ABSTRACT
The rare earth elements (REEs) comprise the elements scandium (Sc, Z = 21) and yttrium (Y, Z = 39) and 14 lanthanides with successive atomic numbers (Z) from 57 to 71. There is a demarcation between light (lanthanum, La; cerium, Ce; praseodymium, Pr; neodymium, Nd; samarium, Sm; and europium, Eu) and heavy (gadolinium, Gd; terbium, Tb; dysprosium, Dy; holmium, Ho; erbium, Er; thulium, Tm; ytterbium, Yb; and lutetium, Lu) REEs. Promethium belongs chemically to the group of lanthanides but is an articial radioactive element that is not found in nature. REEs are often used synonymously in terminology except for Y and Sc, which are treated separately. The reason is that Sc shows a distinctly different geochemical behavior, and Y mimics heavy REEs (Nozaki, 2001).
