Solution mining of salt or halite deposits is just like it sounds. Once the salt deposit is located, fresh and recycled water is injected through a well (or wells) drilled into an underground salt bed or salt dome, usually between 150 and 1,500 meters (500 to 5000 feet) deep. Dissolution of the salt forms a void or cavern in the salt deposit. Salt brine is withdrawn from the cavern and transported by pipeline to an onsite evaporating plant to make dry salt, or to a chemical processing plant for chlor-alkali or other chemical production. Solution mines located at the site of chemical plants are called captive brine wells.
Some salt solution mines consist of a single well with concentric casings extending into the salt cavern. Others consist of several adjacent wells extending into a single large cavern. Brine is withdrawn either through the outer concentric casing in a single well cavern, or through a separate casing in a multiple well salt cavern. The size and shape of solution mined caverns can be measured and controlled with well logging devices and operating techniques, thus minimizing the potential for surface subsidence. After the end of use for salt or chemical production, solution-mined salt caverns are often used to store natural gas ( 1 2 3 ) or other products, including industrial wastes such as oil field wastes ( 1 2 3 ), or to store compressed air ( 1 2 3 4 5 6 7 8 9 ) used to run turbines and generate electricity. The U.S. Department of Energy recognizes the potential of storage in salt with its Strategic Petroleum Reserve and, separate, Waste Isolation Pilot Plant (WIPP) facility for low-level radioactive wastes in a salt deposit in New Mexico.
Solution mining has been done for millenia, apparently first by the Chinese. In North America, solution mining for the production of dry salt is done in Alberta, Kansas, Louisiana, Michigan, New York, Nova Scotia, Ohio, Ontario, Saskatchewan, Tennessee and Texas. In some areas, like Michigan and New York, it has a rich cultural and historical significance, as, for example, in this history of the Dow Chemical Company. The New York Department of Environmental Conservation has a useful set of papers on solution mining and related issues in the Empire State ( 1 2 3 4 5 ).
Cal State-Sacramento posts online a schematic of the Avery Island, LA salt dome.
Kali und Salz (Germany) has further information on solution mining on its company website.
For further information, contact the Salt Institute, the Solution Mining Research Institute or the Ground Water Protection Council. Note our disclaimer.
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