Lanthanum
Lanthanum | ||||||||||||||||||||||||||||
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Pronunciation | /ˈlænθənəm/ | |||||||||||||||||||||||||||
Appearance | silvery white | |||||||||||||||||||||||||||
Standard atomic weight Ar°(La) | ||||||||||||||||||||||||||||
Lanthanum in the periodic table | ||||||||||||||||||||||||||||
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kJ/mol | ||||||||||||||||||||||||||||
Heat of vaporization | 400 kJ/mol | |||||||||||||||||||||||||||
Molar heat capacity | 27.11 J/(mol·K) | |||||||||||||||||||||||||||
Vapor pressure (extrapolated)
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Atomic properties | ||||||||||||||||||||||||||||
Discovery | Carl Gustaf Mosander (1838) | |||||||||||||||||||||||||||
Isotopes of lanthanum | ||||||||||||||||||||||||||||
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Lanthanum is a
Lanthanum usually occurs together with
Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes, scintillators, gas tungsten arc welding electrodes, and other things. Lanthanum carbonate is used as a phosphate binder in cases of high levels of phosphate in the blood seen with kidney failure.
Characteristics
Physical
Lanthanum is the first element and prototype of the lanthanide series. In the periodic table, it appears to the right of the
Among the lanthanides, lanthanum is exceptional as it has no 4f electrons as a single gas-phase atom. Thus it is only very weakly
The lanthanides become harder as the series is traversed: as expected, lanthanum is a soft metal. Lanthanum has a relatively high
Chemical
As expected from
Some lanthanum(II) compounds are also known, but they are much less stable.[16] Therefore, in officially naming compounds of lanthanum its oxidation number always is to be mentioned.
Isotopes
Naturally occurring lanthanum is made up of two isotopes, the stable 139La and the
Compounds
Lanthanum oxide is a white solid that can be prepared by direct reaction of its constituent elements. Due to the large size of the La3+ ion, La2O3 adopts a hexagonal 7-coordinate structure that changes to the 6-coordinate structure of scandium oxide (Sc2O3) and yttrium oxide (Y2O3) at high temperature. When it reacts with water, lanthanum hydroxide is formed:[36] a lot of heat is evolved in the reaction and a hissing sound is heard. Lanthanum hydroxide will react with atmospheric carbon dioxide to form the basic carbonate.[37]
Lanthanum reacts exothermically with hydrogen to produce the dihydride LaH2, a black, pyrophoric, brittle, conducting compound with the calcium fluoride structure.[38] This is a non-stoichiometric compound, and further absorption of hydrogen is possible, with a concomitant loss of electrical conductivity, until the more salt-like LaH3 is reached.[37] Like LaI2 and LaI, LaH2 is probably an electride compound.[37]
Due to the large ionic radius and great electropositivity of La3+, there is not much covalent contribution to its bonding and hence it has a limited
Lanthanum chemistry tends not to involve π bonding due to the electron configuration of the element: thus its organometallic chemistry is quite limited. The best characterized organolanthanum compounds are the cyclopentadienyl complex La(C5H5)3, which is produced by reacting anhydrous LaCl3 with NaC5H5 in tetrahydrofuran, and its methyl-substituted derivatives.[40]
History
In 1751, the Swedish mineralogist
Finally, Mosander explained his delay, saying that he had extracted a second element from cerium, and this he called didymium. Although he did not realise it, didymium too was a mixture, and in 1885 it was separated into praseodymium and neodymium.
