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Message:: [QUOTE="CoinDictionary, post: 1532745, member: 39280"]*The final step is a process called electrorefining. This is done by electrolysis where the copper anodes from the smelter become positive electrodes and thin, three-foot square sheets of pure copper are used as negative electrodes. Forty-five anodes and 46 cathodes are interleaved and immersed in an electrolysis tank filled with a solution of sulfuric acid and copper(II) sulfate.*Oxidation occurs at the anode, where copper metal is converted to copper(II) ions with the release of two electrons. At the cathode the opposite reaction occurs: copper(II) ions are joined with two electrons to form copper metal. During the migration of metal ions from anode to cathode through the aqueous solution, the impurities drop to the bottom of the electrolysis cell. Some of these impurities are gold, silver, nickel, selenium, tellurium, and platinum which are themselves recovered to be used.*After two weeks, the cathodes are pulled from the tank- -- each one about 350 pounds of 99.99% pure copper. These are washed, bundled, and sold. A new set of cathode starter sheets is inserted and the process continues. After two more weeks, the second set of cathodes is pulled and the remainder of the anodes are melted and cast into new full-size anodes.[/QUOTE]