Electrodialysis (ED)

Definition - What does Electrodialysis (ED) mean?

Electrodialysis (ED) is a membrane technique, during which ions are transported through a semipermeable membrane, under the influence of an electric potential. It is a very versatile technology for the separation of difficult mixtures.

ED is very useful for water treatment, aiding in the removal of mineral salts, sulfate, nitrate, etc. from brackish water and seawater. ED is also useful for wastewater reduction or recovery.

Some other applications of electrodialysis include:

  • Water reuse
  • Pre-demineralization
  • Food processing
  • Glycerin purification

Corrosionpedia explains Electrodialysis (ED)

Electrodialysis is a type of dialysis in which undesired ions are removed from solution by means of a direct current passing between two electrodes, one on each side of the membrane. It is used to desalinate or concentrate a liquid process stream containing salts. ED is a highly efficient method for separating and concentrating salts. It is also very useful in reducing salt content of process streams with high amounts of salts.

Electrodialysis uses electrical potential to drive the positive and negative ions of dissolved salts through separate semipermeable synthetic membrane filters. This process leaves fresh water between the filters.

Electrodialysis differs from pressure-driven membrane processes by utilizing electrical current as the main driving force in matter separation. This limits the possible solutes targeted for recovery separation to charged particles. The charged particles must be mobile, and the separation media must be able to transfer the electrical current with relatively low resistance.

Because the membranes used in electrodialysis have the ability to selectively transport ions having positive or negative charge and reject ions of the opposite charge, useful concentration, removal or separation of electrolytes can be achieved by electrodialysis. The ion-permeable membranes used in electrodialysis are essentially sheets of ion-exchange resins. They usually also contain other polymers to improve mechanical strength and flexibility. Cation-selective membranes consist of sulfonated polystyrene, while anion-selective membranes consist of polystyrene with quaternary ammonia.

Pretreatment is sometimes necessary before electrodialysis can take place, otherwise suspended solids can plug the membrane pores. These disturb the selective effect of the membrane.

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