in chemistry, group of metals including those of the lanthanide series and actinide series and usually yttrium, sometimes scandium and thorium, and rarely zirconium. Promethium, which is not found in nature, is not usually considered a rare-earth metal. The metals usually occur together in minerals as their oxides (rare earths) and are somewhat difficult to separate because of their chemical similarity. A subgroup of the rare-earth metals, consisting of those with atomic numbers between 57 and 63 and ytterbium, is often called the cerium metals. Misch metal is an alloy of the cerium metals often used in lighter flints, in alloys with other metals (especially magnesium), and to remove residual gases in the manufacture of vacuum tubes. Individual metals may be isolated as their compounds by ion exchange methods, solvent extraction, or fractional crystallization, and chemically or electrolytically reduced to the pure metal. Uses are discussed in articles on individual elements.
The lanthanide (rare earth) elements. The lanthanides are a series of 14 consecutive elements of the periodic table , comprising lanthanum ...
Tb. Atomic number 65, group IIIB of the periodic table, a rare-earth element of the yttrium subgroup (lanthanide series), aw 158.9254, valences of 3
a series of metallic elements, included in the rare-earth metals, in Group 3 of the periodic table. Members of the series are often called lanthanid