Salt,once called “white gold,” has been a valuable commodity since biblical times. As it was relatively scarce it was used for trading; the word “salary” is derived from the fact that ancient Romans were often paid in salt instead of money.
Before the Industrial Revolution and the introduction of new mining techniques and tools, salt mining was considered expensive, labour-intensive and dangerous.
Global salt production
• China is the world’s largest salt producer, producing 64 million tonnes in 2010. Other leading salt producers are the US, Germany, India and Australia.
• Roughly 55 percent of global salt production is for the chemicals sector.
• Demand for salt is expected to increase by 3.3 percent per year through 2015, to almost 300 million tonnes.
• Solar evaporation accounts for 40 percent of salt production.
Workers in salt mines were in close contact with salt and inhaled it for long periods of time, risking severe dehydration. Few people wanted to work in such an environment, so it was often slaves or prison labourers who toiled in the mines.
Today, salt is harvested in three different ways: through deep-shaft mining, solution mining or solar evaporation. Apart from sea salt, which is produced in salt pans, salt is extracted from mines.
In deep-shaft mining, the salt is usually deposited in old underground seabeds that were buried by tectonic activity over thousands of years. Shafts are sunk down to the floor of the mine. Then the salt is removed, crushed and hauled by a conveyor belt to the surface. This salt is usually sold as rock salt.
In solution mining, wells are erected over salt beds or domes, and water is injected to dissolve the salt. The salt solution (brine) is pumped out and taken to a plant where it is boiled and evaporated, leaving behind the salt, which is then dried and refined. This is how table salt is produced.
The third method of mining salt is through solar evaporation, which is only suitable in places with low rainfall and high evaporation rates. Wind and sun evaporate the seawater from shallow pools, leaving the salt behind. It is then harvested, cleaned and refined. This is the purest form of salt, which can often be almost 100 percent sodium chloride.
Salt is used for everything from cooking and preserving food to purifying aluminium, chlorinating swimming pools and de-icing roads.
As confirmation of the world’s ongoing fascination with salt, many mines have been turned into tourist attractions. The Salina Turda salt mine in Romania’s Transylvania region was turned into a halotherapy (salt therapy) centre and amusement park complete with big wheel, mini-golf course and amphitheatre. The salt mine at Berchtesgaden, Germany, is an interactive museum where visitors dress in miners’ clothing and are taken deep underground in a funicular and a raft.