Lanthanum (pronEng|ˈlænθənəm) is a
chemical elementwith the symbol La and atomic number57.
Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is a
lanthanoid. Found in some rare-earth minerals, usually in combination with ceriumand other rare earth elements. Lanthanum is malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens. It oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly.
Uses of lanthanum include:
lightingapplications, especially by the motion picture industry for studio lighting and projection.
* La2O3 improves the alkali resistance of
glass, and is used in making special optical glasses, such as:
Cameraand telescopelenses, because of the high refractive indexand low dispersion of rare-earth glasses.
* Small amounts of lanthanum added to
steelimproves its malleability, resistance to impact and ductility.
* Small amounts of lanthanum added to
ironhelps to produce nodular cast iron.
* Small amounts of lanthanum added to
molybdenumdecreases the hardness of this metal and its sensitivity to temperature variations.
* Small amounts of lanthanum are present in many pool products to remove the phosphates that feed algae.
Mischmetal, a pyrophoricalloy used in such things as lighter flints, contains 25% to 45% lanthanum.
Lanthanum oxideand the boride are used in electronic vacuum tubes as hot cathodematerials with strong emissivity of electrons. Crystals of LaB6 are used in high brightness, extended life, thermionic electron emission sources for scanning electron microscopes.
Gas tungsten arc weldingelectrodes, as a substitute for radioactive thorium.
Hydrogen sponge alloys can contain lanthanum. These alloys are capable of storing up to 400 times their own volume of hydrogen gas in a reversible adsorption process.
Petroleum cracking catalysts.
* Gas lantern mantles.
* Glass and lapidary polishing compound.
* La-Ba age dating of rocks and ores.
Lanthanum carbonateis used medically as a phosphate binderfor the treatment of hyperphosphatemia. See details below under Biological Role.
Lanthanum nitrateis mainly applied in specialty glass, water treatment and catalyst.
Ceriumactivated Lanthanum bromideis the recent inorganic scintillatorwhich has a combination of high light yield and the best energy resolution.
Lanthanum fluorideis used with Europium flouridein the crystal membraneof Fluoride Ion-Selective Electrodes
Lanthanum oxideis used as a grain growth additive during the liquid phase sintering of silicon nitride.
horseradish peroxidase, lanthanum is used as an electron-dense tracer in molecular biology[cite journal | author=Chau YP, Lu KS | title=Investigation of the blood-ganglion barrier properties in rat sympathetic ganglia by using lanthanum ion and horseradish peroxidase as tracers | journal=Acta Anatomica (Basel) | volume=153 | issue=2 | year=1995 | pages=135–144
pmid=8560966 ] .
* Lanthanum is an intermetallic component of nickel-metal hydride batteries.
Lanthanum was discovered in 1839 by Swedish
chemist Carl Gustav Mosander, when he partially decomposed a sample of cerium nitrate by heating and treating the resulting salt with dilute nitric acid. From the resulting solution, he isolated a new rare earth he called "lantana". Lanthanum was isolated in relatively pure form in 1923.
The word "lanthanum" comes from the Greek "λανθανω" [lanthanō] = to lie hidden.
Lanthanum is the most strongly basic of all the trivalent lanthanoids, and this property is what allowed Mosander to isolate and purify the salts of this element. Basicity separation as operated commercially involved the fractional precipitation of the weaker bases (such as
didymium) from nitrate solution by the addition of magnesium oxide or dilute ammonia gas. Purified lanthanum remained in solution. (The basicity methods were only suitable for lanthanum purification; didymium could not be efficiently further separated in this manner.) The alternative technique of fractional crystallization was invented by Dimitry Mendeleev himself, in the form of the double ammonium nitrate tetrahydrate, which he used to separate the less-soluble lanthanum from the more-soluble didymium in the 1870s. This system would be used commercially in lanthanum purification until the development of practical solvent extraction methods that started in the late 1950s. (A detailed process using the double ammonium nitrates to provide 4N pure lanthanum, neodymium concentrates and praseodymium concentrates is presented in Callow 1967, at a time when the process was just becoming obsolete.) As operated for lanthanum purification, the double ammonium nitrates were recrystallized from water. When later adapted by Carl Auer von Welsbachfor the splitting of didymium, nitric acid was used as solvent to lower the solubility of the system. Lanthanum is relatively easy to purify, since it has only one adjacent lanthanoid, cerium, which itself is very readily removed due to its potential tetravalency.
Lanthanum has no known biological role. The element is not absorbed orally, and when injected its elimination is very slow.
Lanthanum carbonatewas approved as a medication (Fosrenol, Shire Pharmaceuticals) to absorb excess phosphatein cases of end-stage renal failure. Some rare-earth chlorides, such as lanthanum chloride (LaCl3), are known to have anticoagulantproperties.
While Lanthanum has pharmacological effects on several receptors and ion channels, its specificity for the GABA receptor is unique among divalent cations. Lanthanum acts at the same modulatory site on the GABAR as zinc- a known negative allosteric modulator. The Lanthanum cation La3+ is a positive allosteric modulator at native and recombinant GABA receptors, increasing open channel time and decreasing desensitization in a subunit configuration dependent manner.
