 Discovery Information
|
| Who: Carl Mosander |
| When: 1839 |
| Where: Sweden |
|
| Name Origin
|
| Greek: lanthanein (to lie hidden). |
| "Lanthanum" in different languages. |
|
| Sources
|
| Found with other rare earch elements in monazite and bastnasite. Primary producers are the USA, Brazil, India, Sri Lanka and Australia. Around 12500 tons are produced annually. |
|
| Abundance
|
| Universe: 0.002 ppm (by weight) |
| Sun: 0.002 ppm (by weight) |
| Carbonaceous meteorite: 0.29 ppm |
| Earth's Crust: 34 ppm |
| Seawater: |
| Atlantic surface: 1.8 x 10-6 ppm
|
| Atlantic deep: 3.8 x 10-6 ppm
|
| Pacific surface: 2.6 x 10-6 ppm
|
| Pacific deep: 6.9 x 10-6 ppm
|
|
| Uses
|
| Because it gives glass refractive properties, it is used in expensive camera lenses. Also used in lighter flints, studio lighting,
battery electrodes and catalytic converters. Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with
a knife. It is one of the most reactive of the rare-earth metals. It oxidises rapidly when exposed to air. Cold water attacks lanthanum slowly, and hot water attacks it much more rapidly. The metal reacts directly with elemental
carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens. It is a component of misch metal (used for making lighter flints). Some rare-earth chlorides, such as lanthanum chloride (LaCl3), are known to have anticoagulant properties.
|
| Small amounts of lanthanum added to steel improves its malleability, resistance to impact and ductility; added to iron helps to produce nodular cast iron; added to molybdenum decreases the hardness of this metal and its sensitivity to temperature variations.
|
| 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.
|
| Lanthanum Hexaboride (LaB6) crystals are used in high brightness, extended life, thermionic electron emission sources for scanning electron microscopes.
|
|
| History
|
| 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.
|
| 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 ammmonia 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 1870's. This system would be used commercially in lanthanum purification until the development
of practical solvent extraction methods that started in the late 1950's. (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 won Welsbach for the splitting of "didymium", nitric acid was used as solvent to lower the solubiity of the system. Lanthanum is relatively
easy to purify, since it has only one adjacent lanthanoids, cerium, which itself is very readily removed due to its potential tetravalency.
|
|
| Notes
|
| Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly. |
|
| Hazards
|
| In animals, the injection of lanthanum solutions produces glycaemia, low blood pressure, degeneration of the spleen and hepatic
alterations.
|
| Lanthanum dust presents a fire and explosion hazard. |
