With softening, only the ions of the hardeners calcium and magnesium are exchanged. With decarbonisation, on the other hand, the hydrogen carbonate salts of the calcium and magnesium, the so-called carbonate resins, are removed.
This process results in partial desalination of the water. Partial desalination occurs via filtration using a weakly acidic cation exchanger loaded with hydrogen ions.
Carbon dioxide results from decarbonisation and has to be removed in a downstream percolator. In many cases, decarbonisation is preceded by softening. Regeneration primarily occurs with hydrochloric acid.
The graphic shows the water matrix after decarbonisation.