WO 2010/028428 PCT/AU2009/001172 1 TITLE A Cathode and a Method of Forminq a Cathode FIELD OF THE INVENTION The invention relates to a cathode for use in the electrolysis of metal 5 ions and a method of forming said cathode. In particular, although not exclusively, the invention relates to a cathode that is particularly useful for the electrolysis of cobalt ions or nickel ions from a solution. BACKGROUND TO THE INVENTION The electrolysis of metal ions contained in a solution to give a solid 10 metal product is a well known technique for isolating relatively pure metals. A solid cathode is placed into a metal ion solution and an electric current is applied to the cathode. Electro deposition of the metal onto the cathode then occurs. Periodically, the cathode and the attached metal product are removed from the solution. The solid metal product is then stripped from 15 the cathode and, ideally, the cathode is then reused. The material for a cathode is suitably conductive to allow the metal product to deposit. Additionally, the cathode material allows easy removal of the metal product from the cathode, yet the metal product does not separate prematurely. A cathode that is robust such that it may be subjected to repeated deposition 20 and stripping cycles with minimal treatment of the cathode between each cycle is preferred. The electro deposition of cobalt metal presents additional difficulties, as cobalt metal electro deposits contain inherently high internal stresses. The electro deposition of cobalt onto standard flat stainless steel blanks, WO 2010/028428 PCT/AU2009/001172 2 edged by non-conductive edge strips, results in a sheet of cobalt metal which has a tendency to prematurely separate from the cathode. If the non-conductive edge strips are eliminated, the cobalt metal grows around the edges of the cathode, which solves the problem of premature 5 separation of the metal from the cathode. However, the cobalt metal is much more difficult to remove from the cathode and attempts to remove it may easily result in damage to the cathode. Damage to the cathodes may require each cathode be repaired on a frequent basis, which leads to higher plant operating costs. 10 The electro deposition of cobalt as a multiplicity of pieces is advantageous, as these are more easily handled in downstream processing. Previous attempts at resolving the difficulties involved in the electron deposition of cobalt have resulted in the manufacture of cathodes by the 15 application of a non-conductive mask to a stainless steel blank sheet such that a pattern of isolated conductive metal portions are exposed to an electrolysis solution. CA 1,078,324 discloses such a cathode, in which the mask is an epoxy-based paint. The conductive portions are recessed in relation to the 20 masking layer. One problem with this cathode is that the masking film is exposed to a harsh environment both in the electrolytic solution and in the stripping procedures. The masking film easily becomes cracked and damaged, particularly at the edge of the conductive portions. Breakdown of the masking film leads to metal deposits forming on the damaged areas, WO 2010/028428 PCT/AU2009/001172 3 which in turn leads to further damage of the masking film. Thus, the cathode becomes unusable and at regular intervals the cathode must be stripped of the masking film, cleaned and new masking film re-applied. CA 1,066,657 discloses a cathode wherein metal discs are attached 5 to a plate or a wire grid. A non-conductive resin is filled into the interstitial area surrounding the discs. Alternatively, heavy gauge corrugated wires are attached to an assembly and resin is filled into the interstitial area leaving the bends in the wire uncovered. In these cathodes the conductive portions are either flush with or stand proud of the surrounding non 10 conductive resin. OBJECT OF THE INVENTION It is an object of the invention to overcome or at least alleviate one or more of the above problems and provide the consumer with a useful or commercial choice. 15 DISCLOSURE OF THE INVENTION In one form, although it need not be the only or indeed the broadest form, the invention resides in a cathode for receiving electro deposition of metal, the cathode comprising: a planar conductive sheet; and 20 raised portions disposed on at least one surface of the planar conductive sheet, wherein the planar conductive sheet and the raised portions are integrally formed. The cathode may further comprise: a non-conductive material which surrounds the raised portions, WO 2010/028428 PCT/AU2009/001172 4 wherein a surface of the raised portions remains exposed. Preferably, each of the raised portions have a planar top surface, wherein the planar top surface has a shape selected from a substantially circular shape, a substantially square shape, a substantially diamond 5 shape or a substantially lozenge shape. In one preferred embodiment, the raised portions form a front surface array located on a front surface of the planar conductive sheet and a rear surface array located on a rear surface of the planar conductive sheet. Preferably, the front surface array has a substantially similar 10 configuration as the rear surface