What Are Rare Earth Elements (REEs)?
Rare earth elements are a group of seventeen chemical elements that occur together in the periodic table (see image at right). The group consists of yttrium and the 15 lanthanide elements (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). Scandium is found in most rare earth element deposits and is sometimes classified as a rare earth element.
The rare earth elements are all metals and the group is often referred to as the “rare earth metals”. These metals have many similar properties and that often causes them to be found together in geologic deposits.
Some researchers do not consider scandium to be a rare earth element, however the International Union of Pure and Applied Chemistry includes scandium in their rare earth element definition.
Uses of Rare Earth Elements
Rare earth metals and alloys that contain them are used in many devices that people use every day such as: computer memory, DVD’s, rechargeable batteries, cell phones, car catalytic converters, magnets, fluorescent lighting and much more.
During the past twenty years there has been an explosion in demand for many items that require rare earth metals. Twenty years ago there were very few cell phones in use but the number has risen to over 5 billion in use today. The usage of computers and DVDs has grown almost as fast as cell phones.
Many rechargeable batteries are made with rare earth compounds. Demand for the batteries is being driven by demand for portable electronic devices such as cell phones, readers, computers and cameras.
Several pounds of rare earth compounds are in batteries that power electric vehicles and hybrid-electric vehicles. As concerns for energy independence, climate change and other issues drive the sale of electric vehicles the demand for batteries made with rare earth compounds will climb even faster.
Rare earths are used as catalysts, phosphors and polishing compounds. These are used for air pollution control, illuminated screens on electronic devices and optical-quality glass. All of these products are expected to experience rising demand.
Other substances can be substituted for rare earth elements in their most important uses, however, these substitutes are usually less effective and costly.
From the 1950s until the early 2000s cerium oxide was a very popular lapidary polish. It was inexpensive and very effective. The recent price increases have almost eliminated the use of cerium oxide in the lapidary arts.
Major Uses of Rare Earth Elements
Lanthanum comes from the mineral bastnasite, and is extracted via a method called “solvent extraction.” Lanthanum is a strategically important rare earth element due to its activity in catalysts that are critical in petroleum refining. By one estimate, lanthanum “cracking-agents” increase refinery yield by as much as 10%, while reducing overall refinery power consumption.
Cerium is the most abundant of the rare earth elements. Cerium is critical in the manufacture of environmental protection and pollution-control systems, from automobiles to oil refineries. Cerium oxides, and other cerium compounds, go into catalytic converters and larger-scale equipment to reduce the sulfur oxide emissions. Cerium is a diesel fuel additive for micro-filtration of pollutants, and promotes more complete fuel combustion for more energy efficiency.
Neodymium is a critical component of strong permanent magnets. Cell phones, portable CD players, computers and most modern sound systems would not exist in their current form without using neodymium magnets. Neodymium-Iron- Boron (NdFeB) permanent magnets are essential for miniaturizing a variety of technologies. These magnets maximize the power/cost ratio, and are used in a large variety of motors and mechanical systems.
Europium offers exceptional properties of photon emission. When it absorbs electrons or UV radiation, the europium atom changes energy levels to create a visible, luminescent emission. This emission creates the perfect red phosphors used in color televisions and computer screens around the world. Europium is also used in fluorescent lighting, which cuts energy use by 75% compared to incandescent lighting. In the medical field, europium is used to tag complex biochemical agents which helps to trace these materials during tissue research.
Praseodymium comprises just 4% of the lanthanide content of bastnasite, but is used as a common coloring pigment. Along with neodymium, praseodymium is used to filter certain wavelengths of light. So praseodymium finds specific uses in photographic filters, airport signal lenses, welder’s glasses, as well as broad uses in ceramic tile and glass (usually yellow). When used in an alloy, praseodymium is a component of permanent magnet systems designed for small motors. Praseodymium also has applications in internal combustion engines, as a catalyst for pollution control.
