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How is salt made from seawater?

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Quick answer

Sea salt is made by solar evaporation. Seawater is let into a series of shallow ponds, where sun and wind slowly remove water. Unwanted minerals settle out early, and once the brine is saturated, sodium chloride crystals grow in the final pans. Workers rake, wash, dry and often iodise the salt.

Salt is made from seawater by letting sun and wind evaporate the water in a chain of shallow ponds until the brine becomes so concentrated that sodium chloride crystallises out. Workers then rake up the crystals, wash and dry them, and usually add iodine before packing.

Step by step

  1. Seawater is pumped or let in at high tide into a large reservoir pond next to the coast.
  2. The water flows through a series of shallow ponds, growing saltier as sun and wind evaporate it.
  3. Calcium carbonate and gypsum precipitate in the middle ponds and are left behind on their floors.
  4. Saturated brine enters crystallising pans, where sodium chloride forms a crust of crystals over several days.
  5. Workers drain the bitter leftover liquid, rake the salt into heaps and leave it to drain.
  6. The salt is washed, dried, crushed to size and usually fortified with iodine before packing.

Key things to understand

  1. Seawater holds about 35 grams of dissolved salts per litre, and roughly three-quarters of that is sodium chloride.
  2. Pumps or tides fill large, shallow evaporating ponds where sunlight and wind drive off water day after day.
  3. As the brine thickens, less soluble minerals such as calcium carbonate and gypsum settle out first in the early ponds.
  4. The concentrated brine moves into crystallising pans, where sodium chloride reaches saturation and forms cubic crystals on the floor.
  5. The leftover bitter liquid, rich in magnesium salts, is drained off before the salt is harvested, washed and dried.

Labelled diagram

  1. Intake

    Seawater enters a reservoir pond through pumps or sluice gates at high tide.

  2. Evaporating ponds

    Sun and wind remove water, raising the brine's salt concentration step by step.

  3. Gypsum settles

    Less soluble minerals such as calcium sulphate drop out before the salt does.

  4. Crystallising pan

    Saturated brine deposits cubic sodium chloride crystals across the pan floor.

  5. Harvest

    Salt is raked into heaps, drained, washed, dried and iodised.

From seawater to salt crystals in solar ponds

Real-world examples

  • Salt pans around Thoothukudi in Tamil Nadu use seawater and long dry seasons to produce much of southern India's salt.
  • Gujarat produces the majority of India's salt, mostly from coastal and inland brine works using solar evaporation.
  • Fleur de sel is the delicate crust skimmed by hand from the surface of salt pans at Guérande in France.
  • In cold or wet regions, factories boil or vacuum-evaporate brine instead of relying on the sun.

Common mistake

✗ Myth: Sea salt is far healthier than ordinary table salt because of its minerals.

✓ Fact: Both are about 95 percent or more sodium chloride, so they carry similar amounts of sodium by weight. The trace minerals in sea salt are too small to matter much nutritionally.

People also ask

How is salt extracted from sea water?
Salt is extracted mainly by solar evaporation. Seawater is spread across a series of shallow ponds so the sun and wind can evaporate it. As water leaves, other minerals settle first, and when the brine is saturated sodium chloride crystallises. The crystals are raked up, washed and dried.
Why does salt crystallize when water evaporates?
Water can hold only a certain amount of dissolved salt, roughly 360 grams per litre at room temperature. Evaporation removes water but leaves the salt behind, so the brine eventually passes that limit. Sodium and chloride ions then lock together into an orderly cubic lattice, forming visible crystals.
What is left after salt is made from seawater?
After sodium chloride crystallises, a dense, bitter liquid called bittern remains. It is rich in magnesium chloride, magnesium sulphate and potassium salts. Salt works drain it away before harvest, because leaving it would make the salt taste bitter, and some plants recover magnesium and potassium compounds from it.
Why are salt pans so shallow?
Evaporation happens only at the surface, so a thin layer of brine loses a larger share of its water each day. Shallow pans also warm faster in the sun, which speeds evaporation further and shortens the time before crystals appear.
How long does it take to make sea salt?
It depends on climate, but solar salt works usually need weeks to months of dry, sunny weather for brine to pass through every pond. Rain sets the process back by diluting the brine, which is why harvesting is seasonal in most places.
Is sea salt different from rock salt?
Both are mostly sodium chloride. Sea salt comes from evaporating present-day seawater, while rock salt is mined from underground beds left when ancient seas dried up millions of years ago. Trace minerals and crystal size differ slightly between them.
Why is iodine added to salt?
Iodine is added because the body needs it to make thyroid hormones, and many diets lack enough of it. Salt is eaten daily by almost everyone, so adding potassium iodate or iodide to it became a cheap way to prevent iodine deficiency.

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