Since lanthanum's properties differed only slightly from those of cerium, and occurred along with it in its salts, he named it from the Ancient Greek λανθάνειν [lanthanein] (lit. to lie hidden).[42] Relatively pure lanthanum metal was first isolated in 1923.[16]
Occurrence and production
Lanthanum is the third-most abundant of all the lanthanides, making up 39 mg/kg of the Earth's crust, behind neodymium at 41.5 mg/kg and cerium at 66.5 mg/kg. It is almost three times as abundant as lead in the Earth's crust.[46] Despite being among the so-called "rare earth metals", lanthanum is thus not rare at all, but it is historically so named because it is rarer than "common earths" such as lime and magnesia, and historically only a few deposits were known. Lanthanum is considered a rare earth metal because the process to mine it is difficult, time-consuming, and expensive.[16] Lanthanum is rarely the dominant lanthanide found in the rare earth minerals, and in their chemical formulae it is usually preceded by cerium. Rare examples of La-dominant minerals are monazite-(La) and lanthanite-(La).[47]
The La3+ ion is similarly sized to the early lanthanides of the cerium group (those up to samarium and europium) that immediately follow in the periodic table, and hence it tends to occur along with them in phosphate, silicate and carbonate minerals, such as monazite (MIIIPO4) and bastnäsite (MIIICO3F), where M refers to all the rare earth metals except scandium and the radioactive promethium (mostly Ce, La, and Y).[48] Bastnäsite is usually lacking in thorium and the heavy lanthanides, and the purification of the light lanthanides from it is less involved. The ore, after being crushed and ground, is first treated with hot concentrated sulfuric acid, evolving carbon dioxide, hydrogen fluoride, and silicon tetrafluoride: the product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution.[49]
The procedure for monazite, which usually contains all the rare earths as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with
Lanthanum metal is obtained from its oxide by heating it with ammonium chloride or fluoride and hydrofluoric acid at 300–400 °C to produce the chloride or fluoride:[16]
- La2O3 + 6 NH4Cl → 2 LaCl3 + 6 NH3 + 3 H2O
This is followed by reduction with alkali or alkaline earth metals in vacuum or argon atmosphere:[16]
- LaCl3 + 3 Li → La + 3 LiCl
Also, pure lanthanum can be produced by electrolysis of molten mixture of anhydrous LaCl3 and NaCl or KCl at elevated temperatures.[16]
Applications
The first historical application of lanthanum was in gas lantern mantles. Carl Auer von Welsbach used a mixture of lanthanum oxide and zirconium oxide, which he called Actinophor and patented in 1886. The original mantles gave a green-tinted light and were not very successful, and his first company, which established a factory in Atzgersdorf in 1887, failed in 1889.[50]
Modern uses of lanthanum include:
- One material used for anodic material of NiMH batteries can be found in many models of the Toyota Prius sold in the US. These larger nickel-metal hydride batteries require massive quantities of lanthanum for the production. The 2008 Toyota Prius NiMH battery requires 10 to 15 kilograms (22 to 33 lb) of lanthanum. As engineers push the technology to increase fuel efficiency, twice that amount of lanthanum could be required per vehicle.[53][54][55]
- 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. Heat energy is released every time they do so; therefore these alloys have possibilities in energy conservation systems.[28][56]
- pyrophoric alloy used in lighter flints, contains 25% to 45% lanthanum.[57]
- Lanthanum oxide and the boride are used in electronic vacuum tubes as hot cathode materials with strong emissivity of electrons. Crystals of LaB
6 are used in high-brightness, extended-life, thermionic electron emission sources for electron microscopes and Hall-effect thrusters.[58] - Lanthanum trifluoride (LaF
3) is an essential component of a heavy fluoride glass named ZBLAN. This glass has superior transmittance in the infrared range and is therefore used for fiber-optical communication systems.[59] - Cerium-doped gamma rays.[60]
- Carbon arc lamps use a mixture of rare earth elements to improve the light quality. This application, especially by the motion picture industry for studio lighting and projection, consumed about 25% of the rare-earth compounds produced until the phase out of carbon arc lamps.[28][61]
- lenses, because of the high refractive index and low dispersion of rare-earth glasses.[28] Lanthanum oxide is also used as a grain-growth additive during the liquid-phase sintering of silicon nitride and zirconium diboride.[62]
- Small amounts of lanthanum added to malleability, resistance to impact, and ductility, whereas addition of lanthanum to molybdenum decreases its hardness and sensitivity to temperature variations.[28]
- Small amounts of lanthanum are present in many pool products to remove the phosphates that feed algae.[63]
- Lanthanum oxide additive to tungsten is used in
- Various compounds of lanthanum and other rare-earth elements (oxides, chlorides, catalysts.[66]
- Lanthanum-barium radiometric dating is used to estimate age of rocks and ores, though the technique has limited popularity.[67]
- end-stage kidney disease.[68]
- Lanthanum fluoride is used in phosphor lamp coatings. Mixed with europium fluoride, it is also applied in the crystal membrane of fluoride ion-selective electrodes.[16]
- Like horseradish peroxidase, lanthanum is used as an electron-dense tracer in molecular biology.[69]
- Lanthanum-modified bentonite (or phoslock) is used to remove phosphates from water in lake treatments.[70]
- Lanthanum telluride (La3Te4) is considered to be applied in the field of radioisotope power system (nuclear power plant) due to its significant conversion capabilities. The transmuted elements and isotopes in the segment will not react with the material itself, thus presenting no harm to the safety of the power plant. Though iodine, which can be generated during transmutation, is suspected to react with La3Te4 segment, the quantity of iodine is small enough to pose no threat to the power system.[71]
Biological role
Lanthanum has no known biological role in humans. The element is very poorly absorbed after oral administration and when injected its elimination is very slow.
