Rare earth metals are also known by the lightest member, lanthanum, as the lanthanides. Lanthanide is derived from the Greek word lanthanein, which means to lie hidden.
The Rare Earth Metals consist of the f-block elements.
Despite their name, rare earth elements are relatively plentiful in the Earth's crust. Cerium, one of the rare earth elements, is the 25th most abundant element at 68 parts per million, which is similar to the prevalence of Copper. However, rare earth elements are not naturally found in their purified and usable form, leading to the name "Rare" Earth Metals. The first mineral discovered was gadolinite, a compound of Cerium, Yttrium, Iron, Silicon, and other elements.
Many of the rare-earth elements have their names derived from where they were found, yttrium for example was named after the town of Ytterby in Sweden where it was found. Several other elements bear names derived from this location.
Rare Earth Metals can react with a wide variety of metals and non-metals to form a number of different compounds that each have distinct chemical behaviors. For this reason Rare Earth metals are being used more commonly in everyday items. These products include: hybrid cars, hard drives, wind powered turbines, catalytic converters, MRIs, and even iPods.
Info found here: http://en.wikipedia.org/wiki/Rare_earth_element
Obtaining the Rare Earth Metals
Until 1948, most of the world's rare earth metals were found in sand deposits in India and Brazil. In the 1950's, South Africa became the world's rare earth metal source, after veins of monazite were discovered there. Through the 1960's till the 1980's the Mountian pass rare earth mine in California was the leading producer of rare earth metals. India and South Africa still have a margin of the rare earth production market, but today China is clearly the world's leading Rare Earth metal producer. China produced 95% of the worlds rare earth supply ins 2009. Due to recent demand in these rare earth metals for different consumer products-(ie. hard drives, and MRI's)-there has been a strain on the rare earth metal supply. There are growing concerns that if new sources are found there could be a shortage.
Rare earth metals are, themselves, not uncommon. The estimated average concentration of the rare earth elements in the Earth's crust ranges from 150 to 220 parts per million, exceeding the concentrations of many other metals that are mined on an industrial scale, such as copper (55 parts per million) and zinc (70 parts per million). Unlike most commercially mined base and precious metals, however, rare earth elements are rarely concentrated into mineable ore deposits. Rare earth metals are most often found in the forms of monazite, a phosphate mineral; bastnasite, a carbon-fluorine mineral; or in the form of oxides.
Info found here: http://en.wikipedia.org/wiki/Rare_earth_element
Rare earth metals belong to a group in the periodic table known as the Lanthanides (elements 58 to 71). Due to lanthanide contraction, which is caused by poor shielding of nuclear charge by 4f electrons, causing 6s electrons to be drawn toward the nucleus, there is a greater than expected decrease in ionic radii of the lanthanides. Lanthanide contraction increases the similarity in atomic radii between adjacent lanthanides, making it much more difficult to separate these elements from naturally occurring ores and materials.
Due to Oddo-Harkins Rule, lanthanides have varying concentrations in the ores in which they are found. Oddo-Harkins Rule states that even-numbered elements tend to occur more often than odd-numbered elements due to a single, unpaired electron in odd-numbered element electron configurations. These electrons are easily lost or bonded to, causing odd-numbered elements to occur less in their pure forms. When applied to the lanthanides, it was found that even-numbered lanthanides occur in abundances of about 5% in a compound, while odd-numbered lanthanides occur at abundances of about 1%.
Lanthanides tend to adopt a hexagonal closest packed lattice, but some (Ce and Yb) adopt a face-centered structure. Europium adopts a body-centered cubic lattice, and Samarium adopts a rhombohedral lattice.
Lanthanides are most stable at an oxidation state of +3, though Ce may adopt a stable +4 oxidation state and Eu may adopt a +2 oxidation state. The reduction potentials of the lanthanides range from -1.99 V in Eu to -2.35 V in Pr, making the lanthanides highly reducible.
Lanthanides are not particularly soluble in water, but will form strong, complex, chelating ligands, such as in Ce(NO3)6[3-]. Larger (early) lanthanides have been found to coordinate with as many as 9 water molecules in aqueous solution, but later lanthanides coordinate with 8 water molecules in aqueous solution.
Elements and Their Uses
- Scandium - Used for Aerospace components, and mercury vapor lamps.
- Yttrium - Yttrium Aluminium Garnet laser, High temperature superconductors, Microwave filters, energy-efficient light bulbs.
- Lanthanum - High refractive index glass, flint, hydrogen storage, battery-electrodes, camera lenses, fluid catalytic cracking catalyst for oil refineries.
