Salt, chemically known as sodium chloride (NaCl), is foundational to biological life, functioning as an electrolyte that helps nerves and muscles fire correctly. Historically, salt’s ability to preserve food made it a valuable commodity, influencing ancient trade routes, economic systems, and even serving as a form of currency. Today, the methods used to obtain this mineral are diverse, ranging from ancient natural processes to modern industrial technology.
Harvesting Salt from Seawater
The oldest and most traditional method of salt production relies entirely on natural forces: the sun and the wind. This process, known as solar evaporation, begins by channeling seawater into a series of large, shallow, interconnected basins called salterns or salt pans. The goal is to gradually increase the brine concentration as the water moves through these ponds.
As water evaporates, the salinity rises, causing less soluble compounds like calcium carbonate and gypsum to precipitate out first. The highly concentrated brine is then moved into the final, or crystallizing, ponds where sodium chloride reaches saturation and begins to form solid crystals. The continuous action of solar energy and air movement allows a layer of “sea salt” to accumulate on the pond floor. This raw salt is then mechanically harvested, washed, and dried, often yielding a product with high natural purity.
Mining Salt from Earth Deposits
Vast reserves of salt, referred to as rock salt or the mineral halite, exist beneath the earth’s surface as remnants of ancient oceans. Millions of years ago, large bodies of saltwater evaporated in arid climates, leaving behind thick sedimentary layers of salt. These deposits were subsequently buried under layers of rock and sediment, forming the underground salt beds mined today.
The most direct method of extracting this solid halite is dry mining, which physically removes the salt from the earth, similar to coal mining. Miners create deep vertical shafts to access the salt layer and then use drilling, blasting, or continuous mining machines to break up the deposit. This process typically creates large underground caverns supported by pillars of remaining salt.
The extracted rock salt is then crushed and screened into various sizes on the surface. Because this salt is often mixed with natural impurities from the surrounding rock, it is less refined than other types. This mined product is primarily used for industrial applications, such as chemical manufacturing, or for de-icing roads in winter.
Industrial Methods: Brine and Vacuum Evaporation
This industrial process combines solution mining with rapid evaporation. Solution mining starts by drilling wells deep into an underground salt deposit and pumping fresh water down one well to dissolve the salt. This creates a saturated salt solution, or brine, which is then forced back up to the surface through a second well.
Once at the surface, this brine is purified to remove mineral contaminants before being moved into large, sealed industrial evaporators known as vacuum pans. The use of a vacuum lowers the boiling point of the water, allowing the brine to be evaporated rapidly using mechanical heat or steam. This controlled process is designed to promote the swift crystallization of pure sodium chloride.
The result is a fine-grained, highly uniform salt product that is nearly 100% pure. This refined “vacuum salt” is the source for much of the fine-textured table salt and high-purity salt used in food processing and pharmaceutical industries.