Abstract
This is a review of studies on ion-exchange membranes preferentially permselective for monovalent ions, which are used for electrodialytic concentration of sea water. Divalent ions (Ca2+, Mg2+, and SO42-, etc.) should be rejected at the membrane surface not to permeate through the membranes, in order to inhibit formation of scale consisting of CaCO3 and CaSO4, etc. The preferential permselectivity of the cation-exchange membranes is endowed by forming a very thin layer of polycation on the membrane surface. In the case of the anion-exchange membranes, SO42- is less able to penetrate into the embranes than Cl-, and it is considered that the anion-exchange membranes are modified to make their structure more compact although the details are obscure.