array. Alternatively, the front surface array has a substantially different configuration to the rear surface array. In another form, the invention resides in a method of forming a cathode for receiving electro deposition of metal, the method comprising: masking areas of a planar conductive sheet with a masking material 15 to form a masked conductive sheet; applying a chemical to the masked conductive sheet to chemically etch unmasked areas to form a planar conductive sheet having integrally formed raised portions formed in masked areas, and etched areas. The method may further comprise: 20 applying a non-conductive material to the etched areas of the planar conductive sheet. Further features of the present invention will become apparent from the following detailed description.
WO 2010/028428 PCT/AU2009/001172 5 BRIEF DESCRIPTION OF THE DRAWINGS To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only 5 with reference to the accompanying drawings, wherein: FIG. 1 shows a face view of a cathode according to an embodiment of the invention; FIG. 2A shows a cross sectional view of the cathode of FIG. 1; FIG. 2B shows the cross sectional view of FIG. 2A further 10 comprising a non-conductive material; FIG. 3A shows a cross sectional view of a cathode according to a further embodiment of the invention; FIG. 3B shows the cross sectional view of FIG. 3A further comprising a non-conductive material; 15 FIG. 4 shows a face view of a cathode according to a further embodiment of the invention; FIG. 5 shows a face view of a cathode according to another embodiment of the invention; FIG. 6A shows a schematic of the first step of a method of forming a 20 cathode according to an embodiment of the invention; FIG. 6B shows a schematic of the second step of a method of forming a cathode according to an embodiment of the invention; FIG. 6C shows a schematic of the third step of a method of forming a cathode according to an embodiment of the invention; and WO 2010/028428 PCT/AU2009/001172 6 FIG. 6D shows a schematic of the fourth step of a method of forming a cathode according to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION With reference to FIG. 1, there is shown a face view of a cathode 5 100 according to an embodiment of the invention. The cathode 100 comprises a planar conductive sheet 105 and raised portions 110. Suitably, the planar conductive sheet 105 is formed of metal. The raised portions 110 are disposed on at least one surface of the planar conductive sheet 105 and are integrally formed with the planar conductive sheet 105. 10 The raised portions 110 formed on a surface of the planar conductive sheet 105 together form an array. Preferably, the raised portions 110 form a front surface array 111 on a front surface of the planar conductive sheet 105 and a rear surface array 112 on a rear surface of the planar conductive sheet 105. The distance between each raised portion 110 is sufficient such that 15 during a usual electro deposition cycle the electro deposited metal on each raised portion 110 does not contact electro deposited metal on a neighboring raised portion 110. The size and shape of the raised portions 110 may vary. Suitably, each of the raised portions 110 has a planar top surface 113. In one 20 embodiment, the shape of the planar top surface 113 of each raised portion 110 is circular as shown in FIG. 1, of 10-40 mm diameter. Preferably, each circularly shaped raised portion 110 has a 12 mm diameter. Alternatively, raised portions 110, each with a circularly shaped planar top surface 113, with a 30 mm diameter may be contemplated. The distance between the WO 2010/028428 PCT/AU2009/001172 7 centres of the planar top surface 113 of each raised portion 110 of 12 mm diameter is preferably 23 mm. The distance between the centres of the planar top surface 113 of each raised portion 110 of 30 mm diameter is preferably 38 mm. 5 The edges of the cathodes 100 may be covered by non-conductive edge strips 130, 131, 132 to prevent electro deposited metal from growing around the edge of the cathode 100. Conventional edge strips, as are well known in the art, may be used. The cathode 100 is attached to a hanger bar 150 to facilitate the 10 introduction and removal of the cathode 100 from an electrolytic bath and to provide an electrical connection to the cathode. Conventional hanger bars, as are well known in the art, may be used. FIG. 2A shows a cross sectional view of the cathode 100 of FIG. 1. In this embodiment, the front surface array 111 of raised portions 110 is 15 disposed on a front surface and the rear surface array 112 is disposed on a rear surface of the planar conductive sheet 105. The edge strips 130, 132 may also be seen. The thickness of the planar conductive sheet 105 used to manufacture the cathode 100 is preferably thick enough to be suitably rigid, but thin enough to be relatively lightweight. Preferably, the planar 20 conductive sheet 105 is 6 mm thick prior to the formation of the raised portions 110. As shown in FIG. 2A, the front surface array 111 has the same configuration as the rear surface array 112. FIG. 2B shows the cross sectional view of FIG. 2A further WO 2010/028428 PCT/AU2009/001172 8 comprising a non-conductive material 120. The surface of the planar conductive sheet 105, except for the planar top surface 113 of the raised portions 110, is covered with a non-conductive material 120. The non conductive material 120 may be a resin, paint, or the like. The non 5 conductive material 120 suitably is able to withstand the conditions of the electrolytic bath into which the cathode 100 is suspended during use. The surface of the non-conductive material 120 is preferably level with a top surface 113 of the raised portions 110. Alternatively, the raised portions 110 stand proud of the non-conductive material 120. 