Bittern (salt)

Bittern (pl. bitterns), or nigari, is the salt solution formed when halite (table salt) precipitates from seawater or brines. Bitterns contain magnesium, calcium, and potassium ions as well as chloride, sulfate, iodide, and other ions. Bittern is commonly formed in salt ponds where the evaporation of water prompts the precipitation of halite. These salt ponds can be part of a salt-producing industrial facility, or they can be used as a waste storage location for brines produced in desalination processes. Bittern is a source of many useful salts. It is used as a natural source of Mg2+, and it can be used as a coagulant both in the production of tofu and in the treatment of industrial wastewater. Bittern has been extracted for a long time, at least several centuries. The Dutch chemist Petrus Jacobus Kipp (1808–1864) experimented with saturated solutions of bittern. The term for the solution is a modification of "bitter". Bittern is a source of many salts including magnesium sulfate (epsom salt). Multiple methods exist for removing these salts from the bittern, and the method ultimately used depends on the target product. Products that would naturally precipitate from the bitterns crystallize as evaporation proceeds. Products that do not preferentially precipitate from bitterns may precipitate through the addition of another compound or through ion exchange. Potassium-magnesium sulfate double salt, a good fertilizer, is a salt that precipitates from bitterns upon addition of methanol. Ethanol is also used, but it exhibits a preference for potassium sulfate precipitation. The solution can furthermore be used in the production of potash and potassium salts. Tartaric acid is one compound that can facilitate the precipitation of these salts. Magnesium hydroxide (Mg(OH)2) can be derived from bittern. Adding an alkaline solution such as sodium hydroxide (NaOH) or lime will cause magnesium hydroxide to precipitate, although lime is not as effective. Slower addition of the alkaline solution results in the precipitation of larger particles that are easier to remove from solution.