Water Treatment-Water demineralization

Demineralised water is used in many different industrial processes, in several industries: pharmaceutical , chemical,  food, and processing ones, etc.  Water is demineralised by treatment with two different resin containing columns : an acid cation exchange resin, and a basic anion exchange resin.

The type of resin to be used should be defined by the resin producer depending on the requirements. These ion exchange resins need to be regenerated periodically depending on water and resin characteristics. The products regenerating these resins are caustic soda for the anion exchange resin and hydrochloric acid for the cation exchange resin.

Regeneration processes must be defined by the resin producer, but, in general, three steps for the anion resin can be mentioned:

1. Backwash rinsing with water to eliminate fines and any particle coming from the water flow,
2. Injection of a 4% aqueous caustic soda solution in Mg²⁺ and Ca²⁺  free water to avoid precipitation on the resin bed, 
3. Rinsing with about 3 times the resin volumes to eliminate the caustic soda in two progressive phases, a slow one to eliminate the greater part of the caustic soda and a fast one to eliminate the last residue.

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