I.

Introduction

Rare Earth Elements, series of chemical elements of the periodic table. The rare earth elements (or rare earth metals) include the elements with atomic numbers 57 through 71, and, named in order, are lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Yttrium (atomic no. 39) and scandium (atomic no. 21) are sometimes included in the group of rare earth elements. The elements cerium (atomic no. 58) through lutetium (atomic no. 71) are commonly known as the lanthanide series.

II.

Properties

Chemically, most of the rare earth elements are trivalent (see Valence). Cerium alone forms compounds with a valence of +4. Most rare earth compounds are strongly paramagnetic. An alloy composed of iron and of rare earth metals, called misch metal, is pyrophoric. When scratched it gives off sparks capable of igniting flammable gases. It has been used in cigarette lighters, miners’ safety lamps, and automatic gas-lighting devices. Misch metal is also used in making aluminum and magnesium alloys and some types of steel. Europium has been used as a phosphor activator. In a cathode-ray color television tube it has been used to provide the red color seen by the viewer.

III.

Separation

Rare earth elements are separated from other elements in a mineral by precipitation with a suitable reagent. Separation of the rare earth elements from each other by ordinary chemical means is difficult because their chemical properties are similar, and the isolation of an individual element may involve hundreds of fractional crystallizations. With the use of ion-exchange methods the separation of an individual rare earth element can be accomplished with greater ease and precision.

Oxides of the rare earth elements are called rare earths, and are found in minerals that are actually more abundant than those of some other metals, such as those in the platinum group. A major source of rare earths is the mineral monazite. Some other rare minerals that also contain small amounts of rare earths include cerite, gadolinite, and samarskite.