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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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CONTINUED...
MORE ON WATER SOFTENING AND ION EXCHANGE
Now
when this calcium bicarbonate in solution flows through
the exchange material in the softener, the chemical change which occurs
is diagrammed below.
After a vast number
of hardness ions in the water has become affixed to the softening material
through the attraction of positive and negative charges, and most of the
sodium ions have been released, the unit can no longer soften the water.
It has become temporarily exhausted.
In actual practice,
a small number of sodium ions remains on the softening material after
the unit is exhausted. If no new chemical reaction is set into operation
at this point, the incoming calcium bicarbonate ions flow untouched
through the unit.
Just
one of the ions causing hardness is shown for sake of clarity in diagramming.
Actually, most water supplies contain a number of various hardness ions.
The same process in each case applies equally in their removal from the
water.
Water
Entering Softner:
(1)
The calcium ions in the water enter the ion exchange column. Here the
waters pass through the bed of the softening material.
(2)
The softening material consists of fixed irreplaceable anions. Affixed,
that is, chemically bonded to them are mobile, replaceable cations of
sodium.
(3)
As the softening material anions have a greater affinity for the calcium
ions than for sodium ions, it attracts them. In the process the calcium
ions "knock" the sodium ions off the exchange material. As this
continues, the exchange or softening material becomes loaded with calcium
ions. Note that two sodium ions are released for each of the calcium ions
absorbed by the softener.
Water
Leaving Softner:
Water that
contains calcium ions as it enters the softener will have a chemically
equivalent amount of sodium ions in it on leaving the softener.
(4) After
a certain prescribed amount of water has gone through the unit, the calcium
ions will replace all but a small percentage
of the sodium ions in the softener At
this point, the softener is considered (Unit
is now exhausted
and requires regeneration).
(5) Now a rich brine solution is introduced into the softener by backwashing.
Note: to recharge a softener a concentrated solution of the regenerant
(sodium chloride) is accumulated calcium ions free of the softening material.
(6)
The calcium ions and excess
brine solution are rinsed away.
(7) When this process
is completed, the unit is again charged with sodium ions and is ready to
continue the process of softening the water.
RECHARGING
OR REGENERATION
Recharging
or regeneration is necessary at this point. To do this a reverse ion exchange
operation is now put into motion. In this reverse process, it is necessary
to bombard the exchange material with the original type of cations in
a concentrated solution. The affinity of the exchanger for the hardness
ions is overcome by the use of a relatively strong solution of sodium
ions. Generally, sodium chloride in a concentrated solution is used for
this purpose. What occurs in all examples of ion exchange is a "swap"
or balanced exchange of ions.
The
calcium ions in the softening process are not destroyed. They have merely
been replaced in the water by a chemically equivalent amount of sodium
ions. The same type of balanced exchange occurs with whatever other hardness
minerals that are removed from water.
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