Erbium is a silvery-white metal that belongs to the heavy rare earth elements. It is malleable but also quite brittle.
The name is derived from the Ytterby mine near Stockholm.
Erbium was discovered in 1843 by Carl Gustav Mosander. However, the supposedly pure oxide was actually a mixture of oxides of erbium, scandium, holmium, thulium, and ytterbium.
The clarification of this mixture was later achieved by chemists Marc Delafontaine and Per Teodor Cleve. Pure erbium oxide was first produced in 1905 by the French chemist Georges Urbain and the American chemist Charles James.
Erbium Oxide
Occurrence
As a heavy rare earth element (HREE), erbium is more commonly found in HREE-enriched minerals such as xenotime and euxenite. Additionally, erbium occurs in ion-adsorption clays (clay deposits), which, due to their relatively simple processing despite the low percentage of rare earth elements, represent the most important source of HREEs. The primary sources are ion-adsorption clay minerals from southern China (Jiangxi and Guangdong provinces) and Myanmar.
Extraction
After an elaborate separation of other erbium-associated elements, the oxide is converted with hydrofluoric acid into erbium fluoride. It is then reduced to metallic erbium using calcium, producing calcium fluoride as a byproduct. Remaining calcium residues and impurities are removed through an additional vacuum remelting process.
Application
Its unique interaction with light accounts for most of the element’s applications. Unlike cerium or lanthanum, its uses are more specialized but absolutely crucial for modern technologies.
In fiber optic networks, erbium-doped glasses serve as optical amplifiers. These erbium-doped fiber amplifiers (EDFAs) form the backbone of the global internet. They enable data transmission over thousands of kilometers under the oceans without the need for electrical signal regeneration along the way.
In medicine, erbium lasers (Er:YAG lasers — erbium-doped yttrium aluminum garnet) are used in dermatology and dentistry due to their precise and controlled effects.
Besides medical lasers, erbium is also used in other high-precision lasers: erbium-doped crystals (such as Er:YAG, Er:YSGG) are employed in lasers for precise cutting, welding, and marking in industrial applications.
Erbium oxide, which has a beautiful and distinctive pink to rose color, is used as a dye for glass, jewelry, and sunglasses.
(Er₂O₃) exhibits a very attractive and characteristic pink to rose hue.
Besides its optical properties, erbium is useful in nuclear power due to its ability to easily absorb free neutrons. This makes it suitable for use in control rods in nuclear reactors.
Furthermore, erbium alloys are used in cryocoolers for applications at liquid helium temperatures because of their high specific heat capacity.
Dysprosium is a silvery-gray, malleable and ductile metal that belongs to the heavy rare earth elements.
It is highly reactive. Together with holmium, dysprosium has the highest magnetic moment (10.6 μB) of all naturally occurring chemical elements.
The discovery of dysprosium traces back to studies of gadolinite (then still called ytterbite), a mineral from the Ytterby mine near Stockholm, Sweden.
In 1879, Per Theodor Cleve and Jacques-Louis Soret independently discovered through spectroscopic investigations that erbium contained additional elements. Following Cleve’s suggestion, these were named holmium and thulium.
In 1886, Paul Émile Lecoq de Boisbaudran conducted fractionation experiments on holmium and realized that another element must exist. Since the unknown element was experimentally very difficult to isolate and he was unable to obtain a pure fraction, he named it dysprosium, meaning “the inaccessible.”
In 1906, Georges Urbain succeeded in producing pure dysprosium oxide for the first time. In 1936, Wilhelm Klemm and Heinrich Bommer isolated metallic dysprosium for the first time. In 1950, Frank Harold Spedding developed an effective ion-exchange separation method for dysprosium and yttrium.
Occurrence
The occurrence of dysprosium in the continental Earth’s crust is about 5.2 ppm. In terms of abundance, it ranks behind most of the light rare earth elements such as cerium, neodymium, and samarium, but ahead of most heavy rare earths like erbium, ytterbium, and holmium.
Minerals with particularly high dysprosium content include xenotime and gadolinite-(Y). In contrast, ores important for extracting other lanthanides, such as monazite and bastnäsite, contain only small amounts of dysprosium.
The main sources of dysprosium are ion-adsorption clay minerals (clay deposits) found in southern China (Jiangxi and Guangdong provinces) and Myanmar.
In these clay deposits, the rare earth elements are not part of a crystal structure but are adsorbed as ions onto clay particles. This allows for their extraction via ion-exchange processes, which are especially simple and cost-effective. Crucially, these deposits are highly enriched with valuable heavy rare earth elements like dysprosium and terbium.
Extraction
After an elaborate separation of other dysprosium-associated elements, the oxide is converted with hydrofluoric acid to dysprosium fluoride. It is then reduced with calcium to metallic dysprosium, producing calcium fluoride as a byproduct. Remaining calcium residues and impurities are removed through an additional vacuum remelting process. High-purity dysprosium is obtained after vacuum distillation.
Commercial separation is performed by liquid-liquid extraction or ion-exchange methods. The metal is produced by metallothermic reduction of the anhydrous halides using alkali or alkaline earth metals. Further purification of the metal is achieved by vacuum distillation.
Dysprosium exists in three allotropes (structural forms). The α-phase is hexagonally close-packed (HCP) with lattice parameters a = 3.5915 Å and c = 5.6501 Å at room temperature. Upon cooling to approximately 90 K (-183 °C / -297 °F), the ferromagnetic order is accompanied by an orthorhombic distortion of the HCPlattice. The β-phase has lattice parameters a = 3.595 Å, b = 6.184 Å, and c = 5.678 Å at 86 K (-187 °C / -305 °F). The γ-phase is body-centered cubic (BCC) with a = 4.03 Å at 1381 °C (2518 °F).
Application
The main applications of dysprosium are as alloying additions to Nd₂Fe₁₄B permanent magnet materials (where part of the neodymium is replaced by dysprosium) to increase both the Curie temperature and especially the coercive field strength, thereby improving the high-temperature performance of the alloy. The metal is also a component of the magnetostrictive material Terfenol D (Tb₀.₃Dy₀.₇Fe₂).
Due to its relatively high neutron absorption cross-section, dysprosium is used in control rods for nuclear reactors. Its compounds have been employed in the production of laser materials and phosphor activators, as well as in halogen metal vapor lamps.
The economic and technical significance of dysprosium is relatively low. Its annual production is estimated at less than 100 tons. It is used in various alloys, specialty magnets, and, alloyed with lead, as shielding material in nuclear reactors. However, its use in magnets for wind turbines has contributed to making rare earth metals a scarce resource. Additionally, the world’s largest supplier, China, restricts exports to increase domestic value creation.
Dysprosium oxide — Chemically, dysprosium behaves like a typical trivalent rare earth element and forms a series of pale yellow compounds in the +3 oxidation state.
Cerium is a silvery-gray, relatively soft, ductile, paramagnetic, and reactive metal. It is the most abundant lanthanide and occurs about as frequently as copper. Cerium belongs to the group of light rare earth elements.
In 1803, Swedish chemists Jöns Jacob Berzelius and Wilhelm Hisinger discovered the element. Independently, it was also discovered around the same time by German chemist Martin Klaproth. It was named after the dwarf planet Ceres, which had been discovered shortly before.
Like most rare earth elements, cerium was first identified in the form of its oxide — cerium dioxide (cerium(IV) oxide) — and only decades later isolated as a pure metal.
In the second half of the 19th century, Carl Auer von Welsbach successfully developed two products that required the use of cerium: gas mantles and ferrocerium (lighter flints). Auer's gas mantles enabled gas lamps to emit a bright, white light.
As with other rare earth elements, cerium is never found in its pure form in nature. It is extracted from minerals such as xenotime, monazite, and bastnäsite, or from ion-adsorption clays.
Occurrence
Cerium is primarily extracted from cerium-containing monazite and bastnäsite. It also occurs in allanite, zircon, samarskite, and the titanium mineral perovskite. Major producers include the United States, China, Russia, Australia, and India.
In nature, four stable or extremely long-lived isotopes of cerium occur: stable cerium-140 (88,48 percent) and radioactive cerium-142 (11.08 percent), as well as cerium-138 (0,25 percent) and cerium-136 (0,19 percent). Excluding nuclear isomers, a total of 38 radioactive isotopes of cerium have been identified. Their mass numbers range from 119 to 157, with half-lives varying from just 1,02 seconds for cerium-151 to 5 × 10¹⁶ years for cerium-142.
Cer-oxide
Extraction
Cerium metal is produced by electrolysis and metallothermic reduction of its halides using alkali or alkaline earth metals. It exists in four allotropic (structural) forms. The α-phase is face-centered cubic (FCC) with a = 4.85 Å at 77 K (−196 °C or −321 °F). The β-phase forms just below room temperature and is double hexagonally close-packed (DHCP) with a = 3.6810 Å and c = 11.857 Å. The γ-phase is the room temperature form and is face-centered cubic (FCC) with a = 5.1610 Å at 24 °C (75 °F). The δ-phase is body-centered cubic (BCC) with a = 4,12 Å at 757 °C (1,395 °F).
After an elaborate separation of accompanying rare earth elements, cerium oxide is converted into cerium fluoride using hydrofluoric acid. It is then reduced to metallic cerium by calcium, forming calcium fluoride as a by-product. Remaining calcium and other impurities are removed in an additional vacuum remelting step.
Application
Although rare earth elements are classified as critical raw materials, scarcity does not apply to all of them. As previously mentioned, cerium is the most abundant of the rare earth elements. Since rare earths always occur together in deposits and are extracted collectively, this leads to significant and ongoing overproduction of cerium (and lanthanum, the second most abundant rare earth element).
Despite the demand for cerium and lanthanum, it is nowhere near sufficient to absorb the massive supply generated through mining.
Cerium's ability to switch between the oxidation states Ce³⁺ and Ce⁴⁺ makes it especially useful in catalytic and redox-active processes. Its largest application is in automotive exhaust catalysts. In three-way catalytic converters, cerium oxide is a key component. Another major application is in fluid catalytic cracking (FCC) catalysts used in oil refineries.
Cerium oxide (CeO₂) is also an excellent polishing agent for glass, lenses, and silicon wafers.
In the glass and ceramics industries, cerium is added to glass and glazes to achieve specific properties—such as decolorization by removing impurities in glass and ceramic glazes. This results in clearer glass and purer ceramic finishes. Cerium can also impart a yellow tint to glass, which is used as a UV protection feature.
Cerium continues to be used in lighting applications. In energy-saving lamps, it enhances light quality in fluorescent phosphors. In white LEDs, cerium-doped phosphors (e.g., YAG:Ce) are a key component.
When added in small amounts to aluminum or magnesium alloys, cerium improves their corrosion resistance and mechanical properties.
Cerium-based coatings and conversion layers (e.g., on aluminum or steel) offer excellent corrosion protection and are being researched as more environmentally friendly alternatives to chromate-based coatings.
Cerium dioxide–based materials are used as electrolytes in solid oxide fuel cells (SOFCs) due to their ionic conductivity.
Cerium-rich alloys (e.g., with cobalt or iron) can absorb and release hydrogen and are being studied for hydrogen storage technologies.
Cerium is still used today in lighter flints—a commercial application that dates back to the 19th century, introduced by the enterprising chemist Carl Auer von Welsbach.
Unique Properties
The silvery-white, lustrous metal is the second most reactive lanthanide after europium. Superficial damage to its protective yellow oxide layer can ignite the metal. Above 150 °C, it burns with intense glowing to form cerium dioxide. It reacts with water to produce cerium hydroxide.
Cerium occurs in compounds as a trivalent, colorless cation or as a tetravalent, yellow to orange-colored cation.
When exposed to heat, cerium is strongly attacked by ethanol and water. It is also heavily corroded in alkaline solutions, forming cerium hydroxides. In acids, it dissolves to form salts. Because the chemical properties of the rare earth elements are similar, metallic cerium is rarely used in pure form; instead, it is typically employed as part of the mixture obtained during the extraction from rare earth minerals, known as mischmetal.
Like all lanthanides, cerium is slightly toxic. Metallic cerium can ignite at temperatures as low as 65 °C. When finely divided, it can heat up in air without an external energy source and eventually ignite. Its ignition tendency strongly depends on particle size and distribution. Cerium fires must not be extinguished with water, as explosive hydrogen gas would be produced.
Along with praseodymium and terbium, cerium is distinguished from other rare earths by forming compounds in which it exhibits the +4 oxidation state. In solution, it is even the only rare earth element to show a +4 oxidation state. Salts of the Ce⁴⁺ ion (core salts), which are powerful yet stable oxidizing agents, are used in analytical chemistry to determine oxidizable substances such as iron (iron in the +2 oxidation state). Cerium in the +3 oxidation state behaves like a typical rare earth element.
Zirconium is a silvery-shiny, highly corrosion-resistant heavy metal. It is relatively soft and malleable and can be easily processed by rolling, forging, and hammering. It is also a good heat conductor.
Its name is derived from zircon, the most common zirconium mineral, which also contains hafnium. Due to their similar properties, the two elements are difficult to separate from each other. Like ilmenite, zircon is mainly extracted from heavy sand.
Due to its low neutron absorption, the nuclear power industry is one of the most important consumers of zirconium, alongside the chemical industry.
The largest producer is Australia, followed by South Africa.
The Richards Bay Minerals mine in South Africa is one of the largest zircon mines. It is operated by Rio Tinto, one of the largest zirconium producers.
The Australian company Iluka Resources is the leading zircon producer.
History
In 1789, German chemist Martin Heinrich Klaproth analyzed the mineral zircon. The name is derived from the Arabic “zarqun” (gold-colored) or Persian “zargun” (gold-like), inspired by the color of zircon gemstones. In 1824, Swedish researcher Jöns Jakob Berzelius succeeded in producing impure zirconium metal. However, it was unusable due to contamination.
In 1914, Dutch chemists Jan Hendrik de Boer and Anton Eduard van Arkel succeeded in producing high-purity zirconium for the first time.
Industrial use began in the 1940s with the US atomic program, when it was discovered that zirconium has ideal properties for nuclear reactors. In the 1950s, the US company Kroll Metals developed a zirconium alloy that is still used in reactors today.
Since the 1960s, zirconium materials have been used in hip implants and dental crowns.
Application
Zirconium is used as zirconium dioxide and as zirconium metal.
The most important application of zirconium metal is in nuclear power, where it is an important material for fuel rod cladding in nuclear reactors, as it hardly absorbs neutrons and thus does not hinder the chain reaction. However, this zirconium cladding must not contain hafnium. Since zirconium can handle heat and corrosion in cooling water, it's also used in reactor pressure vessel linings.
In the chemical industry, it's used to protect tanks and heat exchangers from harsh chemicals.
Zirconium metal is also good for superalloys in aircraft turbine blades.
Zirconium dioxide is used in medical implants due to its biocompatibility. Other applications include high-temperature ceramics, semiconductors, and wear-resistant coatings.
Occurrence, Mining and Extraction
Zircon, the most important zirconium mineral, contains approximately 50 percent zirconium dioxide. The hafnium content varies depending on the deposit, but ranges between one and four percent.
Due to the strong chemical similarity between hafnium and zirconium, separating the two elements from each other is very complex and expensive. The preferred methods for separating hafnium and zirconium are ion exchange and solvent extraction techniques. For some purposes, however, it is not necessary to separate the two elements.
Australia dominates zircon production with around 30 percent. The country also has by far the largest zircon reserves in the world. The Australian company Iluka Resources is also the global market leader.
South Africa is the second-largest producer of zircon, followed by Mozambique.
The USA also produces zircon. The US company Tronox is one of the top three global players in zirconium, along with Rio Tinto.
Global zircon production amounts to around 1.5 million tons. Zirconium metal production is estimated at 6,000 tons.
Substitution
Chromite and olivine can be used in place of zirconium in some foundry applications. Dolomite and spinel can also replace zirconium in certain high-temperature applications. Niobium (columbium), stainless steel, and tantalum offer limited substitutes for nuclear applications. Titanium and synthetic materials can serve as substitutes in some chemical processing plants. Boron or cadmium-silver-indium alloys are sometimes used in place of hafnium metal in control rods in nuclear power plants. Zirconium can be used interchangeably with hafnium in certain superalloys.
