Elektrodialysis

Electrodialysis is an electrochemical process whereby electrically charged particles, ions, are transported from a raw solution (retentate, diluate) into a more concentrated solution (permeate, concentrate) through ion-selective membranes by applying an electric field. When a salt solution is under the influence of an electric field, as is the case in an electrodialysis module, the charge carriers in the solution come into motion. This means that the negatively charged anions migrate towards the anode and the positively charged cations towards the cathode.

In order to separate salts from a solution, ion-selective membranes, through which only one type of ion can permeate in an ideal case, are arranged in the solution perpendicular to the electric field. Thus negatively charged particles (anions) can pass through an anion exchange membrane on their way to the anode but are selectively retained by the upstream cation exchange membrane. This separation stage results in a concentration of electrolytes in the so-called concentrate loop and a depletion of charge carriers in the so-called diluate loop.

For example, electrodialysis is applied on an industrial scale for the production of table salt from seawater, for the production of drinking water from brackish water, for the treatment of boiler-feed water and the desalination of whey.

However, the key advantages of electrodialysis come into effect particularly in applications for selective substance removal, as for example in

  • Nitrogen removal from drinking water (nitrate, ammonium)
  • Desalination of organic substances
  • Concentration of salts, acids and bases
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