Rare earth elements
Rare earth elements
rare earth elements
The atomic numbers in group IIIB of the periodic system are 21, 39 and 57-71 A collective name for 17 chemical elements. Among them, the 15 chemical elements with atomic numbers from 57 to 71 are collectively called lanthanide elements. 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 called light rare earths; gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium are called heavy rare earths. Rare earth elements are a name left over from history. Solid oxides that are insoluble in water are usually called earth. In the 18th century, these 17 elements were very rare and had not been discovered in large quantities, so they were named rare earth elements. It has been found that they are not rare. In particular, China is very rich in rare earth resources and ranks first in the world in terms of reserves with mining value. From the discovery of yttrium by J. Gadolin of Finland in the town of Uterby near Stockholm, Sweden, in 1794, to the separation of promethium from the fission product of uranium by J.A. Mariinsky of the United States in 1947, it has been more than 150 years.
More than 250 kinds of rare earth minerals have been discovered, the most important ones are bastnasite [(Ce, La) FCO3], monazite [CePO4, Th3 (PO4) 4], and xenotime (YPO4), black rare gold ore [(Y, Ce, Ca) (Nb, Ta, Ti) 2O6], beryllium yttrium ore (Y2FeBe2Si2O10), allanite [(Ca, Ce) 2 (Al, Fe) 3Si3O12 ], cerium silica [(Ce, Y, Pr) 2Si2O7·H2O].
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