Earths, the rare

The moon rocks brought back to earth are only a tiny sample of the moon s surface, but they are enough to show that some elements common on earth may be rare on the moon, and some that are rare here on earth may be common on the moon. So far, as on earth, oxygen and silicon seem to be the most common lunar elements. Early experiments have found more uranium and less potassium, more titanium and less sodium. Oxygen is strikingly absent from some minerals, but natural glass is far more common than it is on earth. The rare, noble gases are fairly abundant, trapped in little bubbles in the rocks. 

Rare-earth metah—a loose term for less well-known metallic elements. They include the so-called rare-earths. The rare-earths are not actually rare (scarce) historically, some of them were just difficult to find, isolate, and identify. 

RARE-EARTH ELEMENTS AND METALS. Sometimes referred to as the fraternal fifteen," because of similarities in physical and chemical properties, the rare-earth elements actually are not so rare. This is attested by Fig. 1, which shows a dry lake bed in California that alone contains well in excess of one million pounds of two of die elements, neodymium and praseodymium. The world s largest rare earth body and mine near Baotou, Inner Mongolia, China is shown in Fig. 2. It contains 25 million tons of rare earth oxides (about one quarter of the world s human reserves. The term rare arises from the fact that these elements were discovered in scarce materials. The term earth stems from die tact that the elements were first isolated from their ores in the chemical form of oxides and that the old chemical terminology for oxide is earth. The rare-earth elements, also termed Lanthanides, are similar in that they share a valence of 3 and are treated as a separate side branch of the periodic table, much like die Actinides. See also Actinide Contraction Chemical Elements Lanthanide Series and Periodic Table of the Elements. 

The lanthanide elements were once known as the rare earths. Lanthanides, however, are not particularly rare. Holmium, one of the less common lanthanides, is still 20 times more abundant than silver on Earth. The rare earth name comes instead from how difficult it was for early chemists to separate all of the lanthanides from one another. Because these elements add electrons to an inner shell, they all show the same face to other elements. This makes them all react very similarly with other elements, and it can be tricky to tell them apart. 

Geneve 36, 41 (1913) Alberston et al. Phys. Rev. 61, 167 (1942). Reviews of prepn, properties and compds of neodymium and other rare earths The Rare Earths, F. H. 

Also digestion in hot sodium hydroxide has been tried. The hydroxides formed are dissolved by dilute hydrochloric acid. Soda ash is added to precipitate a complex carbonate precipitate. This in turn is leached with dilute sulphuric acid, to selectively solubilize the rare earths. The rare earths are then subsequently precipitated as oxalate by adding oxalic acid (Gupta and Krishnamurthy 2005). 

Rare earth. The rare earth on zeolite level has a direct impact on catalyst stability and product selectivity. Directionally, increased rare earth levels on zeolite result in catalysts having enhanced hydrothermal stability. This results in a reduction in catalyst makeup rate. However, changes in product selectivities, especially in the LPG range, will result. Many refiners choose to compensate this loss in LPG olefinicity via the addition of ZSM-5 additive. 

Amalgams are metallic systems in which mercury is one of the components. The solubility of the alkali metals, the alkaline earths, the rare earths and Au, Zn, Cd, Ga, In, n, Sn, Pb, Bi, Ru, Rh, and Pt in mercury is higher than 0.1 atom % [1]. A reversible redox reaction of an amalgam-forming metal ion on a mercury electtode... 

Further analytical work by SSMS on the sample is considered if certain rare earth impurities require lower error limits. Internal referencing is employed in which the reference is an appropriately selected rare earth. The rare earth levels, determined with internal referencing, are then compared to the determinations for these same elements in the original sample. The ratios of these determinations should be constant and this constant can be used as a correction factor for all of the determinations in the original sample. The Laboratory is presently changing the internal standardization step to incorporate the use of isotope dilution when it is practical. 

Rare Earths. The rare earths provide a special topic because many of them have unusually sharp and discrete spectra, relatively unaffected by environment and very readily amenable to spectrophotometric analysis. 

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions. 

Scandium is apparently much more abundant (the 23rd most) in the sun and certain stars than on earth (the 50th most abundant). It is widely distributed on earth, occurring in very minute quantities in over 800 mineral species. The blue color of beryl (aquamarine variety) is said to be due to scandium. It occurs as a principal component in the rare mineral thortveihte, found in Scandinavia and Malagasy. It is also found in the residues remaining after the extrachon of tungsten from Zinnwald wolframite, and in wiikite and bazzite. 

