How Is Table Salt Extracted From The Sea?
A chemist would like to define salts as ionic compounds, which possess some kind of negative ion (s) except for the hydroxide ion (OH-), and positive ion (s) except for the hydrogen ion (H+). But to folks, a ‘salt’ is often a synonym to the commonly used ‘table salt’. In the strict sense this is not a correct assumption. Table salt is a salt but not all salts are table salts. In our day-to-day life we often come across other types of salts like NaHCO3 (sodium hydro carbonate) which is used to soothe stomach acid problems, NH4Cl (ammonium chloride) as a feed supplement for cattle etc.
Salts are formed when ‘acids’ and ‘bases’ undergo a chemical reaction together. This results in the formation of water and a neutral compound, and that neutral compound is known as salt. Salts are fascinating substances. In solid form, salts are insulators but in the molten form they are excellent conductors of heat and electricity. When a pinch of salt is dissolved in water, the water becomes a conductor of electricity. This happens because of the ions present in the salt. In molten state and in dissolved form, these ions are free, and therefore are able to conduct electricity.
Where do these salts come from? The answers vary according to the salt compound we are interested in. Their natural sources include mines, the sea or dry ocean beds. When it comes to the table salt (NaCl), even it has sources as diverse as the mountains of Himalayas and the oceans. But here we are going to concentrate on how this important part of our diet is extracted from the seas.
Extraction:
The chemical formula or chemical shorthand for table salt is ‘NaCl’. Na means an atom of sodium and Cl signifies an atom of chlorine, thus NaCl means for each atom of sodium there is an atom of chlorine – the ratio of the elements is 50:50.The NaCl is a crystalline substance and has ‘face-centered-cubic symmetry’ or in short it has FCC structure. When put in water, or any polar liquid, the structure is disrupted and breaks up into its ions – Na and Cl.
Now this reaction or process is reversible – if the water, or the polar liquid the salt is dissolved into, is made to evaporate, by heating it or by placing it in the sun, the crystals would reappear, thus we will have our salt back. This is the basic principle that is used to separate ‘salt’ from ‘sea-water’ – the most common source of table salt.
In principle, large ponds or reservoirs are constructed near the sea-shore and sea-water is made to accumulate there, by pumps and other artificial means. The reservoirs are kept open, which means that the sunlight in allowed to fall on them. This heats up the water and increases its rate of evaporation and after a certain period of time, say a couple of days, only salt is left in the reservoirs. Now this is not the ‘table salt’, although it forms a major part of the residue. There are still a lot of processes this residue will undergo before it comes to our tables. But with the water already separated, the ‘table salt’ is already in a recognizable form.
Category: Technology