Scandium

Scandium is a chemical element; it has symbol Sc and atomic number 21. It is a silvery-white metallic element found in the d-block of the periodic table. Usually, it is classified as a rare-earth element, together with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia. Scandium is present in most of the deposits of rare-earth and uranium compounds, but it is extracted from these ores in only a few mines worldwide. Because of the low availability and difficulties in the preparation of metallic scandium, which was first done in 1937, applications for scandium were not developed until the 1970s, when the positive effects of scandium on aluminium alloys were discovered. Its use in such alloys remains its only major application. The global trade of scandium oxide is 15–20 tonnes per year. The properties of scandium compounds are intermediate between those of aluminium and yttrium. A diagonal relationship exists between the behavior of magnesium and scandium, just as there is between beryllium and aluminium. In the chemical compounds of the elements in group 3, the predominant oxidation state is +3.

Properties

Chemical characteristics Scandium is a soft metal with a silvery appearance. It develops a slightly yellowish or pinkish cast when oxidized by air. It is susceptible to weathering and dissolves slowly in most dilute acids. It does not dissolve in a 1:1 mixture of nitric acid (HNO3) and 48.0% hydrofluoric acid (HF), possibly due to the formation of an impermeable passive layer. Scandium turnings ignite in the air with a brilliant yellow flame to form scandium oxide.

Isotopes

In nature, scandium is found exclusively as the isotope 45Sc, which has a nuclear spin of 7⁄2; this is its only stable isotope. The known isotopes of scandium range from 37Sc to 63Sc, and the most stable radioisotopes are 46Sc with a half-life of 83.76 days, 47Sc with a half-life of 3.3492 days, 48Sc at 43.67 hours, 44Sc at 4.042 hours, and 43Sc at 3.891 hours. All others have half-lives shorter than an hour, and the majority of these shorter than 15 seconds. The most stable meta state is 44m3Sc with half-life 58.6 hours; this is the lightest isotope with a long-lived isomer. The low mass isotopes are very difficult to create. The initial detection of 37Sc and 38Sc only resulted in the characterization of their mass excess. The primary decay mode of ground-state scandium isotopes at masses lower than the only stable isotope, 45Sc, is electron capture (or positron emission), but the lightest isotopes (37Sc to 39Sc) undergo proton emission instead, all three of these producing calcium isotopes. The primary decay mode for heavier isotopes is beta emission, producing titanium isotopes.

Occurrence In Earth's crust, scandium is not rare. Estimates vary from 18 to 25 ppm, which is comparable to the abundance of cobalt (20–30 ppm). Scandium is only the 50th most common element on Earth (35th most abundant element in the crust), but it is the 23rd most common element in the Sun and the 26th most abundant element in the stars. However, scandium is distributed sparsely and occurs in trace amounts in many minerals. Rare minerals from Scandinavia and Madagascar such as thortveitite, euxenite, and gadolinite are the only known concentrated sources of this element, all of which are sources of other rare earths. Thortveitite can contain up to 45% scandium oxide. The stable form of scandium is created in supernovae via the r-process. Also, scandium is created by cosmic ray spallation of the more abundant iron-peak nuclei. Example reactions are:

28Si + 17 n → 45Sc (r-process) 56Fe + p → 45Sc + 11C + n (cosmic ray spallation)

Production The world production of scandium is in the order of 15–20 tonnes per year, in the form of scandium oxide. The demand is slightly higher, and both the production and demand keep increasing. In 2003, only three mines produced scandium: the uranium and iron mines in Zhovti Vody in Ukraine, the rare-earth mines in Bayan Obo, China, and the apatite mines in the Kola Peninsula, Russia. Since then, many other countries have built scandium-producing facilities, including 5 tonnes/year (7.5 tonnes/year Sc2O3) by Nickel Asia Corporation and Sumitomo Metal Mining in the Philippines. In the United States, NioCorp Development hopes to raise $1 billion toward opening a niobium mine at its Elk Creek site in southeast Nebraska, which may be able to produce as much as 95 tonnes of scandium oxide annually. In each case, scandium is a byproduct of the extraction of other elements and is sold as scandium oxide. To produce metallic scandium, the oxide is converted to scandium fluoride and then reduced with metallic calcium.

Sc2O3 + 6 HF → 2 ScF3 + 3 H2O 2 ScF3 + 3 Ca → 3 CaF2 + 2 Sc Madagascar and the Iveland Municipality–Evje og Hornnes Municipality region in Norway have the only deposits of minerals with high scandium content, thortveitite (Sc,Y)2(Si2O7), but these are not being exploited. The mineral kolbeckite ScPO4·2H2O has a very high scandium content but is not available in any larger deposits. The absence of reliable, secure, stable, long-term production has limited the commercial applications of scandium. Despite this low level of use, scandium offers significant benefits. Particularly promising is the strengthening of aluminium alloys with as little as 0.5% scandium. Scandium-stabilized zirconia enjoys a growing market demand for use as a high-efficiency electrolyte in solid oxide fuel cells. The USGS reports that, from 2015 to 2019 in the US, the price of small quantities of scandium ingot has been $107 to $134 per gram, and that of scandium oxide $4 to $5 per gram. In August 2026, the U.S. Office of Strategic Capital committed a conditional US$400 million loan to Sunrise Energy Metals to construct the Syerston Project in New South Wales, planned as a primary scandium operation yielding 60 tonnes of scandium oxide annually.

Compounds

Scandium chemistry is almost completely dominated by the trivalent ion, Sc3+. The radii of M3+ ions in the table below indicate that the chemical properties of scandium ions have more in common with yttrium ions than with aluminium ions. In part because of this similarity, scandium is often classified as a lanthanide-like element.

Oxides and hydroxides The oxide Sc2O3 and the hydroxide Sc(OH)3 are amphoteric:

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