(i) Explain the steps for extraction of copper from its sulphide ore. Write the balanced equations involved in the process. (ii) What is meant by refining of metals ? Draw a diagram of electrolytic refining of copper and name the substances used as cathode, anode and the electrolyte.
(i) Extraction of copper metal - Copper glance (Cu2S):
1. Concentration of the ore (removal of unwanted metals and gangue to purify the ore) is done by Froth floatation method as it is a sulphide ore.
2. Roasting: Copper glance (Cu2S) is roasted in the presence of air. Roasting turns copper glance (ore of copper) into copper (I) oxide.
3. Reduction: Copper oxide is then heated in the absence of air. This reduces copper (I) oxide into copper metal.
4. Refining impure metal: The reduced metal is purified by electrolytic refining method.
Electrolysis of copper from copper sulphate solution (electrolyte) is done using copper electrodes. The crude copper serves as anode while a thin sheet of pure copper serves as cathode.
The electrolyte consists of an acidic solution of CuSO4. Applying suitable voltage to the electrodes causes,
oxidation of copper metal at the anode (Cu -----> Cu2+ + 2e) and
reduction of Cu2+ to form copper metal at the cathode (Cu2+ + 2e -------> Cu).
As the anodes (impure copper) dissolve away, the cathodes on which the pure metal is deposited grow in size.
The impurities in the copper anode which are more active than copper are readily oxidized at the anode but do not plate out at the cathode because their reduction potentials are more negative than that for Cu2+.