ZA200508974B

ZA200508974B - Cathode plate

Info

Publication number: ZA200508974B
Application number: ZA200508974A
Authority: ZA
Inventors: Webb Wayne Keith
Original assignee: Xstrata Queensland Ltd
Priority date: 2003-05-01
Filing date: 2004-04-30
Publication date: 2007-03-28
Also published as: WO2004097076A1; FI20051107A; BRPI0409851A; US20070051621A1; CA2524878A1; AU2003902095A0; RU2005137321A; PE20050298A1

Description

CATHODE PLATE

FIELD OF THE INVENTION

The present invention relates to electrolytic recovery of metals, and in particular to cathode plates for use in electrolytic recovery of metals.

BACKGROUND OF THE INVENTION

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

There are a number of processes for the electrolytic recovery or refining of metals.

One particularly well known technique is the process for electro refining and/or electro winning of copper and other metals as developed by Mount Isa Mines Limited known as ISA PROCESS™ or ISA PROCESS 2000™ (Trade Marks of Mount Isa

Mines Limited). In an electro refining process, unrefined anodes of a base metal such as copper are placed in an electrolytic bath and separated by cathode plates. Each cathode plate comprises a stainless steel blade held and supported in the bath by a hanger bar.

Application of a current causes the unrefined base metal from the anode to enter the electrolytic bath and subsequently deposit in a purified form on the cathode blade. The thus refined metal is then mechanically stripped from the cathode plate for subsequent handling.

Typically, stripping of the metal from the cathode plate is accomplished by first flexing the cathode blade to cause at least a part of the copper deposit to separate therefrom and then mechanically stripping or gas blasting the remainder of the deposited metal from the blade.

Generally, deposition of the metal on the edge portions of the cathode blade is avoided since this renders the deposited metal more difficult to strip. Edge strip protectors such as plastic strip mouldings, wax coating or a combination of both may be used to avoid deposition of metal on the edge portions of the cathode blade. Generally, the vertical longitudinal edges of the cathode blade are covered by plastic edge strips which may be riveted, glued or otherwise fixed to the cathode blade whilst the horizontal edge may be covered or left exposed.

There have previously been proposed many edge strip/blade configurations generally, however, the edge strips extend to or below the bottom horizontal end edge of the cathode blade. Accordingly, in use, any force applied to the bottom of the cathode blade/edge strip arrangement is transmitted to the edge strips and tends to tear or at least move the edge strips relative to the cathode plate. Any such movement or damage of the edge strip can be extremely detrimental to the process. In particular, it is both costly and time consuming to replace or reposition the edge strip protectors.

Another disadvantage arises from the deposition of metal on that portion of the cathode plate held within the edge strip. While it is intended to provide a close fit between the edge strip and cathode blade, thereby preventing substantial ingress of electrolyte, some material still makes its way between the edge strip and the cathode blade particularly at the lower end. In some instances, the ingress of electrolyte is sufficient to cause metal to be deposited on that portion of the cathode blade held within the edge strip thereby deforming and potentially detaching the edge strip from the cathode blade.

A number of techniques have been used in an effort to prevent such deposition of metal on the edges of the cathode blade held within the edge strips. These include resilient collars on the edge strips or filling the edge strips with suitable sealant such ag silicone. Most of these techniques have now become obsolete by providing closer tolerances between the edge strips and the cathode blade. However, a perennial problem remains, which is the growth of the deposited metal on the exposed lower end portion of the cathode blade, at either end of the bottom edge.

Generally, this does not cause structural failure of the edge strip, however, once the metal is stripped from the cathode blade, these additional deposits or ‘dags’ can remain on the stripped metal providing an unattractive product. In severe cases, these deposits act to bridge the metal sheets stripped from either side of the cathode blade, making their separation more difficult.

Various mechanisms have been proposed to seal the bottom end of the plastic edge strip including providing end caps, filling the end portion with a silicone sealant or indeed covering the entire bottom end edge with an edge strip protector. In

PCT/AUQ0/00668, the present Applicants have proposed an edge strip cap which includes a support member or tab adapted to mate with a complementary recess formed in the lower end comers of the cathode blade. This device performs two functions.

