ISE Fact sheet 2019

Rare earths - important resources for high technology

High-tech and environmental applications of rare earth elements have dramatically increased in variety and significance over the past four decades. Many of these applications are highly specific, as the rare earth substitutes are inferior or unknown, the rare earths have gained a technological importance that is much higher than expected on the basis of their relative unfamiliarity. In fact, although they are more abundant than many known industrial metals, the rare earths tend to focus on non-salable ore deposits. As a result, most of the world's supply comes from very few sources. The United States and Europe were previously largely self-sufficient in terms of rare earths, but have become dependent on imports from China over the last decade.

The rare earth elements (rare earths) form the largest chemically coherent group in the periodic table. Although not commonly known, rare earths are essential for many hundreds of applications. The versatility and specificity of the rare earths has given them a level of technological, environmental and economic importance that is significantly higher than one might expect from their relative unfamiliarity. In 1999 and 2000, more than 90% of the rare earths demanded by the US industry came from deposits in China.

Figure 1. Global production of rare earth elements (1 kt = 106 kg) from 1950 to 2000 in four categories: USA, almost exclusively from Mountain Pass, California; China, from several deposits; all other countries together, mostly from monazite-bearing placers; and global sum. Four production periods are recognizable: the Monazit Placer era, the end of the 19. Century began and 1964 ended abruptly; the mountain pass era 1965 started and ended about 1984; a transitional period from about 1984 to 1991; and the Chinese era, which started around 1991. Source: USGS

Although the 15 naturally occurring rare earths (Table 1, Fig. 2) are generally similar in their geochemical properties, their individual abundances on Earth are by no means equal. In the continental crust and its rare earth ore deposits, the concentrations of the most abundant and least abundant rare earths typically differ by two to five orders of magnitude (Figure 3). As technological applications of rare earths have multiplied in recent decades, demand for some of the lesser-abundant (and previously rather unfrequented rare earths) has risen dramatically.

The diverse nuclear, metallurgical, chemical, catalytic, electrical, magnetic and optical properties of rare earths have led to an ever-expanding variety of applications. These applications range from banal (lighters, glass polishing) to high-tech (phosphors, lasers, magnets, batteries, magnetic cooling) to futuristic (high-temperature superconductivity, safe storage and transport of hydrogen for hydrocarbon economy).

Some applications of rare earth elements

Many applications of rare earths are characterized by a high specificity and a high unit value. For example, color cathode ray tubes and liquid crystal displays used in computer monitors and televisions use europium as a red phosphor; A replacement is not known. Because of its relatively low supply and high demand, the EU is quite valuable - $ 250 to $ 1.700 / kg (for Eu2O3) over the past decade.

Fiber optic telecommunications cables offer much greater bandwidth than the copper wires and cables that have largely replaced them. Fiber optic cables can transmit signals over long distances because they contain periodically spaced lengths of erbium-doped fibers that act as laser amplifiers. It is used in these laser repeaters despite its high cost (~ 700 USD / kg) because it alone has the required optical properties.

The specificity is not limited to the more exotic rare earths like Eu or Er. Cerium, the most abundant and least expensive rare earth, has dozens of applications, some of which are highly specific. For example, Ce oxide is uniquely suited as a polishing agent for glass. The polishing effect of CeO2 depends on both its physical and chemical properties, including the two accessible oxidation states of cerium, Ce, 3 + and Ce4 +, in aqueous solution. Virtually all polished glass products, from ordinary mirrors and eyewear to precision lenses, are equipped with CeO2.

Permanent magnet technology has been revolutionized by alloys containing Nd, Sm, Gd, Dy or Pr. Small, lightweight and high strength rare earth magnets have enabled the miniaturization of numerous electrical and electronic components used in home appliances, audio and video equipment, computers, automobiles, communications systems and military equipment. Many of the latest technological innovations (such as miniaturized portable multi-gigabyte drives and DVD drives) would not be possible without Rare Earth magnets.

The environmental applications of rare earths have increased significantly in the last three decades. This trend will undoubtedly continue given the growing concern over global warming and energy efficiency. Some rare earths are essential components of both petroleum liquid cracking catalysts and automotive pollution control catalysts. The use of rare earth magnets reduces the weight of motor vehicles. The widespread introduction of new energy-efficient fluorescent lamps (using Y, La, Ce, Eu, Gd and Tb) for institutional lighting could potentially lead to a reduction in US carbon dioxide emissions, equivalent to one third of cars currently on the road. The large-scale application of the magnetic refrigeration technology (described below) could also significantly reduce energy consumption and CO2 emissions.

Location in the periodic table

Figure 2. Chemical periodic table with the 16 rare earth elements (rare earths): the lanthanoids La to Lu and Y, whose geochemical behavior is practically identical to that of the heavier lanthanoids. Promethium has no long-lived isotopes and occurs naturally only in tiny amounts on earth. An represents the first 14 actinide elements; Lr is the last actinide.

