Where our salt comes from – a dive into the spectacular and harsh world of salt extraction
Salt is one of the most common and yet most controversial substances on Earth - you can't really live without it, but too much of it might kill you. It used to be very expensive, now it's really cheap, and most of it is used for industrial purposes. It's in the foods we eat, in the planetary oceans, and in us... but where does it come from?
Salt is one of the most common and yet most controversial substances on Earth – you can’t really live without it, but too much of it might kill you. It used to be very expensive, now it’s really cheap, and most of it is used for industrial purposes. It’s in the foods we eat, in the planetary oceans, and in us… but where does it come from?
Salt is actually a mineral composed of sodium chloride (NaCl). In its natural form, it’s called rock salt or halite. Salt is extremely important for the alimentation of all mammals, including humans. Not having enough sodium in your blood can lead to a number of negative symptoms, including headaches, dizziness, and even heart problems. This is unlikely to be a problem in the modern world, but was quite a challenge in the past.
For this purpose, it was sought after since before the Antiquity – the first evidence of extracting salt (by boiling spring water) comes from Romania, and there is evidence of a saltworks in China in about the same period. It was highly valued by the Chinese and Arabs, as well as the Romans and Greeks. Roman soldiers were actually sometimes paid in salt – this is where the word ‘salary’ comes from. For the coastal countries, the resource was accessible by boiling the oceanic water – open ocean has about 35 grams (1.2 oz) of solids per litre, a salinity of 3.5%. But for continental countries, it was a highly disputed resource; wars were fought over salt, as strange as that may sound now; it was a rare and highly valued resource.
But today, we don’t value salt almost at all! We just eat it, without giving it much thought… but where does out salt come from?
The major source of salt today is seawater – seawater is basically an inexhaustible sourface of salt. There are two main techniques to extracting salt from seawater, and you can also mine salt from the depths of the Earth. The main ways of obtaining salt are:
solution mining; in solution mining, wells are erected over salt beds and fresh water is injected to dissolve the salt. The salt solution is then pumped out and taken to a special plant for evaporation – most of the salt we eat is actually produced this say.
solar evaporation; this is the simpler, more old-school way of obtaining salt. You just leave the evaporation part to wind and the Sun, leaving the salt behind. Salt evaporation ponds are filled from the ocean and salt crystals can be harvested as the water dries up. It is usually harvested once a year when the salt reaches a specific thickness. This only works in areas with a specific climate (high temperatures and low precipitations), like in the Mediterranean area.
deep shaft mining; you basically mine salt just like any other mineral. Salt exists as deposits in ancient underground sea beds, and you can mine and then process the rock salt.
manual collection; in some areas, there is so much salt at the bottom of a lake or sea, that you can collect it manually.
In terms of which countries produce the most salt, China once again takes the crown, followed by India, Canada and Germany.
Interestingly enough though, we eat only 6% of the salt we produce, globally. Out of the rest, 12% is used in water conditioning processes, 8% goes for de-icing highways and 6% is used in agriculture. The rest (68%) is used for manufacturing and other industrial processes. PVC, plastics and paper pulp are all obtained with the use of salt.
Andrei's background is in geophysics, and he's been fascinated by it ever since he was a child. Feeling that there is a gap between scientists and the general audience, he started ZME Science -- and the results are what you see today.