Yttrium is rare in bastnasite, so is usually recovered from even more obscure minerals and ores. Still, almost every vehicle on the road contains yttriumbased materials that improve the fuel efficiency of the engine. Another important use of yttrium is in microwave communication devices. Yttrium- Iron-Garnets (YIG) are used as resonators in frequency meters, magnetic field measurement devices, tunable transistors and Gunn oscillators. Yttrium goes into laser crystals specific to spectral characteristics for high-performance communication systems.
Other Rare Earth Elements
Most of the remaining lanthanides fall into the group known as the “heavies” and include: Samarium, Gadolinium, Dysprosium, Terbium, Holmium, Erbium, Thulium, Ytterbium, and Lutetium.
Samarium has properties of spectral absorption that make it useful in filter glasses that surround neodymium laser rods.
Gadolinium offers unique magnetic behavior. Thus this element is at the heart of magneto-optic recording technology, and other technology used in handling computer data.
Dysprosium is a widely used rare earth element that helps to make electronic components smaller and faster.
Terbium is used in energy efficient fluorescent lamps. There are various terbium metal alloys that provide metallic films for magnetooptic data recording.
Holmium is exceedingly rare and expensive. Hence it has few commercial uses.
Erbium has remarkable optical properties that make it essential for use in long-range fiber optic data transmission.
Thulium is the rarest of the rare earth elements. Its chemistry is similar to that of Yttrium. Due to its unique photographic properties, Thulium is used in sensitive X-ray phosphors to reduce X-ray exposure.
Ytterbium resembles Yttrium in broad chemical behavior. When subject to high stresses, the electrical resistance of the metal increases by an order of magnitude. So ytterbium is used in stress gauges to monitor ground deformations caused, for example, by earthquakes or underground explosions.
Lutetium, the last member of the Lanthanide series is, along with thulium, the least abundant. It is recovered, by ion-exchange routines, in small quantities from yttrium-concentrates and is available as a high-purity oxide. Cerium-doped lutetium oxyorthosilicate (LSO) is currently used in detectors in positron emission tomography (PET).
|Did You Know? Tiny amounts of rare earth metals are used in most small electronic devices. These devices have a short life-span and REE recycling is infrequently done. Billions are thrown away each year. Image © Bakaleev Aleksey, iStockphoto.|
Critical Defense Uses of Rare Earth Elements
Rare earth elements play an essential role in our national defense. In the Gulf Wars, night-vision goggles, precision-guided weapons and other defense technology gave the United States military a tremendous advantage. Rare earth metals are key ingredients for making the very hard alloys used to make armored vehicles and projectiles that shatter upon impact in thousands of sharp fragments.
Substitutes can be used for rare earth elements in some defense applications, however, those subsitutes are not as effective and that will diminish military superiority. Several uses of rare earth elements are summarized in the table below (5).
|Defense Uses of Rare Earth Elements|
|Neodymium||laser range-finders, guidance systems, communications|
|Europium||fluorescents and phosphors in lamps and monitors|
|Erbium||amplifiers in fiber-optic data transmission|
|Samarium||pernament magnets that are stable at high temperatures|
|Samarium||“white noise” production in stealth technology|
Are These Elements Really “Rare”?
Rare earth elements are not as “rare” as their name implies. Thulium and lutetium are the two least abundant rare earth elements – but they each have an average crustal abundance that is nearly 200 times greater than the crustal abundance of gold (1). However, these metals are very difficult to mine because it is unusual to find them in concentrations high enough for economical extraction.
The most abundant rare earth elements are cerium, yttrium, lanthanum and neodymium (2). They have average crustal abundances that are similar to commonly used industrial metals such as chromium, nickel, zinc, molybdenum, tin, tungsten and lead (1). Again, they are rarely found in extractable concentrations.
Rare Earth Element Mine Production and Trade
Significant amounts of rare earth elements are produced in only a few countries. China is the dominant producer of rare earth elements and is believed to be responsible for over 95% of the world mine production on a rare earth oxide equivalent basis. Other countries with notable production in 2009 were: Brazil, India, Kyrgyzstan and Malaysia. Minor production may have occurred in Indonesia, Commonwealth of Independent States, Nigeria, North Korea and Vietnam (3). The United States Geological Survey reports that significant exploration and new mining activity is expected from Canada and Australia (3).
|World Mine Production and Reserves (2009 Data)|
|Country||Production (Metric Ton)||Reserves (Metric Ton)|
|Commonwealth of Independent States||
|World total (rounded)||
China’s World Production Dominance
China became the world’s dominant producer of rare earth elements in the early 1990s, when production at the Mountain Pass mine in California began to decline. China’s dominance increased rapidly and in 2000 China accounted for about 90% of world rare earth production. China sold rare earths at such low prices that the Mountain Pass mine and others throughout the world were unable to compete.
