(19)
(11) EP 2 031 097 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
04.03.2009 Bulletin 2009/10

(21) Application number: 07114560.1

(22) Date of filing: 17.08.2007
(51) International Patent Classification (IPC): 
C25C 7/08(2006.01)
(84) Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC MT NL PL PT RO SE SI SK TR
Designated Extension States:
AL BA HR MK RS

(71) Applicant: PAUL WURTH S.A.
1122 Luxembourg (LU)

(72) Inventors:
  • Caufriez, Alain
    4219, Meeffe (BE)
  • Parasch, Fred
    3468, Dudelange (LU)
  • Raynal, Samuel
    4736, P├ętange (LU)

(74) Representative: Ocvirk, Philippe et al
Office Ernest T. Freylinger S.A. 234, route d'Arlon
8001 Strassen
8001 Strassen (LU)

   


(54) Cathode stripping system


(57) Cathode stripping system comprises a cathode stripping device (12) and a conveyor system (14), the conveyor system comprising an upstream storage region (24) in which cathodes (16) to be treated are stored parallel to each other with a first spacing d1.
A cathode handling unit (30) is associated with the cathode stripping device (12) and comprises:
a carriage (32) mobile in the conveying direction and provided with support means (44) for two cathodes with a second spacing d2, the second spacing d2 being greater than the first spacing d1; and
driving means for the carriage (32) designed so that the carriage may perform a reciprocating movement with respect to the cathode stripping device (12) in order to move a cathode (16) to be treated over a distance corresponding to the second spacing d2 from the upstream storage region (24) to the stripping device (12) and concurrently moving a treated cathode over a distance corresponding to the second spacing d2 from the stripping device (12) to the downstream storage region (26).




Description

TECHNICAL FIELD



[0001] The present invention generally relates to the hydrometallurgical production of metals such as zinc, and more specifically to a cathode stripping system for harvesting metal sheets deposited on the cathodes.

BACKGROUND ART



[0002] As it is know, the main steps of hydrometallurgical zinc production are:
  • roasting of zinc sulphur (ZnS) to obtain zinc oxide (ZnO) and eliminate certain impurities;
  • lixiviation to solubilise zinc in the form of zinc sulphate (ZnS04);
  • cementation to eliminate impurities (cobalt, nickel, cadmium and copper) from the zinc sulphate solution;
  • electrolysis to transform zinc sulphate into zinc metal.


[0003] This last step of zinc electrodeposition, typically referred to as electrowinning (also EW), thus consists in performing an electrolysis of the purified zinc solution in electrolytic cells through the flow of direct electrical current between alternating anodes and cathodes. This process allows electrolytically depositing high quality metallic zinc on the cathodes (with a purity of 99,99%).

[0004] In practice, a cathode typically consists of an aluminium plate vertically arranged in the electrolytic cell. This plate is provided on its top edge with a bar having a width slightly greater than the plate's width, which provides for supporting, electrically contacting and handling the cathode. The vertical edges of the cathode plate are generally covered with an insulating strip to avoid zinc deposits thereon. Hence, during electrolysis, metal is deposited on the exposed cathode surfaces, over the height submerged in the electrolytic cell, forming two metallic sheets (one on each side of the cathode plate) linked by their bottom edge.

[0005] The metallic zinc deposits, which strongly adhere to the cathode, must then be removed. This is conventionally carried out by means of a cathode stripping machine. In such machine, stripping typically comprises two successive steps. In the first step, a pair of chisels (or like tools) is used for lifting/taking off one upstream corner of each metal sheet. Next, in the second step, the metal sheets are completely removed and separated from the cathode by means of knives extending over the cathode's width. The stripped cathodes are then cleaned and returned to the electrolytic cells to collect metal again.

[0006] In the conventional layout of a production hall, one distinguishes an electrowinning area and a cathode treatment area, where the cathodes are stripped and cleaned. The typical equipement of such treatment area is illustrated in Fig.8. Reference sign 210 indicates a cathode stripping device. A chain conveyor 214 is associated with device 210. Conveyor 214 comprises a pair of parallel chains 216, which are jointly operated towards the treatment device 210, and which comprise notches for supporting the cathodes by their respective top bars. With respect to the stripping system, cathodes to be treated are loaded in the upstream conveyor region 218, successively reach the stripping device 210 where the metal deposits are removed, and continue their way to the downstream storage region 220, where they can be picked-up to be carried to a cleaning device and then returned to the electrolytic cells. Preferably, the cathodes notches in the conveyor chains 216 are spaced by a distance d, which corresponds to the cathode spacing as they arrive from the electrolytic cells. This permits picking-up the cathodes (in a group of several cathodes) in the electrolytic cells and placing them in the upstream storage region of the conveyor 214 without modifying the cathode spacing.

[0007] It may be noted that the cathode harvesting is generally done while the electrowinning area is running. Therefore, it is not possible to remove all the cathodes from a given cell for collecting the metal deposits, but generally every other or every third cathode is removed from a cell. Assuming every other cathode of a cell is removed in a group, then the spacing between the cathodes is twice the inter-cathode spacing in the cell.

[0008] So in the conveyor the cathodes are stored with the same spacing d that actually existed between these cathodes when picked-up from the cell, typically two or three times the inter-cathode spacing (spacing between two consecutive cathodes).

[0009] This procedure is clearly advantageous as it avoids any additional cathode handling. Since the cathode spacing is not modified during the treatment of the cathodes, stripped cathodes are stored in the downstream conveyor region with the same spacing as in the upstream region, and the cathodes can be returned to the electrolytic cells without modifying their spacing.

[0010] However, although placing the cathodes in the conveyor without modifying their spacing greatly simplifies handling, the spacing may be too narrow for the stripping operation. Indeed, cathode stripping involves moving the cathode and bringing tools to the cathode to act thereon. Cathode handling may cause dangling thereof, so that it may bump into the neighbouring cathodes, i.e. the next cathode to be treated and the last treated cathode. Such cathode dangling may thus interfere during the stripping process and block the system, and more importantly may also damage the cathode. Altogether such events slow down the stripping process. Furthermore, with such equipment, it is difficult for operators to intervene in the case of problems during stripping, due to the reduced accessibility linked with the narrow spacing between cathodes in the stripping machine.

OBJECT OF THE INVENTION



[0011] The object of the present invention is to provide an improved cathode stripping system, which does not comprise the above-mentioned drawbacks. This object is achieved by a cathode stripping system as claimed in claim 1.

GENERAL DESCRIPTION OF THE INVENTION



[0012] According to the present invention, a cathode stripping system comprises:

a cathode stripping device;

a conveyor system associated with the stripping device, the conveyor system comprising:

  • an upstream storage region before the cathode stripping device, in which cathodes to be treated are stored parallel to each other with a first spacing d1;
  • a downstream storage region, in which treated cathodes are stored parallel to each other with a spacing identical to the first spacing;



[0013] According to an important aspect of the invention, a cathode handling unit is associated with the cathode stripping device, the cathode handling unit comprising:
  • a carriage mobile in the conveying direction and provided with support means for two cathodes with a second spacing d2, the second spacing d2 being greater than the first spacing d1;
  • driving means for the carriage designed so that the carriage may perform a reciprocating movement with respect to the cathode stripping device in order to move a cathode to be treated over a distance corresponding to the second spacing d2 from the upstream storage region to the stripping device and concurrently moving a treated cathode over a distance corresponding to the second spacing d2 from the stripping device to the downstream storage region.


[0014] The present cathode stripping system thus includes a cathode handling unit associated with the cathode stripping device that acts as a loading and unloading device. Indeed, the cathode handling unit cooperates with the conveyor and stripping device to pick-up a cathode to be treated in the upstream storage region and deliver the last treated cathode from the stripping machine to the downstream storage region. It is to be noted that the cathode handling unit is distinct from the conveyor system and is mobile relative to the latter, in the forward conveying direction and also in the opposite direction (rearward). Thanks to its support means for two cathodes, the carriage can simultaneously move a cathode to be treated and a stripped cathode. In use, the spacing between the next to be treated cathode in the upstream storage region and the stripping device is the second spacing distance d2. Indeed, the carriage picks up a cathode in the upstream storage region at a distance greater (corresponding to second spacing d2 than the first spacing d1 between cathodes in this storage region, and, concurrently, carries the last stripped cathode to the downstream storage region over a distance corresponding to the second spacing d2, logically corresponding to the spacing between cathode support means in the carriage.

[0015] As a result, the cathode in the stripping is spaced from neighbouring cathodes by a distance corresponding to the second spacing (d2), whereby the cathode handling unit also plays the role of spacer. The greater spacing between the cathode in the stripping device and the upstream and downstream cathodes avoids damaging these cathodes due to dangling of the cathode being stripped. It also facilitates the access for operators, should it be needed. A further appreciable aspect is that the carriage of the handling unit permits delivering the cathode to be stripped in the stripping device with a greater precision than a bulky conveyor.

[0016] As it is conventional in the art, the first spacing d1 may typically correspond to the spacing between the cathodes as they have been removed from the cells. If all cathodes have been removed, the spacing corresponds to the inter-cathode spacing in the cell; if every second or third cathode has been removed, the spacing is 2 or 3 times the inter-cathode spacing. In summary, the spacing d1 corresponds to the the inter-cathode spacing in the cell or to a multiple thereof.

[0017] Preferably, the second spacing d2 is a multiple of the first spacing d1. In practice, the second spacing d2 may correspond to 2, 3, 4 or even 5 times the first spacing d1.

[0018] In one embodiment, the carriage is formed by a pair of bars symmetrically arranged and extending in the conveying direction, each bar being provided with a pair of cathode supports spaced by a distance corresponding to the second spacing d2. Preferably, the cathode supports comprise V-shaped notches for receiving the extremities of the cathodes bars. The driving means of the cathode handling unit comprise means for moving the carriage in the forward conveyor direction but also rearward, and means for guiding the carriage in the vertical direction, so that it may describe a closed loop operating cycle.

[0019] The cathode handling unit being separate from the conveyor system, a control unit may be designed to control its operating cycle and to synchronize its operation with the forward movement of the conveyor system.

[0020] The conveyor system may be a linear chain conveyor extending through the cathode stripping device. It may comprise a pair of spaced chains, the cathodes resting on the conveyor system in-between the chains with the extremities of their top-bars received in support notches defined by the chains.

[0021] The cathode handling unit may be of quite simple construction and adapted to a variety of cathode stripping devices or any other treatment device.

[0022] The present invention thus also concerns a method for conveying a cathode to a treatment device such as a stripping device, wherein cathodes are forwarded to the treatment device on a conveyor system with a first spacing d1 and wherein, in the vicinity of the treatment device, a cathode to be stripped up is picked up from an upstream storage position on the conveyor system to be forwarded over a distance d2 to a treating position, while the treated cathode at the treating position is simultaneously moved forward over distance d2 to a downstream storage position on the conveyor system. The forward movement of the cathodes over distance d2 is carried out by means of a carriage having support means for two cathodes spaced by a distance d2.

BRIEF DESCRIPTION OF THE DRAWINGS



[0023] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1: is a top view of a preferred embodiment of cathode stripping system in accordance with the present invention;

FIG. 2: is a perspective view of the cathode handling unit mounted to the cathode stripping device in the system of Fig.1

FIG. 3: is a detailed, side view of the cathode handling unitof Fig.2;

FIG. 4: is a top view of the cathode handling unit of Fig.2;

FIG. 5: a) to e) are sketches illustrating the operating principle of the cathode handling unit used in the present system;

FIG. 6: is a side view of the cathode handling unit attached to the stripping device (central part of which has been omitted);

FIG. 7: is perspective view of the cathode handling unit (the stripping machine is not shown);

FIG. 8: is a view of a conventional cathode treatment area in a zinc production plant.


DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS



[0024] A preferred embodiment of the present cathode stripping system 10 is shown in Fig.1. It comprises a cathode stripping machine indicated 12 with an associated conveyor 14 for forwarding cathodes 16 to be treated (stripped) towards the stripping machine 12. In the present embodiment, conveyor 14 comprises a pair of chains 18 that are synchronously driven in the forward direction as indicated by arrow 20. The chains 18 are spaced from each other and comprise notches 22 for the cathodes 16; the cathodes 16 are placed in the conveyor so that they rest thereon with their top bars 23 received in the notches 22 (better seen in Fig.7).

[0025] Reference sign 24 indicates the upstream storage region of the conveyor 14 where cathodes to be treated are stored with a first spacing d1. This spacing is determined by the spacing between chain notches 22. As it is known for those skilled in the art, cathodes are typically removed from a cells in groups of several cathodes. Further, it is only rather exceptionally that all cathodes are removed from a given cell, and typically every other or third cathode is removed, to be placed on the conveyor 14. In doing so, there exists a certain spacing between the cathodes that have been removed, that is typically a multiple of the inter-cathode spacing in the cell.

[0026] Preferably, spacing d1 between chain notches 22 is adapted to correspond to the spacing existing between the cathodes as they have been removed from the cell. It allows picking-up cathodes in groups in the electrolysis cells and directly placing them in the upstream storage region 24, without modification of the cathode spacing. After treatment, i.e. after stripping in machine 12, the treated cathodes are stored in the downstream storage region 26 of the conveyor 14.In order to increase spacing between cathodes at the stripping machine 12, the present system 10 comprises a cathode handling unit, generally indicated 30, that is associated with the stripping machine 12. The cathode handling unit 30, which is more closely shown in Figs 2 to 4, comprises a carriage 32 mobile in the conveying direction and provided with support means for two cathodes with a second spacing d2, the spacing d2 being greater than the spacing d1. Preferably, the spacing d2 is a multiple of first spacing d1.

[0027] The handling unit 30 also comprises driving means for the carriage 32 designed so that the carriage 32 may perform a reciprocating movement with respect to the cathode stripping device 12 in order to move a cathode to be treated over a distance corresponding to the second spacing d2 from the upstream storage region 24 to the stripping device 12 and concurrently move a treated cathode over a same distance d2 from the stripping device 12 to the downstream storage region 26.

[0028] The operating principle of the cathode handling unit 30 will be better understood from the sketches a) to e) in Fig.5. Fig.5 a) schematically illustrates the conveyor 14 with the cathodes 16 resting thereon. The conveyor 12 forwards the cathodes from left to right. Cathodes to be treated are stored on the left, before the stripping machine (not represented) and stripped cathodes are on the right hand side in Fig.5 a). The position of the stripping machine 12 is indicated by the vertical, dashed line B. Vertical dashed lines A and C respectively indicate the positions of the next cathode to be treated/stripped, and the last treated cathode in the downstream storage region.

[0029] In order to have a cathode treated by the stripping machine it is necessary to bring a cathode in the stripping position B. In conventional systems such as that of Fig.8, the cathodes are simply brought in the cathode stripping position by forward movement of the conveyor chain.

[0030] It shall be appreciated that in the present system, the cathode handling unit 30 acts as loading/unloading unit that cooperates with the conveyor 14 and the stripping machine 12 to bring a cathode to be stripped from position A to position B, and a stripped cathode from position B to position C, while maintaining a cathode spacing (i.e. d2) at the height of the stripping machine that is greater than the cathode spacing in the storage regions (d1). Of course, the conveyor 14 has its own conveying movement, which typically moves forward by steps corresponding to the distance d1. The movement of the carriage 32 is thus coordinated with that of the conveyor 14.

[0031] Fig.5 b) only shows the carriage 32 of the handling unit and the 3 cathode positions:

A: position of a next to be treated cathode;

B: stripping position;

C: position of the last treated cathode in the downstream storage region.