In many applications, rare earths are beneficial because of their relatively low toxicity. For example, the most common types of rechargeable batteries include either cadmium (Cd) or lead. Rechargeable Lanthanum Nickel Hydride (La-Ni-H) batteries are gradually replacing Ni-Cd batteries in computer and communications applications and could eventually replace lead-acid batteries in automobiles. While more expensive, La-Ni-H batteries offer higher energy density, better charge and discharge characteristics, and less waste disposal or recycling environmental issues. As another example, red and red-orange pigments prepared with La or Ce replace conventional commercial pigments containing Cd or other toxic heavy metals.

The next high tech application of rare earths to reach maturity could be magnetic cooling. The six rare earth ions Gd3 + to Tm3 + have unusually large magnetic moments due to their multiple unpaired electrons. A newly developed alloy, Gd5 (Si2Ge2), with a "giant magnetocaloric effect" near room temperature, is reported to allow magnetic cooling to compete with conventional gas compression cooling. This new technology could be used in refrigerators, freezers and home, commercial and automotive air conditioners. Magnetic cooling is much more efficient than gas compression cooling and does not require refrigerants that are flammable or toxic, that deplete the earth's ozone layer, or contribute to global warming.

Rare earth occurrence

"Rare" earth elements are a historical misnomer. The persistence of the term reflects obscurity rather than true rarity. The most common rare earths are similar in their crust concentration to common industrial metals such as chromium, nickel, copper, zinc, molybdenum, tin, tungsten or lead (Fig. 4). Even the two least abundant rare earths (Tm, Lu) are almost 200 times more abundant than gold. In contrast to common base and precious metals, however, rare earths hardly tend to concentrate on usable ore deposits. As a result, most of the world's rare earths come from just a few sources.

Differences in the frequency of individual rare earths in the upper continental crust of the earth (Fig. 3, 4) represent the superposition of two effects, one nuclear and one geochemical. First, rare earths with even ordinal numbers (58Ce, 60Nd, ...) have a greater cosmic and terrestrial abundance than neighboring rare earths with odd ordinal numbers (57La, 59Pr, ...). Second, the lighter rare earths are more incompatible (because they have larger ionic radii) and therefore more concentrated in the continental crust than the heavier rare earths. In most rare earth deposits, the first four rare earths - La, Ce, Pr and Nd - make up 80 to 99% of the total. Therefore, deposits containing relatively high levels of the scarcer and more valuable heavy rare earths (heavy rare earths: Gd through Lu, Y) and Eu are particularly desirable.

Figure 3. Prices and abundance of rare earth elements. Prices for 1999 or 2000 are in US dollars per kilogram of rare earth metal in two forms: (1) as oxides in packages from 2 to 25 kg with a purity of 95 to 99,99%; (2) as a 0,1-0,45 kg metal block with a purity of 99,9%. Two representative rare earth ores - high grade carbonatite ore from Mountain Pass, California and laterite ion adsorption ore from southern China - are compared to the Earth's upper continental crust. Z, atomic number. Image source USGS

Diagram showing the frequency of chemical elements in the upper continental crust of the earth as a function of the atomic number Figure 4. Frequency (atomic fraction) of the chemical elements in the upper continental crust of the earth as a function of the atomic number. Many of the elements are divided into (partially overlapping) categories: (1) rock-forming elements (main elements in the green area and minor elements in the light green area); (2) rare earth elements (lanthanides, La-Lu and Y; marked in blue); (3) Main industrial metals (worldwide production> ~ 3x107 kg / year; in bold); (4) precious metals (italic); and (5) the nine rarest "metals" - the six platinum group elements plus Au, Re, and Te (a metalloid). Image source: USGS

Rare earth resources

From the discovery of the rare earth (in the 1794-1907 period) to the mid-1950s, some of the rare earths were produced in modest amounts from monazite-containing placers and veins, from pegmatites and carbonatites as well as by-products from uranium and niobium extraction. During this time, the medium and heavy rare earths were generally available in pure form only in quantities of less than a kilogram and were mainly chemical curiosities.

1949 has discovered a carbonatite attack with exceptional light rare earth content (8 to 12% rare earth oxides [REO]) at the Mountain Pass in California's Upper Mojave Desert (Figure 5). The rare earths on the mountain pass are mainly hosted by bastnasite, (Ce, La, Nd, ...) CO3F and related minerals. Until 1966, this single prime deposit (owned by Molycorp, Inc.) was the largest rare earth resource in the US. The early development was largely supported by the sudden demand for EU created by the commercialization of color television. The mountain pass, with an average content of 9,3% and reserves of 20 million tonnes (Mt) REO (with a limit of 5%), is the only large ore deposit that was mined solely for its rare earth content. The mountain range is very much dominated by the light rare earth (Fig. 3, 6). Nonetheless, the large quantities of ore processed and the development of solvent extraction techniques for the large scale separation of individual rare earths allowed for the recovery of several intermediate rare earths. Increased availability in turn led to applications for these exotically exotic elements.

