ION Exchange

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Water hardness is a term used to describe the properties of some dissolved substances which, on boiling, lead to the deposition of metal carbonates (limescale) on heat transfer surfaces. Reactions with soap or detergents leading to scum formation render them ineffective. The main source of hardness is calcium carbonate which is dissolved readily by water containing carbon dioxide,

i.e. CaCO3 (s) + CO2 (aq) + H2O = CA2+ + 2HCO3

This reaction is reversed when CO2 is removed by boiling and CaCO3 deposits. Carbonates can be deposited by boiling and their contribution is known as Temporary Hardness and the remainder as Permanent Hardness. Softening by ion-exchange effectively removes hardness from incoming water supplied, usually down to very low levels.