Pr - Praseodymium

Properties

Praseodymium is a soft, malleable, silvery and ductile metal. It is a member of the Lanthanide group of metals and is the 39th most abundant element within the Earth’s crust. Praseodymium reacts slowly with oxygen forming a flaky, green oxide layer. This oxide layer does not protect the element from further oxidation, and for this reason is often stored in a sealed plastic container or covered with oil, although it is actually less readily oxidised than other rare earth elements. Praseodymium also reacts rapidly with water.

History

In 1841, whilst analysing a sample of cerium, Carl Mosander discovered that this cerium in fact harboured two other elements, which he managed to extract. He named these new elements lanthanum and didymium.  For about 40 years, his discovery went unquestioned until chemists wondered if didymium was actually an element, or if it contained more than one element. These suspicions were confirmed in 1882, when Bohuslav Brauner of Prague was able to demonstrate by means of its atomic spectrum, that it was not a pure metal after all.  However, Brauner was unable to separate didymium, and another chemist, Carl Auer von Welsbach announced in June 1885 that he had succeeded in splitting didymium into its two components: neodymium and praseodymium in the form of their oxides. A pure sample of metallic praseodymium was not produced for another 46 years, until 1931. Praseodymium was named after two Greek words, ‘prasios’, meaning green (reffering to the green colour of its oxide) and ‘didymos’, meaning twin.

Sources

Praseodymium can only be found in two types of ore, namely monazite and bastnasite, in China, USA, Brazil, India, Sri Lanka and Australia.  Circa 2,500 mt are produced annually, with 2 million tonnes of reserves worldwide.

Uses

Praseodymium can be used in glass production to give the glass a yellow tint which filters out infrared radiation, and can be used in goggles to protect the eyes of welders.  When alloyed with magnesium, praseodymium produces a very high strength metal used in aircraft engines.  Praseodymium can be found occurring in everyday products as well, such as colour televisions, fluorescent lamps and energy saving lamps, as well as the pyrophoric alloy used in cigarette lighter flint.

Praseodymium is mildly toxic; in particular, the soluble salts are toxic via ingestion and cause skin and eye irritation.  The non-soluble salts are not toxic.  Praseodymium is most dangerous in a working environment, as vapours can be inhaled with air, causing lung embolisms (particularly during long term exposure).  It can also be a threat to the liver when accumulated in the human body.

Praseodymium is often dumped in the environment via a number of routes: primarily through petrol-producing industries and household rubbish.  It gradually accumulates in the soil at increased concentrations and can damage the cell membranes of water animals, which has a negative impact on reproduction and the function of their nervous systems.