Demineralization by electrodialysis

Abstract

Electrodialysis process using ion-exchange resins in the compartments has been an approach in demineralization of low saline solutions but the difficulty of maintaining and operating such systems is a major bottleneck. The current work has made use of the concept of conducting spacers of anion and cation-exchange type made from polyblends or interpolymers of polyethylene-styrene-divinylbenzene and placing them in juxtaposition with the respective membranes in the cell. The performance of a laboratory size electrodialysis unit using conducting and non-conducting spacers in two configurations and occupying 12.5 and 255 of cell volume and having 11 cell pairs with cross-sectional area of 66 cm 2 in desalting sodium chloride solutions of different concentration ranging from about 1000 ppm to 250 ppm down to 50 ppm or less has been reported. The output of the electrodialysis unit is raised by 2 to 3 times by using conducting spacers instead of the conventional non-conducting Spacers. It has been concluded that this approach offers a practical solution to bridge the gap between the conventional electro-dialysis desalination level of 500-1000 ppm and complete deionization using a scavenging mixed-bed ion-exchange column. The process is continuous and offers an economic alternative to conventional deionization by ion-exchange resin columns and can find application in concentration and recovery of valuable salts from dilute waste streams. This approach in demineralization also dispenses with the regenerant waste disposal problem encountered in ion-exchange resin demineralization plants.