Scandium is a silver-white metal which develops a slightly yellowish or pinkish cast upon exposure to air. A relatively soft element, scandium resembles yttrium and the rare-earth metals more than it resembles aluminum or titanium. 

Yttrium occurs in nearly all of the rare-earth minerals. Analysis of lunar rock samples obtained during the Apollo missions show a relatively high yttrium content. 

Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. It oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly. 

Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25 percent of the rare-earth compounds produced. La203 improves the alkali resistance of glass, and is used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Cerium is an iron-gray lustrous metal. It is malleable, and oxidizes very readily at room temperature, especially in moist air. Except for europium, cerium is the most reactive of the rare-earth metals. It decomposes slowly in cold water and rapidly in hot water. 

Europe) In 1890 Boisbaudran obtained basic fractions from samarium-gadolinium concentrates which had spark spectral lines not accounted for by samarium or gadolinium. These lines subsequently have been shown to belong to europium. The discovery of europium is generally credited to Demarcay, who separated the rare earth in reasonably pure form in 1901. The pure metal was not isolated until recent years. 

As with other rare-earth metals, except for lanthanum, europium ignites in air at about 150 to I8O0C. Europium is about as hard as lead and is quite ductile. It is the most reactive of the rare-earth metals, quickly oxidizing in air. It resembles calcium in its reaction with water. Bastnasite and monazite are the principal ores containing europium. 

Europium is one of the rarest and most costly of the rare-earth metals. It is priced about about 7500/kg. 

Gr. prasios, green, and didymos, twin) In 1841 Mosander extracted the rare earth didymia from lanthana in 1879, Lecoq de Boisbaudran isolated a new earth, samaria, from didymia obtained from the mineral samarskite. Six years later, in 1885, von Welsbach separated didymia into two others, praseodymia and neodymia, which gave salts of different colors. As with other rare earths, compounds of these elements in solution have distinctive sharp spectral absorption bands or lines, some of which are only a few Angstroms wide. 

The element occurs along with other rare-earth elements in a variety of minerals. Monazite and bastnasite are the two principal commercial sources of the rare-earth metals. It was prepared in relatively pure form in 1931. 

Ion-exchange and solvent extraction techniques have led to much easier isolation of the rare earths and the cost has dropped greatly in the past few years. Praseodymium can be prepared by several methods, such as by calcium reduction of the anhydrous chloride of fluoride. 

From gadolinite, a mineral named for Gadolin, a Finnish chemist. The rare earth metal is obtained from the mineral gadolinite. Gadolinia, the oxide of gadolinium, was separated by Marignac in 1880 and Lecoq de Boisbaudran independently isolated it from Mosander s yttria in 1886. 

Terbium has been isolated only in recent years with the development of ion-exchange techniques for separating the rare-earth elements. As with other rare earths, it can be produced by reducing the anhydrous chloride or fluoride with calcium metal in a tantalum crucible. Calcium and tantalum impurities can be removed by vacuum remelting. Other methods of isolation are possible. 

L. Holmia, for Stockholm). The special absorption bands of holmium were noticed in 1878 by the Swiss chemists Delafontaine and Soret, who announced the existence of an "Element X." Cleve, of Sweden, later independently discovered the element while working on erbia earth. The element is named after cleve s native city. Holmia, the yellow oxide, was prepared by Homberg in 1911. Holmium occurs in gadolinite, monazite, and in other rare-earth minerals. It is commercially obtained from monazite, occurring in that mineral to the extent of about 0.05%. It has been isolated by the reduction of its anhydrous chloride or fluoride with calcium metal. 

Ytterbium occurs along with other rare earths in a number of rare minerals. It is commercially recovered principally from monazite sand, which contains about 0.03%. Ion-exchange and solvent extraction techniques developed in recent years have greatly simplified the separation of the rare earths from one another. 

Probably the most extensively applied masking agent is cyanide ion. In alkaline solution, cyanide forms strong cyano complexes with the following ions and masks their action toward EDTA Ag, Cd, Co(ll), Cu(ll), Fe(ll), Hg(ll), Ni, Pd(ll), Pt(ll), Tl(lll), and Zn. The alkaline earths, Mn(ll), Pb, and the rare earths are virtually unaffected hence, these latter ions may be titrated with EDTA with the former ions masked by cyanide. Iron(lll) is also masked by cyanide. However, as the hexacy-anoferrate(lll) ion oxidizes many indicators, ascorbic acid is added to form hexacyanoferrate(ll) ion. Moreover, since the addition of cyanide to an acidic solution results in the formation of deadly... 

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