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The bed of
the softener consists of ion exchange material. The
softening material is made up of permanent insoluble
anions to which sodium cations are chemically bonded.
The hard water enters the exchange tank. As it flows
through it, the hardness cations are drawn to the anions
of the exchange material. In the process the hardness
minerals are absorbed and a chemically equivalent number
of sodium ions are released into the water. In brief,
harmless sodium ions have replaced the trouble-producing
hardness ions.
After a vast number of hardness ions in the water
have 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, though in actual practice a small number of
sodium ions remain in the softening material after the
unit is exhausted.
If no new chemical reaction is set into operation at
this point, the incoming hardness ions flow untouched
through the unit. Recharging or regeneration becomes
necessary. 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 concentrated solution. In this way the
affinity of the exchanger for the hardness ions is
overcome.
What occurs in all examples of ion exchange is a
"swap" or balanced exchange of ions. The
hardness ions are not destroyed. They have merely been
replaced by a chemically equivalent amount of sodium
ions. When the unit is regenerated, these hardness ions
are washed down the drain.
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