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Deionization Systems |
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| Most soluble chemical compounds, when dissolved in water, become ionized; that is, their molecules dissociate into positively and negatively charged components called ions. Since Ion Exchange resins work by exchanging ions, they can be used to clean water of all impurities. Cation resin is used to exchange hydrogen ions (H+) for all positive ions and anion resin is used to exchange hydroxide ions (OH-) for any negative ions. The H+ and OH- ions then combine to form H2O, leaving nothing but pure water in the final product. | |
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Separate Bed DI SystemsIn this kind of DI system, there are separate Ion Exchange columns holding either cation resin or anion resin. The resins must be kept separate because the regenerant for one will completely load the other. For instance, the cation resin must be regenerated with a strong acid. Strong acid would completely load up every site in the anion resin, leaving no sites for ion exchange with the ions we need to remove. |
| The system pictured at the left includes an evaporator to concentrate the waste from the DI unit. Since cation resin is regenerated with acid and anion resin is regenerated with caustic, the two regenerants can be mixed and end up almost neutral. The resulting mixture is treated by the evaporator to remove as much water as possible, reducing the volume needing disposal. | |
MixedBed DI SystemsAlthough using separate anion and cation resin beds will produce fairly pure water, there are some leftover products of the two exchange processes that still contaminate the water. Water can be made even purer by mixing the two different resins together. The resins must still be separated for the regeneration process, however. This is done by using resins with two different densities and then using a controlled flow of water to float the lighter resin to the top. |
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| A mixed Bed DI system can produce water approximately one order of magnitude purer than Two Bed DI systems. | |
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Last updated 3-22-07