What are rare-earth elements and why is everyone looking for them? | Explained

Rare-earth elements are a set of metallic elements in the periodic table. Chemists usually refer to a group of 17 elements when they use this label: the 15 lanthanides from lanthanum to lutetium, and scandium and yttrium. In most classroom periodic tables, the lanthanides are shown as a separate row placed beneath the main periodic table. Scandium and yttrium lie in the main table, in Group 3, above and near the transition metals. Even when they’re not very scarce in the earth’s crust, they tend to be spread out in low concentrations and mixed together with each other in the same minerals, so they’re difficult and expensive to separate. However, countries worldwide are interested in acquiring them because they’re crucial for high-performance magnets , specialised lighting and optics, catalysts, and other components that underpin many green technologies and electronics. History and technology The rare-earth elements are scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, prometheum, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. They’re called ‘rare earths’ for historical reasons. “Earth” was an old chemistry term for oxide powders and many of these elements were first identified as oxides from which they couldn’t be isolated easily. These elements are also rarely found as pure native metals in nature. However, people often use the term ‘rare-earth’ loosely, leading to confusion. Some use ‘rare-earths’ to mean only the lanthanides. Some others bundle rare-earths with ‘strategic’ or ‘critical’ elements such as lithium, cobalt, gallium, and germanium even though the latter aren’t rare-earth elements. The periodic table of elements. | Photo Credit: Sandbh (CC BY-SA) Rare-earth elements show up in many contemporary technologies because of their useful electrical, magnetic and/or optical behaviour. One particularly important application is as permanent magnets. Neodymium-iron-boron magnets, which are the world’s most common magnet type involving a rare-earth element, and which sometimes also include praseodymium and small quantities of heavier rare-earth elements, are used in motors and generators, including in many electric vehicles and in wind turbines. Phosphors - substances that emit light when irradiated - also incorporate europium and terbium while dopants in lasers and optical devices (including in fibre optics) use neodymium and erbium. Rare-earth elements are also used in catalysts, glass and ceramics, polishing powders, and other specialised materials. Magnetic chemistry In permanent magnets, rare-earth atoms have electrons in the 4f shell that behave differently from the other electrons. The 4f electrons are relatively more localised, meaning they stay close to the nucleus, whereas the other electrons become ‘smeared out’ when they become part of bonds in a solid. As a result the 4f electrons maintain a strong magnetic moment, i.e. they behave very faithfully like small magnets. An atom with multiple electrons like this also behaves more strongly like a magnet. Every good permanent magnet needs to have two things: a large magnetisation, meaning many atomic magnetic moments can line up in the same direction to make a strong overall field; and stability, which means once the magnetic moments line up, they don’t easily...

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