Softening and decarbonisation
Softening refers to the removal of hardness-forming calcium and magnesium salts from water by the addition of soda or sodium phosphate or by ion exchangers.
Decarbonisation is achieved by the total or partial removal of hydrogen carbonate ions using weakly acidic cation exchange material. Calcium and magnesium are removed from the water and exchanged for each other. Released hydrogen ions react with the remaining hydrogen carbonates to form H₂O and CO₂, which can be outgassed. This partial desalination results in softening and decarbonisation. Sulphates, chlorides and nitrates remain unaffected. Elimination of carbonate hardness by calcium hydroxide (Ca(OH)₂) (=slaked lime) up to a hardness level of 5-6°dH in about 3h.
