Abstract:
A method for producing self-dunnaged cathode bundles, comprising the steps of forming at least one deformed cathode by bending opposed ends of at least one cathode to form a pair of supports disposed at an angle to a central portion of the at least one deformed cathode, and stacking one or more further cathodes above or below the at least one deformed cathode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application PCT/AU2008/000226, filed on Feb. 20, 2008, which application is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Electrorefining and electrowinning, also known as electroextraction, are processes by which valuable metal ions may be recovered from solution by electrolytic deposition of metal onto a solid substrate acting as an electrode. Electrorefining is commonly used as an extraction process for a large number of metals, including lead, copper, gold, silver, zinc, aluminum, cobalt, chromium and manganese. 
         [0003]    The metal deposited onto the electrode forms sheets known as cathodes. These cathode sheets are removed from the electrode and a number of cathodes are stacked flat to form a cathode bundle, weighing several tonnes, ready for transportation for sale or to a further refining process. Typically, a cathode bundle is strapped to hold the bundle together. When cathode bundles are stacked, pieces of wood, known as dunnage, are inserted between the cathode bundles. This dunnage acts to create a gap between cathode bundles of sufficient size to allow a forklift, or similar vehicle, to pick up and move the cathode bundle. Cathode bundles are also placed on temporary or permanent dunnage located on the ground to enable forklifts to pick up the cathode bundles. 
         [0004]    The use of wood as dunnage presents a number of disadvantages, not least of which is the cost. The cost of the wood alone may amount to hundreds of thousands of dollars per year. In addition, wooden dunnage may leave marks on the cathodes it comes into contact with, which is not only unsightly, but can contaminate the surface of the cathode. In some circumstances, the use of wooden dunnage may also raise quarantine problems when cathode bundles are to be transported internationally. 
       SUMMARY 
       [0005]    It is an object of the invention to provide a self-dunnaged cathode bundle which may overcome at least some of the abovementioned disadvantages, or provide a useful or commercial choice. 
         [0006]    In one form, the present invention resides in a method for producing self-dunnaged cathode bundles, comprising the steps of forming at least one deformed cathode by bending opposed ends of at least one cathode to form a pair of supports disposed at an angle to a central portion of the at least one deformed cathode, and stacking one or more further cathodes above or below the at least one deformed cathode. 
         [0007]    The self-dunnaged cathode bundles may be arranged in a number of different ways. In one embodiment of the invention, the at least one deformed cathode may be placed at the bottom of the cathode bundle and have one or more cathodes positioned above the at least one deformed cathode. In another embodiment, the at least one deformed cathode may be placed at the top of the cathode bundle and have one or more cathodes positioned below the at least one deformed cathode. 
         [0008]    Alternatively, the self-dunnaged cathode bundle may comprise one cathode positioned below the at least one deformed cathode and a plurality of cathodes positioned above the at least one deformed cathode. 
         [0009]    In some embodiments, the at least one deformed cathode may be placed on one or more other cathodes to form a cathode bundle having one or more cathodes positioned below the at least one deformed cathode and one or more cathodes above the at least one deformed cathode. 
         [0010]    In use, the pair of supports of the at least one deformed cathode are long enough to provide a gap between the cathodes of sufficient size to allow the tines of a forklift, or similar device, to pass through and lift the cathode bundle. Self-dunnaged cathode bundles also eliminate the need to use wood as dunnage, substantially reducing operational costs and preserving the surface finish of the cathodes. In addition, by eliminating the use of wood, self-dunnaged cathode bundles reduce the waste generated by the process. 
         [0011]    The supports of the at least one deformed cathode may be bent to any angle that will allow the supports to support the weight of the second plurality of cathodes placed on top of it. Typically, however, the at least one deformed cathode will be bent so that the supports make an angle of from 85-95°, more preferably from 87-93°, and most preferably from 89-91° to the central portion of the at least one deformed cathode. While not narrowly critical, it is preferred that, in use, the supports of the at least one deformed cathode extend downwardly from the central portion of the at least one deformed cathode. However, this invention is not limited to the supports extending downwardly from the central portion of the at least one deformed cathode, and in some aspects the supports may extend upwardly from the central portion of the at least one deformed cathode. 
         [0012]    The process of bending the cathodes may be achieved by a number of known methods. However, it is preferred that the bending is performed mechanically during handling of the cathodes. 
         [0013]    The thickness of a cathode sheet generally tapers towards the outer edges, a phenomena known as feathering. Thus, the placement of the bend in the cathode sheet to form the supports of the deformed cathode must be at a sufficient distance from the outer edge of the cathode sheet to avoid bending the thinnest portion of the cathode. While any distance that avoids the thinnest portion of the cathode would be suitable, it is preferred that the bend is placed from 50-300 mm, more preferably from 75-150 mm, most preferably approximately 100 mm from the outer edge of the cathode. 
         [0014]    In an alternative embodiment of the invention, the at least one deformed cathode may be located at the bottom of the cathode bundle, with a plurality of cathodes stacked above the at least one deformed cathode. 
         [0015]    The number of deformed cathodes may vary depending on the number of cathodes stacked above and the weight of those cathodes as well as the thickness (and hence strength) of the deformed cathode(s). However, typically a pair of cathodes will be bent. This pair of cathodes may be bent separately or together. 
         [0016]    The self-dunnaged cathode bundle is particularly suitable for use with copper, nickel and zinc cathodes, although cathodes made from any metal could equally be stacked together using the present method. Similarly, flat or corrugated cathode sheets may be stacked using the method of the invention. 