In early 2010 China accounted for over 95% of the world’s rare earth production. China is also the dominant consumer of rare earth elements, used mainly in manufacturing electronics products for domestic and export markets. Japan and the United States are the second and third largest consumers of rare earth materials.
In 2010 China announced that they would significantly restrict their rare earth exports to ensure a supply for domestic manufacturing. This announcement triggered some panic buying and rare earth prices shot up to record high levels.
Chinese companies have also been seeking rare earth properties in other countries. For example: in 2009 China Non-Ferrous Metal Mining Company bought a majority stake in Lynas Corporation, an Australian company that has one of the highest outputs of rare earth elements outside of China.
The Dangers of a Dominant World Producer
Supply and demand normally determine the market price of a commodity. As supplies shrink prices go up. As prices go higher those who control the supply are tempted to sell and entrepreneurs start developing new sources of supply.
With rare earth elements the time between an entrepreneur’s decision to acquire a property and the start of production can be several years or longer. There is no quick way to increase supply.
If a single country controls almost all of the production and makes a firm decision not to export then the entire supply of a commodity can be quickly cut off. That is a dangerous situation when new sources of supply take so long to develop.
World Rare Earth Mineral Resources
“Rare earths are relatively abundant in the Earth’s crust, but discovered minable concentrations are less common than for most other ores. U.S. and world resources are contained primarily in bastnäsite and monazite. Bastnäsite deposits in China and the United States constitute the largest percentage of the world’s rare-earth economic resources, while monazite deposits in Australia, Brazil, China, India, Malaysia, South Africa, Sri Lanka, Thailand, and the United States constitute the second largest segment. Apatite, cheralite, eudialyte, loparite, phosphorites, rare-earth-bearing (ion adsorption) clays, secondary monazite, spent uranium solutions, and xenotime make up most of the remaining resources. Undiscovered resources are thought to be very large relative to expected demand.” Quoted from the United States Geological Survey’s Mineral Commodity Summary .
Large undeveloped deposits of rare earth minerals are known to occur in China. Significant deposits are also known in Australia. Exploration is identifying new deposits in Canada and the United States.
Rare Earth Element Outlook
“Rare-earth use in automotive pollution control catalysts, permanent magnets, and rechargeable batteries are expected to continue to increase as future demand for conventional and hybrid automobiles, computers, electronics, and portable equipment grows. Rare-earth markets are expected to require greater amounts of higher purity mixed and separated products to meet the demand. Demand for cerium and neodymium for use in automotive catalytic converters and catalysts for petroleum refining was expected to expand by 6% to 8% per year for the next 5 years if the world economy remains strong.
Rare-earth magnet demand was expected to increase by 10% to 16% per year through 2012, increasing to 45,000 t to 50,000 t by 2012 (Kingsnorth, 2008). Future growth was expected for rare earths in rechargeable NiMH batteries, especially those used in hybrid vehicles, increasing to 10,000 t to 20,000 t REO by 2012. NiMH demand was also expected to increase (moderated by increasing demand for lithium-ion batteries) with increased use in portable equipment, such as camcorders, cellular telephones, compact disk players, digital cameras, digital video disk players, laptop computers, and MPEG audio-layer-3 players.
Increased rare earth use was expected in fiber optics, medical applications that include dental and surgical lasers, magnetic resonance imaging, medical contrast agents, medical isotopes, and positron emission tomography scintillation detectors. Future growth potential was projected for rare-earth alloys employed in magnetic refrigeration (Gschneidner and Pecharsky, 2008).” Quoted from the United States Geological Survey Minerals Yearbook .