TABLE OF CONTENTS The most important and commonly used makeup treatment methods are ion exchange and reverse osmosis. These technologies are mature. Other technologies that have begun to emerge and show promise include electrodialysis reversal (EDR) and electrodeionization (ED I).
The ion exchange process was first truly developed in the early 1900s by a German scientist, Gans, who used synthetic zeolites (sodium aluminum silicates) to exchange calcium and magnesium ions for sodium. This discovery led to the development of water softeners. Then, in the 1930s and 1940s, plastic synthetic ion exchange resins became available, which led to the industry that we know today.
The ion exchange process is dependent upon the efficiency with which water can flow through the exchange media and contact exchange sites. To obtain maximum efficiency, the media must have several properties. These include:
It must have the maximum number of exchange sites
It must have structural integrity
Easy loading of the media into the reaction vessel is required
It must be of reasonable cost
It must be capable of being regenerated efficiently
Small spherical plastic beads have proven to be best for incorporating these factors. The beads behave some what like a fluid, which makes them easier to handle and load/unload into exchange vessels. By far, the most common material from which ion exchange resins are fabricated is polystyrene cross-linked with divinylbenzene (Fig. 5-5), although acrylics are used in some instances. Beads are manufactured in an emulsion process, which allows the polystyrene-divnylbenzene...
