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Salt, an ionic compound made of sodium and chloride ions is indispensable to human life. Our bodies need about 100 g of salt for each 40 kg of weight in order to function properly. Sodium is extremely important in cell processes and in the transmission of signals to and from the brain. It is involved in the regulation of fluids in the human body and plays a central role in blood pressure control. Salt activates several salivary and digestive enzymes, which contribute to a proper digestion and absorption of food in our stomach.
Salt has been part of human life for millennia. It was already used by Egyptians around 6000 BC to preserve their mummies, and then it was traded by Phoenicians and by people near the Mediterranean Sea. Salt has been quoted by famous philosophers and poets. “Salt is born of the purest parents: the sun and the sea” said Pythagoras, also giving an idea of how salt was obtained in ancient Greece. In old Japan, salt was sprinkled on theater stages before each play to drive away evil spirits.
At first, the Chinese were among the pioneers in salt production and trade. They obtained the precious substance from sea water and saline lakes but also through old mining technologies. Salt was a driver for progress in mining techniques in general, but was also a steady and significant source of wealth for the Chinese empire. Imperial Chinese governments kept their monopoly on salt trade and production until the 20th century.
Salt has been traditionally used for thousands of years, both as an effective food preservative and as a seasoning. Before the invention of other, more advanced refrigerating systems, all foods (meat, fish and vegetables) had to be salted in order to be safely preserved for long periods of time. Therefore, salt has undeniably contributed to the development of human civilization.
A long time ago, salt was seen as a highly valued trade commodity and some even used it as currency. The discovery of salt sometimes determined the establishment, as well as the rise and fall of some of the greatest cities and empires on Earth. Salt brought wealth but also wars and revolts throughout history. The ‘gabelle’ was a notorious and very unpopular tax on salt in France, established during the mid-14th century and which lasted until 1946. The famous ‘Gandhi Salt March’ in the 1930’s started in reaction to an increased tax by the British on the salt produced in India under Britain’s monopoly, and which ultimately led to India’s independence in 1947.
Liverpool flourished as a prime exporting port for the salt extracted in British salt mines. The powerful Polish kingdom attained part of its wealth from its great salt extraction sites (such as Wieliczka salt mine in the Krakow area) but saw this vast activity slowly decline after the Germans introduced sea salt, which was considered superior. Today, Wieliczka Salt Mine, the oldest extraction site in Poland dating back to the 12th century is a Unesco World Heritage Site, and was transformed into a museum after extraction operations ceased in 1996.
Venice and Genoa, two of the most powerful Italian seaports fought over the salt access and trade supremacy. Other cities imposed taxes on salt passing through, or became wealthy from the monopoly on the salt trade.
The Romans developed their own technique of salt extraction from the sea. They gathered the saline water in large but shallows basins where it evaporated, leaving the salt to dry out in the sun. Via Salaria, which ran from Rome to the Adriatic coast is considered one of the most important salt trade routes in antiquity and is believed to be one of the main reasons for the growth and development of the future capital of the Roman Empire. Some have even suggested – although this is not well documented – that at some point, Roman legions were paid in salt.
Later, Austrians were the first to develop a new salt extraction technique. Situated in the Salzkammergut area, on the shores of Lake Hallstättersee, lies one of the most beautiful small towns in Austria. Hallstatt is a World Heritage site and is famous not only for its breathtaking scenery but also for being the location of the world’s oldest salt mine.
Hallstatt is believed to be the first place where salt was properly extracted on a large scale, some 7000 years ago, and the expansion of the mining activities helped the whole region flourish. The very name of Salzburg, one of the main Austrian cities, stands as proof of the significance of salt in the area (‘Salz’ is salt in German). In Hallstatt, tourists can visit the old mines now converted into a museum, and learn more about the everyday life of the very first workers, the mining techniques they used and the entire salt production process. In order to enter the underground saline world, you first have to take a funicular up from the town before entering the mine with its carved rock walls. You will then see the 64-meter-long slide which was used in the mining activities and, last but not least, deep down in the tunnels you can discover the oldest wooden staircase in Europe, used by workers 2800 years ago to remove the “white gold” from the mountain. You can also watch a short movie about the daily work routines at the ‘Bronze Age Cinema’. (1) Austrians used a special extraction method: they carved into the rocks of salt and then filled the space with fresh water which was absorbed by the saline walls. The solution was later boiled to extract the salt. At the beginning, wood was the main element used in the process, but increasing salt production paved the way for the development of coal mining, as coal rapidly replaced wood in the various technological stages.
Great Britain was especially quick in making the change to the new type of fuel once the industrial revolution began. Salt was also used in the chemical industry for various other products. Britain obtained its salt from salt mining but also from the sea. ‘Wich’ and ‘wych’ are names traditionally associated with salt production in Britain (Cheshire Middlewich, Nantwich, Northwich or Droitwich).
France obtained salt from saliferous spring waters in the Seille region. The technology used there was pretty simple: boiling water until it evaporated to leave only the salt dust.
Salt varies in colour (the pink Himalayan salt extracted from deep inside the mountains of Pakistan, at the Khewra Salt Mine is famous). It has different levels of purity and sodium concentration, providing opportunities for great marketing strategies and sales revenues. The production process may also vary; it can be extracted from rocks underground, from saline sea water and from natural brines.
