Sodium chloride (NaCl) is a crystalline mineral essential for biological life, providing the dietary minerals sodium and chlorine needed to regulate fluid balance, nerve transmission, and muscle function. Historically, salt was a highly valued commodity, acting as a preservative that allowed food to be stored and transported before refrigeration. The efficient quest to obtain this mineral led to the development of several distinct methods, transforming it from a rare trade item into an accessible household staple and industrial raw material.
Producing Salt Through Solar Evaporation
The oldest method of salt production uses the natural energy of the sun and wind to extract salt from seawater or inland brine sources. This process is practical only in warm, arid climates where evaporation significantly exceeds precipitation. Production begins by channeling the source water into a series of large, shallow, interconnected ponds known as salinas.
The water first moves through concentration ponds, where the brine’s salinity gradually increases. As the volume decreases, less soluble impurities, such as calcium carbonate and gypsum, precipitate out. Once the brine reaches near-saturation, it is transferred into crystallization ponds.
In these final ponds, the high sodium chloride concentration causes the salt to precipitate and form a solid layer on the floor. The resulting product, known as solar salt or sea salt, contains trace minerals that contribute to its characteristic flavor. This sustainable method relies on renewable energy and produces salt with a purity reaching up to 99.7% after washing and processing.
Extracting Salt From Underground Deposits
Vast deposits of rock salt (halite) exist beneath the Earth’s surface, formed millions of years ago by the evaporation of ancient seas. This solid mineral is extracted through deep-shaft mining, similar to methods used for coal. Vertical shafts are bored hundreds to thousands of feet down into the salt layer to allow access for personnel and equipment.
Miners use the “room-and-pillar” technique, employing explosives and cutting machines to break the solid salt into pieces. Between 45 and 65 percent of the salt is removed in a checkerboard pattern, leaving large pillars to support the mine’s roof. The mined salt is crushed underground before being hoisted to the surface.
Due to mineral impurities like shale and anhydrite, this rock salt typically has a purity between 97% and 99% sodium chloride. Its primary use is for industrial applications, such as de-icing roads in winter. This technique offers a direct way to harvest large volumes of salt quickly without surface evaporation.
Manufacturing Highly Purified Salt
The demand for extremely high-purity salt, especially for food-grade and pharmaceutical applications, led to the development of modern industrial processes, starting with solution mining. This technique involves drilling wells into underground salt deposits and injecting fresh water to dissolve the salt layer. The resulting saturated liquid, known as brine, is then pumped back to the surface.
The surface brine undergoes chemical purification to remove trace elements like calcium and magnesium before crystallization. This purified brine is fed into large, sealed industrial vessels called vacuum evaporators. Operating under reduced pressure, these evaporators allow the water to boil and evaporate at a lower temperature, saving significant energy.
The controlled, rapid evaporation produces very fine, uniform salt crystals with exceptionally high purity, frequently reaching 99.8% to 99.98% sodium chloride. This evaporated salt is the standard for finely granulated table salt and is used extensively in high-specification chemical manufacturing. Precise control ensures a consistent product ideal for uses where mineral content must be strictly controlled.
Simplified Methods for Home Production
For individuals interested in creating a small batch of salt from collected seawater or natural brine, the most straightforward approach involves controlled evaporation using heat. The process begins by gathering water from a clean source and filtering it multiple times through a fine cloth to remove sand and organic sediment, preventing unwanted particles from incorporating into the final crystals.
The collected water is then rapidly boiled in a large pot to significantly decrease the volume and concentrate the salt solution. Once the brine is highly concentrated, the heat must be lowered substantially. This prevents scorching and encourages the formation of larger, cleaner crystals. The solution is evaporated until a wet, sandy consistency of salt remains at the bottom of the vessel.
This damp material is spread thinly on a baking sheet and placed in a low oven or sunny spot to allow all residual moisture to fully evaporate. While simple, this technique is time-consuming and produces a far smaller yield than commercial methods. The resulting product’s purity and safety depend entirely on the cleanliness of the original water source and careful management of the evaporation process.