120-407: (Redirected from Rare Earth ) Rare earth may refer to: Rare-earth elements , a group of elements on the periodic table Rare-earth mineral , a mineral substantively composed of these elements Rare-earth magnet , a type of magnet that employs rare earth elements to increase effectiveness Rare Earth hypothesis , the theory that complex life in
240-549: A fissile material . The principal sources of rare-earth elements are the minerals bastnäsite ( RCO 3 F , where R is a mixture of rare-earth elements), monazite ( XPO 4 , where X is a mixture of rare-earth elements and sometimes thorium), and loparite ( (Ce,Na,Ca)(Ti,Nb)O 3 ), and the lateritic ion-adsorption clays . Despite their high relative abundance, rare-earth minerals are more difficult to mine and extract than equivalent sources of transition metals (due in part to their similar chemical properties), making
360-595: A CO 2 -rich primary magma, by fractional crystallization of an alkaline primary magma, or by separation of a CO 2 -rich immiscible liquid from. These liquids are most commonly forming in association with very deep Precambrian cratons , like the ones found in Africa and the Canadian Shield. Ferrocarbonatites are the most common type of carbonatite to be enriched in REE, and are often emplaced as late-stage, brecciated pipes at
480-532: A component of magnets in hybrid car motors." The global demand for rare-earth elements (REEs) is expected to increase more than fivefold by 2030. The REE geochemical classification is usually done on the basis of their atomic weight . One of the most common classifications divides REE into 3 groups: light rare earths (LREE - from 57 La to 60 Nd), intermediate (MREE - from 62 Sm to 67 Ho) and heavy (HREE - from 68 Er to 71 Lu). REE usually appear as trivalent ions, except for Ce and Eu which can take
600-657: A few percent of yttrium). Uranium ores from Ontario have occasionally yielded yttrium as a byproduct. Well-known minerals containing cerium, and other LREE, include bastnäsite , monazite , allanite , loparite , ancylite , parisite , lanthanite , chevkinite, cerite , stillwellite , britholite, fluocerite , and cerianite. Monazite (marine sands from Brazil , India , or Australia ; rock from South Africa ), bastnäsite (from Mountain Pass rare earth mine , or several localities in China), and loparite ( Kola Peninsula , Russia ) have been
720-405: A half-life of 32.5 days. All other radioactive cerium isotopes have half-lives under four days, and most of them have half-lives under ten minutes. The isotopes between Ce and Ce inclusive occur as fission products of uranium . The primary decay mode of the isotopes lighter than Ce is inverse beta decay or electron capture to isotopes of lanthanum , while that of the heavier isotopes
840-544: A maximum number of 25 was estimated. The use of X-ray spectra (obtained by X-ray crystallography ) by Henry Gwyn Jeffreys Moseley made it possible to assign atomic numbers to the elements. Moseley found that the exact number of lanthanides had to be 15, but that element 61 had not yet been discovered. (This is promethium, a radioactive element whose most stable isotope has a half-life of just 18 years.) Using these facts about atomic numbers from X-ray crystallography, Moseley also showed that hafnium (element 72) would not be
960-432: A melt phase if one is present. REE are chemically very similar and have always been difficult to separate, but the gradual decrease in ionic radius from light REE (LREE) to heavy REE (HREE), called the lanthanide contraction , can produce a broad separation between light and heavy REE. The larger ionic radii of LREE make them generally more incompatible than HREE in rock-forming minerals, and will partition more strongly into
1080-404: A melt phase, while HREE may prefer to remain in the crystalline residue, particularly if it contains HREE-compatible minerals like garnet . The result is that all magma formed from partial melting will always have greater concentrations of LREE than HREE, and individual minerals may be dominated by either HREE or LREE, depending on which range of ionic radii best fits the crystal lattice. Among
1200-503: A mine in the village of Ytterby in Sweden ; four of the rare-earth elements bear names derived from this single location. A table listing the 17 rare-earth elements, their atomic number and symbol, the etymology of their names, and their main uses (see also Applications of lanthanides ) is provided here. Some of the rare-earth elements are named after the scientists who discovered them, or elucidated their elemental properties, and some after
1320-455: A much better, though blue, light, and that mixing it with cerium dioxide resulted in a bright white light. Cerium dioxide also acts as a catalyst for the combustion of thorium oxide. This resulted in commercial success for von Welsbach and his invention, and created great demand for thorium. Its production resulted in a large amount of lanthanides being simultaneously extracted as by-products. Applications were soon found for them, especially in
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#17328444772521440-414: A quarry in the village of Ytterby , Sweden and termed "rare" because it had never yet been seen. Arrhenius's "ytterbite" reached Johan Gadolin , a Royal Academy of Turku professor, and his analysis yielded an unknown oxide ("earth" in the geological parlance of the day ), which he called yttria . Anders Gustav Ekeberg isolated beryllium from the gadolinite but failed to recognize other elements in
1560-451: A rare-earth element. Moseley was killed in World War I in 1915, years before hafnium was discovered. Hence, the claim of Georges Urbain that he had discovered element 72 was untrue. Hafnium is an element that lies in the periodic table immediately below zirconium , and hafnium and zirconium have very similar chemical and physical properties. During the 1940s, Frank Spedding and others in
1680-404: A separate group of rare-earth elements (the terbium group), or europium was included in the cerium group, and gadolinium and terbium were included in the yttrium group. In the latter case, the f-block elements are split into half: the first half (La–Eu) form the cerium group, and the second half (Gd–Yb) together with group 3 (Sc, Y, Lu) form the yttrium group. The reason for this division arose from
1800-420: A similar effect. In sedimentary rocks, rare-earth elements in clastic sediments are a representation of provenance. The rare-earth element concentrations are not typically affected by sea and river waters, as rare-earth elements are insoluble and thus have very low concentrations in these fluids. As a result, when sediment is transported, rare-earth element concentrations are unaffected by the fluid and instead