- Cerium - Oxidizing agent, polishing powder, Yellow colors in glass and ceramics, catalyst for self-cleaning ovens, Cracking catalyst for oil refineries. Flints for lighters.
- Praseodymium - Rare-earth magnets, lasers, carbon arc lighting, colorant in glasses and enamels, used in welding goggles glass, flint products.
- Neodymium - Rare-earth magnets, lasers, violet colors in glass and ceramics, ceramic capacitors, hard drive magnets.
- Promethium - Nuclear batteries.
- Samarium - Rare-earth magnets, lasers, neutron capture, masers (Microwave Amplification by Stimulated Emission of Radiation).
- Europium - Red and blue phospors, lasers, mercury-vapor lamps, NMR (Nuclear magnetic resonance).
- Gadolinium - Rare-earth magnets, high refractive index glass or garnets, lasers, x-ray tubes, computer memories, neutron capture, MRI contrast agent, NMR.
- Terbium - Green phosphors, lasers, fluorescent lamps.
- Dysprosium - Rare-earth magnets, lasers.
- Holmium - Lasers.
- Erbium - Lasers, Vanadi
- um steel.
- Thulium - Portable X-ray machines.
- Ytterbium - infrared lasers, chemical reducing agent.
- Lutetium - Positron emission tomography - PET scan detectors, high refractive index glass.
Info found here: http://en.wikipedia.org/wiki/Rare_earth_element
Important Rare Earth Metals
Lanthanum: Lanthanum is used in Toyota Prius car batteries. The batteries are referred to as Nickel-metal hydride batteries, but the metal in question is lanthanum. With the big breakthrough in batteries these Nickel-Lanthanum hydride batteries are almost twice as efficient as the normal lead acid batteries and pack into a smaller space.
Production: Lanthanum is most commonly found in Monazite and bastnasite. The mineral mixtures are crushed and ground. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with sodium hydroxide to pH 3-4. thorium precipitates out of solution as hydroxide and is removed. After that, the solution is treated with ammonium oxalate to convert rare earths to their insoluble oxalate The oxalates are converted to oxides by annealing. The oxides are dissolved in
that excludes one of the main components, cerium, whose oxide is insoluble in HNO. Lanthanum is separated as a double salt with ammonium nitrate by crystallization. This salt is relatively less soluble than other rare earth double salts and therefore stays in the residue.
Europium: Rare earth metals have a long history, it starts with them being found blended together in a metal alloy known as mischmetal in 1891. This Mischmetal became an ingredient in lamp mantels. These devices were hung above ope flames, and they would burn a bright white light, by which people could work by. In 1967 Europium, being the first of the rare earth metals to be isolated was used as a source of red color in TV sets. There had been color TV sets before Europium, but the red color came from phosphors that would glow when hit with electrons or energized particles. These phosphors when hit with energy didn't glow very bright, when Europium was first introduced, it really made that red color pop. Today, europum is still used to produce that red color, but since cathode ray tube TV's are heading towards extiction, Europium is more likely going to be used in white LED-based lights. Some LED lights are produced by mixing different color lights together and Europium is used as one of the ingredients to create a high-quality, attractive shade of white.
Production: Europium is associated with the other rare earth elements and is therefore mined together with them. Separation of the rare earth elements is a step in the later processing. Rare earth elements are found in the minerals bastnasite, loparite, xenotime, and monozite in mineable quantities. The first two are orthophosphate minerals LnPO (Ln denotes a mixture of all the lanthanides except promethium), and the third is a fluorocarbonate LnCOF. Monazite also contains thorium and yttrium, which complicates handling b ecause thorium and its decay products are radioactive. For the extraction from the ore and the isolation of individual lanthanides, several methods have been developed. The choice of method is based on the concentration and composition of the ore and on the distribution of the individual lanthanides in the resulting concentrate. Roasting the ore and subsequent acidic and basic leaching is used mostly to produce a concentrate of lanthanides. If cerium is the dominant lanthanide, then it is converted from cerium(III) to cerium(IV) and then precipitated. Further separation by solvent extraction or ion exchange chromatography yields a fraction which is enriched in europium. This fraction is reduced with zinc, zinc/amalgam, electrolysis or other methods converting the europium(III) to europium(II). Europium(II) reacts in a way similar to that of alkaline earth metals and therefore it can be precipitated as carbonate or is co-precipitated with barium sulfate. Europium metal is available through the electrolysis of a mixture of molten EuCl and NaCl (or CaCl) in a graphite cell, which serves as cathode, using graphite as anode. The other product is chlorine gas.
