Extraction of metals by electrolytic reduction

Extraction of metals

Extraction is the process of obtaining metals from their ores. The ores are reduced to their respective metals in the process. During reduction, the metallic ions gain electrons and become the corresponding metal atoms.

Methods of metal extraction

There are two main methods of extraction:

1. Electrolytic Reduction
2. Chemical Reduction

Some metals and their methods of extraction

Metal	Name of Ore	Extraction Method
Very Reactive Metals	Potassium, Sodium, Magnesium, Aluminium	Electrolysis
Less Reactive Metals	Zinc, Tin, Iron, Lead, Copper	Chemical Reduction
Least Reactive Metal	Gold	Uncombined (Purified by Electrolysis)

Stages of metal extraction

There are four stages in the extraction process:

1. Ore Purification
2. Extraction of the Metal
3. Refining of the Metal
4. Roasting in Air

Ore purification

After mining the ore, it needs to be purified. There are three common methods to purify the ore:

1. Dressing: Removes impurities without decomposing any components within the ore. Methods include:
   1. Hand picking
   2. Blowing
   3. Filtering solids
   4. Sedimentation and Decantation
2. Calcination: A process in which ore is heated in the absence of air to expel water or carbon dioxide.
3. Roasting: Purifies ore by heating it in the presence of air, sometimes with other chemicals, to make chemical changes.

Reduction of oxides to metals

Carbon is used to reduce oxides of zinc and all metals below zinc in the Electromotive Series (E.C.S). Metals above zinc require very high temperatures for reduction, and are therefore extracted through electrolysis.

Extraction of sodium

Sodium is extracted by electrolysis of a mixture of molten sodium chloride and calcium chloride. Calcium chloride is added to lower the temperature from over 800°C to 600°C. The process takes place in Down's Cell, where sodium is liberated at the cathode, and chlorine is liberated at the anode. The two elements are separated by cylindrical iron gauze.

Extraction of aluminium

Aluminium is extracted through electrolysis from its ore, bauxite (hydrated aluminium oxide, Al₂O₃·2H₂O). The purified bauxite is dissolved in molten cryolite (Na₃AlF₆) and electrolyzed. Both the anode and cathode are made of carbon.

Uses of aluminium

1. Used for making kitchen vessels such as pots, pans, etc.
2. Used in moving parts of machines and engines, such as pistons and cylinders.
3. Used for making objects that need to be as light as possible, such as in aerospace and vehicles.
4. Used in overhead tension cables for the distribution of electric power.
5. Used for packing materials for cigarettes, sweets, biscuits, etc.