Rare earth elements are on everyone's lips, and it's no coincidence: They are the silent foundation of much of modern technologyFrom electric motors and wind turbines to screens, fiber optics, and medical equipment, minerals are used in a wide range of applications. Despite their name, they are neither literally "earths" nor, with few exceptions, are they particularly "rare." Even so, their extraction and refining are complex, and this is where much of today's geopolitics is decided.
In addition to the industrial debate, there is a global tension: China dominates production and, above all, refining.And every time the US threatens to restrict exports, entire supply chains tremble. Meanwhile, Europe, Japan, South Korea, and the United States are searching for alternatives: new deposits, recycling, and more efficient design. Let's unravel, without mincing words, what they are, how they were discovered, why they are so useful, where they are located, and what it means to depend on them.
What exactly are rare earth elements?
When we talk about rare earth elements, we are referring to 17 metallic chemical elementsThe 15 lanthanides (from lanthanum to lutetium) plus scandium and yttrium, which often accompany them in the same deposits. Their name comes from the old custom of calling oxides "earths" and from how difficult it was to separate them in the 18th and 19th centuries; that's why the name stuck.
Actually, They are not very rare in the earth's crustCerium, for example, is as common as copper. The problem isn't so much finding them, but rather that they appear very dispersed and mixed with other elements, which complicates and increases the cost of their separation. There is one notable exception: the promethium (Pm) is radioactive and practically does not exist naturally; it is obtained in nuclear reactors from the fission of uranium.
From an astronomical point of view, its presence has a fascinating history: Many of these elements are forged in extreme events such as the merger of neutron stars. Meteorites and enriched marine crusts help scientists reconstruct their origin and distribution in the Solar System, and even inspire strategies for their future exploration.
A laboratory story: from mystery to the periodic table
The saga begins in 1787, when Carl Axel Arrhenius found a very dense black mineral in Ytterby (Sweden)He suspected it held something new and named it "Ytterby's heavy stone." In 1792, the Finnish chemist Johan Gadolin analyzed a sample: he found oxides of silicon, aluminum, and iron, and a significant fraction of an unknown oxide. That mineral, gadolinite, had the idealized formula Be2Faith2Si2O10, and its study would give rise to yttrium (Y) and a whole family of elements.
Shortly after, Vauquelin and Klaproth confirmed the results They suggested the name "gadolinite" for the mineral and "yttrium" for the oxide of the new element, in reference to the place of its discovery. The thread had earlier roots: as early as 1751, Cronstedt had described the "heavy stone of Bastnäs," which Berzelius and Hisinger studied in 1803 and from which they isolated ceria (CeO₄).2) and the element cerium (Ce), named after the planetoid Ceres.
The separations were laborious. In 1830, Carl Mosander isolated metallic cerium and discovered lanthanum (La) starting from cerium. He also identified a supposed "didymium" that decades later turned out to be a mixture of oxides: in 1885, Welsbach would separate praseodymium (Pr) and neodymium (Nd). Mosander also detected in 1844 two oxides that he called erbium and terbium; their names were even interchanged in 1860, reflecting the chaos of the time.
At the end of the 19th century, the list kept growing: Marignac obtained ytterbia; Lars Nilson isolated scandium in 1879; Per Teodor Cleve identified holmia (Ho) and thulia (Tm), and Boisbaudran detected samaria in didymia, from which samarium (Sm) would be isolated. In 1886, Boisbaudran himself obtained gadolinium (Gd).2O3) and dysprosium (Dy) from "impure" fractions; then came europium (Eu, Demarçay, 1901) and lutetium (Lu, Urbain, 1907). The promethium It was confirmed much later (Marinsky, Glendenin and Coryell, 1944–1947) in fission byproducts in Tennessee.
Chemical and physical properties: what makes them unique
Lanthanides are metals electropositives that, as a rule, work in oxidation state +3Throughout the series, the so-called "lanthanide contraction" occurs: the ionic radii progressively decrease due to the increase in the effective nuclear charge felt by the 4f electrons. This detail, which is not insignificant, conditions its chemistry and crystalline structure.
By ionic size, form compounds with high coordination numbers and particular structural patterns. Its Ln oxides2O3 They are polymorphic and adopt several structures (types A, B, and C). With halogens, they form LnX trihalides.3 throughout the entire series, with the exception that cerium also forms the tetrahalide CeX4 with Ce4+.
Another striking family is the hydrides: All rare earth elements form fluorite-type hydrides, generally with approximate stoichiometry LnH2Although non-stoichiometric trihydrides and hydrides exist, binary nitrides, for their part, adopt a very simple but effective "rock salt" type structure.
In magnetism and spectroscopy, its behavior is special. The 4f electrons are the protagonists and are heavily shielded by the 5s layers2 and 5p6so that the chemical environment barely disturbs their energy levels. The spin-orbit coupling constants are large, so the ions usually have a single well-defined ground state (with quantum number J), and the next excited state is sparsely populated at room temperature.
From there emerge their characteristic colors and f–f transitionswhich are practically independent of the compound. To cite a few: Pr3+ dyes green, Nd3+ lilac, Sm3+ in yellow, Eu3+ pale pink, while La3+, This3+ and Gd3+ They are colorless. This "palette" is very useful, for example, in lasers and phosphors.