Erbium: Erbium has a variety of uses, ranging from creating a pink color in glass and decorator vases, to being used in optic fiber cable. In optic fiber cable Erbium amplifies the signal of the light to carry it through the fiber cable. Erbium can also be used in dental surgery and skin treatments because it doesn't build up much heat in the human skin it's pointed at. Erbium is a good example of how rare earth metals work, they aren't used to make up anything, but they are used in small doses in alloys and composites to get reactions that wouldn't happen when they were on their own.
Production: Crushed minerals are attacked by hydrochloric or sulfuric acid that transforms insoluble rare-earth oxides into soluble chlorides or sulfates. The acidic filtrates are partially neutralized with caustic soda (sodium hydroxide) to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. After that the solution is treated with ammonium oxalate to convert rare earths into their insoluble oxalates. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid that excludes one of the main components, cerium, whose oxide is insoluble in HNO3. The solution is treated with magnesium nitrate to
produce a crystallized mixture of double salts of rare-earth metals. The salts are then separated by ion exchange. In this process, rare-earth ions are absorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agent. Erbium metal is obtained from its oxide or salts by heating with calcium at 1450 °C under argon atmosphere.
Neodymium: This element is what is used in things like Ipods, Hard drives, and even wind turbines. This special metal has an extremely strong magnetic field, because of this it has allowed different products like Ipods to even exist. The Sony walkman was one of the most popular portable music players on the market and the reason why Sony could make the Walkman portable was by utalizing the unique strenth of its magnetic field. An element by the name of samarium, this element allowed Sony to develop much smaller and stronger magnets that before were impossible to create with the older less powerful magnets. Since then companies have implemented Neodymium in things like Hard drives, and MP3 players because Neodymium is an even smaller and stronger magnet than samarium. Without an element like Neodymium we would still have much larger and bulkier technology to do the same tasks as the technology we use today.
Production: Neodymium is never found in nature as the free element, but rather it occurs in ores such as monozite and bastnäsite that contain small amounts of all the rare earth metals. Neodymium is typically 10% to 18% of the rare earth content of commercial deposits of the light rare earth element minerals bastnasite and monazite. With neodymium compounds being the most strongly colored for the trivalent lanthanides, that percentage of neodymium can occa
sionally dominate the coloration of rare earth minerals—when competing chromophores are absent. It usually gives a pink coloration. As with neodymium glasses, such minerals change their colors under the differing lighting conditions. The absorption bands of neodymium interact with the visible emission spectrum of mercury vapor, with the unfiltered shortwave UV light causing neodymium-containing minerals to reflect a distinctive green color. This can be observed with monazite-containing sands or bastnasite-containing ore.
Rare Earth Metals, although abuntant, require forceful refining techniques to obtain a pure form of the element. These techniques can result in major enviromental pollution as well as serious concerns for the workers' short term and long term health. Loose monitering of the rare earth metal refinaries have lead to dramatic conquenses in both China and Mayalsia, creating cause for global concern as the demand for inexpensive rare earth metals rises.
In China, many of the waste products of rare earth metal processing is dumped into reservoirs called “rare earth lakes” around the plant. Along with the various oils and toxic chemicals that are deposited into these “lakes”,
there can also be varying concentrations of radioactive uranium and thorium. The toxic waste products of the rare earth processing sites can easily seep into the ground and spread into the surrounding land. Farmers near China’s Baotou plant complain of dying crops, loss of teeth, and loss of hair. The soil in these areas also tests positive for high concentrations of carcinogens and other cancer-causing toxins. Similar soil erosion, soil acidification, and radioactive effects have been reported in other areas where rare earth metals are processed, such as Australia, Mayalsia, and the United States.
With the rise in environmental awareness, there has been increasing necessity for a solution to the pollution caused by rare earth metals. China has begun to cut their production of rare earth metals in favor of sustaining the environment; however, demand for these metals continues to increase as technology develops. In response, the United States has recently reopened up an old rare earth mine in Mountain Pass, California owned by Molycorp Minerals LLC. The mine was originally closed in 1998 due to a series of radioactive spill that contaminated the Ivanpah Dry Lake and surrounding ground water. Since, then, Molycorp plans to invest around 500 million dollars to expand the plant and implement environmentally-friendly processing procedures. These procedures would ideally include the use of less acid and radioactive by-products, as well as safe desposal of toxic byproducts.
Recently, efforts have been dedicated to researching potential recycling methods for rare earth metals. Hitachi, one of the largest companies in Japan, has joined efforts with Panasonic Cor. and Sharp Cor. to develop a clean and relatively cheap way to refine rare earth metals from recycled products. The main difficulty with recycling these metals is extracting them from the products. Currently, they have been able to extract and refine rare earth metals in small amounts without using acid, but complications remain in converting this into a large-scale, automated processing system.