Reduction of Metal:
The calcined or roasted ore is then reduced to the metallic state in either of the following ways:
i. Carbon Reduction: In this process, calcined ore is mixed with coke (reducing agent) and flux and heated strongly in the air in a furnace where the oxide ore is reduced either by carbon or by CO to the metallic state. The oxides of less electropositive metals like Fe, Zn, Sn, Cu, etc are extracted by this method.
ii. Self Reduction: This process is applied to sulphide ores only such as PbS, Cu2S, ZnS, etc. The ore is first partially roasted into the oxide in the air and then smelled with the exclusion of air when the oxide reacts with the unchanged sulfide to produce free metal.
iii. Electrolytic Reduction: Highly electropositive metals like Na, K, Ca, Mg, Al, etc. are extracted by the electrolysis of their oxides hydroxides or chlorides in the fused state. The metal is liberated at the cathodes. Some other salts may have to be added to lower the m.p and hence enhance the electrolysis of the compound.
Thus, Al is extracted by the electrolysis of Al2O3 mixed with cryolite and fluorspar as Al2O3 has high m.p. (2050°) and is not a good conductor of electricity.
iv. Alumino Thermal Process: Al has a strong affinity for oxygen at high temperatures. Oxides of some metals like Cr, Mn, Fe, Mo, etc are reduced to the metallic state by this process where Al-powder, a more active metal is used as a reducing agent.