[0032] Suppose the cathode 162 in position B has been stripped, then the carriage operating cycle is as follows. From the position shown in Fig.5 b), carriage 32 is moved upwards to pick up (lift) the two cathodes 161 and 162 at positions A and B, resulting in the configuration of Fig.5 c). In this configuration, carriage 32 thus carries on its left support means the next cathode to be treated 161 and on the right-hand support means a treated cathode 162. Then the carriage is moved to the right (over a distance equal to d2) until the next cathode to be treated 161 is aligned with position B and the treated cathode 162 is aligned with position C, as shown in Fig.5 d). During this last movement, i.e. while the carriage 32 is moving to the right, the conveyor 14 moves one step forward, i.e. over a distance d1, so that a new cathode 164 to be treated is at position A and so that a pair of empty chain notches is available at position C, in order to receive the last treated cathode 162 moved by carriage 32. Next, carriage 32 is lowered to deposit the cathodes 161 and 162 on the conveyor 14 (see Fig.5 e), and the carriage 32 is returned to the position of Fig.5 b).

[0033] Once the new cathode 161 to be treated is delivered at position B by the carriage 32 of the handling unit 30, the stripping operation in the stripping machine 12 may begin. Upon completion of the stripping, the operating cycle of the handling unit described above may be repeated to move cathode 164 to from position A to B and cathode 161 from position B to C.

[0034] An exemplary embodiment of the cathode handling unit 30 is illustrated in detail in Figs. 2 to 4. It comprises a frame consisting of two triangular wings 36 for mounting to the stripping machine 12, e.g. on the side thereof facing the upstream storage region of the conveyor 12. The frame also includes a spacing member 40 maintaining wings 36 parallel.

[0035] The carriage 32 itself is simply formed by a pair of bars 42 that are symmetrically arranged below the wings 36. Each bar 42 comprises a pair of cathode supports 44 featuring V-shaped notches 46. The carriage bars 42 extend parallel to the conveying direction and the cathode supports 44 are spaced by a distance corresponding to the desired spacing d2. It may further be noted that the spacing between the carriage bars 42 is slightly greater than the width of the conveyor 14, in order to be able to pick-up cathodes traveling on the conveyor 14 by the extremities of their top-bars (see Figs. 6 and 7).

[0036] Driving means are provided for guiding the carriage 32. In the present embodiment, the driving means include a horizontal rail 45 affixed below each wing 36, in which a respective vertical arm 47 is slideably mounted by means of rollers 48. A linear actuator 50 is attached to each wing 36 and connected to each arm 47. Each bar 42 is itself supported by one of the pair of arms 47, which features an integrated vertical lift to which the bar 42 is connected for its vertical actuation. Each lift is formed by a pair of vertical studs 52 with facing side rails in which a rectangular member 54 is slidingly received, and which is connected to a vertically arranged linear actuator 56 (see Fig.3). The carriage bars 42 are fixedly mounted to the sliding members 54 of the lifts. Linear actuators 56 and 50 can be of any appropriate kind (electrical, hydraulic, pneumatic or mechanical/screw).

[0037] The above driving means thus allow movement of the carriage 32 in the in the horizontal direction, parallel to the conveyor 14 (back and forth) as well as in the vertical direction (up and down). Their spatial extension is relatively short. Lengthwise, i.e in the direction of the conveyor, it is sufficient that the carriage be moved over distance d2. In practice, d2 may advantageously be a multiple of spacing d1, e.g. 2, 3, 4 or 5 times spacing d1, as already mentioned.

[0038] Vertically, the carriage 32 is mobile between a lower position where it can travel empty without interfering with the cathode bars 23 resting on the conveyor 14 and an upper position, where it can carry two cathodes without interfering with the chains 18.

[0039] Fig.6 shows a side view of the cathode handling unit 30 mounted on the stripping device 12. In this Figure, only the top and bottom of the stripping device 12 is shown for a better reading of the drawing. In Fig.7, which is a perspective view of the handling unit 30, the stripping device has been omitted also for an easier readability.

