The water demineralization process is based on the properties of the resins (ion exchangers) to remove unwanted ions from water, replacing them with others. This treatment uses two types of ion exchange resins, cationic and anionic, with hydrogen (H+) for the cationic ones and oxidrile (OH- ) for the anionic ones, as functional group to be replaced with other ions which determine water salinity. The contact between the ion exchange resins and water occurs in pressure vessels supplied with perfectly filtered water: the operation of the ion exchange resins, in fact, can be impaired if substances in suspension in the water deposit on the resin beds. The demineralizers are designed so as to ensure the uniform flow of water and regeneration agents through the resin bed. The cationic and anionic resins have the capacity to be regenerated, thus, when they are exhausted, the DEMI S system lets hydrochloric acid flow in the column with cationic resins and lets sodium hydroxide flow in the column with anionic resins, restoring resin work.
The electrodemineralization (EDI – electronic demineralization, also known as CDI – continuos demineralization) is an evolution of the process of demineralization ion exchange mixed bed. EDI in the cations and anions present in the water are exchanged on a resin with ions H + and OH-, producing demineralized water, the difference with the traditional method is that the process is continuous, since the resin is regenerated for means of semipermeable membranes by imposing an electric field current. There is therefore no longer necessary to interrupt the normal operation of the plant to carry out the chemical regeneration with hydrochloric acid and soda. The ions H + and OH-are generated on-site for dissociation of the water molecule. The water is fed in pretratatta compartments filled with resin and delimited by membranes selectively permeable to cations and anions. At the end of these compartments are positioned electrodes that allow the migration of ions through these membranes adjacent to the compartments where it’s collected a concentrated solution. This solution is removed by imposing a flow rate of movement and a purge.