Minerals and types of deposits
Although they have been described more than 180 minerals containing rare earthsOnly about 25 of these minerals attract real economic interest. Among the most important are bastnaesite (REE fluorocarbonate), monazite (phosphate), xenotime (yttrium phosphate), loparite (complex oxide rich in Ce, Na, Ca, Ti and Nb), cerite (silicate) and gadolinite (silicate with REE, beryllium and iron).
The large deposits associated with these minerals are related to four main geological contexts. First, the carbonatitesigneous rocks with more than 50% carbonates, such as Bayan Obo (China) or Mountain Pass (USA). Second, alkaline igneous rocks such as the Nepheline syenites of Lovozero (Russia). Third, lateritic clays that are formed by in situ alteration; Southeast China exploits more than 250 deposits of this type. Fourth, pleasure-type deposits in which monazite is concentrated, such as the one in Matamulas (Ciudad Real).
There is also evidence of enrichment in cobalt manganese crusts in the ocean depths, whose exploitation is still being researched. It's not science fiction: these are scenarios with real resources, although their economic and environmental viability is being closely evaluated.
Production, reserves and refining: the power of the bottleneck
The figures vary depending on the source and the year, but the pattern is the same: China clearly dominates the sectorHistorically, annual production of rare earth oxides (REOs) has been around 160.000 tons, while in recent years it has reached hundreds of thousands of tons (for example, nearly 390.000 tons in some estimates). China provides the majority of the supply, easily exceeding 70% of the market; in refining, it accounts for approximately 90% of the capacity.
Among the pursuers are United States as the second producer, Myanmar (often under the umbrella of Chinese companies), Australia, Thailand y NigeriaIn terms of reserves, the USGS estimates around 90 million tons of REO equivalent globally: nearly half in China, about 21 Mt in Brazil, around 7 Mt in India, approximately 6 Mt in Australia and about 4 Mt in Russia; other sources also detail very relevant figures in Vietnam y Greenland, in addition to Norway with an identified deposit of ~1,57 Mt.
Europe has a dependence of around 90% and its current production is minimal. Spain It appears on the map with potential: in addition to the pleasure of Matamulas (Ciudad Real), there are expectations in Galicia, Castilla-La Mancha, Andalusia, and Extremadura. The Matamulas deposit has been estimated to contain around 29,9 million tons of monazite, and it has been suggested that it could contribute around 2.000 tons per year of REO, although all of this It is subject to technical, economic and environmental feasibility.
Technological and everyday applications
Its list of uses is too long to fit in a tweet. To start with the most well-known, neodymium-iron-boron (Nd) permanent magnets2Fe14B) They have revolutionized electric motors, wind turbines, headphones, speakers, hard drives, and sensors. Dysprosium and terbium are added to improve their performance at high temperatures, especially in wind turbines and electric vehicles.
In optics and photonics, Lanthanides are unbeatableNeodymium is the heart of lasers such as YAG (yttrium aluminum garnet), YLF (yttrium lithium fluoride), or YVO.4 (yttrium vanadate), which emits in the infrared (around 1054–1064 nm) and is used in medicine and dentistry. Europium and terbium activate red, green, and blue phosphors for LED and fluorescent displays. Erbium enables amplification in optical fibers down to 1.55 μm for telecommunications.
Cerium, for its part, It shines as a catalyst and polishing agentLanthanum is found in self-cleaning furnaces, in catalytic cracking for refining, and in the polishing of glass and optics. It is also a component of alloys that spark in lighters (ferrocerium). Lanthanum increases the refractive index of optical glass and is used in lenses and as a component of Ni-MH batteries.
Yttrium (Y) is used to YAG lasersphosphorescent screens, high-temperature superconductors (YBCOs), Stabilized zirconia (YSZ) for advanced ceramics, and yttrium iron garnet (YIG) Scandium (Sc) is found in microwave filters. It is also used in coatings for energy-saving and white LED lamps, spark plugs, and as an additive in steels. Scandium strengthens aluminum alloys in aerospace and enhances metal halide lamps.
In magnetostrictors, combinations such as terphenol-D (terbium + iron) and galfenol Gadolinium and iron have applications in sonar, actuators, and robust sensors. In medicine, gadolinium is a contrast agent in magnetic resonance imagingHolmium is used in surgical lasers. Thulium has been used in portable X-ray machines and compact lasers.
Medical imaging: phosphors and intensifying screens
Before the full digital age, and even today in specific devices, intensifying screens with rare earth phosphors They transform X-rays into visible light to reduce the dose to the patient. Their typical compounds include activators that determine the emitted color.
- Gd2O2S:Tb (terbium-activated gadolinium oxysulfide): emits green around 540 nm.
- La2O2S:Tb (larthanum oxysulfide activated with terbium): also green ~540 nm.
- Y2O2S:Tb (terbium-activated yttrium oxysulfide): emission in the blue (approx. 450–500 nm).
- LaOBr:Tm (thulium-activated lanthanum oxybromide): blue 450–500 nm.
