Dissolved alkaline earth metals form the hardness. Main contributors are Calium and Magnesium. The dissociation forms of carbonic acid deliver the anions for the carbonate hardness.
Boiler scale consists mainly of a stable crystal form of calcium carbonate (Calcite). Scale occurs when saturation limits are exceeded. Less stable crystal forms like Aragonite are also possible.
Ion exchangers remove Calcium and Magnesium cations by substituting them with 2 moles Sodium anions from table salt. Sodium salts stay in the water. Calcium and Magnesium leave the ion exchangers with their waste water als chlorides.
Physical treatment of hardness aims at forming less stable crystal forms like Aragonite without removing hardness chemically.
Theory Water hardness
german  C. Meyer |
english C. Meyer |
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