HOW SALT MANUFACTURED
                          
The Solar Evaporation Cultivation

The oldest known method of salt production is solar evaporation. Believed to have originated with the people who lived along the shores of the Seas, solar evaporation remains an effective method of producing salt. It is still done in much the same way as in ancient times, only on a much larger and more efficient scale. Salt water is let into shallow ponds where the sun evaporates the water, concentrating the salt in the brine.
As the specific gravity of the brine increases, it is moved from basin to basin to promote fractional crystallization and remove most of the impurities until, finally, the water has entirely evaporated. The deposit of salt which is left behind can now be gathered and processed. Although confined to warm, windy climates with low levels of rainfall, solar evaporation accounts for about 30% of all salt production in the world.

Satellite Picture of Salt Pans IN Boinaire & IN India

Since 1992 India’s salt production became almost double in 2006 they produced 16.0 Million tons of salt in 2006. So their chemical industries rapidly boomed in production of like Soda ash, Caustic Soda Hydrochloric acid, Bromine, Chloral kali etc.

Rapid industrialisation in China has instigated of growth in the salt industry. There production and uses of salt reached to 50.6 million tons in 2006 from 28.1 million tons in 1992.

Solar Salt Cultivation in Pictures.
                     
Above pictures are from solar salt cultivation.




Pure Sodium cloride or PDV Salt. (100% NaCl)

It is a high purity processed, product, which is produced from purified brine. The process involves dissolving of salt (Rock or Solar salt) in to water and making a saturated (brine) solution of salt. The saturated raw brine is pumped to the purification plant where calcium, magnesium, carbonate, bi-carbonate and other impurities present along with the salt and other chemicals and impurities are removed, prior to the evaporation process, to produce pure salt. The saturated purified brine is fed to the continuous evaporation plant where crystallization takes place. Water is evaporated from purified brine using multiple-effect to give pure; snow white salt. This is the most common process for the production of industrial and edible salt in Northern Europe. The vacuum evaporation process removes all unwanted materials and impurities. Without a doubt, it is the purest, cleanest salt. Over the past century the annual production of salt world-wide has increased from 10 million tonnes to 225 million tonnes today. In the mid-1800’s salt's value as an important raw material for the chemical industry was also established when the Solvay process in Belgium was successfully use for the conversion of salt to synthetic soda ash.

The Worldwide Pure Salt Use: The annual world production of salt recently reached a massive 225 million tons. Approximately one-third of total production is by solar evaporation of sea water (solar salt); another third is produced mining rock salt deposits,
both underground and on the surface (rock salt); and the balance is gathered as brines, mainly by solution mining. Brines or Brine made from solar salt can be used directly or thermally evaporated to produce vacuum salt. The purity of solar salt can not be reach to Vacuum Evaporated salt which is usually 99.5 to 99.9% pure.

The chemical industry is the largest consumer of salt using about 60% of total production. The industry predominantly converts the salt into chlorine, caustic and soda ash, without which petroleum refining, petrochemistry, organic synthesis, glass production and so on would not be possible. The second largest user of salt is humankind. Humans need about 30% of total salt production to support their physiological functions and eating habits. Salt for food is the most 'taken for granted' commodity; available from thousands of sources in hundreds of qualities as table, cooking and industrial salt for food production.

About 10% of salt production is used for road de-icing, water treatment, production of cooling brines and other smaller applications.
Whatever the use of salt, industrialised salt production worldwide is focused on the recovery of pure sodium chloride only, clear of all 'impurities'. The purer the salt, the more valuable it is. In the chemical industry any contamination of the sodium chloride feedstock may have serious, even lethal consequences. For example:
 “In the salt brine of electrolytic cells, excessive magnesium will cause hydrogen evolution on the anode. Hydrogen and chlorine form an explosive mixture. Explosion in the cells or in the chlorine liquefaction may damage the equipment and release chlorine to the environment. Chlorine gas is highly poisonous and dangerous. Stringent safety measures are taken in the chloralkali industry to avoid this happening but the elimination of magnesium is of prime concern.”V. M. Sedivy, Salex Salt Refining Process Report, Krebs Swiss, Zurich Switzerland.

The 'impurities' in natural salt that the chemical industries refer to are any mineral or organic elements other than the single chemical, sodium chloride. Sea water contains an extraordinary number of other mineral elements in a complex and dynamic natural equilibrium. The crystal salt used in the processed food industry, whether stored in silos or used in a shaker must retain free-flowing properties.Magnesium on the surface of the crystals absorbs humidity from the air and makes the salt damp. Silos cannot be emptied and shaker holes get blocked. The salt loses market and value. To overcome these hurdles, the industry adds free-flowing agents and anti-caking agents, along with processed inorganic iodine in the form of potassium iodide. Only Vacuum Evaporation Process can produce high purity salt which called PDV Salt.  (Pure Dried Vacuum Salt)

Applications
PDV 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.

Characteristics of high-purity salt are
PDV 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.” High sodium chloride, more than 99.5%; and very low calcium and magnesium, or (Calcium and magnesium free); and tight specifications for sediment, less than 0.05 % extraneous matter." PDV 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. The purer the salt, the more valuable it is.  
The Vacuum Evaporation Process
The highest purity salt is produced in what are called "Vacuum Evaporation Plants." These large, modern facilities produce a variety of salts for which purity is essential, such as table salt, food processing salt, for chemicals and water softening salt. Virtually all food grade salt sold or used in the United States and Europe is produced by vacuum evaporation of brine. The evaporation process is a modern and highly sophisticated method of salt production.
Vacuum Evaporated Salt has been produced using a unique method: by making salt concentrate / saturated raw brine (about 24% salt) from seawater/ solar salt or rock salt as the first step, then The saturated raw brine is pumped to the purification plant where calcium, magnesium, sulphate, other chemicals and impurities are removed, prior to the evaporation process. This method is necessary to produce pure salt. The salt produced through this process is a high-purity, perfectly-crystallized product consisting of over 99.5% sodium chloride.Most evaporated salt is processed for packaging, using various quality control methods to assure, for example, that food grade salt is safe for human consumption. Table salt is often fortified with iodine and sometimes fluoride and other additives.  Evaporated salt has always been very important in the U.S. and Europe.Evaporated salt sales in the U.S. reached 4.3 million tons in 2004. 

Read More:
● Properties of Salt
● Salt Uses
● Chemicals From Salt
● The Economics of Salt