While lanthanum has pharmacological effects on several receptors and ion channels, its specificity for the
Lanthanum is an essential cofactor for the methanol dehydrogenase of the
Precautions
Hazards | |
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GHS labelling: | |
Danger | |
H260 | |
P223, P231+P232, P370+P378, P422[74] | |
NFPA 704 (fire diamond) |
Lanthanum has a low to moderate level of toxicity and should be handled with care. The injection of lanthanum solutions produces hyperglycemia, low blood pressure, degeneration of the spleen and hepatic alterations.[citation needed] The application in carbon arc light led to the exposure of people to rare earth element oxides and fluorides, which sometimes led to pneumoconiosis.[75][76] As the La3+ ion is similar in size to the Ca2+ ion, it is sometimes used as an easily traced substitute for the latter in medical studies.[77] Lanthanum, like the other lanthanides, is known to affect human metabolism, lowering cholesterol levels, blood pressure, appetite, and risk of blood coagulation. When injected into the brain, it acts as a painkiller, similarly to morphine and other opiates, though the mechanism behind this is still unknown.[77] Lanthanum meant for ingestion, typically as a chewable tablet or oral powder, can interfere with gastrointestinal imaging by creating opacities throughout the GI tract; if chewable tablets are swallowed whole, they will dissolve but present initially as coin-shaped opacities in the stomach, potentially confused with ingested metal objects such as coins or batteries.[78]
Prices
The price for a (metric) ton [1000 kg] of Lanthanum oxide 99% (FOB China in USD/Mt) is given by the Institute of Rare Earths Elements and Strategic Metals as below $2,000 for most of the period from early 2001 to September 2010 (at $10,000 in the short term in 2008); it rose steeply to $140,000 in mid-2011 and fell back just as rapidly to $38,000 by early 2012.[79] The average price for the last six months (April to September 2022) is given by the Institute as follows: Lanthanum Oxide - 99.9%min FOB China - 1308 EUR/mt and for Lanthanum Metal - 99%min FOB China - 3706 EUR/mt.[80]
Notes
- ^ The thermal expansion of α-La is anisotropic: the parameters (at 20 °C) for each crystal axis are αa = 2.9×10−6/K, αc = 9.5×10−6/K, and αaverage = αV/3 = 5.1×10−6/K.[3]
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Further reading
- The Industrial Chemistry of the Lanthanons, Yttrium, Thorium and Uranium, by R. J. Callow, Pergamon Press, 1967
- Extractive Metallurgy of Rare Earths, by C. K. Gupta and N. Krishnamurthy, CRC Press, 2005
- Nouveau Traite de Chimie Minerale, Vol. VII. Scandium, Yttrium, Elements des Terres Rares, Actinium, P. Pascal, Editor, Masson & Cie, 1959
- Chemistry of the Lanthanons, by R. C. Vickery, Butterworths 1953