Extraction of Highly Reactivity MetalsThe metals which are high up in the reactivity series, like sodium, potassium, calcium, magnesium, etc., cannot be obtained by the use of chemical reducing agents. Such highly reactive metals are obtained by electrolytic reduction of their fused chlorides. For example, sodium is obtained by the electrolytic reduction of fused sodium chloride in a 'Downs cell'. Similarly, calcium is obtained by the reduction of fused calcium chloride.
Similarly, aluminium is obtained by the electrolytic reduction of aluminium oxide.
Electrolytic Reduction of Alumina
A mixture of pure alumina (Al2O3) and cryolite (Na3AlF6) is subjected to eletrolytic dissociation in an electrolytic cell. Cryolite lowers the melting point of the mixture. Aluminium is obtained at the cathode.
The oxygen gas, evolved at anode, reacts with carbon anodes and forms carbon dioxide gas
Carbon (graphite) anodes burn away and hence they must be replaced from time to time. The highly reactive metals like sodium, calcium, aluminium, etc., can also be used as reducing agents.