Everything You Need to Know About Rare Earth Metals.

The name rare earths

Rare earths must be understood in light of their history and the beginnings of their extraction.

They are called rare because in the past it was assumed that the metals in this group were rare. In fact, some of the raw materials are not rare at all. Cerium, for example, is as common as copper or nickel.

They are earths, because rare earths used to be extracted only as oxides of certain minerals. Earths is the older term for oxides.

The 17 rare earths

Rare earths never occur alone but always in association with each other. For the lanthanides, a rough division can be made into cerite earths (atomic numbers 58-64) and ytter earths (atomic numbers 65-71) in terms of which elements tend to occur together and have particular similarities to each other.

The rare earths consist of the chemical elements of the 3rd group of the periodic table: Scandium (atomic number 21), Yttrium (39), Lanthanum (57), and the 14 elements following lanthanum, the lanthanides. They include Cerium (58), Praseodymium (59), Neodymium (60), Promethium (61), Samarium (62), Europium (63), Gadolinium (64), Terbium (65), Dysprosium (66), Holmium (67), Erbium (68), Thulium (69), Ytterbium (70) and Lutetium (71).

A basic distinction is made between light and heavy rare earths. On average, more than 95% of rare earth occurrence is accounted for by the four light rare earths Cerium, Lanthanum, Neodymium and Praseodymium. Consequently, the share of the 13 heavy rare earths – Dysprosium, Erbium, Europium, Gadolinium, Holmium, Lutetium, Promethium, Samarium, Scandium, Terbium, Thulium, Ytterbium and Yttrium – is less than 5%.

Many rare earths are particularly relevant to industry and thus for everyday use. We present them here in more detail. Click the buttons to learn more!

Dysprosium
Neodymium
Praseodymium
Terbium
Yttrium
Ytterbium
Thulium
Scandium
Samarium
Promethium
Lutetium
Gadolinium
Europium
Erbium
Lanthanum
Cerium
Holmium
Rare earths, like technology metals, belong to the so-called strategic metals. These metals are of crucial importance for technological innovation. However, more than 90 percent of all rare earths are mined and processed in China, which results in a dangerous market dominance. European industry is massively dependent on the supply readiness in China.

Rare earths, like technology metals, belong to the so-called strategic metals. These metals are of crucial importance for technological innovation. However, more than 90 percent of all rare earths are mined and processed in China, which results in a dangerous market dominance. European industry is massively dependent on the supply readiness in China.

CHARACTERISTICS

Rare earths are silver-coloured metals that tarnish quickly in air and are relatively soft. They are strongly electropositive, reactive, and have low conductivity. They react with water and dilute acids to form hydrogen. When ignited in air, they burn to form La2O3 (in the case of cerium, CeO2), and some of the elements, such as terbium and ytterbium, are even pyrophoric in a finely divided state. That is, they self-ignite. Basicity, melting point, and density increase from left to right in the periodic table. Europium and ytterbium are exceptions.

Rare earths have special spectroscopic properties. They exhibit a discrete energy spectrum in the solid state (unlike semiconductors, for example). The reason for this is the special structure of their electron shells. Optical transitions take place within the 4f shell, which is shielded from the outside by the larger occupied 5s, 5p, and 6s shells. A band structure cannot form because of this shielding for the f orbitals. The absorption lines are exposed due to the different electronic environment in the crystal for the individual ions of the elements. The inhomogeneous line width ranges from tens to several hundred gigahertz, depending on the crystal.

The chemical properties of almost all rare earths are almost identical.

They can be distinguished from each other by the slight differences in their weights. Differences in their 4f electrons also give some rare earths special properties. Gadolinium, for example, is the only rare earth element that is ferromagnetic – that is, it sticks to magnets like iron. Lanthanum is the only superconductor among them.

OCCURRENCE & EXTRACTION

Rare earth elements do not occur purely as metals or oxides but are extracted from ores and processed into rare earth metals (SEM) or rare earth oxides (SEO). They are mainly found in the minerals bastnäsite, monazite, and xenotime. Here, the raw materials always occur in association with other rare earths. The proportion of rare earths in bastnäsite and xenotime is 55-60%, in monazite only 30-35%.

Since the properties of the individual earths are so similar, the separation process is particularly costly and complicated. Furthermore, it is subject to strict environmental regulations, since the ore always contains small concentrations of radioactive thorium.

Rare earth deposits are concentrated in China, Brazil, Vietnam, Russia, India, and Australia. The most famous rare earths mines are Bayan Obo in China (50% of China’s rare earth production comes from here), Mount Weld in Australia (owned by Lynas, which can be considered the only competitor to China), and Mountain Pass in California. Rare earths are mainly extracted in China, Malaysia, and Thailand.

Aerial view Bayan Obo / Allen & Simmon NASA/GSFC/METI/ERSDAC/JAROS

AREAS OF APPLICATION

Rare earths are needed in many branches of industry. The most important application is in powerful permanent magnets used, for example, in wind turbines and headphones.

Rare earths are also used for lamps and lasers, LED technology, catalytic converters, accumulators, and even in nuclear power plants. Next, we will briefly discuss the most important uses for rare earths.

MAGNETIC TECHNOLOGY

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High-performance permanent magnets, which are used in wind turbines, electric motors, magnetic resonance tomographs, and headphones account for a large proportion of the total consumption of rare earths. The most commonly used alloy is neodymium, which is composed of iron and boron (NdFeB). NdFeB magnets are extremely powerful but susceptible to corrosion, and their magnetic field is stable only up to about 80 °C. By adding dysprosium, this value can be raised to about 200 °C. NdFeB magnets are protected from corrosion by the addition of cobalt or a coating.

Their high magnetic stability (coercive force) is why NdFeB magnets have largely displaced the previously most-powerful magnets made of iron, aluminium, nickel, and cobalt (Alnico). However, Alnico magnets are still in demand for high-temperature applications.

NdFeB magnets are so strong that if more than one magnet is swallowed, intestinal perforation can occur. That’s why children’s toys containing these magnets should only be used under supervision. Magnets larger than three to four cubic centimetres are practically impossible to separate by hand.

OTHER APPLICATIONS

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Numerous rare earths can be found in the field of lighting technology. Europium and yttrium, for example, are used in LEDs and plasma displays. Scandium is needed for the glaringly bright lighting found in soccer stadiums. Erbium, ytterbium and, to a lesser extent, dysprosium are used in lasers. Erbium also plays a role in fibre-optic cables.

Some rare earths are also used in medicine. Scandium, for example, is used in X-ray technology, and gadolinium is used as a contrast agent in magnetic resonance imaging. In positron emission tomography, on the other hand, lutetium is used. Holmium is another rare earth element that plays a role in medical technology.

But there are also numerous other applications for rare earths. Praseodymium, for example, improves UV absorption, which is why it is also used in eye-protection lenses (such as those used in welding goggles). Neodymium is used in alloys with magnesium to produce high-strength metals for aircraft engines. Terbium is used in the manufacture of semiconductors and serves as an activator for fluorescent phosphors. Together with zirconium dioxide, it’s also used as a stabilizer in one of the most important technologies of the future: high-temperature fuel cells.

AREAS

OF APPLICATION

Rare earths are needed in many branches of industry. The most important application is in powerful permanent magnets used, for example, in wind turbines and headphones.
Rare earths are also used for lamps and lasers, LED technology, catalytic converters, accumulators, and even in nuclear power plants. Next, we will briefly discuss the most important uses for rare earths.

Magnetic technology

Learn more
High-performance permanent magnets, which are used in wind turbines, electric motors, magnetic resonance tomographs, and headphones account for a large proportion of the total consumption of rare earths. The most commonly used alloy is neodymium, which is composed of iron and boron (NdFeB). NdFeB magnets are extremely powerful but susceptible to corrosion, and their magnetic field is stable only up to about 80 °C. By adding dysprosium, this value can be raised to about 200 °C. NdFeB magnets are protected from corrosion by the addition of cobalt or a coating.

Their high magnetic stability (coercive force) is why NdFeB magnets have largely displaced the previously most-powerful magnets made of iron, aluminium, nickel, and cobalt (Alnico). However, Alnico magnets are still in demand for high-temperature applications.

NdFeB magnets are so strong that if more than one magnet is swallowed, intestinal perforation can occur. That’s why children’s toys containing these magnets should only be used under supervision. Magnets larger than three to four cubic centimetres are practically impossible to separate by hand.

OTHER APPLICATIONS

Learn more
Numerous rare earths can be found in the field of lighting technology. Europium and yttrium, for example, are used in LEDs and plasma displays. Scandium is needed for the glaringly bright lighting found in soccer stadiums. Erbium, ytterbium and, to a lesser extent, dysprosium are used in lasers. Erbium also plays a role in fibre-optic cables.

Some rare earths are also used in medicine. Scandium, for example, is used in X-ray technology, and gadolinium is used as a contrast agent in magnetic resonance imaging. In positron emission tomography, on the other hand, lutetium is used. Holmium is another rare earth element that plays a role in medical technology.

But there are also numerous other applications for rare earths. Praseodymium, for example, improves UV absorption, which is why it is also used in eye-protection lenses (such as those used in welding goggles). Neodymium is used in alloys with magnesium to produce high-strength metals for aircraft engines. Terbium is used in the manufacture of semiconductors and serves as an activator for fluorescent phosphors. Together with zirconium dioxide, it’s also used as a stabilizer in one of the most important technologies of the future: high-temperature fuel cells.

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