Firstly, the support member provides a shoulder portion adapted to abut a complementary surface on the cathode blade and thereby support and reduce relative movement of the cathode blade in the edge strip. Further, the bottom edge portion concealed within the edge strip is spaced from the exposed bottom edge portion of the cathode blade, thereby minimising metal deposition on the concealed bottom edge portion.

However, even this system has its own disadvantages and it is an object of the present invention to overcome or at least ameliorate one or more of the disadvantages of the prior art, or provide a commercial alternative thereto. :

DISCLOSURE OF THE INVENTION

Accordingly, in a first aspect, the present invention provides a cathode plate comprising a cathode blade and a hanger bar attached to the upper end portion thereof to support the cathode blade in an electrolytic bath, the area of the blade being defined by the hanger bar at the upper periphery, two substantially parallel spaced apart side edges extending from the hanger bar and defining the side periphery of the blade and a bottom end edge substantially parallel to the hanger bar and defining the lower periphery of the blade, wherein the side and bottom edges terminate short of the respective lower and side peripheries of the blade, with corner edge portions extending between and connecting opposite ends of the bottom edge to the respective side edges.

The comer edge portion which connects each of the bottom edges with its respective vertical edges may be a substantially straight edge or may be curved. In one embodiment, the corner edge portion includes a substantially straight edge with a curved transition portion connecting the straight corner edge with one or both of the horizontal bottom edge or vertical side edges of the cathode blade. : . Indeed, in some instances, the corner edge portion may be a mixture of both curved and straight edge portions.

In a preferred embodiment, the side edges are covered by edge strips which terminate adjacent the junction of the corner edge portion with a respective side edge.

The above arrangement aims to ameliorate some of the aforementioned disadvantages. In particular, by cropping or cutting the normal right angle corners from the cathode blade, there is no need for a bottom plug in the edge strip. Silicone or other similar filler material may be used to fill the bottom of the edge strip and thereby inhibit copper growth in that area.

In a preferred embodiment, the bottom edge and/or corner edge portions include a groove such as a V-groove to assist in separation of the copper into two separate sheets, from the cathode blade.

Unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of examples only, with reference to the accompanying drawings in which:

Figure 1 is a front elevational view of a cathode plate in accordance with a first embodiment of the present invention;

Figure 2 is an enlarged view of a corner of the cathode plate of figure 1;

Figure 3 is a cross sectional view of the bottom edge of the cathode plate shown in figures 1 and 2;

Figure 4 is a front elevational view of a cathode plate in accordance with the second embodiment of the present invention;

Figure 5 is an enlarged view of a comer of the cathode plate shown in figure 4; and

Figure 6 is a cross sectional view of the bottom edge of the cathode plate shown in figures 3 and 4.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring firstly to figures 1 and 2, the cathode plate 1 comprises a cathode blade 10 and hanger bar 20 connected along the top edge of the blade 10. As is well known in the art, the hanger bar 20 supports the blade 10 within an electrolytic bath and provides electric current to the blade for deposition of metal.

On the other three sides, the area of the blade is defined by side edges 30 and horizontal bottom edge 40. The periphery of the blade 10 is defined by hanger bar 20 at the upper periphery, side edges 30, at the side peripheries and bottom edge 40 at the lower periphery. The side edges extend downwardly from hanger bar 20 but terminate short of the lower periphery. Bottom edge 40 similarly terminates short of the side periphery defined by side edges 30. Either end of the horizontal edge 40 is joined to its respective side edge 30 by means of corner edge portion 50. In the embodiment shown, comer edge portion 50 is a straight edge between bottom edge 40 and side edges 30 angled at about 45° to both. It should be appreciated that in other embodiments the angle between corner edge portion 50 and bottom edge 40 or side edges 30 may be an angle other than 45° without departing from the scope of the invention.

Edge strips 100 extend along vertical side edges 30 preferably terminating at the junction between corner edge portion 50 vertical edge 30. As shown more clearly in figure 2, the bottom end 110 of edge strip 100 is preferably bevelled to match the shape of corner edge portion 50. This bottom end 110 is preferably infilled with plastic or a sealant to reduce ingress of electrolytic solutions when placed in the electrolytic bath.

Bottom edge 40 and in some cases, corner edge portions 50 may be formed with a groove 150 as shown in figure 3. This groove 150, in this case a V-groove, assists in separation of the deposited metal sheets from each other by forming a fault line.