1920-437: A stable +4 state that does not oxidize water. It is considered one of the rare-earth elements . Cerium has no known biological role in humans but is not particularly toxic, except with intense or continued exposure. Despite always occurring in combination with the other rare-earth elements in minerals such as those of the monazite and bastnäsite groups, cerium is easy to extract from its ores, as it can be distinguished among
2040-567: A substitute for its radioactive congener thoria , for example in the manufacture of electrodes used in gas tungsten arc welding , where ceria as an alloying element improves arc stability and ease of starting while decreasing burn-off. The first use of cerium was in gas mantles , invented by Austrian chemist Carl Auer von Welsbach . In 1885, he had previously experimented with mixtures of magnesium , lanthanum, and yttrium oxides, but these gave green-tinted light and were unsuccessful. Six years later, he discovered that pure thorium oxide produced
2160-423: A temperature of 400 °C (752 °F). These elements and their compounds have no biological function other than in several specialized enzymes, such as in lanthanide-dependent methanol dehydrogenases in bacteria. The water-soluble compounds are mildly to moderately toxic, but the insoluble ones are not. All isotopes of promethium are radioactive, and it does not occur naturally in the earth's crust, except for
2280-515: A trace amount generated by spontaneous fission of uranium-238 . They are often found in minerals with thorium , and less commonly uranium . Though rare-earth elements are technically relatively plentiful in the entire Earth's crust ( cerium being the 25th-most-abundant element at 68 parts per million, more abundant than copper ), in practice this is spread thin across trace impurities, so to obtain rare earths at usable purity requires processing enormous amounts of raw ore at great expense, thus
2400-457: A valence of 3 and form sesquioxides (cerium forms CeO 2 ). Five different crystal structures are known, depending on the element and the temperature. The X-phase and the H-phase are only stable above 2000 K. At lower temperatures, there are the hexagonal A-phase, the monoclinic B-phase, and the cubic C-phase, which is the stable form at room temperature for most of the elements. The C-phase
2520-413: Is beta decay to isotopes of praseodymium . Some isotopes of neodymium can alpha decay or are predicted to decay to isotopes of cerium. The rarity of the proton-rich Ce and Ce is explained by the fact that they cannot be made in the most common processes of stellar nucleosynthesis for elements beyond iron, the s-process (slow neutron capture ) and the r-process (rapid neutron capture). This
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#17328444772522640-475: Is also an essential component as a dopant for phosphors used in CRT TV screens, fluorescent lamps, and later white light-emitting diodes . The most commonly used example is cerium(III)-doped yttrium aluminium garnet (Ce:YAG) which emits green to yellow-green light (550–530 nm) and also behaves as a scintillator . Cerium salts, such as the sulfides Ce 2 S 3 and Ce 3 S 4 , were considered during
2760-474: Is an exception because of the stability of the empty f-shell in Ce and the fact that it comes very early in the lanthanide series, where the nuclear charge is still low enough until neodymium to allow the removal of the fourth valence electron by chemical means. Cerium has a variable electronic structure . The energy of the 4f electron is nearly the same as that of the outer 5d and 6s electrons that are delocalized in
2880-461: Is called the bixbyite structure, as it occurs in a mineral of that name ( (Mn,Fe) 2 O 3 ). As seen in the chart, rare-earth elements are found on Earth at similar concentrations to many common transition metals. The most abundant rare-earth element is cerium , which is actually the 25th most abundant element in Earth's crust , having 68 parts per million (about as common as copper). The exception
3000-649: Is considered intermediate-valent. Alkyl , alkynyl , and alkenyl organocerium derivatives are prepared from the transmetallation of the respective organolithium or Grignard reagents, and are more nucleophilic but less basic than their precursors. Cerium was discovered in Bastnäs in Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger , and independently in Germany by Martin Heinrich Klaproth , both in 1803. Cerium
3120-599: Is high, weathering forms a thick argillized regolith, this process is called supergene enrichment and produces laterite deposits; heavy rare-earth elements are incorporated into the residual clay by absorption. This kind of deposit is only mined for REE in Southern China, where the majority of global heavy rare-earth element production occurs. REE-laterites do form elsewhere, including over the carbonatite at Mount Weld in Australia. REE may also be extracted from placer deposits if
3240-638: Is insoluble in HNO 3 and hence precipitates out. Care must be taken when handling some of the residues as they contain Ra , the daughter of Th, which is a strong gamma emitter. Cerium has two main applications, both of which use CeO 2 . The industrial application of ceria is for polishing, especially chemical-mechanical planarization (CMP). In its other main application, CeO 2 is used to decolorize glass. It functions by converting green-tinted ferrous impurities to nearly colorless ferric oxides. Ceria has also been used as
3360-570: Is not toxic when eaten, but animals injected with large doses of cerium have died due to cardiovascular collapse. Cerium is more dangerous to aquatic organisms because it damages cell membranes; it is not very soluble in water and can cause environmental contamination. Cerium oxide, the most prevalent cerium compound in industrial applications, is not regulated in the United States by the Occupational Safety and Health Administration (OSHA) as
3480-518: Is not very toxic either; it does not accumulate in the food chain to any appreciable extent. Because it often occurs together with calcium in phosphate minerals, and bones are primarily calcium phosphate , cerium can accumulate in bones in small amounts that are not considered dangerous. Cerium nitrate is an effective topical antimicrobial treatment for third-degree burns , although large doses can lead to cerium poisoning and methemoglobinemia . The early lanthanides act as essential cofactors for
3600-565: Is now known to be pure ceria. It was not until Carl Gustaf Mosander succeeded in removing lanthana and "didymia" in the late 1830s that ceria was obtained pure. Wilhelm Hisinger was a wealthy mine-owner and amateur scientist, and sponsor of Berzelius. He owned and controlled the mine at Bastnäs, and had been trying for years to find out the composition of the abundant heavy gangue rock (the "Tungsten of Bastnäs", which despite its name contained no tungsten ), now known as cerite, that he had in his mine. Mosander and his family lived for many years in
