Magnesium chloride
Magnesium chloride is the name for the chemical compound with the formula MgCl and its various hydrates MgCl(HO). Anhydrous MgCl contains 25.5% elemental magnesium by mass. These salts are typical ionic halides, being highly soluble in water. The hydrated magnesium chloride can be extracted from brine or sea water. In North America, magnesium chloride is produced primarily from Great Salt Lake brine. It is extracted in a similar process from the Dead Sea in the Jordan Valley. Magnesium chloride, as the natural mineral bischofite, is also extracted (by solution mining) out of ancient seabeds, for example, the Zechstein  seabed in northwest Europe. Some magnesium chloride is made from solar evaporation of seawater. Anhydrous magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. Hydrated magnesium chloride is the form most readily available. Structure, preparation, and general properties. MgCl crystallizes in the cadmium chloride motif, which features octahedral Mg centers. Several hydrates are known with the formula MgCl(HO), and each loses water at higher temperatures: "x" = 12 (−16.4 °C), 8 (−3.4 °C), 6 (116.7 °C), 4 (181 °C), 2 (about 300 °C). In the hexahydrate, the Mg  is also octahedral, but is coordinated to six water ligands. The thermal dehydration of the hydrates MgCl(HO) ("x" = 6, 12) does not occur straightforwardly. Anhydrous MgCl is produced industrially by heating the chloride salt of hexammine complex [Mg(NH)]. As suggested by the existence of some hydrates, anhydrous MgCl is a Lewis acid, although a weak one. In the Dow process, magnesium chloride is regenerated from magnesium hydroxide using hydrochloric acid: It can also be prepared from magnesium carbonate by a similar reaction. Derivatives with tetrahedral Mg are less common. Examples include salts of (N(CH))MgCl and adducts such as MgCl(TMEDA ). Applications. Precursor to Mg metal. Anhydrous MgCl is the main precursor to metallic magnesium. The reduction of Mg into metallic Mg is performed by electrolysis in molten salt. As it is also the case for aluminium, an electrolysis in aqueous solution is not possible as the produced metallic magnesium would immediately react with water, or in other words that the water H would be reduced into gaseous H before Mg reduction could occur. So, the direct electrolysis of molten MgCl in the absence of water is required because the reduction potential to obtain Mg is lower than the stability domain  of water on an E–pH diagram (Pourbaix diagram). The production of metallic magnesium at the cathode (reduction reaction) is accompanied by the oxidation of the chloride anions at the anode with release of gaseous chlorine. This process is developed at a large industrial scale. Dust and erosion control. Magnesium chloride is one of many substances used for dust control, soil stabilization, and wind erosion mitigation. When magnesium chloride is applied to roads and bare soil areas, both positive and negative performance issues occur which are related to many application factors. Catalyst support. Ziegler-Natta catalysts, used commercially to produce  polyolefins, contain MgCl as a catalyst support. The introduction of MgCl supports increases the activity of traditional catalysts and allowed the development of highly stereospecific catalysts for the production of polypropylene. Ice control. Magnesium chloride is used for low-temperature de-icing of highways, sidewalks, and parking lots. When highways are treacherous due to icy conditions, magnesium chloride helps to prevent the ice bond to the pavement, allowing snow plows to clear the roads more efficiently. Magnesium chloride is used in three ways for pavement ice control: Anti-icing, when maintenance professionals spread it onto roads before a snow storm  to prevent snow from sticking and ice from forming; prewetting, which means a liquid formulation of magnesium chloride is sprayed directly onto salt as it is being spread onto roadway pavement, wetting the salt so that it sticks to the road; and pretreating, when magnesium chloride and salt are mixed together before they are loaded onto trucks and spread onto paved roads. Calcium chloride damages concrete twice as fast as magnesium chloride. The amount of magnesium chloride is supposed to be controlled when it is used for de-icing as it may cause pollution to the environment. Nutrition and medicine . Magnesium chloride is used in nutraceutical and pharmaceutical preparations. Cuisine. Magnesium chloride (E511) is an important coagulant