From 1965 to the mid-1980, Mountain Pass was the dominant source of rare earth, and the United States and Europe were largely self-sufficient in rare earths. Since 1985, the production of rare earths in China has increased dramatically (Fig. 1). The Chinese rare earth production mainly comes from two sources. The most important is the iron-niobium-rare earth deposit Bayan Obo in Inner Mongolia. This deposit has geological affinities for both carbonatite rare earth deposits and hydrothermal iron oxide (Cu-Au-rare earth) deposits such as Olympic Dam, Australia, and Kiruna, Sweden. The scores on Bayan Obo are 3% through 6% REO; Reserves are at least 40 Mt, possibly considerably more. The second major source for Chinese rare earths is ionic adsorbed ores in lateritic weathering crusts developed on granite and syenite rocks in tropical south China. These oxides are characterized by a relatively high content of heavy rare earths (Fig. 6) and in particular by a simple extraction of the rare earths.

The number of workable rare earth deposits that are already severely limited by the geochemical properties of the rare earths has also been influenced by environmental and regulatory factors in recent years. Monazite, the most abundant rare earth mineral, generally contains elevated levels of thorium. Th is itself only slightly radioactive, but is accompanied by highly radioactive daughter intermediates, especially radium, which can accumulate during processing. Concern about radioactivity concerns has largely eliminated monazite as a significant source of rare earths and has concentrated on the few occurrences of rare earths found in other low-thene minerals, particularly bastnasite.

Problems with the supply of rare earth elements

In recent years, the only domestic source of rare earth, the mine in Mountain Pass, California, was sporadically busy. Due to environmental and regulatory problems with the main sewage pipe, the rare earth separation plant (solvent extraction) has been shut down. Mountain Pass currently produces only bastnäsite concentrates and sells segregated rare earths only from inventories that were produced before shutdown. Even after the regulatory situation has been resolved, Mountain Pass's long-term viability as a provider of separate rare earths for high-tech applications is threatened by market factors.

Photo with the rare earth mine Mountain Pass

Molycorp Mine, Clark Mountain

Clark Mountain

Molycorp mine

In the years 1999 and 2000, almost all (more than 90%) of the separated rare earths used in the United States and Europe were either imported directly from China or from countries that imported their vegetable feed from China. The surprisingly rapid transition from self-sufficiency before 1990 to almost complete dependency on imports from a single country is today associated with a number of causal factors. This includes much lower labor and regulatory costs in China than in the United States and Europe. Continuing to expand the electronics and other manufacturing industries in Asia; the favorable number, size and favorable heavy rare earth content of Chinese deposits; and the ongoing environmental and regulatory issues at the Mountain Pass. China now dominates the world's rare earth markets (Figure 1) and raises some important rare earth supply issues for the United States and Europe and the EU:

(1) The United States and Europe risk losing their long-term leadership in many areas of rare earth technology. By transferring expertise in Rare Earth Processing Technology and Rare Earth applications from the US and Europe to Asia, China has been able to build a significant Rare Earth Industry that outshines all other countries in the production of ore and refined products , The Chinese Ministry of Science and Technology recently announced a new national basic research program. Among the first priority projects to be funded by 15 was "Basic Research for Rare Earth Materials" (Science, 18, December 1998, p. 2171).

(2) The US dependence on imports from China is emerging at a time when rare earths are increasingly being used in defense applications, including jet fighter engines and other aircraft components, missile guidance systems, electronic countermeasures, underwater mine detection, missile defense, ranging, spaceborne satellite powering and communications systems have gained in importance.

(3) The availability of Chinese rare earths for US markets depends on continued stability in China's domestic and economic affairs and on its relations with other countries.

(4) Although the current low rare earth prices caused by abundant supply from China are weighing on manufacturers, particularly the Molycorp mountain pass, low prices are also encouraging the development of new applications. For example, a recent chemistry text states that "For many years, the main use of lutetium was to study the behavior of lutetium ..." Several promising applications for Lu are known, but most are associated with high costs. If the price of Lu dropped from many thousands to several thousand dollars per kilogram (Figure 3), undoubtedly additional high-tech applications would follow, even for these least-abundant rare earths. The size of the role of the United States and Europe in the future expansion of rare earth technology and markets remains an important but open question.

Figure 6. Proportions of individual rare earths in two representative ores: Bastnasite, dominated by La, Ce and Nd, where Eu to Lu plus Y are only 0,4%; and lateritic ion adsorption ore, Y-dominated. Dark blue and light blue sectors stand for lanthanides with even or odd atomic numbers (see Fig. 2, 3). Yttrium is marked in green. Image source: USGS

The rare earth elements are essential to a diverse and growing spectrum of high technology applications that make up an important part of the United States and Europe's industrial economy. Long term shortages or unavailability of rare earths would force significant changes in many technological aspects of Western society. Well-known and potential domestic rare earth sources can therefore become an increasingly important topic for scientists and policymakers in the public and private sector.

Sources: US Geological Survey | Geological Department | Mineral Resources Team | Home Office | Roskill | Institute for Rare Earths and Metals

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