3720-445: Is possible to observe the serial trend of the REE by reporting their normalized concentrations against the atomic number. The trends that are observed in "spider" diagrams are typically referred to as "patterns", which may be diagnostic of petrological processes that have affected the material of interest. According to the general shape of the patterns or thanks to the presence (or absence) of so-called "anomalies", information regarding
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3840-517: Is slow with cold water but speeds up with increasing temperature, producing cerium(III) hydroxide and hydrogen gas: Four allotropic forms of cerium are known to exist at standard pressure and are given the common labels of α to δ: At lower temperatures the behavior of cerium is complicated by the slow rates of transformation. Transformation temperatures are subject to substantial hysteresis and values quoted here are approximate. Upon cooling below −15 °C, γ-cerium starts to change to β-cerium, but
3960-428: Is so because they are bypassed by the reaction flow of the s-process, and the r-process nuclides are blocked from decaying to them by more neutron-rich stable nuclides. Such nuclei are called p-nuclei , and their origin is not yet well understood: some speculated mechanisms for their formation include proton capture as well as photodisintegration . Ce is the most common isotope of cerium, as it can be produced in both
4080-443: Is synthetically produced in nuclear reactors. Due to their chemical similarity, the concentrations of rare earths in rocks are only slowly changed by geochemical processes, making their proportions useful for geochronology and dating fossils. Rare-earth elements occur in nature in combination with phosphate ( monazite ), carbonate - fluoride ( bastnäsite ), and oxygen anions. In their oxides, most rare-earth elements only have
4200-517: Is the highly unstable and radioactive promethium "rare earth" is quite scarce. The longest-lived isotope of promethium has a half-life of 17.7 years, so the element exists in nature in only negligible amounts (approximately 572 g in the entire Earth's crust). Promethium is one of the two elements that do not have stable (non-radioactive) isotopes and are followed by (i.e. with higher atomic number) stable elements (the other being technetium ). The rare-earth elements are often found together. During
4320-465: Is the most common representative of the monazites, with "-Ce" being the Levinson suffix informing on the dominance of the particular REE element representative. Also the cerium-dominant bastnäsite-(Ce) is the most important of the bastnäsites. Cerium is the easiest lanthanide to extract from its minerals because it is the only one that can reach a stable +4 oxidation state in aqueous solution. Because of
4440-427: Is the only theoretically stable isotope . None of these decay modes have yet been observed, though the double beta decay of Ce, Ce, and Ce have been experimentally searched for. The current experimental limits for their half-lives are: All other cerium isotopes are synthetic and radioactive . The most stable of them are Ce with a half-life of 284.9 days, Ce with a half-life of 137.6 days, and Ce with
4560-465: Is the second element of the lanthanide series. In the periodic table, it appears between the lanthanides lanthanum to its left and praseodymium to its right, and above the actinide thorium . It is a ductile metal with a hardness similar to that of silver . Its 58 electrons are arranged in the configuration [Xe]4f 5d 6s , of which the four outer electrons are valence electrons . The 4f, 5d, and 6s energy levels are very close to each other, and
4680-456: Is the vivid red cerium(III) sulfide (cerium sulfide red), which stays chemically inert up to very high temperatures. The pigment is a safer alternative to lightfast but toxic cadmium selenide-based pigments . The addition of cerium oxide to older cathode-ray tube television glass plates was beneficial, as it suppresses the darkening effect from the creation of F-center defects due to the continuous electron bombardment during operation. Cerium
4800-467: Is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with sodium hydroxide to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. After that, the solution is treated with ammonium oxalate to convert rare earths to their insoluble oxalates . The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid, but cerium oxide
4920-449: Is usually lacking in thorium and the heavy lanthanides beyond samarium and europium , and hence the extraction of cerium from it is quite direct. First, the bastnäsite is purified, using dilute hydrochloric acid to remove calcium carbonate impurities. The ore is then roasted in the air to oxidize it to the lanthanide oxides: while most of the lanthanides will be oxidized to the sesquioxides Ln 2 O 3 , cerium will be oxidized to
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5040-671: The Ames daughter project (now the Ames Laboratory ). Production of extremely pure cerium in Ames commenced in mid-1944 and continued until August 1945. Cerium is the most abundant of all the lanthanides and the 25th most abundant element, making up 68 ppm of the Earth's crust. This value is the same of copper , and cerium is even more abundant than common metals such as lead (13 ppm) and tin (2.1 ppm). Thus, despite its position as one of
5160-530: The Belousov–Zhabotinsky reaction , cerium oscillates between the +4 and +3 oxidation states to catalyze the reaction. Organocerium chemistry is similar to that of the other lanthanides , often involving complexes of cyclopentadienyl and cyclooctatetraenyl ligands. Cerocene (Ce(C 8 H 8 ) 2 ) adopts the uranocene molecular structure. The 4f electron in cerocene is poised ambiguously between being localized and delocalized and this compound
5280-841: The Manhattan Project as advanced refractory materials for the construction of crucibles which could withstand the high temperatures and strongly reducing conditions when casting plutonium metal. Despite desirable properties, these sulfides were never widely adopted due to practical issues with their synthesis. Cerium is used as alloying element in aluminium to create castable eutectic aluminium alloys with 6–16 wt.% Ce, to which other elements such as Mg, Ni, Fe and Mn can be added. These Al-Ce alloys have excellent high temperature strength and are suitable for automotive applications (e.g. in cylinder heads ). Other alloys of cerium include Pu-Ce and Pu-Ce-Co plutonium alloys , which have been used as nuclear fuel . Other automotive applications for
5400-563: The Oddo–Harkins rule : even-numbered REE at abundances of about 5% each, and odd-numbered REE at abundances of about 1% each. Similar compositions are found in xenotime or gadolinite. Well-known minerals containing yttrium, and other HREE, include gadolinite, xenotime, samarskite , euxenite , fergusonite , yttrotantalite, yttrotungstite, yttrofluorite (a variety of fluorite ), thalenite, and yttrialite . Small amounts occur in zircon , which derives its typical yellow fluorescence from some of
