Electro deionization A process that removes ionizable species from liquids using an electrical potential to influence ion transport. The most general term for electrochemical deionization processes. It can be a batch or a continuous process. Electrical deionization is actually a combination of • Ion exchange membranes (Anion membranes and Cation membranes) • Ion exchange resins • DC electric potential Electricity is the driving force for this whole process of electro deionization. Ions transferred from product (dilute) compartments to reject (concentrate) compartments. Anion membranes only allow anions to diffuse through it and it does not allow the cations to pass through it. Similarly Cation membranes allow cations to diffuse through it and it does not allow anion to pass through it. Electro deionization remove Dissolved salts, Carbon dioxide (CO2), Dissolved silica, Ammonia (NH3) and some organics. Salts in water naturally occur as charged ions anions (-) Cl- and cations (+) Na+. When DC potential is applied the system anions moves to anod and cations moved to cathode means salts are moved to opposite electrodes. Electricity and ion exchange membranes create dilute solution and concentrated solution. Salts transfer out of product stream and trapped in reject stream. Ion exchange resins enhance the transfer of ions in dilute solution under influence of electric field. Resins are orders of magnitude more conductive than solution. They catalyze splitting of water into H+ & OH- which are used for the regeneration of ion exchange resins. The most important property is transport ion conduction more important Film diffusion and Particle diffusion Resins are continuously regenerated with hydrogen and hydroxide forms. Weakly ionized compounds are removed.

Bachelor 09 November 2009