ACS Chemistry for Life

The 17 rare earth elements, or lanthanides, consist of elements 21 (scandium), 39 (yttrium), and 57 (lanthanum) to 71 (lutetium). The rare earths were so named because of their low concentration in minerals which were scarce. However, some of the elements are not as rare as once thought. Today, the rare earths are used in color television picture tubes, glass polishes, ceramic glazes, protective goggles, lasers, and superconductors. Most recently, some have been used in diagnostic imaging in the field of nuclear medicine.

The story of their discovery is probably the most confusing and complex of any of the elements. The search for and identification of the rare earth elements constituted an integral part of the development of science and technology in the late 19th and early 20th centuries. Several factors made their identification difficult: the chemical and physical properties of the different elements are quite similar; the elements were isolated as “earths” or oxides of the elements; and the methods of separation and purification depended on laborious fractional precipitation and crystallization techniques. Compounding the difficulties of separation were a lack of good methods for identification and assessment of purity and a lack of knowledge of the number of rare earth elements that existed.

A University of New Hampshire (UNH) professor, Charles James (1880-1928), all but forgotten today, was well known and highly respected by his contemporaries for his contribution to rare earth chemistry.  James’s use of bromates and double magnesium nitrates for fractional crystallization became known as the “James Method.” Developed in the early 1900s, his method was used widely by others and remained the best for separating rare earth elements until the advent of ion exchange in the 1940s.

Visit  National Historic Chemical Landmarks  to learn more about the separation of rare Earth elements.

Excerpted with permission, National Historic Chemical Landmarks Program
www.acs.org/landmarks