5520-533: The rare-earth metals or rare earths , and sometimes the lanthanides or lanthanoids (although scandium and yttrium , which do not belong to this series, are usually included as rare earths), are a set of 17 nearly indistinguishable lustrous silvery-white soft heavy metals . Compounds containing rare earths have diverse applications in electrical and electronic components, lasers, glass, magnetic materials, and industrial processes. Scandium and yttrium are considered rare-earth elements because they tend to occur in
5640-486: The upper mantle (200 to 600 km depth). This melt becomes enriched in incompatible elements, like the rare-earth elements, by leaching them out of the crystalline residue. The resultant magma rises as a diapir , or diatreme , along pre-existing fractures, and can be emplaced deep in the crust , or erupted at the surface. Typical REE enriched deposits types forming in rift settings are carbonatites, and A- and M-Type granitoids. Near subduction zones, partial melting of
5760-428: The "heavy" group from 6.965 (ytterbium) to 9.32 (thulium), as well as including yttrium at 4.47. Europium has a density of 5.24. Rare-earth elements, except scandium , are heavier than iron and thus are produced by supernova nucleosynthesis or by the s-process in asymptotic giant branch stars. In nature, spontaneous fission of uranium-238 produces trace amounts of radioactive promethium , but most promethium
5880-474: The 1g 7/2 proton orbital. The abundances of the cerium isotopes may differ very slightly in natural sources, because Ce and Ce are the daughters of the long-lived primordial radionuclides La and Nd, respectively. Cerium exists in two main oxidation states, Ce(III) and Ce(IV). This pair of adjacent oxidation states dominates several aspects of the chemistry of this element. Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with
6000-568: The 4 f orbital which acts against the electrons of the 6 s and 5 d orbitals. The lanthanide contraction has a direct effect on the geochemistry of the lanthanides, which show a different behaviour depending on the systems and processes in which they are involved. The effect of the lanthanide contraction can be observed in the REE behaviour both in a CHARAC-type geochemical system (CHArge-and-RAdius-Controlled ) where elements with similar charge and radius should show coherent geochemical behaviour, and in non-CHARAC systems, such as aqueous solutions, where
6120-580: The Ce(IV) derivatives CeF 4− 8 and CeF 2− 6 . The chloride gives the orange CeCl 2− 6 . Cerium(IV) oxide ("ceria") has the fluorite structure, similarly to the dioxides of praseodymium and terbium . Ceria is a nonstoichiometric compound , meaning that the real formula is CeO 2−x , where x is about 0.2. Thus, the material is not perfectly described as Ce(IV). Ceria reduces to cerium(III) oxide with hydrogen gas. Many nonstoichiometric chalcogenides are also known, along with
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#17328444772526240-498: The LREE. This has economic consequences: large ore bodies of LREE are known around the world and are being exploited. Ore bodies for HREE are more rare, smaller, and less concentrated. Most of the current supply of HREE originates in the "ion-absorption clay" ores of Southern China. Some versions provide concentrates containing about 65% yttrium oxide, with the HREE being present in ratios reflecting
6360-400: The United States (during the Manhattan Project ) developed chemical ion-exchange procedures for separating and purifying rare-earth elements. This method was first applied to the actinides for separating plutonium-239 and neptunium from uranium , thorium , actinium , and the other actinides in the materials produced in nuclear reactors . Plutonium-239 was very desirable because it is
6480-449: The accompanying HREE. The zirconium mineral eudialyte , such as is found in southern Greenland , contains small but potentially useful amounts of yttrium. Of the above yttrium minerals, most played a part in providing research quantities of lanthanides during the discovery days. Xenotime is occasionally recovered as a byproduct of heavy-sand processing, but is not as abundant as the similarly recovered monazite (which typically contains
6600-448: The anhydrous rare-earth phosphates, it is the tetragonal mineral xenotime that incorporates yttrium and the HREE, whereas the monoclinic monazite phase incorporates cerium and the LREE preferentially. The smaller size of the HREE allows greater solid solubility in the rock-forming minerals that make up Earth's mantle, and thus yttrium and the HREE show less enrichment in Earth's crust relative to chondritic abundance than does cerium and
6720-858: The core of igneous complexes; they consist of fine-grained calcite and hematite, sometimes with significant concentrations of ankerite and minor concentrations of siderite. Large carbonatite deposits enriched in rare-earth elements include Mount Weld in Australia, Thor Lake in Canada, Zandkopsdrift in South Africa, and Mountain Pass in the USA. Peralkaline granites (A-Type granitoids) have very high concentrations of alkaline elements and very low concentrations of phosphorus; they are deposited at moderate depths in extensional zones, often as igneous ring complexes, or as pipes, massive bodies, and lenses. These fluids have very low viscosities and high element mobility, which allows for
6840-503: The cracking of petroleum. This property of cerium saved the life of writer Primo Levi at the Auschwitz concentration camp , when he found a supply of ferrocerium alloy and bartered it for food. The photostability of pigments can be enhanced by the addition of cerium, as it provides pigments with lightfastness and prevents clear polymers from darkening in sunlight. An example of a cerium compound used on its own as an inorganic pigment
6960-408: The crude yttria and found the same substances that Mosander obtained, but Berlin named (1860) the substance giving pink salts erbium , and Delafontaine named the substance with the yellow peroxide terbium . This confusion led to several false claims of new elements, such as the mosandrium of J. Lawrence Smith , or the philippium and decipium of Delafontaine. Due to the difficulty in separating
7080-735: The crystallization of large grains, despite a relatively short crystallization time upon emplacement; their large grain size is why these deposits are commonly referred to as pegmatites. Economically viable pegmatites are divided into Lithium-Cesium-Tantalum (LCT) and Niobium-Yttrium-Fluorine (NYF) types; NYF types are enriched in rare-earth minerals. Examples of rare-earth pegmatite deposits include Strange Lake in Canada and Khaladean-Buregtey in Mongolia. Nepheline syenite (M-Type granitoids) deposits are 90% feldspar and feldspathoid minerals. They are deposited in small, circular massifs and contain high concentrations of rare-earth-bearing accessory minerals . For
