment surface 48.

The lower horizontal of the frame, on one side of the abutment surface 48, is not continuous but has a gap 50 in it. On the other side of the abutment surface 48 the lower horizontal has an upwardly open recess 52 in it. The recess 52 is aligned with the gap 50.

In Figure 8 an anode 54 is illustrated. The anode comprises a hanger bar 56 and an anode plate or blade 58. The lead encapsulation of the anode is referenced 60 and the exposed end of the hanger bar is referenced 62. The hanger bar is preferably fabricated as described above.

The encapsulating lead 60 has end faces 64 and it is possible for acid to creep past the faces 64 and between the hanger bar 56 and the lead 60 causing corrosion.

The end faces 64 are coated with an acid resistant compound. Preferably a compound with some adhesive properties is used. The polyurethane compound "Sikaflex" is suitable. "Sikaflex" is a registered trade mark. The exposed ends 62 of the hanger bar 56 are then both passed through sealing caps 46 and the sealing caps displaced on the hanger bar until the abutment surfaces 48 are against the layers of sealing compound. The part of the cap 46 to the left of the abutment surface 48 as viewed in Figure 6 overlaps the end of the lead sheath. The edge of the anode plate 58 enters the gap 50.

If it is found that too little compound has been applied to obtain adequate sealing an additional amount can be forced in through the recess 52. Likewise, excess compound can be squeezed out through the recess 52. The stainless steel strips and blocks can be replaced by strips and blocks of a copper alloy. When a copper alloy is used it is not necessary to sandblast or deposit a layer of copper. However, a layer of tin can be deposited onto the strips and blocks to promote adhesion between the hanger bar and the lead which encapsulates it.

The hanger bar 66 shown in Figures 9 and 10 is of stainless steel or a copper alloy. Holes 68 are drilled through the bar 66 from its upper surface 70 (Figure 9) to its lower surface 72 (Figure 10). The end portions 74, 76 of the hanger bar 66 do not have holes drilled in them.

The bar is placed in a mould and the portion thereof which has the holes 68 in it encapsulated in lead. The lead fills the holes 68. The portions 74, 76 protrude from the lead sheathing and form the electrical connections to the hanger bar.

Claims

CLAIMS:

1. An electrode for use in electrowinning or electrorefining and which comprises a hanger bar and an electrode plate depending from the hanger bar, the hanger bar having openings in it extending from the underside of the hanger bar to the top surface of the hanger bar and the electrode plate having portions which are in said openings.

2. A hanger bar comprising two parallel strips of steel between which there are blocks of steel, the blocks and strips being welded together, there being slots through said hanger bar which slots are bounded by the strips and the blocks, and the surfaces of the blocks and strips having a layer of deposited copper thereon.

3. A hanger bar as claimed in claim 2, wherein the strips and the blocks are of stainless steel.

4. A hanger bar as claimed in claim 2 or 3 and comprising three spaced apart blocks which, with the strips, define two slots separated by a centre one of the blocks.

5. An electrode comprising a hanger bar as claimed in claim 2, 3 or 4 and a blade with tongues which are in said slots and a notch which receives said centre block.

6. A method of fabricating a hanger bar, the method comprising providing a number of steel blocks, providing two strips of steel, welding the strips to the blocks so that the blocks lie between the strips, there being slots extending through the hanger bar from its bottom surface to its top surface, and depositing a layer of copper onto the blocks and strips.

7. A method as claimed in claim 6 and including the step of sandblasting the blocks and the strips before depositing the copper layer.

8. A method of fabricating a hanger bar as claimed in claim 6 or 7 and including the further steps of depositing a layer of tin onto the previously deposited copper layer and then depositing a second layer of copper onto the deposited tin.

9. An anode for use in electrorefining or electrowinning which comprises a hanger bar and an anode blade extending downwardly from the hanger bar, there being a component attached to the blade below the hanger bar which component defines a downwardly open cavity into which acid mist evolved during electrorefinning or electrowinning rises and is trapped therein.

10. An anode as claimed in claim 9, wherein said component is of inverted channel shape with a web thereof uppermost and two flanges thereof extending downwardly from the web.

11. An anode as claimed in claim 10, wherein one of the flanges of said component is secured to the anode blade by an adhesive compound.

12. An anode as claimed in claim 9, 10 or 1 1 , wherein holes are provided in the web of said component, the holes having in them plugs of a material which permits oxygen to permeate through but prevents liquid from passing through.

13. An anode as claimed in claim 9, 10, 11 or 12, wherein the anode blade is a planar sheet and said component is in the form of an elongate strip.

14. An anode as claimed in claim 13, wherein there is a component on each side of the anode blade.

15. An electrode for use in electrorefining or electrowinning, the electrode comprising a hanger bar and a plate attached to and extending downwards from the hanger bar, the hanger bar, apart from the end portions thereof, being encapsulated by a lead sheath, there being sealing caps in the form of rectangular frames through which said end portions of the hanger bars pass and which sealing caps seal any gap between the adjacent end of the lead sheath and the hanger bar to inhibit ingress of acid between the sheath and the hanger bar.

16. An electrode as claimed in claim 15 and in which the ends of the sheath are coated with an acid resistant sealing compound and the sealing caps are in contact with said sealing compound.

17. An electrode as claimed in claim 2 with the modification that said strips and said blocks are of a copper alloy.

18. A method of producing an electrode as claimed in claim 1 which comprises drilling holes in a hanger bar, the holes extending from the upper surface to the lower surface, placing the bar in a mould and feeding lead into the mould to encapsulate the bar, the lead entering said holes.