The rare earth elements form the largest chemically coherent group in the periodic table. Though generally unfamiliar, the rare earths are essential for hundreds of applications. The versatility and specificity of the rare earths has given them an increased level of technological, environmental, and economic importance.
There are 15 rare earth elements within the chemical group called lanthanides. Scandium and yttrium are also usually included as they have similar chemical properties and occur together. The lanthanides consist of the following: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. The lanthanides are often broken into two groups: light rare earth elements (LREEs) - lanthanum through samarium (atomic numbers 57-62) and the heavier rare earth elements (HREEs) – europium through lutetium (atomic numbers 63-71). Yttrium is typically classified as a heavy element. The term “Rare Earth” is actually a misnomer. They are not rare at all, being found in low concentrations throughout the Earth’s crust. However, their concentrations range from ten to a few hundred parts per million by weight. Therefore, finding them where they can be economically mined and processed presents a real challenge.
During the past 40 years, with the technological development, the number of applications for rare earths has increased significantly and today these elements are of critical importance to all developed economies. They are found in many advanced products within the following sectors: mechanical/metallurgical, glass and ceramics, electronics, chemical, optical, energy, life sciences, sensors and instrumentation, and consumer products.
Although rare earths comprise significant amounts of many minerals, almost all production has come from less than 10 minerals. Extraction from a potentially economic rare earth resource is strongly dependent on its REE mineralogy. Minerals that are easily broken down, such as the carbonate bastnaesite, are more desirable than those that are difficult to dissociate, such as the silicate allanite.
For more information, please see http://www.reeworld.com.