380 



UNITED STATES MINERAL RESOURCES 



Sfiawater, brines 

 precipitated Mg(OH)j 



Dolomite 

 CaCOj • MgCOj 



Evaporite minerals 



FiGUKE 44. — Use of the principal raw materials of 

 magnesium. 



oxides (dead-burned magnesite, periclase, and dead- 

 burned dolomite) used to make refractories. Sea 

 water and magnesium-rich brines are treated with 

 lime or caustic-calcined dolomite to precipitate mag- 

 nesium hydroxide, which can be converted either to 

 chemicals or refractories or to magnesium chloride, 

 from which the metal can be extracted in electro- 

 lytic cells. When heated with ferrosilicon, caustic- 

 calcined dolomite yields magnesium metal. Byprod- 

 uct magnesium bitterns resulting from treatment 

 of evaporite minerals are used to prepare mag- 

 nesium oxide and have been used in the past in 

 electrolytic cells to recover the metal. Forsterite 

 molded into brick is fired at 3,000°F to produce a 

 refractory that is inert to certain flue dusts and 

 gasses, and when ground, the mineral forms a su- 

 perior foundry molding sand. 



The United States is virtually self-suflScient in 

 magnesium-bearing raw materials, although its re- 

 sources of low-cost low-lime magnesite are small; 

 the country is a net exporter of magnesium metal 

 and a net importer of magnesium compounds. 



EXPLOITATION 



Mining of magnesite deposits began in California 

 in 1886, in Washington in 1916, and in Nevada in 

 1937; it ended in California in 1950 and in Wash- 

 ington in 1968. The large-scale use of calcined dolo- 

 mite as a refractory began during World War I, 

 and mining of brucite in Nevada began in 1934. 

 Recovery of magnesium metal from deep-well Michi- 

 gan brines began in 1916; sea-water recovery of 

 magnesium oxide for metal production began in 

 1940, and in subsequent years sea-water magnesia 

 supplanted magnesite as the prime source of refrac- 

 tory raw material. Magnesium metal was extracted 

 from dolomite and magnesite on a large scale dur- 

 ing World War II, but its recovery from these 



sources ceased in the following years. Deep-well 

 magnesium brines in Texas were developed in 1970, 

 and the brines of Great Salt Lake, Utah, were under 

 development in 1972 by two companies for the re- 

 covery of magnesium compounds and the metal. 

 Forsterite, the magnesium-rich variety of olivine, 

 has been mined in North Carolina since 1933, and 

 in Washington since 1956. 



Since World War II, dolomite has provided the 

 largest single source of magnesium-bearing com- 

 pounds in the United States. More than 2 million 

 short tons of dead-burned dolomite was produced 

 annually in the midsixties, but changes in steel- 

 making reduced its consumption to 1 million tons in 

 1971 ; another several hundred thousand tons of 

 caustic-calcined dolomite is used annually to precipi- 

 tate magnesium hydroxide from sea water and 

 brines. Reported production of magnesite reached a 

 peak in 1956, when 690,000 short tons of crude 

 magnesite was produced. Since then, production has 

 not been reported, but in 1972 the Washington de- 

 posits were not mined, and therefore the production 

 for that year was probably less than in 1969. About 

 1 million tons of brucite was mined from the Ne- 

 vada deposits during 1934-66, but annual rates of 

 production are not reported. Olivine production 

 similarly is not reported but probably is on the 

 order of several tens of thousands of tons per year. 



Under categories currently reported by the U.S. 

 Bureau of Mines, refractory magnesia sold and used 

 by producers totaled 627,000 short tons in 1971 and 

 802,000 short tons in 1970; shipments of caustic- 

 calcined and specified magnesias (exclusive of mag- 

 nesia used in manufacture of the metal) totaled 

 102,000 short tons in 1971 and 122,000 short tons 

 in 1970. Magnesium metal production was 123,000 

 short tons in 1971, continuing a rising trend of the 

 previous several years. Figures on the amounts of 

 magnesium compounds obtained from sea water, 

 deep-seated brines, magnesite, and brucite are not 

 available (Chin, 1971a, b). 



Outside the United States, about 12 million tons 

 of magnesite is mined annually; most is from de- 

 posits of crystalline magnesite, but more than 1 

 million tons is from deposits of bone magnesite. The 

 consumption of bone magnesite has been increasing 

 in recent years because this refractory possesses 

 high strength and is resistant to high temperatures, 

 properties desirable in the linings of basic-oxygen 

 steel furnaces. 



About 120,000 tons of magnesium metal is pro- 

 duced annually outside the United States. Rated 

 capacity of plants recovering magnesia from sea 

 water outside the United States totals 1.1 million 



