Rare earths are lanthanide elements in the periodic table of chemical elements-La, Ce, Pr, Nd, Pm, Sm, Eu, Gd and Tb. RaRE earth (re or r) for short. The word rare earth is a name left over from history. Rare earth elements were discovered at the end of 18. At that time, people often called water-insoluble solid oxides soil. Rare earth is generally separated in oxide state, which is relatively rare, so it is named rare earth. Lanthanum, cerium, praseodymium, neodymium, promethium, samarium and europium are usually called light rare earth or cerium group rare earth; Gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium yttrium are called heavy rare earths or yttrium rare earths. According to the similarity and difference of physical and chemical properties of rare earth elements, some of them are divided into three groups (some are classified as sparse elements), that is, the light rare earth groups are lanthanum, cerium, praseodymium, neodymium and promethium; The medium rare earth group is samarium, europium, gadolinium, terbium and dysprosium; The heavy rare earth groups are holmium, erbium, thulium, ytterbium, lutetium and yttrium. The discovery of these rare earth elements, from the separation of yttrium by Finn J. Gadolin in 1794 to the preparation of promethium by J. A. Malinschi in 1947, lasted for more than 50 years. Most rare earth elements were discovered by some European mineralogists, chemists and metallurgists. Polonium was obtained by Malinschi, L.E. Grand Ning and C.D. Corell of the United States from rare earth elements in uranium fission products through ion exchange separation. In the past, it was thought that promethium did not exist in nature until 1965, when a phosphate factory in Finland treated apatite, a trace of promethium was found. The average content of rare earth elements in the crust is 165.35× 10-6 (thomas lee, 1976). Rare earth elements mainly exist in the form of single minerals in nature. At present, there are more than 250 kinds of rare earth minerals and minerals containing rare earth elements in the world, among which 50 ~ 65 kinds of rare earth minerals can be regarded as independent rare earth minerals with a rare earth content of ∑ REE > 5.8%. The important rare earth minerals are mainly fluorocarbon and phosphate. The general characteristics of rare earth minerals are: first, the lack of sulfide and sulfate (only a few), which shows that rare earth elements have oxygen affinity; Second, the silicate of rare earth is mainly island-shaped, without layered, frame-shaped and chain-shaped structure; Thirdly, some rare earth minerals (especially complex oxides and silicates) are amorphous; Fourthly, the distribution of rare earth minerals is mainly silicate and oxide in magmatic rocks and pegmatite, and fluorocarbon and phosphate are mainly in hydrothermal deposits and weathered crust deposits. Most yttrium-rich minerals occur in granite and pegmatite, aerogenic hydrothermal deposits and related hydrothermal deposits. Fifth, rare earth elements are often born in the same mineral because of their similar atomic structure, chemistry and crystal chemistry, that is, cerium rare earth elements and yttrium rare earth elements often exist in the same mineral, but these elements do not exist in the same amount. Some minerals are mainly rare earths containing cerium, while others are mainly yttrium. At present, more than 250 kinds of rare earth minerals and minerals containing rare earth elements have been discovered, and the only industrial minerals suitable for current smelting conditions are 10: 1) cerium group minerals containing rare earth (lanthanum, cerium and neodymium): bastnaesite, bastnaesite and monazite. 2) Minerals rich in samarium and gadolinium: beryl, niobium yttrium ore and black rare gold ore. 3) Rare earth minerals containing yttrium (yttrium, dysprosium, erbium, thulium, etc.). ): xenotime, bastnaesite, yttrium dissolved stone, brown yttrium ore, black rare gold ore. In nature, dispersed elements mainly exist in related metal minerals, such as sphalerite, which is generally rich in cadmium, germanium, gallium and indium. Some also contain thallium, selenium and tellurium; Chalcopyrite, tetrahedrite and chalcopyrite are often rich in thallium, selenium and tellurium, and some are also rich in indium and germanium. Galena is also often rich in indium, thallium, selenium and tellurium; Molybdenite and bornite are rich in rhenium, and some are also rich in selenium. Pyrite is usually rich in thallium, gallium, selenium and tellurium. Although nearly 200 rare and dispersed elemental minerals have been discovered, there are only rare independent germanium, selenium and tellurium deposits, and the scale of the deposits is not large.