Although lanthanum belongs to chemical elements group called
rare earth metals, it is not rare at all. Lanthanum is available in relatively large quantities (32 ppm in Earth’s crust). "Rare earths" got their name since they were indeed rare as compared to the "common" earths such as lime or magnesia, and historically only a few deposits were known. Monazite(Ce, La, Th, Nd, Y)PO4, and bastnäsite(Ce, La, Y)CO3F, are the principal ores in which lanthanum occurs, in percentages of up to 25 to 38 percent of the total lanthanoid content. Lanthanum is more generally enriched in bastnäsite as opposed to monazite, in commercial orebodies. Until 1949, bastnäsite was a rare and obscure mineral, not even remotely contemplated as a potential commercial source for lanthanoids. In that year, the vast deposit at Mountain Pass, Californiawas discovered. This discovery alerted geologists as to the existence of a whole new class of rare earth deposit, the rare-earth bearing carbonatite, other examples of which soon surfaced, particularly in Africa and China.
"See also "
Naturally occurring lanthanum is composed of one stable (139La) and one
radioactive(138La) isotope, with the stable isotope, 139La, being the most abundant (99.91% natural abundance). 38 radioisotopes have been characterized with the most stable being 138La with a half-lifeof 105×109 years, and 137La with a half-life of 60,000 years. Most of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half lives that are less than 1 minute. This element also has 3 meta states.
The isotopes of lanthanum range in
atomic weightfrom 117 u (117La) to 155 u (155La).
Lanthanum has a low to moderate level of toxicity, and should be handled with care. In animals, the injection of lanthanum solutions produces
glycaemia, low blood pressure, degeneration of the spleenand hepatic alterations.
* [http://periodic.lanl.gov/elements/57.html Los Alamos National Laboratory – Lanthanum]
* "The Industrial Chemistry of the Lanthanons, Yttrium, Thorium and Uranium", by R.J. Callow, Pergamon Press 1967
* "Chemistry of the Lanthanons", by R.C. Vickery, Butterworths 1953
* "Nouveau Traite de Chimie Minerale, Vol. VII. Scandium, Yttrium, Elements des Terres Rares, Actinium", P. Pascal, Editor, Masson & Cie 1959
* "Extractive Metallurgy of Rare Earths", by C.K. Gupta and N. Krishnamurthy, CRC Press 2005
* [http://www.webelements.com/webelements/elements/text/La/index.html WebElements.com – Lanthanum]
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lanthanum — Symbol: La Atomic number: 57 Atomic weight: 138.9055 (From the Greek word lanthanein, to line hidden) Silvery metallic element belonging to group 3 of the periodic table and oft considered to be one of the lanthanoids. Found in some rare earth… … Elements of periodic system
lanthanum — [lan′thənəm] n. [ModL: so named (1839) by G. Mosander (see ERBIUM) < lanthana, lanthanum oxide, lit., the hidden one < Gr lanthanein, to be hidden (see LATENT): it had previously been undetected in the mineral cerite] a soft, malleable,… … English World dictionary
Lanthanum — Lan tha*num (l[a^]n th[.a]*n[u^]m), n. [NL., fr. Gr. lanqa nein to lie hid, to be concealed.] (Chem.) A rare element of the rare earth group of the metals, of atomic number 57, allied to aluminum. It occurs in certain rare minerals, as cerite,… … The Collaborative International Dictionary of English
lanthanum — salts are used as a negative stain in electron microscopy, and as calcium channel blockers … Dictionary of molecular biology
lanthanum — metallic rare earth element, 1841, coined in Modern Latin by Swedish chemist and mineralogist Carl Gustav Mosander (1797 1858), who discovered it in 1839, from Gk. lanthanein to lie hidden, escape notice, from PIE root *ladh to be hidden (see… … Etymology dictionary
lanthanum — /lan theuh neuhm/, n. Chem. a rare earth, trivalent, metallic element, allied to aluminum, found in certain minerals, as monazite. Symbol: La; at. wt.: 138.91; at. no.: 57; sp. gr.: 6.15 at 20°C. [ < NL (1841), equiv. to lanthan ( < Gk lanthánein … Universalium
lanthanum — lantanas statusas T sritis chemija apibrėžtis Cheminis elementas. simbolis( iai) La atitikmenys: lot. lanthanum angl. lanthanum rus. лантан … Chemijos terminų aiškinamasis žodynas
lanthanum — noun [lɑ˧nˈðaː˨nɔ˧m] a) A metallic chemical element (symbol La) with an atomic number of 57. b) lanthanum See Also: lanthana, lanthanate, lanthanide, lanthanite, lanthanoid, lanthanon … Wiktionary
lanthanum — lantanas statusas T sritis fizika atitikmenys: angl. lanthanum vok. Lanthan, n rus. лантан, m pranc. lanthane, m … Fizikos terminų žodynas
lanthanum — noun Etymology: New Latin, from Greek lanthanein to escape notice more at latent Date: 1841 a white soft malleable metallic element that occurs in rare earth minerals see element table … New Collegiate Dictionary