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What is meant by refining of metals? Name the most widely used method of refining impure metals produced by various reduction processes. Describe with the help of a labeled diagram how this method may be used for refining of copper.
A small electric current is passed through the cell. Atoms from the anode enter the electrolyte. The copper from the anode gets converted into copper sulphide. An equal number of copper atoms from the solution get deposited on the cathode. This is to keep the concentration of the solution constant. Impurities from the anode block either remain in solution or collect below the anode, as they are unable to displace copper from the sulphate solution. The insoluble impurities remain in the electrolyte and are called anode mud.
Copper sulphate solution contains ions of Cu+ and SO4–. The following reactions take place at the anode and cathode when an electric current is passed.
At cathode: $Cu^{2^{+}} + 2^{e^{-}} → Cu$
At anode: $Cu-2e^{-} → Cu^{2^{+}}$
Pure copper is removed from the cathode. Some metals like gold, silver are present in the anode and can be recovered separately.