Humans’ consumption of salt has a very long story, with many changes, and has characteristics which have caused various nations to obtain the exclusive rights to its production, among which, have been the Chinese who have used salt since around 3,000 B.C.
In ancient Greece slaves were encouraged to consume salt. In Rome, soldiers received their wages in the form of salt, and, in England, the term “Slatary” (“Saltary”)and, in France, the term “Slarie” (“Salrie”) were later derived from this fact.
Salt has no cultural or political effect, but is recognized as an important mineral from the economic standpoint. In 1993, as far as tonnage is concerned, it ranked eighth in the world among mineral, fuel, and metal products. Salt is one of the most popular and recognized matters in the world, and, it is this very fact that has led to its being considered unimportant.
Of the 44 million tons of salt produced in the US, approximately 58 percent of them are used in the production of chemical products including hydrochloric acid, sodium carbonate, sodium metal,… In advanced countries, rock salt is exploited in the form of liquid. The empty spaces, created in the supply of salt, are suitable spots for the storage of petroleum composites and surplus radioactive matters. Salt is also found in the sea, lakes, and ponds in liquid or solidform.
The largest portion of salt in the world exists in the ocean waters in the form of liquid.The amount of salt present in ocean waters is between 1% and 5%, and its average amount is 3.5%. the changes in the amount of salt, in the seas and oceans, depends on the degree of evaporation, percent of ice, and the level of salts present in the river water. In coastal areas, where the rate of evaporation of sea water is high, salt is obtained from the sea.In the coasts of lakes, enclosed within the continent, with a high rate of evaporation, salt is produced, andthese lakes are suitable for obtaining salt. Solid salt reserves are found in the form of playa, layers of salt, and salt domes. Salt, along with sand and clay, is found in basins in hot and dry regions.During rainy seasons, soluble matters are carried by water, and, due to high rate of evaporation, these matters are driven toward the ground surface. Saline layers, along with clay shale, bog lime, clay, and anhydrites become clear. Saline domes are considered among important sources of salt.
The degree of purity of rock salt varies between 90% and 98.5% sodium chloride. The cases of usage of rock salts with a degree of purity less than 95, which is more common, are mainly in the cases of road surface ice and agricultural. Rock salts, with various percentages of purity, are used for different products, but, rock salt, with 98.4% purity is mainly used in the chemical industry, in chlor-alkali factories. Certain salts, with a high degree of purity, which is approximately 99.9%, are used as table salt or other household use.