Lanthanide abundances

Selective Oxidation. Cerium, the most abundant lanthanide, can be separated easily after oxidation of Ce(III) to Ce(IV), simplifying the subsequent separation of the less abundant lanthanides. Oxidation occurs when bastnaesite is heated in air at 650°C or when the hydroxides are dried in air... 

Cerium ranks ca 25th in abundance in the earth s cmst (3), and cerium, which occurs at 60 ppm cmstal abundance, not lanthanum at 30 ppm, is the most abundant lanthanide. 

Holmium is the 12th most abundant of the rare-earths found in the Earths crust. Although it is the 50th most abundant element on Earth, it is one of the least abundant lanthanide metals. It is found in gadolinite and the monazite sands of South Africa and Austraha and in the beach sands of Florida and the Carolinas in the United States. Monazite sand contains about a 50% mixture of the rare-earths, but only 0.05% by weight is holmium. Today, small quantities of holmium are produced by the ion-exchange process. 

Thulium was discovered in 1879 by Cleve and named after Thule, the earliest name for Scandinavia. Its oxide thulia was isolated by James in 1911. Thulium is one of the least abundant lanthanide elements and is found in very small amounts with other rare earths. It occurs in the yttrium-rich minerals xenotime, euxenite, samarskite, gadolinite, loparite, fergusonite, and yttroparisite. Also, it occurs in trace quantities in minerals monazite and... 

Under the same conditions, in contrast to what is observed for calix[4]arene-bearing CMPO moieties, with CPil2, distribution ratios of lanthanides increase from the lightest lanthanide, lanthanum, to europium. Americium can be easily separated from the lightest lanthanides (separation factor DAm/La > 20, DAm/Ce =15, /lAlll,Nd = 10, UAi /si = 7.5, DAm/Eu = 6), which are the most abundant lanthanides in fission-product solution. Cavitands bearing picolinamide (Cv5) or thiopicolin-amide (Cv6) residues seems much less selective than their calixarene counterparts, giving SAm/Eu < 2.18... 

Two patterns emerge from these data. First, that the lighter lanthanides are more abundant than the heavier ones secondly, that the elements with even atomic number are more abundant than those with odd atomic number. Overall, cerium, the most abundant lanthanide... 

Lanthanides is the name given collectively to the fifteen elements, also called the elements, ranging from lanthanum. La, atomic number 57, to lutetium, Lu, atomic number 71. The rare earths comprise lanthanides, yttrium, Y, atomic number 39, and scandium. Sc, atomic number 21. The most abundant member of the rare earths is cerium, Ce, atomic number 58 (see Ceriumand cerium compounds). 

Cerium [7440-45-17, Ce, at no. 58, is the most abundant member of the series of elements known as lanthanides. Lanthanide (Ln) is a collective name for the fifteen elements from at no. 57 (La) to 71 (Lu), also called the 4f elements. Rare-earth (RE) metal is the collective name for elements 21 (Sc), 39 (Y), plus 57 (La) to 71 (Lu). The label /, /is used herein for elements having atomic numbers from 57 to and the label heavj for numbers - 64 to 71. 

Apart from the unstable (half-life 2.623 y) of which traces occur in uranium ores, the lanthanides are actually not rare. Cerium (66 ppm in the earth s crust) is the twenty-sixth most abundant of all elements, being half as abundant as Cl and 5 times as abundant as Pb. Even Tm (0.5 ppm), the rarest after Pm, is rather more abundant in the earth s crust than is iodine. 

Cerium, an element in the lanthanide series, has a number of radioactive isotopes. Several of these are produced in abundance in nuclear fission reactions associated with nuclear industry operations or detonation of nuclear devices. This report summarizes our present knowledge of the relevant physical, chemical, and biological properties of radiocerium as a basis for establishing radiation protection guidelines. 

Yttrium (j Y) is often confused with another element of the lanthanide series of rare Earths— Ytterbium ( Yb). Also confusing is the fact that the rare-earth elements terbium and erbium were found in the same minerals in the same quarry in Sweden. Yttrium ranks second in abundance of all 16 rare-earth, and Ytterbium ranks 10th. Yttrium is a dark silvery-gray hghtweight metal that, in the form of powder or shavings, will ignite spontaneously. Therefore, it is considered a moderately active rare-earth metal. 

The ores from which rare-earth elements are extracted are monazite, bastnasite, and oxides of yttrium and related fluorocarbonate minerals. These ores are found in South Africa, Australia, South America, India, and in the United States in Cahfomia, Florida, and the Carolinas. Several of the rare-earth elements are also produced as fission by-products during the decay of the radioactive elements uranium and plutonium. The elements of the lanthanide series that have an even atomic number are much more abundant than are those of the series that have an odd atomic number. 

Lanthanum is the fourth most abundant of the rare-earths found on the Earth. Its abundance is 18 ppm of the Earth s crust, making it the 29th most abundant element on Earth. Its abundance is about equal to the abundance of zinc, lead, and nickel, so it is not really rare. Because the chemical and physical properties of the elements of the lanthanide series are so similar, they are quite difficult to separate. Therefore, some of them are often used together as an alloy or in compounds. 

Cerium is the 25th most abundant element on Earth. It is also the most abundant rare-earth metal in the lanthanide series. Its major ores are monazite and bastnasite. Cerium is found in the Earth s crust in 46 ppm, which is about 0.0046% of the Earth s crust. Cerium is mixed with other elements in its ores, making it difflcult to find, isolate, and identify. Its existence was unknown until about 1803... 

Of all the 17 rare-earths in the lanthanide series, terbium is number 14 in abundance. Terbium can be separated from the minerals xenotime (YPO ) and euxenite, a mixmre of the following (Y, Ca, Er, La, Ce, Y, Th)(Nb, Ta, Ti O ). It is obtained in commercial amount from monazite sand by the ion-exchange process. Monazite may contain as much as 50% rare-earth elements, and about 0.03% of this is terbium. 

Lutetium is the 60th most abundant element on Earth, and it ranks 15th in the abundance of the rare-earths. It is one of the rarest of the lanthanide series. It is found in monazite sand (India, Australia, Brazil, South Africa, and Florida), which contains small amounts of all the rare-earths. Lutetium is found in the concentration of about 0.0001% in monazite. It is difficult to separate it from other rare-earths by the ion-exchange process. In the pure metallic form, lutetium is difficult to prepare, which makes is very expensive. 

Symbol Ce atomic number 58 atomic weight 140.115 a rare-earth metal a lanthanide series inner-transition /-block element metaUic radius (alpha form) 1.8247A(CN=12) atomic volume 20.696 cm /mol electronic configuration [Xe]4fi5di6s2 common valence states -i-3 and +4 four stable isotopes Ce-140 and Ce-142 are the two major ones, their percent abundances 88.48% and 11.07%, respectively. Ce—138 (0.25%) and Ce—136(0.193%) are minor isotopes several artificial radioactive isotopes including Ce-144, a major fission product (ti 284.5 days), are known. 

Crustal content data, as summarized in Table I, indicate clearly that the lanthanides are at least as abundant as many of the elements considered common and supplies are potentially unlimited. 

The earth s crust is again a good source of lanthanides. Although the name rare earths is still used to denote the lanthanide elements, and scandium and yttrium, in the strictest sense of the word rare they are more plentiful than many of our common elements. It comes as a surprise to many people when a comparison of the relative abundance of the lanthanides and other elements in the earth s crust is made. Table 4... 

Table 4. Natural abundance of the lanthanides and some common elements...

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