Sodium chloride is the basic raw material for many chemical compounds
such as NaOH, Na2CO3, Na2SO4, HCl,
Na2PO4, Sodium Chlorate, Sodium Chlorite and its source
of many other products through its derivatives. Practically all the chlorine
products in the world is manufactured by electrolysis of Sodium Chloride (NaCl),
a common salt is manufactured in three different ways;
evaporation of sea water
- Mining of
- From well
1. From saturated Brine by Multiple Effect
contains water 73.5%, sodium chloride 26.3%, calcium sulphate 0.12%, calcium
chloride 0.003%, magnesium chloride 0.007%.
sheet of process is given below;
- The Brine is
first aerated to remove most of the H2S.
- Addition of
chloride will remove H2S by displacement reaction.
- Brine is then
pumped to settling tank where it is treated with caustic soda and soda ash to
remove calcium, magnesium and ferric ions. Caustic soda and soda ash are
blended in the miser to be taken to settling tank.
- In the
Multiple Effect Evaporator (MEE) water is removed and salt crystals are removed
- The slurry is
sent to washer, where the salt crystals are washed with fresh brine.
- The washed
slurry is filtered, mother liquor is return to the evaporators and salt
crystals from the filter are dried and screened.
- Salt thus
produced from the typical brine is 99.8% purity or even greater.
- The finest
grade (some times made by grinding) is a flour salt, the next coarsest is table
salt and finally the industrial salt.
salt has the following composition;
Iodide (KI) : 0.01%
- Stabilizer Na2CO3 : 0.1%
- Sodium Thio Sulphate
2. From Saturated Brine by Open Pan
- Salt in the
form of hopper-like crystal (grainer salt) is made by causing the salt crystal
to form on the surface of brine held in an open pan.
- The grainer
is a flat open pan 4.5 to 6.0 m width and 45 – 60 m long and about 60cm deep.
Beneath the pan steam coils system provided for reciprocating the flakes for
- The saturated
brine mixed with circulating brine from the grinder is treated to 1200C
at which temperature calcium sulphate is soluble and remove at that
- The precipitated
calcium sulphate is removed from gravellier which consist of bed of stones.
- The purified
brine is flash cooled to remove the remaining calcium sulphate.
- The slurry is
then pumped to the grinders where evaporation takes place at 960C.
- A wet salt
crystals obtain from the grinder are centrifuged, dried and screened.
- When the
incoming brine has been treated salt of 99.98% sodium chloride can be obtained.
3. From Rock Salt Mining
About 35% of
salt produced comes from mines of 8 different stages which are operated to
produce rock salt. The salt deposits varying color from light reddish brown to
half grey. The purity is 98.5%. After the rock is blasted loose they are
crushed and then screened at the surface level. The remaining process is the
series of grinding, screening to obtain the salft of crystal of various sizes.
4. From Sea Water by Solar Evaporation
exceeds precipitation, the statistics of 125mm of rain corresponding to 840mm
By-products of Normal Salt (also called as value added products)
Manufacture of sodium sulfates from
salt and sulfuric acid
2NaCl + H2SO4
---> 2HCl + Na2SO4
+ 10H2O -> Na2SO4 + 2HCl
Di-oxide, air, steam are passed over specially prepared porous common salt. The
reaction is as follows;
2NaCl + SO2
+ 1/2O2 + H2O ---> Na2SO4