Deionizers
CWG is a leading provider of deionization
solutions. Our water deionizers are rugged,
pre-engineered, pre-assembled, standardized
units that minimize expensive installation and
start-up costs. We have designed our
Deionization systems to maximize the efficiency
and repeatability of the unit during the service
and regeneration modes
The Process of
Deionization or Ion-exchange
In the context of water purification,
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.
Deionization
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.
Electrodeionization
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
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