7200-425: The decreased solubility of cerium in the +4 oxidation state, cerium is sometimes depleted from rocks relative to the other rare-earth elements and is incorporated into zircon , since Ce and Zr have the same charge and similar ionic radii. In extreme cases, cerium(IV) can form its own minerals separated from the other rare-earth elements, such as cerianite -(Ce) and (Ce,Th)O 2 . Bastnäsite, Ln CO 3 F,
7320-413: The difference in solubility of rare-earth double sulfates with sodium and potassium. The sodium double sulfates of the cerium group are poorly soluble, those of the terbium group slightly, and those of the yttrium group are very soluble. Sometimes, the yttrium group was further split into the erbium group (dysprosium, holmium, erbium, and thulium) and the ytterbium group (ytterbium and lutetium), but today
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#17328444772527440-403: The dioxide CeO 2 . This is insoluble in water and can be leached out with 0.5 M hydrochloric acid, leaving the other lanthanides behind. The procedure for monazite , (Ln,Th)PO 4 , which usually contains all the rare earths, as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it
7560-409: The electron structure is also an important parameter to consider as the lanthanide contraction affects the ionic potential . A direct consequence is that, during the formation of coordination bonds, the REE behaviour gradually changes along the series. Furthermore, the lanthanide contraction causes the ionic radius of Ho (0.901 Å) to be almost identical to that of Y (0.9 Å), justifying the inclusion of
7680-651: The element showing the anomaly and the predictable one based on the average of the normalized concentrations of the two elements in the previous and next position in the series, according to the equation: where [ REE i ] n {\displaystyle [{\text{REE}}_{i}]_{n}} is the normalized concentration of the element whose anomaly has to be calculated, [ REE i − 1 ] n {\displaystyle [{\text{REE}}_{i-1}]_{n}} and [ REE i + 1 ] n {\displaystyle [{\text{REE}}_{i+1}]_{n}}
7800-417: The existence of an unknown element. The fractional crystallization of the oxides then yielded europium in 1901. In 1839 the third source for rare earths became available. This is a mineral similar to gadolinite called uranotantalum (now called " samarskite ") an oxide of a mixture of elements such as yttrium, ytterbium, iron, uranium, thorium, calcium, niobium, and tantalum. This mineral from Miass in
7920-511: The following observations apply: anomalies in europium are dominated by the crystallization of feldspars . Hornblende , controls the enrichment of MREE compared to LREE and HREE. Depletion of LREE relative to HREE may be due to the crystallization of olivine , orthopyroxene , and clinopyroxene . On the other hand, the depletion of HREE relative to LREE may be due to the presence of garnet , as garnet preferentially incorporates HREE into its crystal structure. The presence of zircon may also cause
8040-433: The form of Ce and Eu depending on the redox conditions of the system. Consequentially, REE are characterized by a substantial identity in their chemical reactivity, which results in a serial behaviour during geochemical processes rather than being characteristic of a single element of the series. Sc, Y, and Lu can be electronically distinguished from the other rare earths because they do not have f valence electrons, whereas
8160-566: The fractionation of trace elements (including rare-earth elements) into the liquid phase (the melt/magma) into the solid phase (the mineral). If an element preferentially remains in the solid phase it is termed 'compatible', and if it preferentially partitions into the melt phase it is described as 'incompatible'. Each element has a different partition coefficient, and therefore fractionates into solid and liquid phases distinctly. These concepts are also applicable to metamorphic and sedimentary petrology. In igneous rocks, particularly in felsic melts,
8280-405: The geographical locations where discovered. A mnemonic for the names of the sixth-row elements in order is "Lately college parties never produce sexy European girls that drink heavily even though you look". Rare earths were mainly discovered as components of minerals. Ytterbium was found in the "ytterbite" (renamed to gadolinite in 1800) discovered by Lieutenant Carl Axel Arrhenius in 1787 at
8400-448: The heavy rare-earth elements (HREE), and those that fall in between are typically referred to as the middle rare-earth elements (MREE). Commonly, rare-earth elements with atomic numbers 57 to 61 (lanthanum to promethium) are classified as light and those with atomic numbers 62 and greater are classified as heavy rare-earth elements. Increasing atomic numbers between light and heavy rare-earth elements and decreasing atomic radii throughout
8520-515: The laboratory. The six nitrate ligands bind as bidentate ligands . The complex [Ce(NO 3 ) 6 ] is 12-coordinate, a high coordination number which emphasizes the large size of the Ce ion. CAN is a popular oxidant in organic synthesis , both as a stoichiometric reagent and as a catalyst. It is inexpensive, stable in air, easily handled, and of low toxicity. It operates by one-electron redox. Cerium nitrates also form 4:3 and 1:1 complexes with 18-crown-6 (the ratio referring to that between
8640-474: The lanthanides by its unique ability to be oxidized to the +4 state in aqueous solution. It is the most common of the lanthanides, followed by neodymium , lanthanum , and praseodymium . Its estimated abundance in the Earth's crust is 68 ppm . Cerium was the first of the lanthanides to be discovered, in Bastnäs , Sweden. It was discovered by Jöns Jakob Berzelius and Wilhelm Hisinger in 1803, and independently by Martin Heinrich Klaproth in Germany in
8760-470: The latter among the REE. The application of rare-earth elements to geology is important to understanding the petrological processes of igneous , sedimentary and metamorphic rock formation. In geochemistry , rare-earth elements can be used to infer the petrological mechanisms that have affected a rock due to the subtle atomic size differences between the elements, which causes preferential fractionation of some rare earths relative to others depending on
8880-418: The logarithm to the base 10 of the value. Commonly, the rare-earth elements are normalized to chondritic meteorites , as these are believed to be the closest representation of unfractionated Solar System material. However, other normalizing standards can be applied depending on the purpose of the study. Normalization to a standard reference value, especially of a material believed to be unfractionated, allows
