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Did
you know?
Reverse osmosis is the finest water filtration method known. This process will
allow the removal of particles as small as ions from a solution. It is used
to purify water and remove salts and other impurities in order to improve the
color, taste or properties of the fluid. R.O. uses a membrane that is semi-permeable,
allowing the fluid that is being purified to pass through it, while rejecting
other ions and contaminants from passing.
This technology uses a process
known as crossflow to allow the r.o. membrane to continually clean itself. This
is the reason of why an r.o. element can last many years before clogging or
need replacement. This
water purification process requires a driving force to push the fluid through
the membrane, and the most common force is household water pressure or pressure
from a booster pump. The higher the pressure, the larger the driving force and
efficiency.
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WATER
DEIONIZATION PROCESS EXPLAINED
The process
used for removal of all dissolved salts from water is referred to asdeionization.
Deionization requires the flow of water through two ion exchange materials
in order to effect the removal of all salt content.
Deionization. The terms demineralization and deionization are used somewhat interchangeably
by the industry. While the term demineralization is generally better understood,
deionization is especially apt.
The
passage of water through the first exchange material removes the calcium
and magnesium ions just as in the normal softening process.
Unlike home equipment, deionization units also remove all other positive
metallic ions in the process and replace them with hydrogen ions instead
of sodium ions.
As the metallic
ions in the water affix themselves to the exchange material, the latter
releases its hydrogen ions on a chemically equivalent basis. A sodium
ion (Na+) displaces one hydrogen ion (H+) from the exchanger; a calcium
ion (Ca++) displaces two hydrogen ions; a ferric ion (Fe+++) displaces
three hydrogen ions, etc. (Recall that home softeners also release two
sodium ions for every calcium or magnesium ion they attract.)
This exchange
of the hydrogen ions for metallic ions on an equivalent basis is chemical
necessity that permits the exchange material to maintain a balance of
electrical charges.
Now because of the relatively
high concentration of hydrogen ions, the solution is very acid.
At this point the deionization
process is just half complete. While the positive metallic ions have been
removed, the water now contains positive hydrogen ions, and the anions
originally in the raw water.
The partially treated
water now flows through a second unit, this time an anion exchange
material normally consists of replaceable hydroxyl anions and fixed irreplaceable
cations.
Now the negative ions
in solution (the anions) are absorbed into the anion exchange material.
Released in their place are hydroxyl anions.
WATER
CONTAINING VARIOUS MINERAL CONTAMINANTS ENTERING HERE
All that emerges from
such a two unit system is ion-free water. It still contains the positive
hydrogen ions released in the initial exchange plus the negative hydroxyl
ions released in the second exchange.
What has become of these
two ions? Through the magic of chemistry they have combined (positive
to negative) to produce water molecules which are in no way different
from the water in which they were produced.
The result of this two-stage
ion exchange process is water that is mineral-free.
Equipment for use in
the deionization process may be of several types. Available are both multiple
bed and single bed units. Multiple bed units have pairs of tanks, one
for the cation exchanger, the other for the anion exchanger. Single bed
units incorporate both the cation and anion exchangers, mixed in a single
tank.
Deionized water has
a wide range of uses in industry. Chemical production, pharmaceuticals,
electroplating, television tube production and leather goods processing
are among the many diversified applications for deionized water.
Efforts to produce mineral-free
water through multiple distillation have proved to be extremely complex
and require elaborate and costly equipment.
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