Pure Salt
Pure salt is almost pure sodium chloride and has all its inherent properties. Although it is in a highly purified state, it still contains traces of magnesium, which can absorb moisture from the atmosphere and render the salt lumpy. Pure salt comes in the form of small colourless crystals or a white granular powder, free from visible contamination with clay, grit and other extraneous adulterants and impurities. Care is taken during manufacture, by modifying its crystalline nature, to see that it does not cake hard during storage.
Specification: IS-797-1982 grade -1 (reaffirmed 1988)
| Characteristics | Requirements | Units |
|---|---|---|
| Moisture | 1.0 on dry basis | %, max |
| Sodium chloride (as NaCl) | 99.5 | %, max |
| Matter insoluble in water | 0.05 | %, max |
| Calcium salts (as Ca) | 0.03 | %, max |
| Magnesium salts (as Mg) | 0.01 | %, max |
| Sulphates (as SO4) | 0.2 | %, max |
| Iron compounds (as Fe) | 10 | PPM**, max |
| ** PPM is parts per million; to convert % to PPM, multiply % into 10,000; 1 PPM is 1/ 10,00,000. |
Storage
Pure salt should be stored in a dry place and away from any direct contact with humid air. Also, the sacks should not be piled more than about 12 bags high. Hard lump formation can then be avoided in most cases.
Salt, when it comes into contact with air of relative humidity of about 75 per cent, will absorb moisture and turn lumpy. Conversely, any moisture in the salt will be lost if the relative humidity is below 75 per cent. This is the inherent property of salt. If dry salt is allowed to absorb moisture, a thin film of saturated brine is formed on the surface of the crystals.
If salt is then allowed to dry, the water evaporates from the brine, cementing individual crystals together and causing a caking of the mass. Similarly, in a dry store un-dried salt will dry out again, leading to cakin
Applications
Pure salt has a number of industrial applications. It is converted to brine, which is then used to make caustic soda. The industrial uses of pure salt include its vital application in the chlor-alkali industry, and in the manufacture of soda ash and iodised salt. In the chlor-alkali industry, a host of vital chemicals are manufactured using salt and brine.
As an industrially pure grade of sodium chloride, pure salt finds application in industries which need to use it in a solid form. It is used in the manufacture of sodium hydrosulphate, salting-out of dyes and as a bulking agent in optical whiteners. It can also be used in the dairy industry after bacteriological immunisation.
Packing
- 50-kg laminated HDPE bags with a polythene liner.