Oceans envelop 70 percent of Earth's surface, host a huge assortment of geological processes accountable for the formation and concentration of mineral resources, and are the crucial storehouse of many materials eroded or dissolved from the land surface. Thus, oceans hold massive quantities of materials that presently serve as major resources for humans. At present, direct extraction of resources is limited to salt; magnesium; placer gold, tin, titanium, and diamonds; and fresh water. This article focuses on extraction of magnesium from sea water. Magnesium is a copious and crucially useful element which has several industrial applications in addition to being essential to human health. It is the third most common dissolved mineral in seawater, and many sources of magnesium are actually mineral deposits left behind by oceans. During the Second World War especially, when magnesium was highly sought after, several companies established facilities to extract magnesium from seawater. Magnesium is also extracted from highly concentrated brine wells, and, the fascinating thing is, it is also possible to extract magnesium from seawater. Brine wells can be found in numerous places all over the world, and they have been used historically as a source of salt as well as magnesium. Brine is water saturated or nearly saturated with salt (usually sodium chloride).
Magnesium was first isolated by Sir Humphry Davy, an English chemist, through the electrolysis of a mixture of magnesium oxide (MgO) and mercuric oxide (HgO) in 1808. Currently, magnesium can be extracted from the minerals dolomite (CaCO3. MgCO3) and carnallite (KCl.MgCl2.6H2O), but is most often obtained from seawater.
Magnesium is dissolved in sea water at a concentration of about 1,000 parts per million and is the only metal directly extracted from sea water. Every cubic kilometer of seawater contains about 1.3 billion kilograms of magnesium (12 billion pounds per cubic mile). At present, around 60 percent of the magnesium metal and many of the magnesium salts produced in the United States are extracted from sea water electrolytically. In 1997, about 110,000,000 kg of magnesium was produced in the United States. Most of this magnesium was extracted from sea water. In fact, there is enough magnesium dissolved in the Earth’s oceans to supply all of our magnesium needs for the next 1,000 years. The remaining portion of the magnesium metal and salts is extracted from ancient ocean deposits where the salts precipitated during evaporation or formed during the process of ‘diagenesis’ which uses the minerals magnesite (MgCO3) and dolomite.
Depending on the exact compound required, other ingredients such as sulfuric acid may be mixed with the slurry to generate a different end product. Since a variety of magnesium compounds are used in industrial processes, these exclusive treatments can create a range of targeted products. The substance may also be turned back into magnesium hydroxide in the case of milk of magnesia, a solution of magnesium in water which is used to treat an assortment of intestinal complaints.
Magnesium chloride is the name for the chemical compounds with the formulas MgCl2. Magnesium chloride is extracted from seawater. It consists of an ion of magnesium and two ions of chlorine. It is widely used as a magnesium supplement. Industrially, it is produced by a process called Dow's process, wherein magnesium present in seawater is treated with slaked lime to form magnesium hydroxide, which is further treated with hydrochloric acid to form magnesium chloride. Magnesium chloride as the natural mineral bischofite (a hydrous magnesium chloride mineral) is also extracted (solution mining) out of ancient seabeds, for example the Zechstein (a unit of sedimentary rock layers) seabed in northwest Europe. Anhydrous magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. Hydrated magnesium chloride is the form usually used in prescription oral magnesium supplements.