         [0017]    In another form of the invention there is provided a self-dunnaged cathode bundle comprising at least one dunnage cathode having a pair of supports disposed at an angle to a central portion, and one or more cathodes stacked above or below the at least one dunnage cathode. 
         [0018]    Preferably the dunnage cathode is formed by bending. 
         [0019]    In a preferred embodiment of the invention the at least one dunnage cathode is positioned at the bottom of the self-dunnaged cathode bundle and have one or more cathodes positioned above the at least one dunnage cathode. In another embodiment, the at least one dunnage cathode may be placed at the top of the cathode bundle and have one or more cathodes positioned below the at least one dunnage cathode. 
         [0020]    Alternatively, the self-dunnaged cathode bundle may comprise one or more cathodes positioned below the at least one dunnage cathode and a plurality of cathodes positioned above the at least one dunnage cathode. 
         [0021]    The number of dunnage cathodes may vary depending on the number of cathodes stacked above and the weight of those cathodes as well as the thickness (and hence strength) of the dunnage cathode(s). However, typically the at least one dunnage cathode will comprise a pair of cathodes. 
         [0022]    In some embodiments, the cathode bundle is secured together by use of an appropriate material, such as tie wire or tie strap. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    An embodiment of the invention will be described with reference to the following drawings in which: 
           [0024]      FIG. 1  illustrates an end view of a self-dunnaged cathode bundle according to an embodiment of the present invention. 
           [0025]      FIG. 2  illustrates transportation of a self-dunnaged cathode bundle according to an embodiment of the present invention. 
           [0026]      FIGS. 3A-3D  illustrate a number of alternative embodiments for the arrangement of cathodes within the self-dunnaged cathode bundle. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    In  FIG. 1  there is shown a self-dunnaged cathode bundle  10  comprising a first plurality of cathode sheets  11  and a second plurality of cathode sheets  12  stacked on top of each other. Inserted between the first plurality of cathode sheets  11  and the second plurality of cathode sheets  12  there are a pair of deformed cathode sheets  13 . Each deformed cathode sheet comprises a pair of supports  14  extending downwardly from an central portion  15  of the deformed cathode. The bend  16  in the cathode sheet is located a sufficient distance from the outer edges  17  of the cathodes to avoid bending the cathode at a point where the thickness of the cathode has tapered. The angle between the supports  14  and the central portion  15  of the deformed cathode is approximately 90°. 
         [0028]    Once the cathode bundle  10  is stacked, strapping  18  is applied in order to hold the cathodes in place during transportation. The length of the supports  14  of the pair of deformed cathodes  13  creates a void  19  between cathodes in the cathode bundle  10  of sufficient height to allow the passage of the tines of a forklift or similar device. Thus, the cathode bundle  10  may be simply moved and transported without the need for wooden dunnage. 
         [0029]      FIG. 2  illustrates a cathode bundle  10  when being transported. The completed cathode bundle  10  has strapping  18  applied to hold the bundle  10  together when it is being moved. The void  19  created between the first plurality of cathodes  11  and second plurality of cathodes  12  by the deformed cathodes  13  allows a forklift  20  to pick up and move the cathode bundle  10 . 
         [0030]      FIG. 3A  illustrates another embodiment of the invention in which the deformed cathode  13  is placed at the bottom of the self-dunnaged cathode bundle  10 . A plurality of cathodes  21  may then be positioned on top of the deformed cathode  13 . Alternatively,  FIG. 3B  shows an arrangement wherein the self-dunnaged cathode bundle  10  is formed by positioning the deformed cathode  13  on top of a plurality of cathodes  21 . In yet another embodiment of the invention, illustrated in  FIG. 3C , a single cathode  22  is positioned underneath a pair of deformed cathodes  13  and then a plurality of further cathodes  21  is positioned above the pair of deformed cathodes  13  to form the self-dunnaged cathode bundle  10 . In yet another embodiment of the invention, illustrated in  FIG. 3D , a single cathode  22  is positioned underneath a pair of deformed cathodes  13  and then a plurality of further cathodes  21  is positioned above the pair of deformed cathodes  13  to form the self-dunnaged cathode bundle  10 . In this embodiment of the invention the supports  14  of the pair of deformed cathodes  13  extend upwardly from the central portion  15  of the pair of deformed cathodes  13 . 
         [0031]    Those skilled in the art will appreciate that, in normal practice, self-dunnaged cathode bundles are generally strapped together using any suitable strapping material, such as, for instance, tie wire or tie strap. However, this strapping material has been omitted from  FIGS. 3A to 3D  for clarity. It will be apparent that some of the self-dunnaged cathode bundles shown in  FIGS. 3A to 3D  will require the use of lesser amounts of strapping material than others. However, the choice as to which particular self-dunnaged cathode bundle will be desired for use may depend on a number of operational factors. 
         [0032]    The self-dunnaged cathode bundle provides a number of significant advantages over existing cathode bundles. By eliminating the use of wooden dunnage, metal refineries may save hundreds of thousands of dollars per year, as well as reducing the amount of waste wood generated by the process. The maintenance requirements needed to replace damaged permanent wooden dunnage are avoided. Occupational health and safety issues caused by wooden dunnage (such as tripping hazards) are also largely overcome. In addition, self-dunnaged cathode bundles eliminate quarantine issued that may arise from using wooden dunnage. Also advantageously, bending the cathodes does not adversely affect the cathode&#39;s chemical or physical properties, and the bent cathodes are still suitable for further downstream processing. 
         [0033]    Those skilled in the art will appreciate that the present invention may be susceptible to variations and modifications other than those specifically described. It will be understood that the present invention encompasses all such variations and modifications that fall within its spirit and scope.