Extracting Metals in Middle of Reactivity Series

Calcination is a process in which ore is heated in the absence of air or air might be supplied in limited quantity. Roasting involves heating of ore lower than its melting point in the presence of air or oxygen. Calcination involves thermal decomposition of carbonate ores.

Smelting – it involves heating the roasted or calcined ore (metal oxide) to a high temperature with a suitable reducing agent. The crude metal is obtained in its molten state.
Fe₂O₃+3C(coke)→2Fe+3CO₂

Aluminothermic reaction – also known as the Goldschmidt reaction is a highly exothermic reaction in which metal oxides usually of Fe and Cr are heated to a high temperature with aluminium.
Fe₂O₃+2Al→Al₂O₃+2Fe+heat
Cr₂O₃+2Al→Al₂O₃+2Cr+heat

Extraction of Metals Towards the Top of the Reactivity Series

Electrolytic reduction:

1. Down’s process: Molten NaCl is electrolysed in a special apparatus.

At the cathode (reduction):
Na⁺(molten)+e⁻→Na(s)
Metal is deposited.

At the anode (oxidation):
2Cl⁻(molten)→Cl₂(g)+2e^–
Chlorine gas is liberated.

2. Hall’s process: Mixture of molten alumina and a fluoride solvent usually cryolite, (Na₃AlF₆) is electrolysed.

At the cathode (reduction):
2Al³⁺+6e^–→ 2Al(s)
Metal is deposited.

At the anode (oxidation):
6O₂^– → 3O₂(g)+12e^–
Oxygen gas is liberated.

The metals at the top of the reactivity series are highly reactive. They cannot be obtained from their compounds by heating with carbon, because these metals have more affinity for oxygen than carbon. Hence, for the extraction of such metals electrolytic reduction method is used.