[0040] Turning back to Fig.2, the cathode handing device 30 has been mounted to a conventional stripping device 12, which comprises the typical knives and traction bar for lifting the cathode against the knives to remove the metal deposits. It may be appreciated that the present handling unit is extremely flexible and can be in fact mounted to a variety of stripping or other devices, where it is desired to increase cathode spacing before stripping/treatment. The handling unit could alternatively be designed as self-standing and arranged in the vicinity of the stripping device.

[0041] It may also be noted that in the present embodiment, the carriage 32 deposits the cathode to be treated at position B back on the conveyor chains 18. For the stripping operation, the stripping device comprises hooks that lift the cathode from the conveyor to remove the metal sheets.

[0042] Alternatively, the system can be designed so that the carriage deposits the cathode to be stripped directly in hooks in the stripping device. This is advantageous because the precision of the handling unit is easier to control than that of a large conveyor, which for its operation needs some operating play/clearance.

[0043] Therefore, it will be understood that a pair of shorter, independent conveyors, one upstream and the other downstream of the stripping machine, could be used instead of a single conveyor traversing the stripping machine 12.

[0044] As it may be noted from Fig.6, in the present embodiment the spacing between chain notches is d1 so that cathodes can rest thereon with a spacing d1. There however remains a small gap between notches 22 which could also accommodate cathode bars. Hence, it is possible to store cathodes with a spacing d1 and d1/2. Alternatively, a chain could have notches spaced by a distance d1/2, and it would be possible to store cathodes with a spacing d1 by placing them in every other notch.


Claims

1. Cathode stripping system comprising :

a cathode stripping device;

a conveyor system associated with the stripping device, the conveyor system comprising:

- an upstream storage region before the cathode stripping device, in which cathodes to be treated are stored parallel to each other with a first spacing d1;

- a downstream storage region, in which treated cathodes are stored parallel to each other;

characterized by
a cathode handling unit associated with the cathode stripping device, comprising:

- a carriage mobile in the conveying direction and provided with support means for two cathodes with a second spacing d2, the second spacing d2 being greater than the first spacing d1; and

- driving means for the carriage designed so that the carriage may perform a reciprocating movement with respect to the cathode stripping device in order to move a cathode to be treated over a distance corresponding to the second spacing d2 from the upstream storage region to the stripping device and concurrently moving a treated cathode over a distance corresponding to the second spacing d2 from the stripping device to the downstream storage region.


 
2. Cathode stripping system according to claim 1, wherein the second spacing d2 is a multiple of the first spacing d1.
 
3. Cathode stripping system according to claim 1 or 2, wherein the first spacing d1 correspond to the inter-cathode spacing in an electrolytic cell, or to a multiple thereof.
 
4. Cathode stripping system according to claim 1, 2 or 3, wherein the carriage is formed by a pair of bars symmetrically arranged and extending in the conveying direction, each bar being provided with a pair of cathode supports spaced by a distance corresponding to the second spacing d2.
 
5. Cathode stripping system according to any one of the preceding claims, wherein the cathode supports comprise V-shaped notches.
 
6. Cathode stripping system according to any one of the preceding claims, wherein the driving means of the cathode handling unit comprise means for moving the carriage in both directions of the conveying direction, and means for guiding the carriage in the vertical direction, so that its operating cycle may describe a closed loop.
 
7. Cathode stripping system according to any one of the preceding claims, comprising a control unit designed to control the operating cycle of the cathode handling unit and to coordinate its operation with the forward movement of the conveyor system.
 
8. Cathode stripping system according to any one of the preceding claims, wherein said conveyor system extends linearly through the cathode stripping device.
 
9. Cathode stripping system according to any one of the preceding claims, wherein said conveyor system comprises a pair of spaced chains; and the cathodes rest on the conveyor system in-between the chains with the extremities of their top-bars received in notches defined by the chains.
 




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