The invention is related to the electrorefining of metal and in particular to improved bipolar electrodes used in the bipolar series method of electrorefining metal.
In the electrorefining of metal using the series method, a series of bipolar electrodes, unconnected to any electrical circuit, are located between an anode and cathode pair in a cell. When the cell is in operation, metal is plated on the surface of each bipolar electrode that faces the anode; metal is etched away from the surface of the bipolar electrode facing the cathode.
When a series electrode deposition cell is employed for electrorefining of a metal such as copper, the bipolar electrode is typically a slab of that metal. A series cell would normally include only one style of bipolar electrode except for the end anode, which would be slab of the particular crude metal, and the end cathode, which might be a sheet of the same metal or an inert metal (i.e. a starting sheet).
There are many advantages in utilizing series electrodeposition cells for electrorefining. Principal among them are the use of much lower cell currents than in the parallel system of electrodeposition and the elimination of electrical contacts to all but the end electrodes of the cell. The advantage of the series system becomes even greater at high current densities where the parallel system would require the use of low resistance clamps for every electrode, thus complicating the operation and rendering the attainment of the desired close spacing very difficult.
Several problems associated with the series method of electrorefining were solved by an apparatus described in U.S. Pat. No. 3,979,275, which described a method and apparatus for series electrorefining which employed shields to block current bypass and also included an air agitation system to provide the necessary convection to prevent stagnation of the electrolyte used. The system described in the patent has many virtues, but has not in general been applied because of the difficulties in introducing the crude copper slabs to the electrorefining cells.
For example, in the series electrorefining of massive copper, the following methods of fabricating composite bipolar electrodes are possible. The electrode may be cast, by either a blank-up or a blank-down procedure. Pressing, rolling, or explosion-bonding to form a metallurgical bond between crude copper and the blank may be used. Copper may be fastened to the blank by bolts, rivets, or clamps. Electrodeposition may be used. Simple stacking of the plate of impure copper on a permanent blank may be used if there is a horizontal or inclined disposition of the electrodes. All of these methods have disadvantages. An object of the invention accordingly is to provide an improved method and apparatus for introducing the crude copper to an electrorefining system.
The method and apparatus are also useful for directly converting cement (or precipitate) copper into saleable cathode copper. Cement copper when it arrives from the precipitation plant is a finely divided mixture of metallic copper and copper oxides. Material that has been stored in open piles has an analysis that approximates copper oxide. This material, which is wet and contaminated with iron and other impurities, is usually converted into saleable copper by drying it and adding it to the feed to reverbatory furnaces or converters for eventual conversion into anode for electrorefining, or by dissolving the copper in recirculated electrolyte to produce cupric sulfate which is fed to an electrowinning process. The dissolving step requires an oxidation step to convert metallic copper and cuprous copper to the divalent state. A process of drying and fire-refining to produce a lower quality fire-refined product may also be used. These preliminary steps may be avoided with the invention.
Another object of the invention is therefore to provide an improved bipolar electrode that can be used for the electrorefining of cement copper as well as massive copper.
Other objects of the invention will in part be obvious and will in part appear hereinafter.