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Explain the electrometallurgy of aluminium. |
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Answer» Solution :(i) In the method Hall - Herold process, electrolysis is carried out in an iron tank lined with carbon which acts as a cathode. (ii) The carbon blocks immersed in the electrolyte acts as a anode. (iii) A 20% solution of alumina, obtained from the bauxite ore is mixed with molten Cryolite and is taken in the electrolysis chamber. (iv) About 10% calcium chloride is ALSO ADDED to the solution. Calcium chloride helps to lower the melting point of the mixture. (v) The fused mixture is maintained at a temperature of above 1270 K. (vi) The chemical reactions involved in this process are Ionisation of alumina `Al_(2)O_(3) rarr 2Al^(3+) + 3O^(2-)` Reaction at cathode `2Al^(3+) ("melt") + 3e^(-)rarr Al_((l))` Reaction at anode `2O^(2-)("melt") rarr O_(2) + 3e^(-)` (vii) SInce carbo n acts as anode the following reaction takes place. `C_((s)) + O^(2-)("melt") rarr CO + 2e^(-)` `C_((s)) + 2O^(2-)("melt") rarr CO_(2) + 4e^(-)` (viii) DUE to the above two reactions, anodes are slowly consumed during the electrolysis. The pure ALUMINIUM is formed at the cathode and settles at the bottom. (ix) The net electrolysis reaction can be written as follows. `4AL^(3+)("melt") + 6O^(2-)("melt") + 3C_((s)) rarr 4Al_((l)) + 3CO_(2(g))` |
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