Solar salt is produced by the action of sun and wind on seawater ( 1 2 ) or natural brine in lakes; both temperature and salinity are important. The water evaporates in successive ponds until the brine is fully concentrated and salt crystallizes on the floor of the crystallizing ponds. Solar salt plants must be located in areas of low rainfall and high evaporation rates, and where suitable low-cost is available. In the Mediterranean, for example, saltworks succeed because evaporation exceeds rainfall by a factor of 3:1; that advantage is even greater in Australia where it can reach 15:1.
Seawater contains about 3.5% (by weight) dissolved minerals. Sodium chloride is 77% of that amount, or about 2.7% of seawater. The other 0.8% consists chiefly of calcium, magnesium and sulfate ions. As seawater evaporates, its volume decreases and the concentration of sodium chloride in the resulting brine increases. Thus, saltworks generally extract as sodium chloride a bit over 2% of the weight of the influent seawater. This means that solar saltworks are often quite extensive in area. Often, the concentrating ponds will have distinct coloration, a pink or red, depending on the salt concentration and what species of plants and animals find it habitable. Salt crystals begin to form when the brine concentration reaches 25.8 % sodium chloride (NaCl). As evaporation proceeds, a layer of salt builds up on the earthen crystallizer floors to a thickness of 10 to 25 cm (4-10 in). Sometimes, a layer of salt remains in the crystallizers as "salt floors" to provide support for "harvesting" equipment and to lessen the chance of clay or soil contamination of the salt. A modern, properly operated solar salt plant can produce salt that is more than 99.7 % NaCl (dry basis). In the Dead Sea, salt producers have to contend with "salt mushrooms."
After the salt "crop" reaches the appropriate thickness, the salt is harvested (usually once a year) with mobile equipment, washed, and placed on stockpile to drain. The principal impurities in solar salt are small amounts of calcium and magnesium sulfate, and magnesium chloride. Clean brine, made by dissolving fine salt, is used to wash the salt to remove small amounts of impurities such as these. Seawater can also be used, but salt losses increase due to dissolution. Depending on the intended use, solar salt may be crushed, screened and dried in kiln or fluidized-bed dryers. Because of its high purity and large crystal size, solar salt is widely used to regenerate water softeners.
Solar salt sales in the United States has increased about 50% over the past twenty years to 6.1 million tons in 2005.
For further information, contact the Salt Institute. San Francisco Bay hosts a Cargill Salt solar facility (see some great facility photos). Just west of Phoenix, AZ, in Glendale, Morton Salt operates a hybrid solution mine solar operation (great YouTube video). Australian saltmakers Cheetham Salt (see About Salt-Salt from the Sea), Salinor (Brazil)( 1 2 ), and Shark Bay Resources Pty Ltd also have useful information about solar salt production. Solar salt production is common in hot or tropical locations like the Bahamas and Bonaire ( 1 2 3 4 ) in the Caribbean, Mexico ( 1 2 ) (the world's largest saltworks is in Guerrero Negro, Baja California Sur -- you may wish to view an amateur video of the salt harvest at this facility), Thailand, Namibia or the Dead Sea in Israel/Jordan. Even non-tropical locations such as Europe and eastern China can make solar salt. Surprisingly, in equatorial climates, solar production can even be done at some elevation as in the Cusco, Peru salinas and the Uyuni salinas in Bolivia ( 1 2 3 4 5 6 7 8 9 10 ).
Operating saltworks can be important, if semi-artificial, ecosystems and, after use for salt production, can be returned to valuable wetlands. Information is online about salt marshes and ecology, including saltwater species of plants and animals ( 1 2 3 ) and how saltworks provide valued habitat for wildlife and, particularly, birds ( 1 2 ). Saltworks are also prime eco-tourism destinations ( 1 2 3 ). Closed saltworks can be converted into valuable conservation areas as is being done at the south end of San Francisco Bay ( 1 2 3 4 ). Note our disclaimer.
Solar saltworks are often long-standing witnesses to social and economic activity far back into history. Check out this website from Spain for more on this (site is in Spanish).
If you'd like salt-related information delivered automatically via a
newsreader, you can subscribe to our Salt
Institute NewsCentral service or add any of our
feeds to your
newsreader. The RSS feed for solar
salt production can also be accessed via your Web browser.
[About Salt Institute] [About salt] [About the salt industry] [News] [SI Member Business (password required] [E-Mail Salt Institute]
