Here you go from www.saltinstitute.org Solar Salt Production 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.