The arrangement shown in figures 1 to 3 provide significant advantages over conventional cathode plates. Providing corner edge portion 50 instead of the normal right angle junction between the side 30 and bottom edges 40 effectively spaces the bottom end 110 of the edge strip 100 from bottom end edge 40 of the cathode plate.

This in turn reduces the opportunity for deposition of metal at and around the bottom end 110 of edge strip 100.

In addition, the need for an end cap on the plastic strip 100 is removed since the

Applicants have found that with such a ‘cropped corner’ type cathode blade, the end of the plastic strip may be simply sealed with a filler such as silicone.

Further, as mentioned above, plastic edge strips can be damaged in loading and stripping operations since the edge strip can, in some cases, extend slightly below the bottom edge 40. Accordingly, when the cathode plate is dropped or placed on a surface, the entire weight of the cathode plate is supported by the plastic edge strips on either side of the cathode plate. In some stripping machines, the plate is supported by the hanger bar. In others, it is supported along its lower edge, potentially damaging the bottom ends of the plastic edge strip.

The arrangement shown in figures 1 to 3 spaces the end of the plastic edge strips 100 at a significant distance from the bottom end edge 40 thereby virtually eliminating the possibility of any impact damage to the plastic edge strips 100.

A further embodiment is shown in figures 4 to 6 which correspond with the views shown in figures 1 to 3.

In this embodiment the corner edge portion 50 includes a curved transition portion 60. This curved transition portion 60 has been found to assist in consistent and smooth separation of the deposited metal from the cathode blade 100. The ‘sharper’ transition shown in figure 1 can, in some instances, lead to inconsistent stripping, jagged bottom edges or ‘dags’ of material left on the separated material. The Applicants have found that providing a curved or ‘smoother’ transition from the bottom edge 40 to the corner edge portion 50, allows the deposited metal to separate more smoothly and consistently from the cathode blade 10. The curvature of transition portion 60 may be of any appropriate radius.

It will be understood that the corner edge portion shown in figures 1 to 6 are only two embodiments of a wide variety of corner edge portions which may be used. The corner edge portion may be a curved section of consistent or differing radius, or could be made up of a number of segments of straight or curved edges.

As with figures 1 to 3, the embodiments shown in figures 4 to 6 can include the V- groove 150 formed in the bottom edge 40 and extended through transition portion 60 along corner edge portion 50 toward the vertical edge.

It will be understood that the cathode plate shown may be embodied in other forms without departing from the spirit or scope of the present invention.

Claims

1. A cathode plate comprising a cathode blade and a hanger bar attached to the upper end portion thereof to support said cathode blade in an electrolytic bath, the area of said blade being defined by said hanger bar at the upper periphery, two substantially parallel spaced apart side edges extending from said hanger bar and defining the side periphery of said blade and a bottom end edge substantially parallel to said hanger bar and defining the lower periphery of said blade; wherein said side and bottom edges terminate short of the respective lower and side peripheries of said blade, with corner edge portions extending between and connecting opposite ends of the bottom edge to the respective side edges.

2. A cathode plate according to claim 1 wherein said corner edge portion, which connects each of the bottom edges with its respective vertical edges, is a substantially straight edge or is curved.

3. A cathode plate according to claim 1 wherein said corer edge portion includes a substantially straight edge with a curved transition portion connecting the straight comer edge with one or both of the horizontal bottom edge or vertical side edges of the cathode blade.

4. A cathode plate according to claim 1 wherein said comer edge portion is a mixture of both curved and straight edge portions.

5. A cathode plate according to any one of the preceding claims wherein said side edges are covered by edge strips which terminate adjacent the junction of said corner edge portion with a respective side edge.

6. A cathode plate according to any one of the preceding claims wherein said bottom edge and/or corner edge portions include a groove such as a V-groove to assist in separation of the copper into two separate sheets, from the cathode blade.

! | WO 2004/097076 PCT/AU2004/000565

7. A cathode plate according to any one of the preceding claims wherein the right corners of said cathode plate are cropped or cut and silicone or other similar filler material is used to fill the bottom of the edge strip and thereby inhibit copper growth in that area.

8. A cathode plate according to any one of the preceding claims wherein said corner edge portions extend between and connect opposite ends of the bottom edge to the respective side edges substantially at an angle of 45 degrees.

9. A cathode plate substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.