Salt

Common salt is sodium chloride, NaCl. It can be made in a laboratory by reacting sodium with chlorine. However, it is found naturally in large amounts in seawater or in underground deposits. It is often obtained either by evaporating seawater or by mining underground deposits.

Mining

Large earth-moving equipment is used to extract rock salt. This type of salt is used to treat icy roads in the winter. It lowers the melting point of the ice on the roads so that it melts - even when the temperature is below 0°C.

Salt can also be mined by solution mining. Water is pumped down into the salt deposit. Salt dissolves in the water, forming a concentrated salt solution. This is then pumped up to the surface ready for use in the chemical industry. Solution mining is a continuous process that is safer than sending miners underground.

Mining for salt can lead to subsidence. This happens when insufficient salt is left underground after mining. The weight of the ground above causes the ground to sink downwards and this subsidence can damage buildings and roads.

Uses of sodium chloride

Salt is widely used in the food industry as a preservative and flavour enhancer. It is vital for human health - we need sodium in our diet to allow our bodies to carry out essential functions. However, too much salt in the diet is associated with high blood pressure.

Sodium chloride is the raw material for the manufacture of hydrogen, chlorine and sodium hydroxide. Electrolysis is used. The electrolysis of sodium chloride solution (brine) is an important industrial process because hydrogen, chlorine and sodium hydroxide have many uses.