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EDUCATOR’S PAGE REExamining a


Previously Unimportant Group of Elements


Michael J. Urban, MEM-1910


What do efficiency light bulbs, cell phone cameras, catalytic converters, and computer monitors have in common? Not a whole lot, except that they all typically incorporate rare earth elements in some of their components. Rare earth ele- ments (REE) are highly prized for their unique properties, allowing them to be used in a variety of electronic and other applications. While the United States once led the world in the excavation and production of these precious resources, the largest global producer is presently China.


What are They?


The rare earth elements (REEs) are essentially those elements found in the lanthanide series1 of the periodic table -  used to describe them, the least abun- dant of them (thulium and lutetium) are still more plentiful than gold (1), while the others are found in quantities com- parable to that of industrial metals like nickel and copper (2). A bigger problem with them is that they are generally dif- ficult and often costly to extract, and only found in a few geologic contexts.


At an elemental level, the REEs all have the same valence electron con- figurations2 and this accounts for their tendency to exhibit similar physical properties: in general, most are sil-


ver-gray-white metals (3). Yttrium and scandium are often included with the lanthanides because they have similar properties3. Of the REEs, only prome- thium is essentially absent from the Earth’s crust because it has no long-lived isotopes4.


How are They Used and Why are They Important?


As implied in the introduction, the applications of REEs are diverse. REEs are used as phosphors in television and        the red and green, respectively], fiber-  Ho, Sm], devices requiring permanent              are many additional uses for REEs too.


Neodymium, along with other REEs, are magnetic and can be used to build permanent magnets. Neodymium-iron- boron (NIB) magnets, developed in the 1980s, are small, powerful, and inex- pensive, making them ideal for the digital age when so many electronic components require magnets (e.g., disk drives). Magnetic REEs and lanthanum, for rechargeable batteries, are used as


components in electric and hybrid cars in order to reduce weight. Cerium is used in the manufacture of catalytic converters for vehicles: the presence of cerium oxide in catalytic converters increases the efficiency of the reactions that change nitrogen oxide and carbon monoxide to nitrogen and carbon dioxide, respec- tively, by absorbing or releasing oxygen during the combustion process (5).


What Materials are They Found In?


The REEs can be found in economi- cally viable quantities in carbonatites, certain clays5, and mineral-bearing placer deposits (1). Carbonatites are calcite-rich, silica poor, igneous rocks derived from alkaline magmas (6). These rocks are often mined for copper and other metals, but REEs can be obtained as byproducts. Some clays, although containing minimal concentrations of REEs, require less processing, and there- fore, are a better source material (1). The minerals bastnäsite, monazite, and xenotime contain REEs as part of their chemical structure and all can be found as accessory minerals in carbonatites (7). Bastnäsite is a carbonate-fluorine mineral and a principal ore for REEs. Monazite and xenotime are phosphate minerals that occur as placer deposits in beach sands, and both may be accessory minerals in granite (8).


1. The lanthanide, or lanthanoid, series includes lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and Lutetium (Lu).


2. The lanthanides have one electron in the 5d orbital and two in the 6s orbital; they fill the 4f orbital sequentially with increasing atomic number. In this case, the 5d and 6s electrons represent the outermost valence electrons – those that are responsible for their properties (Stwertka, 2002) and involve themselves in bonding.


3. Both yttrium (Y) and scandium (Sc) have one electron in their outermost “d” orbital and two in their outermost “s” orbital, just like the lanthanides.


4. Promethium (Pr) has no long-lived isotopes, but it has been synthesized in the laboratory and in nuclear reactors. The longest-lived isotope, Pr-145, has a half-life of 17.7 years (Stwertka, 2002).


5. Ion-adsorption clays. 36 TPG  Apr.May.Jun 2016 www.aipg.org


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