POTASSIUM COMPOUND

Potassium nitrate, essential in the manufacture of black gun powder, was produced by the Chinese, who had developed gun powder by the tenth century AD. The process involved the leaching of soil in which nitrogen from urine had combined with mineral potassium. By the early 1800s, potassium nitrate had become a strategic military chemical and was stiU produced, primarily in India, by using the ancient Chinese method. The caUche deposits in Chile are the only natural source of potassium nitrate (2). These deposits are not a rich source of potassium nitrate, purifying only to about 14% as K O. 

In 1840, potassium was recognized as an essential element for plant growth (6). This discovery and the invention in 1861 of a process to recover potassium chloride from mbbish salt, a waste in German salt mines, started the modem potassium chemical industry (5). Potassium compounds produced throughout the world in 1993 amounted to ca 22 million metric tons as K O equivalent (4), down from ca 24 million t in 1992, having fallen annually from 32 million t in 1989 (2). Estimated production capacity was between 29 and 32 million t in 1992 (2). 

Between 1869 and the beginning of World War I, most of the world s supply of potassium salts came from the Stassfurt deposits in Germany. During World War I, U.S. production, measured as K2O, rose from 1000 metric tons in 1914 to 41,500 t in 1919. Following the end of World War I, U.S. production declined as imports increased. By the time the United States entered World War II, however, production had expanded enough to meet domestic needs. Since then, production has fluctuated, but has fallen below consumption as of the mid-1990s. Total annual U.S. demand peaked at 6.9 X 10 t in 1979 and has leveled off at approximately 5.1 to 5.5 million t. Canada is the principal potash exporter. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Four minerals are the principal commercial sources of potash (Table 2). In all ores, sodium chloride is the principal soluble contaminant. Extraneous water-iasoluble material, eg, clay and siUca, is a significant contaminant ia some of the evaporates being mined from underground deposits. Some European potassium ores contain relatively large amounts of the mineral kieserite, MgS04-H2 0. It is recovered for captive use to produce potassium sulfate compounds or is marketed ia relatively pure form as a water-soluble magnesium fertilizer. 

The industrial term potash usually refers to potassium carbonate (K2C03) but also can be used in reference to potassium hydroxide (KOH), potassium chloride (KC1), potassium sulfate (K2S04), potassium nitrate (KN03), or collectively to all potassium salts and to the oxide (K20). Another term, caustic potash, is used in reference to potassium hydroxide, and muriate of potash is commonly used in reference to potassium chloride. 

Deposits of sylvinite (43% by weight potassium chloride and 57% by weight sodium chloride) account for large amounts of naturally occurring potassium. The potassium chloride can be separated by either fractional crystallization or flotation. Brine is also a valuable source of potassium chloride. A small amount of potassium sulfate is isolated from natural deposits, and potassium nitrate is manufactured by two processes. 

NaN03 + KC1 - KN03 + NaCl 4KC1 + 4HN03 + 02 - 2KN03 + Cl2 + H20 

Potassium hydroxide is made by electrolysis of potassium chloride solutions in cells that are exactly analogous to those for sodium hydroxide production. 

Potassium perthiocarbonate, K2CS4, and its adducts K2CS4,nL (L = MeOH or Mc2NH, n = 1 L = H20, n = 0.5) have been prepared and characterized by t.g.a., tensiometry, X-ray diffraction, and i.r. spectroscopy. The adducts have the characteristics of inclusion compounds in which the geometry and arrangement of the CS - ions in the crystal allow the inclusion of MeOH but not the larger PrOH molecules. 

The crystal structure of potassium orthostannate, K4Sn04, has been determined as triclinic, with space group PI and a = 6.48, b = 6.51, c = 9.70A, a = 71.82, /3 = 99.89, and 7 = 113.13°. The compound consists of discrete tetrahedral Sn04 groups which are bounded by cations.  

Billaud, D. Balesdent, and A. Harold, Bull. Soc. chim. France, 1974, 2402. D. Billaud and A. Herold, Bull. Soc. chim. France, 1974, 11, 2407. 

respectively. Preparation of potassium antimony disulphide, K8b82, from an aqueous solution of KH8 and 86283 under mild hydrothermal conditions provides a monoclinic form, space group C2/c, with a = 8.75, 6 = 8.98, c = 

3 = 121.6°, d(expt.) = 3.19, d(calc.) = 3.26 for Z = 4. The structure consists of 8682 chains built up from trigonal bipyramids which share edges. The K ions between these chains have nearly octahedral co-ordination.  

Finogenova, B. A. Popovkin, and G. F. Voronin, Khim. Soyas Poluproo. 

Zviedre, J. Ozols, and A. levins, Lato. P.S.R. Zinat. Akad. Vestis, Kim. Ser., 1972, 

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Potassium is never found free in nature, but is obtained by electrolysis of the hydroxide, much in the same manner as prepared by Davy. Thermal methods also are commonly used to produce potassium (such as by reduction of potassium compounds with CaC2, C, Si, or Na). 

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