Throughout history, salt pits have been used to dissolve underground halite deposits and extract them in the form of brine. A typical salt well consists of a pipe that has been drilled into a salt bed or dome, water, pumping equipment, and sometimes the infrastructure needed for evaporation. The process of extracting halite from a salt well typically involves pumping water into a tank, which can dissolve it in a brine solution. This solution can then be pumped to the surface and sold in solution or exposed to an evaporation process to result in a dry, granulated salt product.
Salt pits were historically used to tan leather, since salt is a preservative.
Salt has been used throughout history as a dietary supplement and seasoning, and also for utilitarian uses such as tanning leather and preserving meat. Evidence of salt mining was discovered as early as the 4th century BC in China, although it is likely that the process existed even before that. In ancient China, salt deposits were typically reached through bamboo holes buried deep in the ground. Due to the difficulty in extracting salt using ancient technology and the widespread nature of halite deposits and salt domes, it was an important commodity throughout much of early human history.
Most salt beds and domes lie about 500 to 1,000 feet (150 to 1,500 meters) below the surface, and natural salt springs are one of the ways new salt pits have traditionally been located. In these locations, artesian wells coincide with salt domes, and water dissolves some of the salt as it seeps to the surface. When drilling in the nearby area, the tubes can be extended into the salt dome to facilitate the extraction process. When water is pumped into a salt bed or dome, it tends to dissolve the mineral in a brine solution within an empty space known as a salt cave. The brine can then be pumped out of the cave for evaporation into salt crystals or use in various industrial applications.
Brine from a salt pit is usually evaporated on the spot. This was traditionally achieved by pottery or iron pot methods, although a variety of modern techniques are now used. In other cases, the brine may be piped to an external processing plant. Some chemical plants also employ captive brine wells on site so that salt solution for various chemical processes can be conveniently purchased. One use for a captive salt well is the chlor alkali process, which uses electrolysis to remove hydrogen, chlorine, and sodium hydroxide from brine.