Lanthanum La

Discovery

In 1839 the Swedish chemist Carl Gustaf Mosander, a student of Berzelius, was studying ceria, which was then thought to be the oxide of a single element. By partially decomposing cerium nitrate with heat and extracting it with dilute nitric acid, he obtained a new oxide distinct from cerium's.

Mosander named it lanthana, because it had been "hidden" in ceria. He later found that lanthana itself contained another substance, which he called didymium; didymium was eventually split into praseodymium and neodymium.

Because the rare earths are so similar chemically, separating them was painstaking, and reasonably pure lanthanum metal was not produced until 1923.

Origin of the name

The name comes from the Greek lanthanein, "to lie hidden", recalling how it hid within cerium minerals. The symbol is La, and the whole lanthanide series is named after it.

Main uses

• Petroleum refining: lanthanum stabilises the zeolites in fluid catalytic cracking catalysts, helping refineries turn more crude oil into petrol. This is one of its biggest uses.
• Nickel–metal hydride batteries: lanthanum-based alloys absorb and release hydrogen in the negative electrodes of hybrid car batteries and rechargeable cells.
• Optical glass: lanthanum oxide gives glass a high refractive index with low dispersion, allowing thinner, sharper camera and telescope lenses.
• Electron sources: lanthanum hexaboride cathodes produce bright electron beams in electron microscopes.
• Medicine: lanthanum carbonate is a phosphate binder that lowers blood phosphate in patients with kidney disease.
• Other: it is a component of mischmetal, the rare earth alloy used in lighter flints.

Isotopes

Natural lanthanum consists of stable lanthanum-139 (about 99.9%) and a trace of radioactive lanthanum-138 (about 0.09%), which has a half-life of roughly 100 billion years. Lanthanum-140 (half-life about 1.7 days) forms from the decay of the fission product barium-140 and is measured in reactor research and radiation monitoring.

In everyday life

Lanthanum is extracted with other rare earths from ores such as bastnäsite and monazite, and China is the largest producer.

Its toxicity is relatively low, but the metal powder can ignite in air and compound dust can irritate the lungs. In daily life it appears in hybrid car batteries, camera lenses and some aquarium products that remove phosphate. In research, lanthanum hydride made headlines for superconducting at relatively high temperatures, only a few tens of degrees below 0 °C, though only under enormous pressures.