In a very simple way: letting the liquid evaporate and collecting the salt at the end of the process. However, it is not enough to let the water steam in dozens of tanks and then gather the seasoning. If manufacturers did just that, all they would get is a gray, bitter-tasting slurry with only 78% sodium chloride, popular table salt. This is because sea water, in addition to containing a lot of salt, also has calcium and magnesium compounds, which need to be removed from the final product. The task of the salt flats is precisely to make this separation.
The work begins when the liquid is pumped from coastal salt lakes, which have at least twice the amount of salt than the ocean – you can also do the process directly with sea water, but the yield is much lower. When evaporating in tanks under the sun, the water becomes more and more pasty. At that time, the tendency is for the solid elements to begin to separate from the liquid and concentrate at the bottom of the tank.
The secret is that each compound goes to the bottom at a different time, as the density of this broth increases. First, there are the calcium compounds, which are excluded from the mixture. Then there is the table salt itself, which can be removed from the tanks in the form of coarse salt or sent to a series of machines that manufacture fine salt. “During this phase, the remaining water evaporates under controlled temperature and pressure, so that the crystals come out small and uniform”, says mechanical engineer Maximilian Bosch, from the National Salt Refinery, in Cabo Frio (RJ).
At the end of the process, before being packaged, the seasoning that arrives at Brazilian supermarkets also receives a small amount of iodine, a substance used to prevent goiter, a serious disease that attacks the throat.
Natural selection
The secret of salt pans is to remove impurities from the water used as raw material.
1. When taken from the sea or coastal lagoons, salt water goes into huge evaporation tanks. Connected by floodgates, each occupies an area equal to ten football fields and is only 20 centimeters deep. As the liquid dries, the concentration of solid elements increases. When they occupy 17% of the water volume, the calcium compounds present in the oceanic juice concentrate at the bottom and separate from the mixture2. The dense water is now called brine and falls into crystallization frames, tanks dozens of square meters and 2 centimeters deep. Evaporation continues until the level of solid elements reaches 25%. There, the concentration of sodium chloride – kitchen salt – reaches its maximum value, and can follow two paths
3a. If the brine is used in the production of coarse salt, it continues to dry under the sun until all the sodium chloride has coalesced into crystals. Afterwards, the salty pebbles, up to 3 centimeters in diameter, are removed by workers with squeegees or machines. The remaining water is discharged into sluices on the sides of the crystallization frames
3b. If the brine serves as the basis for the production of refined salt, it is removed from the crystallization frames just before the formation of crystals and passes through filters to eliminate impurities. Afterwards, it is pumped into heaters, where the mixture reaches 120ºC, and continues to evaporate in vacuum chambers. In these devices, the brine is subjected to a controlled pressure to generate tiny crystals, much smaller than coarse salt.
4. The refined salt crystals are now ready, but still contain water. The solid part continues to separate from the liquid in centrifuges, which resemble washing machines: inside a cylinder that rotates at high speed, the water flows to the bottom, while the salt is deposited on the sides. Even after centrifugation, the salt still carries a slight moisture. Therefore, the mixture is placed in special ovens, heated to 200ºC, which dry and sterilize the product before it is packaged.