Water Deionizers: Process Explained
There are many ways to deionize water, some are small and simple, while others are large and complex. The method used will be determined considering the volume of water deionizers and the desired purity. Deionization or ion exchange is a rapid and reversible process, in which impurity ions present in the water are replaced by ions released by an ion-exchange resin. Ion exchange resin has an attraction for dissolved inorganics, which are typically about 95% of known water contaminants.
The resin must be periodically regenerated to restore it to the original ionic form. There are 2 basic types of resin:
- cation-exchange resins – release Hydrogen (H+) ions or other positively-charged ions in exchange for impurity cations
- anion-exchange resins – release Hydroxyl (OH-) ions or other negatively-charged ions in exchange for impurity anions
Calcium and Magnesium ions are removed when the water passes through the first ion exchange material. The exchange material releases its Hydrogen ions on a chemically-equivalent basis as metallic ions in the water affix themselves to the exchange material. A Sodium ion (Na+) displaces one Hydrogen ion (H+), a Calcium ion (Ca++) displaces 2 Hydrogen ions and a Ferric ion (Fe+++) displaces 3 Hydrogen ions and so on.
The solution will become very acid as a result of a relatively high concentration of hydrogen ions, and, at this point, the deionizaion process is only half complete. Water now contains positive Hydrogen ions and the anions originally in the water before treatment. The partially treated water will flow through a second unit with anion exchange material, which consists of replaceable Hydroxyl anions and fixed irreplaceable cations.
The negative ions in solution (anions) will be absorbed into the anion exchange material, which releases Hydroxyl anions. The result of the entire process will be ion-free water, which contains:
- positive Hydrogen ions released in the initial exchange
- negative Hydroxyl ions released in the second exchange
Now, through their combination, these ions have produced water molecules, which are not different in any ways from the water in which they were produced. This two-stage ion exchange process results in mineral-free water.
Deionization Advantages and Disadvantages
Advantages of deionization include:
- removes over 98% of contaminants
- no wasted water
- no need for electricity
- fast flow rate
- no need for a storage tank
- relatively inexpensive initial capital investment
- regenerable (service deionization)
Purified water is a must not only for human consumption but for a variety of other purposes, including meeting the requirements of medical, pharmacological, chemical and industrial applications.
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water, with the sole goal of producing water that fits a specific purpose.
Distilled water and deionized (DI) water are the most common forms of purified water. The first order of business is to determine what is meant by high purity for the proposed application, and we must consider suspended solids, dissolved solids, dissolved gases, organics and the biology of the water.
In general, the methods used to purify water include:
- physical processes (filtration, sedimentation, distillation)
- biological processes (slow sand filters, biologically active carbon)
- chemical processes (flocculation, chlorination)
- electromagnetic radiation processes (ultraviolet light)
If it is used in combination with activated carbon, deionization can remove organic chemicals and parasites, and can protect the resin from chlorine. The limitations of this process involve a diminished capacity when used on water supplies with a high mineral content.
Also, it does not effectively remove particles, pyrogens or bacteria. If the resin is not regenerated at proper intervals, contaminants can return to the water. Deionization beds can generate resin particles and culture bacteria over time. It also has high operating costs in the long run.
Next week, we will talk about water ionizers, the process and the advantages and disadvantages of owning such a water treatment system. Contact us at 760.734.5787 and talk with one of our water experts today!