Salt has multifarious used in the lives of man. Not only for cooking, salt is used as preservatives for fish, meat and a host of other items. Salt is an important ingredient in the chemical industry for the manufacture of sodium bicarbonate, caustic soda, sodium sulphate, hydrochloric acid, chlorine, bleaching powder, different chlorates and other sodium and chlorine compounds. Apart from these, salt is also used in the making of soap, paint, artificial rubber and for the purification of water. In the field of metallurgy, salt has found its use in temperature-regulation, metal-smelting and purification. In the field of agriculture, salt is utilized in the preparation of animal fodder and for farming. In the cold regions, salt is being used in removing ice from the town area.
Common salt is known as halite in its natural form, its chemical composition being NaCl(Na 39.34 per cent; Cl 60.66 per cent). Halite is easily recognized from its salty taste, water solubility and cubic crystal for. In nature, common salt is found in plenty; there is no dearth of it. The consumption of salt (mainly sea-salt) for edible and industrial purposes in India in 1986 was 7.3 million tons.
Origin: In nature salt originates in three ways:
- Salt is found as rock salt, occurring as bedded sedimentary strata, at times associated with gypsum. This type of rock salt forms as a result of evaporation of inland sea or lagoon. Sometimes salt is found on the top of oil-bearing dome occurring as salt-plug.
- Salt deposit form by the evaporation of shallow lake in the desert area.
- In recent period, salt is recovered from salt lakes, sea or underground brine solutions.
Occurrence in India: In India, salt is available in plenty.
Himachal Pradesh: In Mandi district, rock-salt beds are found in association with the limestone, shale and sandstone belonging to the Sabathu or the Krol Group of rocks. The salt is deep brown, opaque and contains unwanted clayey impurities, although at times transparent cubic crystals of rock-salt are found. India’s total production of rock-salt comes from this state. The rock-salt produced from the Mandi mines is not suitable for human consumption as the content of sodium chloride is low. The salt is generally used as cattle feed.
Rajasthan: Salt is available from a few shallow lakes in the arid region, the most important among them being the Sambhar lake (Jaipur district), Didwana lake (Sikar district) and Panchpadro lake (Jodhpur district). A group of geologist believes that salt had been deposited in the latter lake driven by air from the Runn area of Kachchh (Gujarat). But another group of geologists say that these lakes are remnants of the ancient Ththys Sea and thus the sea salt had been impregnated in the soil.
The latest idea about the salt in the Sambhar Lake ascribed its origin to the biochemical activites. In the rainy season, the salt thus formed gets dissolved in the lake water, fed by four tributaries. It has been found that the salty lake-water contains about 86 per cent dissolved salt and the clayey deposit under the water up to a depth of 3 meters contains 5.21 per cent NaCl (common salt). Apart from sodium chloride, the salt water contains sodium sulphate and sodium carbonate, which are also recovered from the water for commercial use.
Other States: Salt is recovered from the salt-water wells of the Khargoja and Kuda area in Kachchh, Gujarat. In Assam, salt is also recovered from the salt-water springs of Jorhat and Sadiya districts as well as from the salt-water wells of Cachar district (Assam) and Manipur.
Efforts are also being made to recover salt from the salty ground-water in Gurgaon and Rohtak districts of Haryana.