9000-470: The lower sesquioxide are as a catalytic converter for the oxidation of CO and NO x emissions in the exhaust gases from motor vehicles. The early lanthanides have been found to be essential to some methanotrophic bacteria living in volcanic mudpots , such as Methylacidiphilum fumariolicum : lanthanum, cerium, praseodymium, and neodymium are about equally effective. Cerium is otherwise not known to have biological role in any other organisms, but
9120-472: The main grouping is between the cerium and the yttrium groups. Today, the rare-earth elements are classified as light or heavy rare-earth elements, rather than in cerium and yttrium groups. The classification of rare-earth elements is inconsistent between authors. The most common distinction between rare-earth elements is made by atomic numbers ; those with low atomic numbers are referred to as light rare-earth elements (LREE), those with high atomic numbers are
9240-411: The melting point. Naturally occurring cerium is made up of four isotopes: Ce (0.19%), Ce (0.25%), Ce (88.4%), and Ce (11.1%). All four are observationally stable , though the light isotopes Ce and Ce are theoretically expected to undergo double electron capture to isotopes of barium , and the heaviest isotope Ce is expected to undergo double beta decay to Nd or alpha decay to Ba. Thus, Ce
9360-459: The metallic state, and only a small amount of energy is required to change the relative occupancy of these electronic levels. This gives rise to dual valence states. For example, a volume change of about 10% occurs when cerium is subjected to high pressures or low temperatures. In its high pressure phase (α-Cerium), the 4f electrons are also delocalized and itinerate, as opposed to localized 4f electrons in low pressure phase (γ-Cerium). It appears that
9480-522: The metals (and determining the separation is complete), the total number of false discoveries was dozens, with some putting the total number of discoveries at over a hundred. There were no further discoveries for 30 years, and the element didymium was listed in the periodic table of elements with a molecular mass of 138. In 1879, Delafontaine used the new physical process of optical flame spectroscopy and found several new spectral lines in didymia. Also in 1879, Paul Émile Lecoq de Boisbaudran isolated
9600-634: The methanol dehydrogenase of the methanotrophic bacterium Methylacidiphilum fumariolicum SolV, for which lanthanum, cerium, praseodymium, and neodymium alone are about equally effective. Like all rare-earth metals, cerium is of low to moderate toxicity. A strong reducing agent, it ignites spontaneously in air at 65 to 80 °C. Fumes from cerium fires are toxic. Cerium reacts with water to produce hydrogen gas, and thus cerium fires can only be effectively extinguished using class D dry powder extinguishing media. Workers exposed to cerium have experienced itching, sensitivity to heat, and skin lesions. Cerium
9720-688: The most part, these deposits are small but important examples include Illimaussaq-Kvanefeld in Greenland, and Lovozera in Russia. Rare-earth elements can also be enriched in deposits by secondary alteration either by interactions with hydrothermal fluids or meteoric water or by erosion and transport of resistate REE-bearing minerals. Argillization of primary minerals enriches insoluble elements by leaching out silica and other soluble elements, recrystallizing feldspar into clay minerals such kaolinite, halloysite, and montmorillonite. In tropical regions where precipitation
9840-415: The name "rare" earths. Because of their geochemical properties, rare-earth elements are typically dispersed and not often found concentrated in rare-earth minerals . Consequently, economically exploitable ore deposits are sparse. The first rare-earth mineral discovered (1787) was gadolinite , a black mineral composed of cerium, yttrium, iron, silicon, and other elements. This mineral was extracted from
9960-560: The new element samarium from the mineral samarskite . The samaria earth was further separated by Lecoq de Boisbaudran in 1886, and a similar result was obtained by Jean Charles Galissard de Marignac by direct isolation from samarskite. They named the element gadolinium after Johan Gadolin , and its oxide was named " gadolinia ". Further spectroscopic analysis between 1886 and 1901 of samaria, yttria, and samarskite by William Crookes , Lecoq de Boisbaudran and Eugène-Anatole Demarçay yielded several new spectral lines that indicated
10080-471: The nitrate and the crown ether ). Classically, CAN is a primary standard for quantitative analysis. Cerium(IV) salts, especially cerium(IV) sulfate , are often used as standard reagents for volumetric analysis in cerimetric titrations . Due to ligand-to-metal charge transfer , aqueous cerium(IV) ions are orange-yellow. Aqueous cerium(IV) is metastable in water and is a strong oxidizing agent that oxidizes hydrochloric acid to give chlorine gas. In
10200-424: The normalized concentration, [ REE i ] sam {\displaystyle {[{\text{REE}}_{i}]_{\text{sam}}}} the analytical concentration of the element measured in the sample, and [ REE i ] ref {\displaystyle {[{\text{REE}}_{i}]_{\text{ref}}}} the concentration of the same element in the reference material. It
10320-427: The normalized concentrations of the respectively previous and next elements along the series. The rare-earth elements patterns observed in igneous rocks are primarily a function of the chemistry of the source where the rock came from, as well as the fractionation history the rock has undergone. Fractionation is in turn a function of the partition coefficients of each element. Partition coefficients are responsible for
10440-432: The observed abundances to be compared to the initial abundances of the element. Normalization also removes the pronounced 'zig-zag' pattern caused by the differences in abundance between even and odd atomic numbers . Normalization is carried out by dividing the analytical concentrations of each element of the series by the concentration of the same element in a given standard, according to the equation: where n indicates
10560-456: The ore. After this discovery in 1794, a mineral from Bastnäs near Riddarhyttan , Sweden, which was believed to be an iron – tungsten mineral, was re-examined by Jöns Jacob Berzelius and Wilhelm Hisinger . In 1803 they obtained a white oxide and called it ceria . Martin Heinrich Klaproth independently discovered the same oxide and called it ochroia . It took another 30 years for researchers to determine that other elements were contained in
10680-414: The others do, but the chemical behaviour is almost the same. A distinguishing factor in the geochemical behaviour of the REE is linked to the so-called " lanthanide contraction " which represents a higher-than-expected decrease in the atomic/ionic radius of the elements along the series. This is determined by the variation of the shielding effect towards the nuclear charge due to the progressive filling of