used in the preparation of tofu from soy milk. In Japan it is sold as "nigari" (, derived from the Japanese word for "bitter"), a white powder produced from seawater after the sodium chloride has been removed, and the water evaporated. In China, it is called "lushui" (卤水). Nigari or Iushui is, in fact, natural magnesium chloride, meaning that it is not completely refined (it contains up to 5% magnesium sulfate and various minerals). The crystals originate from lakes in the Chinese province of  Qinghai, to be then reworked in Japan. Millions of years ago, this region was home to an ancient ocean that gradually dried up and of which only salty lakes with brackish water saturated with salt where magnesium chloride crystallizes remain today. It is an inexpensive dietary supplement providing magnesium, hence its interest in view of a general deficit in our current consumption (to be in full health, the human body must in particular benefit from a balance between calcium and magnesium). It is also an ingredient in baby formula milk. Gardening and horticulture. Because magnesium is a mobile nutrient, magnesium  chloride can be effectively used as a substitute for magnesium sulfate (Epsom salt) to help correct magnesium deficiency in plants via foliar feeding. The recommended dose of magnesium chloride is smaller than the recommended dose of magnesium sulfate (20 g/l). This is due primarily to the chlorine present in magnesium chloride, which can easily reach toxic levels if over-applied or applied too often. It has been found that higher concentrations of magnesium in tomato and some pepper plants can make them more susceptible to disease caused by infection of the bacterium "Xanthomonas campestris", since magnesium is essential for  bacterial growth. Occurrence. Magnesium values in natural seawater are between 1250 and 1350 mg/l, around 3.7% of the total seawater mineral content. Dead Sea minerals contain a significantly higher magnesium chloride ratio, 50.8%. Carbonates and calcium are essential for all growth of corals, coralline algae, clams, and invertebrates. Magnesium can be depleted by mangrove plants and the use of excessive limewater or by going beyond natural calcium, alkalinity, and pH values. The most common mineral form of magnesium chloride is its hexahydrate, bischofite. Anhydrous compound occurs very rarely, as chloromagnesite. Magnesium chloride-hydroxides, korshunovskite and nepskoeite, are also very  rare. Toxicology. Magnesium ions are bitter-tasting, and magnesium chloride solutions are bitter in varying degrees, depending on the concentration of magnesium. Magnesium toxicity from magnesium salts is rare in healthy individuals with a normal diet, because excess magnesium is readily excreted in urine by the kidneys. A few cases of oral magnesium toxicity have been described in persons with normal renal function ingesting large amounts of magnesium salts, but it is rare. If a large amount of magnesium chloride is eaten, it will have effects similar to magnesium sulfate, causing diarrhea, although the sulfate also contributes to the laxative  effect in magnesium sulfate, so the effect from the chloride is not as severe. Plant toxicity. Chloride (Cl) and magnesium (Mg) are both essential nutrients important for normal plant growth. Too much of either nutrient may harm a plant, although foliar chloride concentrations are more strongly related with foliar damage than magnesium. High concentrations of MgCl ions in the soil may be toxic or change water relationships such that the plant cannot easily accumulate water and nutrients. Once inside the plant, chloride moves through the water-conducting system and accumulates at the margins of leaves or needles, where dieback  occurs first. Leaves are weakened or killed, which can lead to the death of the tree. Locomotive boiler problem. The presence of dissolved magnesium chloride in the well water (bore water) used in locomotive boilers on the Trans-Australian Railway caused serious and expensive maintenance problems during the steam era. At no point along its route does the line cross a permanent freshwater watercourse, so bore water had to be relied on. No inexpensive treatment for the highly mineralised water was available, and locomotive boilers were lasting less than a quarter of the time normally expected. In the days of  steam locomotion, about half the total train load was water for the engine. The line's operator, Commonwealth Railways, was an early adopter of the diesel-electric locomotive.