Reduction of Metal Oxides To Free Metal

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

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

Self Reduction

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.