Ion-exchange membrane

An ion-exchange membrane is a

Ion-exchange membranes are therefore electrically conductive. They are often used in desalination and chemical recovery applications, moving ions from one solution to another with little passage of water.[2]

Important examples of ion-exchange membranes include the

Structure and composition

An ion-exchange membrane is generally made of

The so-called heterogeneous ion-exchange membranes have low cost and a thicker composition with higher resistance and a rough surface that can be subject to fouling. Homogeneous membranes are more expensive, but have a thinner composition with lower resistance and a smooth surface, less susceptible to fouling. Homogeneous membrane surfaces can be modified to alter the membrane permselectivity to protons, monovalent ions, and divalent ions.^[3]

Selectivity

The selectivity of an ion-exchange membrane is due to

The selectivity to the transport of ions of opposite charges is called its permselectivity.^[3]

Applications

Ion-exchange membranes are traditionally used in electrodialysis or diffusion dialysis by means of an electrical potential or concentration gradient, respectively, to selectively transport cationic and anionic species. When applied in an electrodialysis desalination process, anion- and cation-exchange membranes are typically arranged in an alternating pattern between two electrodes (an anode and a cathode) within the electrodialysis stack. A galvanic potential is supplied as a voltage generated at the electrodes.^[3]

A typical industrial electrodialysis stack consists of two chambers: a product-water chamber and a concentrate-reject chamber. During stack operation, salts are transferred from the product to the concentrate. As a result, the reject stream is concentrated up while the product stream is desalted.^[3]

Exemplary applications of ion-exchange membranes utilized in electrodialysis and EDR include seawater desalination, industrial wastewater treatment of highly scaling waters, food and beverage production, and other industrial wastewaters.^[3]

References