Rare earth elements
rare earth element
Periodic system, group IIIB, the atomic number of 21, 39, and 57 ~ 71 of the 17 chemical elements collectively. The 15 chemical elements with atomic numbers 57 to 71 are collectively known as the lanthanides. Rare earth elements include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium are usually referred to as light rare earths; gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium are referred to as heavy rare earths. Rare earth elements is the name of the historical legacy, usually insoluble solid oxides called earth, and in the 18th century, these 17 elements are very rare has not been found in large quantities, and thus named rare earth elements. It has been found that they are not rare, especially China's rare earth resources are very rich, with mining value of the reserves accounted for the world's first. From 1794 Finland J Gadolin from Sweden Stockholm near the town of ütterby found yttrium began, has been to the United States in 1947 JA Mariinsky from the fission products of uranium in the separation of promethium, *** through more than 150 years.
More than 250 rare-earth minerals have been discovered, the most important of which are cerium lanthanum fluorocarbon [(Ce, La)FCO3], monazite [CePO4, Th3(PO4)4], yttrium phosphorite (YPO4), black rare-earth gold ore [(Y, Ce, Ca) (Nb, Ta, Ti)2O6], and silicoberyllium yttrium ore (Y2FeBe2Si2O10), brown cordite [(Ca,Ce)2(Al,Fe)3Si3O12], and cerussite [(Ce,Y,Pr)2Si2O7-H2O].
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