Throughout history, salt wells have been used to dissolve subterranean halite deposits and extract them in the form of brine. A typical salt well consists of a pipe that has been drilled down into a salt bed or dome, water, pumping equipment, and sometimes the infrastructure required for evaporation. The process of extracting halite from a salt well typically involves pumping water into a deposit, which can dissolve it into a brine solution. This solution can then be pumped to the surface and either sold in solution or exposed to an evaporative process to result in a dry, granular salt product.
Salt has been used throughout history as a dietary supplement and spice, and also for utilitarian uses such as tanning leather and preserving meat. Evidence of salt mining has been discovered from as early as the fourth century BCE in China, though it is likely that the process existed even earlier than that. In ancient China, salt deposits were typically reached by driving bamboo drills deep into the ground. Due to the difficulty in extracting salt using early technology and the widely spread out 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 way that new salt well sites have traditionally been located. In these locations, artesian wells coincide with salt domes, and the water dissolves some salt as it percolates to the surface. By drilling in the nearby area, pipes may be extended into the salt dome to facilitate the extraction process. When water is pumped into a salt bed or dome, it will tend to dissolve the mineral into a brine solution inside a void space known as a salt cave. Brine may then be pumped out of the cave for evaporation into salt crystals or use in various industrial applications.
The brine from a salt well is often evaporated onsite. This was traditionally achieved through pottery or iron pan methods, though a variety of modern techniques are now used. In other cases, the brine can be piped to an offsite processing plant. Some chemical plants also employ captive brine wells onsite so that the salt solution for various chemical processes can be procured conveniently. One use for a captive salt well is the chloralkali process, which uses electrolysis to remove hydrogen, chlorine, and sodium hydroxide from the brine.