Also called smelting, it is carried out after calcination or roasting of ores. In this process, the oxide ores are converted into the metallic state by reduction.
Smelting is a process in which the oxide ore in molten state is reduced by carbon or other reducing agents to free metal.
Carbon as Reducing Agent
This method is used for the isolation of iron, tin and zinc metals from their respective oxides. The oxide ores are strongly heated with charcoal or coke. Reduction occurs by the action of carbon or carbon monoxide which is produced by the partial combustion of coke or charcoal.
Fe2O3 + 3C → 2Fe + 3CO
SnO2 + 2C → Sn + 2CO
ZnO + C → Zn + CO
Other Reducing Agents
Oxide ores which cannot be reduced by carbon or metals which show affinity to carbon by forming metal carbides, are reduced by reducing agents like aluminium, sodium, magnesium or hydrogen.
Oxide like chromium oxide or manganese oxide are reduced by aluminium powder is a highly exothermic reaction. This process is known as Goldschmidt's Alumino-thermite reduction method.
Cr2O3 + 2Al → 2Cr + Al2O3 + Heat
3Mn3O4 + 8Al → 9Mn + 4Al2O3 + Heat
This is applied to the sulphide ores of copper, mercury and lead . The ores are heated in air, a part of these sulphide ores is changed into the oxide or sulphate which then reacts with the remaining part of the sulphide ore to give the metal and sulphur dioxide.