The Chemical processes by which it is extracted

Mercury cell electrolysis Mercury cell electrolysis was the first method used to produce chlorine on an industrial scale. Titanium anodes are located above a liquid mercury cathode, a solution of sodium chloride is positioned between the electrodes. When an electrical current is applied chloride is released at the titanium anodes, whilst the sodium dissolves into the mercury cathode forming an amalgam.

The amalgam can be regenerated into mercury by reacting it with water producing hydrogen and sodium hydroxide. These are useful byproducts.

This method consumes vast amounts of energy and there are also concerns about mercury emissions.

Diaphragm cell electrolysis An asbestos diaphragm is deposited on an iron grid cathode preventing the chlorine forming at the anode and the sodium hydroxide forming at the cathode from re-mixing.

This method uses less energy than the mercury cell, but the sodium hydroxide is not as easily concentrated and precipitated into a useful substance.

Membrane cell electrolysis The electrolysis cell is divided into two by a membrane acting as an ion exchanger. Saturated sodium chloride solution is placed in the anode compartment whilst distilled water is placed in the cathodes compartment.

This method is nearly as efficient as the diaphragm cell and yet produces very pure sodium hydroxide.