10800-457: The oxides with the hydrogen halides. The anhydrous halides are pale-colored, paramagnetic, hygroscopic solids. Upon hydration, the trihalides convert to complexes containing aquo complexes [Ce(H 2 O) 8-9 ] . Unlike most lanthanides, Ce forms a tetrafluoride, a white solid. It also forms a bronze-colored diiodide, which has metallic properties. Aside from the binary halide phases, a number of anionic halide complexes are known. The fluoride gives
10920-446: The principal ores of cerium and the light lanthanides. Enriched deposits of rare-earth elements at the surface of the Earth, carbonatites and pegmatites , are related to alkaline plutonism , an uncommon kind of magmatism that occurs in tectonic settings where there is rifting or that are near subduction zones. In a rift setting, the alkaline magma is produced by very small degrees of partial melting (<1%) of garnet peridotite in
11040-440: The processes at work. The geochemical study of the REE is not carried out on absolute concentrations – as it is usually done with other chemical elements – but on normalized concentrations in order to observe their serial behaviour. In geochemistry, rare-earth elements are typically presented in normalized "spider" diagrams, in which concentration of rare-earth elements are normalized to a reference standard and are then expressed as
11160-502: The pyrophoric alloy known as " mischmetal " composed of 50% cerium, 25% lanthanum, and the remainder being the other lanthanides, that is used widely for lighter flints. Usually iron is added to form the alloy ferrocerium , also invented by von Welsbach. Due to the chemical similarities of the lanthanides, chemical separation is not usually required for their applications, such as the addition of mischmetal to steel as an inclusion modifier to improve mechanical properties, or as catalysts for
11280-421: The rare-earth elements relatively expensive. Their industrial use was very limited until efficient separation techniques were developed, such as ion exchange , fractional crystallization, and liquid–liquid extraction during the late 1950s and early 1960s. Some ilmenite concentrates contain small amounts of scandium and other rare-earth elements, which could be analysed by X-ray fluorescence (XRF). Before
11400-409: The rock retains the rare-earth element concentration from its source. Cerium Cerium is a chemical element ; it has symbol Ce and atomic number 58. It is a soft , ductile , and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the oxidation state of +3 characteristic of the series, it also has
11520-433: The s- and r-processes, while Ce can only be produced in the r-process. Another reason for the abundance of Ce is that it is a magic nucleus , having a closed neutron shell (it has 82 neutrons), and hence it has a very low cross section towards further neutron capture. Although its proton number of 58 is not magic, it is granted additional stability, as its eight additional protons past the magic number 50 enter and complete
11640-485: The same ore deposits as the lanthanides and exhibit similar chemical properties, but have different electrical and magnetic properties . The term 'rare-earth' is a misnomer because they are not actually scarce, although historically it took a long time to isolate these elements. These metals tarnish slowly in air at room temperature and react slowly with cold water to form hydroxides, liberating hydrogen. They react with steam to form oxides and ignite spontaneously at
11760-461: The same house as Berzelius, and Mosander was undoubtedly persuaded by Berzelius to investigate ceria further. The element played a role in the Manhattan Project , where cerium compounds were investigated in the Berkeley site as materials for crucibles for uranium and plutonium casting. For this reason, new methods for the preparation and casting of cerium were developed within the scope of
11880-489: The same year. In 1839 Carl Gustaf Mosander became the first to isolate the metal. Today, cerium and its compounds have a variety of uses: for example, cerium(IV) oxide is used to polish glass and is an important part of catalytic converters . Cerium metal is used in ferrocerium lighters for its pyrophoric properties. Cerium-doped YAG phosphor is used in conjunction with blue light-emitting diodes to produce white light in most commercial white LED light sources. Cerium
12000-624: The seafloor, bit by bit, over tens of millions of years. One square patch of metal-rich mud 2.3 kilometers wide might contain enough rare earths to meet most of the global demand for a year, Japanese geologists report in Nature Geoscience ." "I believe that rare[-]earth resources undersea are much more promising than on-land resources," said Kato. "[C]oncentrations of rare earths were comparable to those found in clays mined in China. Some deposits contained twice as much heavy rare earths such as dysprosium,
12120-487: The sedimentary parent lithology contains REE-bearing, heavy resistate minerals. In 2011, Yasuhiro Kato, a geologist at the University of Tokyo who led a study of Pacific Ocean seabed mud, published results indicating the mud could hold rich concentrations of rare-earth minerals. The deposits, studied at 78 sites, came from "[h]ot plumes from hydrothermal vents pull[ing] these materials out of seawater and deposit[ing] them on
12240-419: The sequential accretion of the Earth, the dense rare-earth elements were incorporated into the deeper portions of the planet. Early differentiation of molten material largely incorporated the rare earths into mantle rocks. The high field strength and large ionic radii of rare earths make them incompatible with the crystal lattices of most rock-forming minerals, so REE will undergo strong partitioning into
12360-497: The series causes chemical variations. Europium is exempt of this classification as it has two valence states: Eu and Eu . Yttrium is grouped as heavy rare-earth element due to chemical similarities. The break between the two groups is sometimes put elsewhere, such as between elements 63 (europium) and 64 (gadolinium). The actual metallic densities of these two groups overlap, with the "light" group having densities from 6.145 (lanthanum) to 7.26 (promethium) or 7.52 (samarium) g/cc, and
12480-425: The so-called rare-earth metals , cerium is actually not rare at all. Cerium content in the soil varies between 2 and 150 ppm, with an average of 50 ppm; seawater contains 1.5 parts per trillion of cerium. Cerium occurs in various minerals, but the most important commercial sources are the minerals of the monazite and bastnäsite groups, where it makes up about half of the lanthanide content. Monazite-(Ce)
