Extraction of Aluminium



A soft, silvery-white, corrosion resistant metal. It is the most abundant metal in the earth’s crust as it makes up 8% of the crust and it is the third most abundant element after oxygen and silicon. Bauxite ore (Al2O3.xH2O) is the major source of aluminium till date which is a mixture of hydrated aluminium oxide. Aluminium can also be recovered from cryolite (Na3AlF6) and alunite. It is also found in gemstones such as garnet, topaz and chrysoberyl. The chemical symbol of this metal is Al.

Hall-Heroult process

Hall-Heroult process is widely used in the extraction of aluminium. In Hall-Heroults process, pure Al2O3 is mixed with CaF2 or Na3AlF6. This results in lowering of the melting point of the mixture and increases its ability to conduct electricity.  A steel vessel with  lining of carbon and graphite rods is used. The carbon lining acts as cathode and graphite acts as anode. When electricity is passed through the electrolytic cell which consists of carbon electrodes oxygen is formed at the anode. This oxygen formed reacts with the carbon of the anode to form carbon monoxide and carbon dioxide. In this method of production of aluminium for every 1 kg of Al produced, approximately 0.5 Kg of carbon anode is burnt. The overall reaction is:

2Al2O3 + 3C \(\rightarrow\) 4Al + 3CO2

The electrolytic reactions are:

At the cathode:

Al 3+ + 3e \(\rightarrow\) Al (l)

At the anode:

C (s) + O2- \(\rightarrow\) CO (g) + 2e

C (s) + 2O2- \(\rightarrow\) CO2 (g) + 4e

Aluminium is used in a wide range of applications in the field of transport, construction etc. Aluminium foils are used in the food industries for wrapping of food. The dust of this metal is used in paints. It is used in the extraction of manganese and chromium from its oxides. As it is a soft metal and it can be moulded into any shape it is used in the manufacturing of storage cans.

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Practise This Question

In the commercial electrochemical process for Aluminium extraction, the electrolyte used is: