Lanthanum

Author: Robert Husted, Mollie Boorman

History

(Greek lanthanein: to lie hidden) Mosander in 1839 extracted lanthana from impure cerium nitrate and recognized the new element.

Lanthanum was isolated in relatively pure form in 1923. Ion exchange and solvent extraction techniques have led to much easier isolation of the so-called "rare-earth" elements.

Sources

Lanthanum is found in rare-earth minerals such as cerite, monazite, allanite, and bastnasite. Monazite and bastnasite are principal ores in which lanthanum occurs in percentages up to 25 percent and 38 percent respectively. Misch metal, used in making lighter flints, contains about 25 percent lanthanum.

The availability of lanthanum and other rare earths has improved greatly in recent years. The metal can be produced by reducing the anhydrous fluoride with calcium .

Properties

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 oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly.

The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens.

At 310ºC, lanthanum changes from a hexagonal to a face-centered cubic structure, and at 865ºC it again transforms into a body-centered cubic structure.

Isotopes

Natural lanthanum is a mixture of two stable isotopes, ¹³⁸La and ¹³⁹La. Twenty three other radioactive isotopes are recognized.

Uses

Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25 percent of the rare-earth compounds produced. La₂O₃ improves the alkali resistance of glass, and is used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron.

There is current interest in hydrogen sponge alloys containing lanthanum. These alloys take up to 400 times their own volume of hydrogen gas, and the process is reversible. Every time they take up the gas, heat energy is released; therefore these alloys have possibilities in an energy conservation system.

Handling

Lanthanum and its compounds have a low to moderate acute toxicity rating; therefore, care should be taken in handling them.