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What is a rare earth metal?

In contradiction to their name, rare earth metals (circled on the periodic table to the right) are not particularly rare but they tend to be present with other compounds and only in very small quantities, making mining them extremely cost inefficient. In the past, rare earth metals were not particularly valuable so mines that produced them generally were mining for other more valuable metals and produced rare earth metals as a by-product. As science progressed, the importance of rare earth metals grew. They are used as catalysts and as pigments for glass and ceramics. In addition, they are being used extensively in new "green technology" such as in hybrid car batteries and solar cells. They also have uses in miniature nuclear batteries, lasers repeaters, superconductors and magnets.

Why are they important?

In the U.S., many mineral deposits have been mined so that mining companies have shifted their focus to over-seas deposits, specifically China. Since rare earth are generally a by-product form other mines, the U.S. produces an insignificant portion of the world's supply, however China which is still mining for other metals produces 97% of the world's supply. This has caused consumers of rare earth metals to be nervous. With so much production from one country, any shift in policy could cause major problems. This was apparent when China cut exports of rare earth elements by more than 70%, disrupting manufacturing in Japan, Europe and the US and causing prices to skyrocket 40%. To make matters worse, the demand for rare earth metals is increasing. By 2015, global demand for rare earths is expected to reach 205,000 tons.
Due to the market domination by China, there has been a drive in the U.S. to reopen some closed mines in the United States. Molycorp Minerals and Rare Element Resources are two of the premiere U.S. companies trying to do just this. However, the issue still remains that China is the only country with the facilities necessary for final processing of the mined material. China's stronghold over the market and cut in exports has been directly reflected on the stock value of rare earth metals.
Another important point is that currently there is no method for recycling rare earth metals. Because they are typically only used in very very small quantities -- fractions of a percent of a material's weight -- it is difficult and expensive to extract them in any appreciable amount. To exacerbate the problem, they are also mostly inert and will not easily react with other chemicals. Extensive efforts are being made to research a means of recovering rare earth metals from secondary sources such as scrap electronics and batteries. Such a process would make the United States less reliant on China for our rare earth supplies.
It could also prove very lucrative for the inventor of the method; a 300g sample of Europium like the one pictured is worth just over $25,000.
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What are rare earth metals used for?

Rare earth metals have various applications, particularly in electronics and communication. They are, however, infrequently used in their metallic form but instead are usually dopants in other materials. Some applications include Europium in cathode ray tubes (CRT) and liquid crystal displays (LCD), Erbium in fiber optic cables, Lanthanum in fuel cells, and several rare earth metals such as Neodymium and Samarium in magnets.
Europium oxide (Eu2O3) is doped into phosphorescent Y2O3 which narrows the wavelengths of light emitted by the yttria and allows the phosphor to give a much more intense red light [brittanica]. Europium oxide does this by creating inhomogeneities in the crystal structure of yttria because of differences in ion size. In fiber optics, at regular distance intervals there is a section of cable that acts as a laser amplifier to strengthen the signal running through the cable. This amplifier is created by doping regular fiber optic cable with trace amounts of Erbium, which slightly alters the optical properties of the cable.
One of the most commonly known uses of rare earth metals, especially Neodymium, is in rare earth magnets. These magnets are notoriously strong because of their large effective magnetic moment. The valence electrons in a rare earth metal exist in S and F orbitals. Elements like Neodymium, Samarium, Gadolinium, Dysprosium, andPromethium have large numbers of unpaired electrons in these orbitals, which allows the angular momentum to be maximized. This results in a strong magnetic effect that can be manipulated for use in small actuators in hard drive read/write heads or in massive motors like those seen in wind turbines. The image here shows an example of the neodymium magnets used in a wind turbine motor.
Lanthanum is used in several different cathode materials for fuel cell applications. It is temperature resistant and matches the thermal expansion properties of yttria-stabilized zirconia (YSZ), which is a common material in fuel cells. YSZ has a high mobility for oxygen vacancies, which allows H2 fuel to interact with air to produce electrical current and output steam as an exhaust gas. Materials like lanthanum strontium magnetite act as electrodes for this reaction.

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