12600-401: The southern Ural Mountains was documented by Gustav Rose . The Russian chemist R. Harmann proposed that a new element he called " ilmenium " should be present in this mineral, but later, Christian Wilhelm Blomstrand , Galissard de Marignac, and Heinrich Rose found only tantalum and niobium ( columbium ) in it. The exact number of rare-earth elements that existed was highly unclear, and
12720-444: The strong oxidizing agents peroxodisulfate or bismuthate . The value of E (Ce /Ce ) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72 V is representative. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state. Cerium forms all four trihalides CeX 3 (X = F, Cl, Br, I) usually by reaction of
12840-766: The subducting plate within the asthenosphere (80 to 200 km depth) produces a volatile-rich magma (high concentrations of CO 2 and water), with high concentrations of alkaline elements, and high element mobility that the rare earths are strongly partitioned into. This melt may also rise along pre-existing fractures, and be emplaced in the crust above the subducting slab or erupted at the surface. REE-enriched deposits forming from these melts are typically S-Type granitoids. Alkaline magmas enriched with rare-earth elements include carbonatites, peralkaline granites (pegmatites), and nepheline syenite . Carbonatites crystallize from CO 2 -rich fluids, which can be produced by partial melting of hydrous-carbonated lherzolite to produce
12960-399: The system under examination and the occurring geochemical processes can be obtained. The anomalies represent enrichment (positive anomalies) or depletion (negative anomalies) of specific elements along the series and are graphically recognizable as positive or negative "peaks" along the REE patterns. The anomalies can be numerically quantified as the ratio between the normalized concentration of
13080-479: The time that ion exchange methods and elution were available, the separation of the rare earths was primarily achieved by repeated precipitation or crystallization . In those days, the first separation was into two main groups, the cerium earths (lanthanum, cerium, praseodymium, neodymium, and samarium) and the yttrium earths (scandium, yttrium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). Europium, gadolinium, and terbium were either considered as
13200-504: The title Rare earth . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Rare_earth&oldid=1193207291 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Rare-earth element The rare-earth elements ( REE ), also called
13320-439: The transfer of one electron to the 5d shell is due to strong interelectronic repulsion in the compact 4f shell. This effect is overwhelmed when the atom is positively ionised; thus Ce on its own has instead the regular configuration [Xe]4f , although in some solid solutions it may be [Xe]4f 5d . Most lanthanides can use only three electrons as valence electrons, as afterwards the remaining 4f electrons are too strongly bound: cerium
13440-432: The transformation involves a volume increase and, as more β forms, the internal stresses build up and suppress further transformation. Cooling below approximately −160 °C will start formation of α-cerium but this is only from remaining γ-cerium. β-cerium does not significantly transform to α-cerium except in the presence of stress or deformation. At atmospheric pressure, liquid cerium is more dense than its solid form at
13560-407: The trivalent Ce 2 Z 3 (Z = S , Se , Te ). The monochalcogenides CeZ conduct electricity and would better be formulated as Ce Z e . While CeZ 2 are known, they are polychalcogenides with cerium(III): cerium(IV) derivatives of S, Se, and Te are unknown. The compound ceric ammonium nitrate (CAN) (NH 4 ) 2 [Ce(NO 3 ) 6 ] is the most common cerium compound encountered in
13680-484: The two ores ceria and yttria (the similarity of the rare-earth metals' chemical properties made their separation difficult). In 1839 Carl Gustav Mosander , an assistant of Berzelius, separated ceria by heating the nitrate and dissolving the product in nitric acid . He called the oxide of the soluble salt lanthana . It took him three more years to separate the lanthana further into didymia and pure lanthana. Didymia, although not further separable by Mosander's techniques,
13800-464: The universe is exceptionally rare as a proper noun: Rare Earth: Why Complex Life Is Uncommon in the Universe , a book by Peter Ward and Donald E. Brownlee Rare Earth (band) , an American musical group Rare Earth Records , a subsidiary of Motown Records which produced rock music Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with
13920-529: The valence changes from about 3 to 4 when it is cooled or compressed. Like the other lanthanides, cerium metal is a good reducing agent , having standard reduction potential of E = −2.34 V for the Ce /Ce couple. It tarnishes in air, forming a passivating oxide layer like iron rust. A centimeter-sized sample of cerium metal corrodes completely in about a year. More dramatically, metallic cerium can be highly pyrophoric : Being highly electropositive , cerium reacts with water. The reaction
14040-477: Was named by Berzelius after the asteroid Ceres , formally 1 Ceres, discovered two years earlier. Ceres was initially considered to be a planet at the time. The asteroid is itself named after the Roman goddess Ceres , goddess of agriculture, grain crops, fertility and motherly relationships. Cerium was originally isolated in the form of its oxide, which was named ceria , a term that is still used. The metal itself
14160-492: Was in fact still a mixture of oxides. In 1842 Mosander also separated the yttria into three oxides: pure yttria, terbia, and erbia (all the names are derived from the town name "Ytterby"). The earth giving pink salts he called terbium ; the one that yielded yellow peroxide he called erbium . In 1842 the number of known rare-earth elements had reached six: yttrium, cerium, lanthanum, didymium, erbium, and terbium. Nils Johan Berlin and Marc Delafontaine tried also to separate
14280-494: Was once thought to be in space group I 2 1 3 (no. 199), but is now known to be in space group Ia 3 (no. 206). The structure is similar to that of fluorite or cerium dioxide (in which the cations form a face-centred cubic lattice and the anions sit inside the tetrahedra of cations), except that one-quarter of the anions (oxygen) are missing. The unit cell of these sesquioxides corresponds to eight unit cells of fluorite or cerium dioxide, with 32 cations instead of 4. This
14400-407: Was too electropositive to be isolated by then-current smelting technology, a characteristic of rare-earth metals in general. After the development of electrochemistry by Humphry Davy five years later, the earths soon yielded the metals they contained. Ceria, as isolated in 1803, contained all of the lanthanides present in the cerite ore from Bastnäs, Sweden, and thus only contained about 45% of what
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