Europium

Europium is a chemical element on the periodic table whose symbol is Eu and its atomic number is 63.

It was discovered in 1890 by Paul Emile Lecoq de Boisbaudran and isolated for the first time by Eugène Demarçay, who gave it its current name, in 1901. It owes its name to the European continent.

History

An early reference to the element later called europium was found in 1885 William Crookes. By examining the fluorescence spectrum of samarium-yttrium mixtures, he was able to measure signals of an unusual orange spectral line that was stronger in mixtures of the elements than in pure materials. He named this spectral line, which points to an unknown element, the "abnormal line", the hypothetical element S_δ. Paul Émile Lecoq de Boisbaudran made another discovery on the way to the unknown element in 1892, when he discovered three previously unknown blue spectral lines in the spark spectrum of samarium in addition to the Crookes abnormal line. In 1896 Eugène-Anatole Demarçay postulated the existence of a hitherto unknown element between samarium and gadolinium based on ultraviolet spectra, with which he realized in 1900 that this element must be the same element suspected by Crookes and Boisbaudran. In 1901, Demarçay succeeded in isolating it by fractional crystallization of the double salts of samarium nitrate/magnesium europium. He named the element europium after the continent of Europe. By analogy with europium, Glenn T. Seaborg, Ralph A. James, and Leon O. Morgan in 1948 also named the actinide, which is directly below of europium on the periodic table, as a continent americium.

The first important technical application of the element was the production of europium doped yttrium vanadate. Discovered in 1964 by Albert K. Levine and Frank C. Palilla, this red phosphorus soon played an important role in the development of color television. For this application, the first mine for the extraction of rare earth elements, which had been at California Mountain Pass, greatly enlarged.

Features

Pure Euro

Europium is the most reactive of all the rare earth elements. It is dangerous in the work environment, due to the fact that the vapors and gases can be inhaled with the air. This can cause pulmonary emboli, especially from long-term exposures. It can also be a threat to the liver when it accumulates in the human body.

Eu(II) vs. Eu(III)

Although normally trivalent, europium readily forms divalent compounds. This behavior is unusual for most lanthanides, which almost exclusively form compounds with an oxidation state of +3. The +2 state has a 4f⁷ electron configuration because the half-filled f shell provides more stability. In terms of size and coordination number, europium(II) and barium(II) are similar. Barium and europium(II) sulfates are also highly insoluble in water. Divalent europium is a mild reducing agent that oxidizes in air to form Eu(III) compounds. Under anaerobic, and particularly geothermal, conditions, the divalent form is stable enough that it tends to incorporate into calcium and other alkaline earth minerals. This ion exchange process is the basis of the 'negative europium anomaly', the low europium content in many lanthanide minerals such as monazite, relative to the abundance of chondritics. Bastnasite tends to show less negative europium anomaly than monazite, and is therefore the main source of europium today. The development of easy methods to separate divalent europium from the other (trivalent) lanthanides made europium accessible even when present in low concentration, as is often the case.

Existence

Monazite

Europium does not occur in nature as a free element. Many minerals contain europium, the most important sources being bastnasite, monazite, xenotime, and loparite-(Ce). No europium-dominated minerals are known, despite a single finding of a possible minute phase of the Eu-O or Eu-O-C system in lunar regolith.

The scarcity or abundance of europium in minerals relative to other rare earth elements is known as the europium anomaly. Europium is commonly included in trace element studies in geochemistry and petrology to understand formation processes igneous rocks (rocks formed by cooling magma or lava). The nature of the found europium anomaly helps to reconstruct relationships within an igneous rock assemblage. The average crustal abundance of europium is 2–2.2 ppm.

Divalent europium (Eu²⁺) in small amounts is the activator of the bright blue fluorescence of some samples of the mineral fluorite (CaF₂). The reduction of Eu³⁺ to Eu²⁺ is induced by irradiation with energetic particles. The most prominent examples of this have been observed in the vicinity of Weardale and adjacent areas of the Northern England; it was the fluorite found here that gave the fluorescence its name in 1852, although it was not until much later that europium was determined to be the cause.

In astrophysics, the signature of europium in the stellar spectrum can be used to classify stars and inform theories of how or where a particular star was born. For example, in 2019 astronomers identified higher-than-expected levels of europium within the star J1124+4535, supporting the hypothesis that this star originated from a dwarf galaxy that collided with the Milky Way billions of years ago. years.

Production

Europium is associated with other rare earth elements and is therefore mined along with them. The separation of the rare earth elements occurs during post processing. Rare earth elements are found in minerals. bastnasite, loparite-(Ce), xenotime, and monazite in extractable amounts. Bastnasite is a group of related fluorocarbonates, Ln(CO₃)(F,OH). Monazite is a group of related orthophosphate minerals LnPO
4 (Ln expresses a mixture of all lanthanides except Prometheus), loparite-(Ce) is an oxide, and xenotime is an orthophosphate (Y,Yb,Er,...)PO₄. Monazite also contains thorium and yttrium, which complicates its handling because thorium and its decay products are radioactive. For the extraction of the mineral and the isolation of the individual lanthanides, various methods have been developed. The choice of method is based on the concentration and composition of the ore and on the distribution of the individual lanthanides in the resulting concentrate. Roasting of the ore, followed by acid and base leaching, is used primarily to produce a lanthanide concentrate. If cerium is the dominant lanthanide, then it is converted from cerium(III) to cerium(IV) and then precipitated. Further separation by solvent extraction or ion exchange chromatography produces a fraction that is enriched in europium. This fraction is reduced with zinc, zinc/amalgam, electrolysis, or other methods that convert europium(III) to europium(II). Europium(II) reacts similarly to alkaline earth metals and can therefore be precipitated as carbonate or coprecipitated with barium sulfate. Europium metal is available via electrolysis of an EuCl_{3 mixture.} and NaCl (or CaCl₂) melted in a graphite cell, which serves as the cathode, using graphite as the anode. The other product is chlorine gas.

A few large deposits produce or did produce a significant amount of world production. The Bayan Obo iron ore deposit in Inner Mongolia contains significant amounts of bastnäsite and monazite and is, with an estimated 36 million tonnes of rare earth element oxides, the largest known deposit. Mining operations of the The Bayan Obo deposit made China the largest supplier of rare earth elements in the 1990s. Only 0.2% of the rare earth element content is europium. The second major source of rare earth elements between 1965 and its closure in the late 1990s was the Mountain Pass rare earth mine in California. The bastnäsite mined there is especially rich in light rare earth elements (La-Gd, Sc and Y) and contains only 0.1% europium. Another great source of rare earth elements is loparite found on the Kola Peninsula. It contains, in addition to niobium, tantalum and titanium, up to 30% rare earth elements and is the largest source of these elements in Russia.

Applications

There are no commercial applications for metallic europium, although it has been used to contaminate some types of plastics to make lasers. Since it is a good neutron absorber, europium is being studied for use in nuclear reactors.

It is one of the chemical elements that form fluorescent compounds used in devices such as color televisions, fluorescent lamps, and glass. All of its rare chemical compounds have comparable properties.

Specifically, europium oxide (Eu₂O₃) is widely used as a fluorescent substance in television sets and as an activator of other phosphors based on yttrium.