Deionized water is water that has had all of the ionized particles removed. This is important because, once you remove any organic materials from the water supply, the vast majority of dissolved impurities in modern water supplies are ions such as calcium, sodium, chlorides, etc. An ion is a molecule that has a positive or a negative charge; iron ions, for example, have a positive charge. One of the ways to effectively purify water, then, is to remove these ions and replace them with hydrogen (H+) and hydroxyl (OH-) ions, which combine to make water. Check out our page about what DI water is to learn more terms and definitions related to deionization.
Before passing through a deionization (DI) system, water is usually filtered and often pushed through a reverse osmosis (RO) membrane. These pre-filtering steps do a good job of removing the organic matter and a majority of other contaminants. That means that the water is very clean before it enters the DI system. Check out our infographic on how RO and DI can work together.
Two ion-exchange resins are used to deionize the water. Positively charged ions (cations) and negatively charged ions (anions) are exchanged for hydrogen (H+) and hydroxyl (OH-) ions, respectively, due to the resin's greater affinity for other ions. After passing through both types of resin at least once, all that's left is highly purified water. Once depleted of exchange capacity, the resin bed is regenerated with concentrated acid and caustic, which strips away accumulated ions through physical displacement, leaving hydrogen or hydroxyl ions in their place.
DEIONIZED WATER AND ITS USES
For many years, the process for how to make deionized water was complicated and expensive. With the introduction of modern deionization resins, mixed bed resin media, and removable DI resin cartridges, however, it's become much more affordable for businesses to make high purity water on site. Deionized water uses include aquariums and fish tanks, electronics manufacturing, pharmaceutical and laboratory production, and much more. Even car washes can use DI water for the final rinse!
TYPES OF DEIONIZER
Once you know to make deionized water and what deionized water is used for, you need to understand the different deionizer types. Each of these deionizer systems is effective, but some are better suited to specific industries or purposes.
There are four basic types of deionizers:
Portable exchange tanks
A two-bed system uses separate cation and anion resin beds. Mixed-bed deionizers utilize both resins in the same vessel. The highest quality water is produced by mixed-bed deionizers, but two-bed deionizers have a larger capacity. Both cartridge and portable exchange tank units can be used until the resin is exhausted, after which it is replaced. Automatic units are permanent fixtures and the resin is regenerated on site. Continuous deionizers, mainly used in labs for polishing, do not require regeneration.