Water-softening processes remove hardness from water, which is categorised according to the total content of calcium and magnesium ions present.
The salts that cause hardness are usually present in water as sulphates, chlorides, nitrates (permanent hardness), carbonates or hydrogen carbonates (temporary hardness), which are generally soluble but precipitate as a result of heating or evaporation, forming limescale or similar. The presence of these substances damages industrial plants due to their corrosive action and the scaling they produce.
Water can be softened to remove hardness using lime or resins.
To treat water with hardness which is totally or partially of a carbon nature (temporary hardness), the most frequently adopted treatment process is lime-soda softening, which enables a general reduction in water salinity with the precipitation of calcium and magnesium carbonates.
The process is carried out in purification systems with scraper bridges, complete with a sludge removal and dewatering system and suitable dosing of reactants.
If the hardness is mainly of a permanent nature it is dealt with using resin plants, which still also reduce carbon hardness.
In this case water-softening filters are used (manual or automatic) whereby the water is filtered over a bed of ionic-exchange resins, which consist of a polymer with sodium (Na+) ions that are exchanged with the passing calcium and magnesium ions in the water. The calcium and magnesium ions are then retained by the resin, which is subsequently regenerated for treatment with brine.
Resin plants are provided complete with valves, instrumentation, regeneration unit, and pre-assembled skid solutions on request.