Rare-earth element

A rare-earth element is one of 17 metals: the 15 lanthanides, scandium, and yttrium. Their similar chemistry and frequent occurrence together make them difficult to separate.

Lanthanide: One of the 15 metallic elements from lanthanum to lutetium, commonly characterized by filling the 4f electron shell. The lanthanides form the largest and defining part of the rare-earth group.
4f orbital: An atomic orbital with angular momentum quantum number three, occupied progressively across the lanthanide series. Its electrons underlie many characteristic magnetic and optical properties of lanthanides.
Neodymium magnet: A powerful permanent magnet made primarily from a neodymium–iron–boron alloy. Neodymium magnets are a major use of rare-earth elements in motors and generators.
Ytterby: A village on the Swedish island of Resarö associated with the discovery of several chemical elements. The minerals found near Ytterby yielded multiple rare-earth elements and inspired several element names.
Rare-earth element mining: The extraction of rare-earth-bearing ores and their processing into usable concentrates or compounds. Mining supplies essential materials but can disturb land and generate chemically complex waste.
Scandium: A lightweight metallic element with atomic number 21, classified as a transition metal. Scandium is included despite its different position and lighter mass because its chemistry resembles the group’s.
Oxidation state: The formal charge assigned to an atom in a compound under a specified electron-bookkeeping convention. Most rare earths favor the +3 state, while some also show stable alternatives.
Phosphor: A material that emits light after absorbing energy, often used in displays and lamps. Europium and terbium compounds provide characteristic colors in many phosphors.
Carl Gustaf Mosander: A Swedish chemist who separated several new substances from minerals in the early nineteenth century. Mosander’s separations helped establish that supposedly single rare-earth materials contained multiple elements.
Rare-earth element separation: The industrial isolation of individual rare-earth elements from mixtures using chemical or physical processes. Similar ionic properties make separation energy-, reagent-, and infrastructure-intensive.

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