- YTaO4:Tm (thulium-activated yttrium tantalate): blue-ultraviolet between 450–500 nm.
Compared to classic calcium tungstate, These phosphors convert radiation more efficientlyThey allow for higher speeds and, with optimized technical parameters, reduce dose. The downside is that faster screens can increase quantum and radiographic "noise"; the balance between detail and dose is key.
Energy and green transition: three steps of impact
If we order their energy role, they are drawn three overlapping stepsFirst, direct energy production: wind turbines use Nd-Fe-B magnets with around 30% neodymium in the magnetic fraction, and dysprosium and terbium additives for thermal stability. In the nuclear and space science fields, promethium-147 has been used in betavoltaic batteries very low power for probes and possible military applications.
Second, efficiency in consumption: fluorescent and LED lighting with europium, terbium, and yttrium phosphors; compact, high-performance electric motors thanks to neodymium and dysprosium magnets; and Ni-MH batteries whose cathodes are formulated with rare earth alloys with typical proportions of cerium (45–50%), lanthanum (25%), neodymium (15–20%) and praseodymium (5%).
Third, means that facilitate energy management: rare earth hydrides for hydrogen storage in crystal lattices and release it with slight heating; isotopes such as Sm, Gd, Dy, Ho and Er in reactor control; and a crucial role of La and Ce in catalytic converters in automobiles and in CeO-type additives2 in fuels, which reduce the combustion temperature of soot and promote the cleaning of particulate filters.
In the market, beyond energy, Approximately half of the production is consumed in magnets and catalysisIn terms of economic value, magnets and luminescent materials stand out. Consumption by element is highly skewed: neodymium (~49%) and praseodymium (~20%) dominate due to their use in magnets; followed by lanthanum (~6%), cerium (~4%), and terbium (~4%); the rest are below 2%. Terbium and lutetium are among the most expensive due to their relative scarcity and the difficulty of separating them.
Geopolitics, trade and recycling: the pieces on the board
In recent years, Beijing has announced strict export controls This includes rare earth elements as well as extraction and processing technologies. With a near-monopoly—and close to 90% of refining—it can control the flow of resources to suit its interests. This affects the United States, the European Union, Japan, and South Korea, all of which are heavily dependent on its Asian neighbor.
International summits have served as a stage for this tension: US and Chinese leaders have discussed this matter in Asia-Pacific forumsNegotiations are underway to postpone restrictions and buy time. Japan has sought strategic agreements to secure its supply chains, while South Korea is concerned about its dependence on automotive and electronics.
Ukraine has also been looked at for its subsoil, although Their proven reserves of rare earth elements are not so plentiful. as hinted. In parallel, the military dimension of these elements is obvious: an F-35 fighter jet incorporates more than 400 kg of rare earth elements, and a Virginia-class nuclear submarine can require more than 4.000 kg. All of this underscores their strategic importance.
Solutions? Several, but none of them quick. Opening a mine can take up to 30 years From discovery to production. The most sensible thing in the short and medium term is to promote the recycling (Urban mining): Today it does not exceed 1% of the total. Europe is moving in that direction, and Spain has put forward its Mineral Raw Materials Action Plan 2025–2029. Even so, mining projects will be needed, and above all, separation and refining capacity outside of China.
Myths and curiosities: neither "lands" nor so "rare"
The name is misleading. They are not "lands" in the colloquial sense, but rather metals whose oxides were discovered first. Nor are they so "rare" in abundance: cerium, for example, is among the 25 most common elements in the Earth's crust. What is rare—and radioactive—is promethium, which is practically absent in nature.
Their chemistry is captivating: f–f transitions color ions and glasses, and its "immunity" to environmental changes means that the color of, for example, Eu3+ or Nd3+ It is highly reproducible regardless of the compound. This spectroscopic stability explains its success in lasers, phosphors, and calibration standards.
As a historical curiosity, Ytterby It is the "little village of the four elements": yttrium, terbium, erbium, and ytterbium (and their echo in dozens of minerals and oxides). It is also paradoxical that names like holmium (for "Holmia," Stockholm) or lutetium (for Lutetia/Paris) remind us that science is often as much a human and geographical adventure as it is a chemical one.
To close the technological loop, Nd-Fe-B magnets are cheaper and more powerful than samarium-cobalt magnets. in many uses, and that's why they dominate in headphones, hard drives and sensors; didymium (a mixture of Pr and Nd) colors glass and protects eyesight in welding goggles, and Nd-doped crystals are protagonists of modern photonics.
Viewed in perspective, this entire journey – from the Mineralogy from the 18th century to critical economics of the 21st century– shows why we depend so heavily on these discrete metals. Their combination of magnetic, optical, and catalytic properties has no easy substitute, and that's why their value chain, from mining to recycling, deserves so much attention.
The key idea to keep in mind is that The strategic value of rare earth elements does not lie in their mere abundance.but rather in their geographic concentration, the dominance of refining, and the technical difficulty of separating them. Therefore, to strengthen resilience, we need both new responsible projects, local processing capacity, more recycling, and designs that use less material without sacrificing performance.