Common salt is a vital ingredient of human
food and an important raw material for various industries. Salt,
mainly, is produced by solar evaporation of sea water or saline
water. Salt thus produced is called Raw Solar salt. The chemical
name of pure salt is Sodium Chloride (NaC1) This salt contains a
large percentage of physical and chemical impurities.
Insolubles, like, dirt, clay and other extraneous material form
part of physical impurities. Soluble impurities are mostly
present as calcium and magnesium salts. The raw common salt also
contains moisture varying from 4 to 6 %.
Common salt is recognized all over world as a stable vehicle in
which to carry iodine. Iodine deficiency is one of the major
nutritional problem. Its most simple manifestation is goiter, a
swelling of the thyroid gland, which often grows to large
proportion. But much more serious than goiter are the mental and
other developmental disorders caused by iodine deficiency.
The success of salt iodisation, however, depends primarily on
the quality of salt to be iodized. Moisture and impurities in
salt tend to destroy its iodine content. So, mixing iodine
compound with salt is not the solution. Salt has to be refined
and dried to enable it to retain the iodine content put into it.
So, refining and drying ensure.
- Iodine content in edible salt
- Purity and Hygiene
- Convenience in usage as it becomes free flowing
- Good visual appearance because of dryness and whiteness
The concept of salt being used as a carrier
for imparting iodine is being extended to impart other micro
nutrients and tasty flavors & ingredients. Only refined and
dryed salt is capable of carrying and retaining such ingredients
and flavours.
Refining of salt is also essential for its use as raw material
in chlor- alkali industries. Use of dryed refined salt in place
of dirty and unhygienic solar salt in industries, like, food
processing, textile, detergent, dyes, chemicals and others,
enhances quality and appearance of their products.
Refining of salt is done mainly by two processes :-
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Mechanical Refining |
Vacuum Crystallization |
The basic difference in the two processes is that in a
mechanical salt refining plant, raw salt is washed with
saturated solution of salt whereas in a vacuum salt refining
plant, salt is completely dissolved and then after purification
is recrystallized.
Vacuum crystallization process can give the purest grade of
salt, but the cost of setting up of a vacuum crystallization
plant is many times higher than the cost of setting up of a
mechanical refining plant of comparable capacity. Hence, the
choice of salt refining & processing machinery would depend
upon the purity requirement and end use of the refined salt.
