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3
Description
3.1
Introduction to softeners
3.1.1
Softening principles
Softening is an ion exchange process where the hard ions are getting exchange by soft ions,
typically sodium or potassium. This is achieved by placing the water in contact with an ion
exchange resin and ensuring the contact time is appropriate for the flow rate to produce.
The basic chemistry of softening resins is very simple: the resin is made of small polymer beads
with chemical functionality that selectively captures the divalent ions (such as Ca
hardness ions) and releases in exchange less tightly held monovalent ions, usually sodium (Na
or less frequently potassium. Here below is shown the chemical reactions mechanism for
softening:
Hardness
The
means that under certain conditions, the reactions can be reversed. This is due to the
equilibrium between the water composition and the amount of hardness that can be removed. This
reverse reaction is observed at different kinetics and at high monovalent ions concentration.
Usually for softening this conditions are obtained using concentrated NaCl (or KCl) solutions that
are put in contact with the resin. This is called regeneration:
Saturated
Exhausted resin
brine
bead
The service and regeneration reaction can be done over and over, so softening systems last years.
A softener consists of different components:
• a tank, filled with softening resin;
• a valve, that will direct the inlet water flow on the resin bed so that the softening or
regeneration reaction can take place;
• a timer, that will control when the regeneration phases have to be done;
Ref. MKT-IM-037 / D - 25.10.2021
Resin bead
Installer manual Evolio 255 740-760 - Description
Exhausted resin
bead
Regenerated
Waste
resin bead
2+
2+
and Mg
-
+
)
Soft water
Excess
salt
15 / 90
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