Posts Tagged ‘ion exchange’

Water Deionizers And Deionization Solutions

Mixed Bed DeionizersThe Process of Deionization or Ion-exchange

In the context of water purification systems, 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. The impurity ions are taken up by the resin, which must be periodically regenerated to restore it to the original ionic form. (An ion is an atom or group of atoms with an electric charge. Positively-charged ions are called cations and are usually metals; negatively-charged ions are called anions and are usually non-metals).

The following ions are widely found in raw waters:

Cations Anions
Calcium (Ca2+) Chloride (Cl)
Magnesium (Mg2+) Bicarbonate (HCO3)
Sodium (Na+) Nitrate (NO3)
Potassium (K+) Carbonate (CO32-)
Iron (Fe2+) Sulfate (SO42-)

Ion Exchange Resins

There are two basic types of resin – cation-exchange and anion-exchange resins. Cation exchange resins will release Hydrogen (H+) ions or other positively charged ions in exchange for impurity cations present in the water. Anion exchange resins will release hydroxyl (OH) ions or other negatively charged ions in exchange for impurity anions present in the water.

The application of ion-exchange to water treatment and purification

There are three ways in which ion-exchange technology can be used in water treatment and purification: first, cation-exchange resins alone can be employed to soften water by base exchange; secondly, anion-exchange resins alone can be used for organic scavenging or nitrate removal; and thirdly, combinations of cation-exchange and anion-exchange resins can be used to remove virtually all the ionic impurities present in the feedwater, a process known as deionization. Water deionizers purification process results in water of exceptionally high quality.


For many laboratory and industrial applications, high-purity water which is essentially free from ionic contaminants is required. Water of this quality can be produced by deionization.The two most common types of deionization are:

  • Two-bed deionization
  • Mixed-bed deionization

Two-bed deionization

The two-bed deionizer consists of two vessels – one containing a cation-exchange resin in the hydrogen (H+) form and the other containing an anion resin in the hydroxyl (OH) form. Water flows through the cation column, whereupon all the cations are exchanged for hydrogen ions.To keep the water electrically balanced, for every monovalent cation, e.g. Na+, one hydrogen ion is exchanged and for every divalent cation, e.g. Ca2+, or Mg2+, two hydrogen ions are exchanged. The same principle applies when considering anion-exchange. The decationised water then flows through the anion column. This time, all the negatively charged ions are exchanged for hydroxide ions which then combine with the hydrogen ions to form water (H2O).

Mixed-bed deionization

In mixed-bed deionizers the cation-exchange and anion-exchange resins are intimately mixed and contained in a single pressure vessel. The thorough mixture of cation-exchangers and anion-exchangers in a single column makes a mixed-bed deionizer equivalent to a lengthy series of two-bed plants. As a result, the water quality obtained from a mixed-bed deionizer is appreciably higher than that produced by a two-bed plant.

Although more efficient in purifying the incoming feedwater, mixed-bed plants are more sensitive to impurities in the water supply and involve a more complicated regeneration process. Mixed-bed deionizers are normally used to ‘polish’ the water to higher levels of purity after it has been initially treated by either a two-bed deionizer or a reverse osmosis unit.


EDI Electrodeionization Systems remove ions from aqueous streams, typically in conjunction with reverse osmosis (RO) and other purification devices. Our high-quality deionization modules continually produce ultrapure water up to 18.2MW/cm. EDI may be run continuously or intermittently

More detail visit Reverse Osmosis Systems..

Home Filtration of Tap Water

It’s like clockwork. Every few days a new product is launched in the market with promises of being the best way of home filtration of tap water. How does one choose a water purifier out of this huge variety of choices?

To find out which purifiers are good for home filtration of tap water, we first need to understand the nature of the water being supplied in our homes.

This water contains a lot of impurities inside. Starting from chemicals like chlorine and chloramine, heavy metals like lead and asbestos to other chemicals like pesticides and prescription drugs – all of them are commonly found in tap water.

Types of Water Purifiers

The most basic kind of water filter that you can get is one containing just a carbon filter. These purifiers are able to remove the dirt in the water and simple chemicals like chlorine too. But anything more complex like metals or pesticides are beyond these systems – something more advanced is needed for them.

Water Distillers work on the principles of distillation. Basically the water to be purified is taken in a container which is then heated to vaporize the water. The water vapors are then collected in a separate container and cooled down to get purified water – since the impurities have been left behind in the first container.

This is good enough for removing dirt and metals from the water, but any kind of contaminants which have a boiling point similar to that of water will also get vaporized and will be present in the purified water too. Chlorine for example, cannot be removed from the water by these filters because of this very reason.

Reverse Osmosis Systems purifier have become quite popular lately. These systems purify the water by forcing it to pass through a semi permeable membrane. This membrane allows water to pass through but the contaminants which have a bigger molecular size than the pores of the membrane are blocked and left behind.

This technique is all right for removing the big impurities like dirt from the water. But chemicals like chlorine and pesticides, which have very small molecules, are not filtered out by these systems. Another disadvantage is that minerals like calcium and magnesium which are necessary for our body’s proper functioning are also removed from the water by these purifiers.

The best way for home filtration of tap water, is in fact to use a cutting edge filter that can remove all these contaminants, and preserve the minerals in the water at the same time. One with the combined technologies of carbon filtration, ion exchange and sub micron filtration.

Go to Water Purification Systems for more about water filtration.