Ion exchange
is a Reverseible process in which ions are
released from an insoluble permanent material
(resin) in exchange for other ions in a surrounding
solution; the direction of the exchange depends
upon the affinities of the ion exchanger for
the ions present, and the concentration of
the ions in the solution.
The ion exchange process:
In water treatment this process adds and
removes ions from water. In general the
resin is used as the exchange site.
Resins are basically classified as either
cationic or anionic. The choice of resin
for a particular application will depend
on the ion or ions to be removed and recovered,
and the chemistry of the process.
In (demineralization, deionisation), for
example, bicarbonate [HCO3-], chloride [CL-]
and sulphate [SO4--] anions are removed
from the solution in exchange for a chemically
equivalent number of hydroxide anions [OH-]from
the anion exchange resin.
Further in demineralization , for example,
calcium [Ca++], magnesium [ Mg++] and potassium
[K+] anions are removed and exchanged for
a chemically equivalent number of hydrogen
cations [H+] from the cation exchange resin.
In softening, calcium [Ca++] and magnesium
[ Mg++] are removed from a solution in exchange
for a chemically equivalent number of sodium
anions[ Na+] from the anion exchange resin.
Mixed bed ion exchanger is used for total
demineralization of water. Here both a cation
exchanger and an anion exchanger are incorporated
into the same
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