Historically, salt mining – and mining in general – was considered one of the most dangerous and costly activities. Hundreds of thousands of workers probably died in the process, either crushed in work accidents deep down in mines, due to the long-term effects of inhaling harmful vapours during work or by dehydration caused by prolonged contact with the salt.
Although it is now considered a cheap but indispensable part of our modern everyday life, salt was scarce during the period spanning the Industrial Revolution. Salt mines were mostly operated by underpaid workers, slaves or convicted felons, mainly because of the hard and dangerous work it involved.
Nowadays, most modern salt exploitations are owned by big multinational companies, such as Cargill, Compass Minerals or Akzo Nobel. Although production is largely streamlined, the techniques are not substantially different from those used thousands of years ago.
Today, China is the largest salt producer worldwide, followed by the USA and India. In 2020, about 270 million metric tons of salt were been produced (1), some 10 million metric tons less than the previous years. The total global production was evaluated at approximately 28.5 billion US dollars (the last two centuries have seen a decline in the price of salt).
While the leading top consumers are the Chinese, the largest salt exporter is currently the Netherlands (in 2018, total export was 319.93 million US dollars).
Europe is the second largest salt producing region in the world and the EU salt industry consists of an association of crystallised salt producers in 18 European countries. Its members have a combined turnover of more than 1.5 billion euros and employ nearly 9 000 people.
Their declared vision is “to be the voice of the salt industry in Europe and to promote the values and benefits of salt as an essential building block for the chemical industry and the energy sector and as a vital mineral for health, safety and nutrition”.(2)
Today, Germany is the leading European producer of salt, followed by the Netherlands, Poland, Switzerland and the UK.
Nowadays, 60% of the salt produced in Europe comes from solution mining. This method consists in pumping water into the underground salt deposits (up to 400 meters deep) and forcing it out through other pipes. The resulting brine is a highly saturated salt solution which is left to evaporate, and from which highly pure salt is ultimately extracted. There are substantial salt reserves throughout the continent, with a long tradition in mining operations. Solnitsata, in Bulgaria, is one of the oldest salt exploitations in Europe, supplying salt to the Balkans.
In Germany, Rheinberg, Heilbronn and Berchtesgaden, with the latter being the oldest active salt mine in that country. In Italy, Racalmuto, Realmonte and Petralia. In Poland, Klodawa, the biggest salt mine still in operation are all important names on the ‘salt map’.
As early as approximately 6000 BC, some of the early Neolithic salt production facilities have been discovered in Poiana Slatinei, in modern day Romania. The country also has the largest European salt mine at Slanic, in Prahova County, about 100 km from Bucharest. This mine was extensively exploited from 1912 to 1970.
The vast spaces created by the excavation activities are currently open to visitors who can access the 14 breathtaking underground galleries by minivan. Each gallery is 55 meters high and leads to the heart of the salt deposit. The special, saline micro-climate and constant temperatures in the mines are highly appreciated for their healing properties, and the mine now features a special area used exclusively for medical purposes. Its carved walls and sculptures made out of salt, depicting important historical figures are also a big attraction. Due to the very large size of the premises, after exploitation ceased in 1970, it has also been used for a number of aeromodelling shows. The salt mine features an old elevator, which is no longer in use but can still be seen. Interestingly, there are no metallic parts used in its construction, as metal may rust more rapidly when in contact with salt.
Turda salt mine, also in Romania, is considered the world’s most spectacular natural underground formation shaped by human activity. It is one of the oldest salt mines in Europe, dating back to Roman times. It was discovered by digging up the salt deposited after the evaporation of the sea that covered the entire region millions of years ago. The large salt reserves still remaining are now estimated to be able to fully cover the salt consumption needs of the entire planet for 60 years!.(3)
After mining operations ceased in 1932, it was turned into a huge tourist attraction. It is one of the tourist sites listed in the prestigious Michelin Travel Guide for Romania (rated with two stars). Each year, hundreds of thousands of people come to visit and explorie the saline labyrinths. There are spa accommodations, a sports park, a lake with boats, a minigolf, bowling and even a Ferris wheel, all underground. In 2020, a Guinness World record was set there. Two athletes, Rhiannan Iffland from Australia and Constantin Popovici from Romania, dived from a 20 metre-high platform into the underground lake. At 120 metres below ground, this is the deepest underground body of water in which a dive has ever been performed. Needless to say, this event drew even more attention to the place.
Other than the food industry, the main consumer of salt is the chemical industry. It is an essential ingredient for obtaining over 50% of all modern chemicals. It is used for the production of rubber, paper, glass, textiles, caustic soda. For chlorine production, a process known as electrolysis is used, where an electric current is sent through saline water which interacts with the chloride ion in the salt thus creating chlorine. Salt also remains the best de-icing solution today.
A number of salt reserves have recently been discovered on Mars, fueling hopes for some sort of sustainability for a future human colony on that planet. It may also offer some clues as to the reasons why Mars dried out.
For millennia, as is still the case today, people have acknowledged the importance of salt; there can be no proper life without it. Even in Biblical times, salt is mentioned numerous times. In various contexts, it is referred to metaphorically as signifying permanence, loyalty, durability, fidelity, value, and purification.
After all, “there must be something strangely sacred about salt” (Kahlil Gibran).