10 FIG. 3A shows a cross sectional view of a cathode 100 according to a further embodiment of the invention. The front surface array 111 has a different configuration to the rear surface array 112. It will be appreciated by a person skilled in the art that many variations of the configurations of arrays of raised portions 110 on each surface of the planar conductive 15 sheet 105 may be contemplated. FIG. 3B shows the cross sectional view of FIG. 3A further comprising a non-conductive material 120. FIG. 4 shows a face view of a cathode 400 according to a further embodiment of the invention. In this embodiment, the planar top surface 20 113 of the raised portions 410 are diamond shaped. Diamond shaped raised portions 410 provide a greater conductive area than circular shapes on the face of the cathode 400, as diamond shapes "pack" more efficiently than circular shapes. The diamond shaped raised portions 410 may also WO 2010/028428 PCT/AU2009/001172 9 provide for easier removal of electron deposited metal, due to points at the corners. FIG. 5 shows a face view of a cathode 500 according to a further embodiment of the invention where the planar top surface 113 of the raised 5 portions 510 are in the shape of a lozenge. The lozenge shaped raised portions 510 each have two parallel straight edges joined by arcuate sections extending outwardly from the centre of the lozenge shaped raised portion 510. Lozenge shaped raised portions 510 provide a high ratio of conductive area to non-conductive area of the cathode 500. Preferably the 10 distance between the parallel straight edges of a lozenge shaped raised portion 510 is about 10-15 cm and the arcuate sections have radii of about 5-10 cm. Neighbouring centres of the lozenge shaped raised portions 510 are preferably about 20-30 cm apart. In a particularly preferred embodiment, the distance between the parallel straight edges of a lozenge 15 shaped raised portion 510 is 12 cm and the radius of the arcuate sections is 8 cm. The centres of the lozenge shaped raised portions 510 are preferably spaced 27 cm apart in a row, and the distance between the centres of the lozenge shaped raised portions 510 of adjacent rows is preferably 22 cm. 20 The raised portions 110 of the cathode 100 are preferably formed by chemically etching the surface of the planar conductive sheet of metal 105. FIGS 6A, 6B, 6C and 6D show a first, second, third and fourth step, respectively, of a schematic of a method of forming the cathode 100 according to an embodiment of the invention. In the first step (FIG. 6A), WO 2010/028428 PCT/AU2009/001172 10 areas of the planar conductive sheet 105 which will form the raised portions 110 are masked with a masking agent 610. Preferably, the masking agent is an adhesive tape. A particularly preferable masking agent is an adhesive vinyl tape. 5 In the second step (FIG. 6B), remaining un-masked surface is suitably etched to a depth of up to about 5 mm. In a preferred embodiment, the remaining surface is etched to a depth of 1 mm. Preferably, the chemical etching is performed by spraying a masked planar conductive sheet of metal with a ferric chloride solution 620 until a suitable depth of 10 metal has been etched away. In the third step (FIG. 6C), the masking agent is removed from the formed raised portions 110 and in a fourth step (FIG. 6D), a non-conductive material 120 is applied to the etched surface to result in the finished cathode 100. 15 Suitably, raised portions 110 are formed by the chemical etching process on both a front surface and a rear surface of the planar conductive sheet 105 of the cathode 100. The cathode 100 with raised portions 110 formed by chemical etching of a sheet of metal 105 is quick and easy to manufacture. As the 20 raised portions 110 are level with or proud of the surrounding non conductive material 120, removal of electro deposited metal is less likely to cause damage to the non-conductive material 120. Throughout the specification the aim has been to describe the invention without limiting the invention to any one embodiment or specific WO 2010/028428 PCT/AU2009/001172 11 collection of features. Persons skilled in the relevant art may realize variations from the specific embodiments that will nonetheless fall within the scope of the invention. For example, the size and shape of the cathode may vary, as may the size, number and shape of the raised portions. 5 Additionally, more than one type of shape of raised portion may be used on a cathode. It will be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit and scope of the invention.