Rare earth abundance

Rare earth abundance patterns, particularly of the clay fraction, may also help determine the origin of the terrestrial components. Rare earth patterns in clay fractions of sediments tend to inherit the patterns of the rocks from which they originated [24]. In figure 2 are shown several samples of the rare earth abundance patterns of nitric-acid-insoluble residues from the Danish boundary layer and the limestones above and below. Such patterns along with the other chemical data may indicate the... 

Rore earth obundonces in somples Rare earth abundances in average chondrite... 

Figure 2. Rare earth abundance patterns as normalized to the data of Masuda et al. (except for Tb) for the Leedy L6 meteorite (30).

Evensen, M.N., Hamilton,P.J., Onions.P.K., 1978.Rare earth abundance in chondrite meteorites. Geochimlca et. Cosmochimica Acta, 42, 1199-1212. 

Ottonello G. (1980). Rare earth abundance and distribution in some spinel peridotite xenoliths from Assab (Ethiopia). Geochim. Cosmochim. Acta, 44 1885-1901. 

Evenson N. M., Hamilton P. J., and O Nions R. K. (1978) Rare-earth abundances in chondritic meteorites. Geochim. Cosmochim. Acta 42, 1199-1212. 

Morten L. and Obata M. (1990) Rare earth abundances in the eastern Alpine peridotites, Nonsberg area, northern Italy. Euro. J. Mineral. 2, 643-653. 

Mungall J. E., Frape S. K., and Gibson I. L. (1987) Rare-earth abundances in host granitic rocks and fracture-filling gypsum associated with saline groundwaters from a deep borehole, Atikokan, Ontario. Can. Mineral. 25, 539-543. 

Coryell C.G., Chase J.W, and Winchester J.W., 1963, A procedure for geochemical "-interpretation of terrestrial rare-earth abundance patterns. J. CeopAys. Hes. 68, 559-566. 

The solar system began to form about 4.55 Ae ago from a rotating disk of dust and gas (the solar nebula) which had sepatated from a larger molecular cloud a little earlier. The original composition of this disk can be obtained from two sources. The first of these are the spectral data from the sun. Rare earth abundances may be obtained both from photospheric absorption lines and coronal emission lines. These data are given in table 6 as atomic abundances relative to Si = 10 atoms (Aller 1987) and give the composition of the outer layers of the sun. 

Rare earth abundances in natural materials have become an important geo-chemieal tool. The rare earth elements comprise a uniquely coherent group wherever one rare earth appears, all others are present as well. The group is coherent because under most natural conditions ail members share a common (3+) oxidation state, with anomalous behavior occurring under some conditions for Ce (4+) and Eu (2+). Natural materials differ substantially from each other in concentrations of the rare earths as a group and in abundances of individual rare earths relative to each other. In most natural situations, chemical separations within the rare earth group occur as a smooth function of atomic number. This makes it possible to find genetic relationships among diverse natural materials and to determine by what processes some natural materials formed. 

Ragland, P.C., A.O. Brunfelt and P.W. Wei-gand, 1971, Rare earth abundances in Mesozoic dolerite dikes from eastern United States, in Brunfelt, A.O. and E. Steinnes,... 

Cerium is the most abundant so-called rare-earths metal. It is found in a number of minerals including ahanite (also known as orthite), monazite, bastnasite, cerhe, and samarskite. Monazite and bastnasite are presently the two more important sources of cerium. 

Thorium occurs in thorite and in thorianite. Large deposits of thorium minerals have been reported in New England and elsewhere, but these have not yet been exploited. Thorium is now thought to be about three times as abundant as uranium and about as abundant as lead or molybdenum. Thorium is recovered commercially from the mineral monazite, which contains from 3 to 9% Th02 along with rare-earth minerals. 

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

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). 

Comparing the relative abundance of the rare earths and the other elements Hsted in Table 1, the rare earths are not so rare. Cerium, the most abundant of the rare-earth elements is roughly as abundant as tin thuHum, the least abundant, is more common than cadmium or silver. Over 200... 

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. 

Cerium is the most abundant rare earth metal. Pure cerium ignites when scratched by even a soft object. It has four known isotopes l36Ce (atomic mass = 135.907 amu), 138Ce (atomic mass = 137.905 amu), 140Ce (atomic mass = 139.905 amu), and 142Ce (atomic mass = 141.909 amu). Ce-140 and Ce-142 are fairly abundant. Which is the more abundant isotope ... 

The large amounts of natural gas (mainly methane) found worldwide have led to extentive research programs in the area of the direct conversion of methane [1-3]. Ihe oxidative transformation of methane (OTM) is an important route for the effective utilization of the abundant natural gas resources. How to increase catalyst activity is a common problem on the activation of methane. The oxidation of methane over transition m al oxides is always high active, but its main product is CO2, namely the product of deep oxidation. It is because transition metal oxides have high oxidative activity. So, they were usually used as the main corrqtonent of catalysts for the conqilete oxidation of alkane[4]. The strong oxidative activity of CH4 over tran on metal oxides such as NiO indicates that the activation of C-H bond over transition metal oxides is much easier than that over alkaline earth metal oxides and rare earth metal oxides. Furthermore, the activation of C-H bond is the key step of OTM reaction. It is the reason that we use transition metal oxides as the mam conq>onent of the OTM catalysts. However, we have to reahze that the selectivity of OTM over transition metal oxides is poor. 

The silver gray metal can be cut with a knife, although it only melts at 1545 °C (for comparison, iron 1538 °C). It is the rarest of the "rare earths", but is nevertheless more abundant than iodine, mercury, and silver. Thulium has few applications, especially because it is relatively expensive. The element occurs naturally as a single isotope, namely 169Tm (compare bismuth). The artificial, radioactive 170Tm is a transportable source of X-rays for testing materials. Occasionally used in laser optics and microwave technology. 

Some rare earth compounds are used in glassmaking. Cerium is the most abundant, and its compounds are used to polish glass. Lanthanum compounds are used in making glass lenses, and praseodymium compounds color glass green. 

The historical background is presented for the asteroid-impact theory that is based on the iridium anomaly found in rocks frm the Cretaceous-Tertiary boundary. Recent measurements of Ir, Pt, and Au abundances from such rocks in Denmark have shown that the element abundance ratios are different from mantle-derived sources and agree with values for chondritic meteorites within one standard deviation of the measurement errors (7-10%). Rare-earth patterns for these rocks are... 

Trace elements and rare-earth elements (REEs) of the same calcite samples used for the stable isotope analysis have significantly lower concentration of REE as well as most trace elements relative to typical carbonatites. The total REE contents of the Ulsan carbonates range from 3 to 17 ppm, which are much lower than any igneous rocks and even lower than those of some sedimentary rocks. REE and trace-element abundances may have changed sufficiently due to alteration, thus, affecting petrogenetic... 

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