Editing Rare-earth element (section)

==Discovery and early history==

Rare earths were mainly discovered as components of minerals. The term "rare" refers to these rarely found minerals and "earth" comes from an old name for oxides, the chemical form for these elements in the mineral.<ref name="Gschneidner-1964">{{Cite book |last=Gschneidner |first=Karl A. |url=https://books.google.com/books?id=04ghAQAAMAAJ |title=Rare Earths: The Fraternal Fifteen |date=1964 |publisher=U.S. Atomic Energy Commission, Division of Technical Information |language=en}}</ref>{{rp|5}} The adjective "rare" may also mean strange or extraordinary.<ref name=Zepf-2013/>{{rp[|12}} In 1787, a mineral discovered by Lieutenant [[Carl Axel Arrhenius]] at a quarry in the village of [[Ytterby]], Sweden, <ref name="Gschneidner-1964"/>{{rp|9}} reached [[Johan Gadolin]], a [[The Royal Academy of Turku|Royal Academy of Turku]] professor, and his analysis yielded an unknown [[oxide]] which he called [[yttrium(III) oxide|yttria]].<ref name="auto">{{cite web |website=[[Science History Institute]] |title=The History and Future of Rare Earth Elements |date=October 18, 2019 |url=https://www.sciencehistory.org/learn/science-matters/case-of-rare-earth-elements-history-future |access-date=January 31, 2023}}</ref>  

[[Anders Gustav Ekeberg]] isolated [[beryllium]] from the gadolinite but failed to recognize other elements in the ore. After this discovery in 1794, a mineral from [[Bastnäs]] near [[Riddarhyttan]], Sweden, which was believed to be an [[iron]]–[[tungsten]] mineral, was re-examined by [[Jöns Jacob Berzelius]] and [[Wilhelm Hisinger]]. In 1803, they obtained a white oxide and called it [[cerium(IV) oxide|ceria]]. [[Martin Heinrich Klaproth]] independently discovered the same oxide and called it ''ochroia''. It took another 30 years for researchers to determine that other elements were contained in the two ores ceria and yttria. The similarity of the rare-earth metals' chemical properties made their separation difficult.

In 1839, [[Carl Gustav Mosander]], an assistant of Berzelius, separated ceria by heating the nitrate and dissolving the product in [[nitric acid]]. He called the oxide of the soluble salt ''lanthana''. It took him three more years to separate the lanthana further into ''didymia'' and pure lanthana. Didymia, although not further separable by Mosander's techniques, was in fact still a mixture of oxides.

In 1842, Mosander separated the yttria into three oxides: pure yttria, terbia, and erbia. All the names are derived from the town name "Ytterby". The earth giving pink salts he called ''terbium''. The one that yielded yellow peroxide he called ''erbium''.<ref>{{Cite book |last=Mingos |first=D. Michael P. |url=http://link.springer.com/10.1007/430_2019_50 |title=The Discovery of the Elements in the Periodic Table |series=Structure and Bonding |date=2019 |publisher=Springer Berlin Heidelberg |location=Berlin, Heidelberg |doi=10.1007/430_2019_50}}</ref>
By then the number of known rare-earth elements had reached six: yttrium, cerium, lanthanum, didymium, erbium, and terbium.

[[Nils Johan Berlin]] and [[Marc Delafontaine]] tried also to separate the crude yttria and found the same substances that Mosander obtained. In 1860, Berlin named the substance giving pink salts ''erbium''. Delafontaine named the substance with the yellow peroxide, ''terbium''. This confusion led to several false claims of new elements, such as the ''mosandrium'' of [[J. Lawrence Smith (chemist)|J. Lawrence Smith]], or the ''philippium'' and ''[[decipium]]'' of Delafontaine. Due to the difficulty in separating the metals, and determining the separation is complete, the total number of false discoveries was dozens,<ref>''[https://www.osti.gov/scitech/servlets/purl/789650 History of the Origin of the Chemical Elements and Their Discoverers]''</ref><ref>{{cite book |author1=Stephen David Barrett |author2=Sarnjeet S. Dhesi |title=The Structure of Rare-earth Metal Surfaces |url=https://books.google.com/books?id=7fxpDQAAQBAJ&pg=PA4 |year=2001 |publisher=World Scientific |isbn=978-1-86094-165-8 |page=4}}</ref> with some putting the total number of discoveries at over a hundred.<ref>''[https://archive.org/stream/OnRareAndScatteredMetalsTalesAboutMetals/On_Rare_And_Scattered_Metals__Tales_About_Metals On Rare And Scattered Metals: Tales About Metals]'', Sergei Venetsky</ref>

