PYROCRYSTAL S.r.l. projects, manufactures and install on a turnkey basis, ionic
exchange demineralization plants on one or more lines.
If necessary could be also installed pre-treatment plants such as
dual-media filters quartz-anthracite, or active carbons filters. For the final
polishing are generally employed mixed-bed units.
It has been observed that organic compounds could react selectivally towards
anions and cations, fixing to itself in substitution of one radical, and then go
back to the originary form through a substitution process.
Those compounds, of different nature, are called ionic exchange resins and are
employed in the removal of positive and negative ions from different nature
dissolvents. They look like little spheres having variable diameters from half
to two millimetres.
It is, so, possible to conceive a system to remove salts by-means those resins.
A ionic exchange demineralizer is constituted by one or more chambers, filled
with one or more ionic exchange resins kind, through which the fluid to be
treated will flow.
Considering the (most common) case of water, the demineralizer is constituted of
a first chamber, called cationic exchanger, in which the metallic ions react
with resins, being fixed to them, and then being substituted by hydrogen atoms,
CaSO4 + 2 H+ ------> H2SO4 + Ca++
It will be obtained a strongly acid water, practically free from metallic ions.
The exchanger is called cationic as in the water will remain cations;
incorrect term but of common use.
If inlet water owns much bicarbonates, we'll obtain the following reaction:
2 NaHCO3 + H+ ------> Na2CO3 + CO2 + H2O
As Carbon Dioxide could be separated through physical media, on convenience, the
water flooding from the cationic exchanger could pass through a decarbonatation
tower, where the Carbon Dioxide will be separated in counter-current air flow.
Water coming from the cationic exchanger, eventually de-gazed, will flow into
the anionic exchanger, where the acid radicals are exchanged with hydroxyls OH+,
and the reaction is:
H2SO4 + 2 OH+ ------> 2 H2O + SO4--
In this way also acid radicals have been removed, obtaining pure water.
In some cases, anionic and cationic resins are mixed, and the treatment comes up
into one only chamber. This kind of equipment is called mixed-bed, and has
an inferior efficiency in terms of mass exchange, but much superior in terms of
Resins, cationic and anionic, has a certain number of radicals available for the
exchange; once ended, the exchange ends. It is possible to reconstitute the
radicals through a chemical process called regeneration. After a counter-current
wash to remove any eventual solid in suspension and resins powder produced
during working process, resins are put in contact with an active solution:
- in case of cationic resin, a solution of strong acid (more frequently
Hydrochlorate, to times Sulfuric or, exceptionally of other nature) and will
obtain the following reaction (supposing Calcium removal):
Ca++ + 2 HCl ------> CaC2 + 2 H+
in case of anionic resin, a strong base (frequently Caustic Soda, at
times ammonia) to obtain the following reaction:
SO4-- + 2 NaOH ------> Na2SO4 + 2 OH+.
Using HCl and NaOH, it will be obtained an eluate composed by chlorides of
different metals and Sodium salts.