where does salt come from?

The Dead Sea, Israel
The Dead Sea is the world's deepest hypersaline lake and with 30 percent salinity, it’s 8.6 times saltier than the ocean
Salar de Uyuni, Bolivia
Salt decomposing site on the Salar de Uyuni, the 2nd biggest salt lake in the world at 3600m altitude
Salar de Uyuni, Bolivia
Salt lake Salar de Uyuni, Bolivia
Thar desert - India
Salt harvested from the hyper saline brine water in one of the Playa lakes, Thar desert - India
Salt Fields, 1.5 hours from Bangkok - Thailand
Sea water is allowed to flood the fields where it is isolated and left to evaporate

Salt is one of the few useful and abundant minerals on earth.

Its origins go back to the beginning of time and it can be found all around us. Underground deposits are found in both sedimentary layers and domal deposits and some salt found on the surface are the dried up residues of ancient seas. Some salt has even arrived with us from outer space discovered in meteors and it is known to be present on the surface of Mars.

However, our biggest source of salt can be found in our seas and oceans. With an average of 26 million tonnes per cubic kilometre, sea water offers a seemingly inexhaustible supply which if extracted, would cover the world’s total land mass to a depth of 35 metres.

There are many different types and grades of salt and a number of different methods of production. White salt is produced by evaporating ‘solution-mined’ brine in pressure vessels. The rock salt we use for gritting roads comes from mines of ancient underground salt deposits while in hot countries the natural energy of the sun is used to evaporate brine produced from sea water. Even with sea water all around us most salt production on the British Isles is either mined or extracted from brine using a vacuum method. The UK is amongst the industry’s world leaders in terms of technology yet we produce only about 4% of the world’s total ouput.

Salt Production

In 2006, more than 200 million tons of salt were produced in the world. China is the largest producer, with 48 million tons, followed closely by the United States, with 46 million tons [source: Salt Institute]. Salt is generally produced one of three ways: deep-shaft mining, solution mining or solar evaporation.

Deep-Shaft Mining

Deep-shaft mining is much like mining for any other mineral. Typically, the salt exists as deposits in ancient underground seabeds, which became buried through tectonic changes over thousands of years. Many salt mines use the "room and pillar" system of mining. Shafts are sunk down to the floor of the mine, and rooms are carefully constructed by drilling, cutting and blasting between the shafts, creating a checkerboard pattern. After the salt is removed and crushed, a conveyor belt hauls it to the surface. Most salt produced this way is used as rock salt.

Solution Mining

In solution mining, wells are erected over salt beds or domes (deposits of salt forced up out of the earth by tectonic pressure) and water is injected to dissolve the salt. Then the salt solution, or brine, is pumped out and taken to a plant for evaporation. At the plant, the brine is treated to remove minerals and pumped into vacuum pans, sealed containers in which the brine is boiled and then evaporated until the salt is left behind. It is then dried and an anti-caking agent is added to keep it free flowing. Most table salt is produced this way.

When solution mines are located near chemical plants, they are called brine wells, and the salt is used for chemical production. After the salt is removed from a salt mine, the empty room often stores other substances, like natural gas or industrial wastes.

Solar Evaporation

Salt is harvested through solar evaporation from seawater or salt lakes. Wind and the sun evaporate the water from shallow pools, leaving the salt behind. It is usually harvested once a year when the salt reaches a specific thickness. After harvest, the salt is washed, drained, cleaned and refined. This is the purest way to harvest salt, often resulting in nearly 100 percent sodium chloride. Only areas with low annual rainfall and high evaporation rates - Mediterranean countries and Australia, for example - can have successful solar evaporation plants. Usually machines perform this harvest, but in some areas it is still done by hand.