===Spectroscopic identification===
There were no further discoveries for 30 years, and the element [[didymium]] was listed in the periodic table of elements with a molecular mass of 138. In 1879, [[Marc Delafontaine|Delafontaine]] used the new physical process of [[atomic emission spectroscopy|optical flame spectroscopy]] and found several new spectral lines in didymia. Also in 1879, [[Paul Émile Lecoq de Boisbaudran]] isolated the new element ''[[samarium]]'' from the mineral [[samarskite]].

In 1886, the samaria earth was further separated by Lecoq de Boisbaudran. A similar result was obtained by [[Jean Charles Galissard de Marignac]] by direct isolation from samarskite. They named the element ''[[gadolinium]]'' after [[Johan Gadolin]], and its oxide was named "[[gadolinium(III) oxide|gadolinia]]".

Further spectroscopic analysis between 1886 and 1901 of samaria, yttria, and samarskite by [[William Crookes]], Lecoq de Boisbaudran and [[Eugène-Anatole Demarçay]] yielded several new [[spectral line]]s that indicated the existence of an unknown element. In 1901, the [[fractional crystallization (chemistry)|fractional crystallization]] of the oxides yielded ''[[europium]]''.

In 1839, the third source for rare earths became available. This is a mineral similar to gadolinite called ''uranotantalum'', now called "[[samarskite]]", an oxide of a mixture of elements such as yttrium, ytterbium, iron, uranium, thorium, calcium, niobium, and tantalum. This mineral from [[Miass]] in the southern [[Ural Mountains]] was documented by [[Gustav Rose]]. The Russian chemist R. Harmann proposed that a new element he called "[[ilmenium]]" should be present in this mineral, but later, [[Christian Wilhelm Blomstrand]], Galissard de Marignac, and [[Heinrich Rose]] found only [[tantalum]] and [[niobium]] ([[columbium]]) in it.

The exact number of rare-earth elements that existed was highly unclear, and a maximum number of 25 was estimated. Using [[X-ray emission spectroscopy|X-ray spectra]] [[Henry Moseley|Henry Gwyn Jeffreys Moseley]] confirmed the atomic theory of [[Niels Bohr]] and simultaneously developed the theory of atomic numbers for the elements.<ref>{{Cite book |last=Heilbron |first=J. L. |title=H. G. J. Moseley: the life and letters of an English physicist, 1887-1915 |last2=Moseley |first2=H. G. J. |date=1974 |publisher=University of California Press |isbn=978-0-520-02375-8 |location=Berkeley}}</ref> Moseley found that the exact number of lanthanides had to be 15, revealing a missing element, [[promethium|element 61]], a radioactive element with a half-life of 18 years.<ref>{{Cite web |title=Separation of Rare Earth Elements |url=https://www.acs.org/education/whatischemistry/landmarks/earthelements.html |access-date=2025-04-02 |website=American Chemical Society |language=en}}</ref>

Using these facts about atomic numbers from X-ray crystallography, Moseley also showed that [[hafnium]] (element 72) would not be a rare-earth element. Moseley was killed in [[World War I]] in 1915, years before hafnium was discovered. Hence, the claim of [[Georges Urbain]] that he had discovered element 72 was untrue. Hafnium is an element that lies in the periodic table immediately below [[zirconium]], and hafnium and zirconium have very similar chemical and physical properties.