Salt, or sodium chloride (NaCl), is extracted from natural sources like seawater or underground deposits. This mineral is required for various biological functions in humans and animals. Obtaining salt involves large-scale industrial methods, such as mining and solar evaporation, as well as small-scale methods that can be done at home.
The Chemical Identity of Table Salt
Table salt is an ionic compound with the chemical formula NaCl. It is composed of positively charged sodium ions (\(\text{Na}^+\)) and negatively charged chloride ions (\(\text{Cl}^-\)) held together by an ionic bond. This bond forms when a single electron transfers from a sodium atom (a highly reactive metal) to a chlorine atom (a toxic gas).
This transfer neutralizes the extreme reactivity of the individual elements, resulting in the stable, electrically neutral compound. In its solid state, the ions arrange themselves into a highly ordered, repeating three-dimensional pattern called a cubic crystal lattice. These ions are necessary for regulating fluid balance, nerve impulse transmission, and muscle function in the body.
Global Sourcing: Extraction Methods
The world’s commercial salt supply is acquired through two primary large-scale techniques. The first method involves extracting rock salt from subterranean deposits formed by the evaporation of ancient seas. This process, known as rock salt mining, uses large machinery and sometimes blasting to remove the solid salt from underground beds.
Once the salt is brought to the surface, it is crushed and sieved for various applications, ranging from road de-icing to industrial use. A related method, called solution mining, involves injecting water into an underground salt deposit to dissolve the salt and create a concentrated brine. This brine is then pumped to the surface and often processed using a vacuum evaporator that boils the solution at lower temperatures to force the salt crystallization.
The second major method is solar evaporation, which relies on climate conditions with high evaporation rates. Seawater or water from saltwater lakes is channeled into a series of large, shallow, interconnected ponds called salt pans. The sun and wind naturally evaporate the water over weeks or months, progressively concentrating the brine.
As the water concentration decreases, impurities like calcium carbonate precipitate first. This leaves a highly concentrated sodium chloride solution that is moved to a final crystallization pond. Once a thick layer of salt crystals forms on the pond floor, it is mechanically harvested, washed to remove minor impurities, and dried for packaging.
Practical Steps for Making Salt at Home
Small batches of salt can be created at home, typically by mimicking the solar evaporation process using high-salinity water. The first step involves collecting the source water, ideally from a location with pristine water quality, since pollutants will become concentrated. After collection, the water should be filtered. Allow the water to sit so sediment can settle, then siphon or pour the clean water through a fine mesh or cloth to remove any sand or debris.
The next step is to reduce the volume of water through evaporation, which can be done by boiling the water in a large pot over high heat. As the water level drops, the heat should be reduced to a lower setting to prevent the salt from scorching on the bottom of the pan. Continuously stirring the solution as it nears dryness helps prevent burning and promotes crystal formation.
Alternatively, the water can be poured into shallow, non-reactive dishes and left in a sunny, warm location to evaporate naturally over several days. Once the liquid is nearly gone and a damp, crystalline paste remains, the salt can be spread onto a baking sheet and dried completely in a low-temperature oven or allowed to air-dry overnight. Homemade salt from local water sources may contain trace minerals, and purity cannot be guaranteed without specialized laboratory testing.