Niobium abundance

Niobium, discovered by Hatchett ia 1801, was first named columbium. In 1844, Rosed thought he had found a new element associated with tantalum (see Tantalum AND tantalum compounds). He called the new element niobium, for Niobe, daughter of Tantalus of Greek mythology. In 1949, the Union of Pure and Apphed Chemistry setded on the name niobium, but in the United States this metal is stiU known also as columbium. Sometimes called a rare metal, niobium is actually more abundant in the earth s cmst than lead. 

Pegmatite deposits are the most abundant. They contain a variety of minerals including tantalum, niobium, lithium and beryllium, as well as REE and zircon. 

Titanium is the most abundant metal in the earth crust, and is present in excess of 0.62%. It can be found as dioxy titanium and the salts of titanium acids. Titanium is capable of forming complex anions representing simple titanites. It can also be found in association with niobium, silicates, zircon and other minerals. A total of 70 titanium minerals are known, as mixtures with other minerals and also impurities. Only a few of these minerals are of any economic importance. 

Niobium is the 33rd most abundant element in the Earths crust and is considered rare. It does not exist as a free elemental metal in nature. Rather, it is found primarily in several mineral ores known as columbite (Fe, Mn, Mg, and Nb with Ta) and pyrochlore [(Ca, NaljNbjOg (O, OH, F)]. These ores are found in Canada and Brazil. Niobium and tantalum [(Fe, Mn)(Ta, Nbl Og] are also products from tin mines in Malaysia and Nigeria. Niobium... 

The abundance of niobium in the earth s crust is estimated to be in the range 20 mg/kg and its average concentration in sea water is 0.01 mg/L. The metal also is found in the solar system including the lunar surface. Radionucleides niobium-94 and -95 occur in the fission products of uranium-235. 

Hafnium had lain hidden for untold centuries, not because of its rarity but because of its dose similarity to zirconium (16), and when Professor von Hevesy examined some historic museum specimens of zirconium compounds which had been prepared by Julius Thomsen, C. F. Rammelsberg, A. E. Nordenskjold, J.-C. G. de Marignac, and other experts on the chemistry of zirconium, he found that they contained from 1 to 5 per cent of the new element (26, 27). The latter is far more abundant than silver or gold. Since the earlier chemists were unable to prepare zirconium compounds free from hafnium, the discovery of the new element necessitated a revision of the atomic weight of zirconium (24, 28). Some of the minerals were of nepheline syenitic and some of granitic origin (20). Hafnium and zirconium are so closely related chemically and so closely associated in the mineral realm that their separation is even more difficult than that of niobium (columbium) and tantalum (29). The ratio of hafnium to zirconium is not the same in all minerals. 

Vanadium, niobium and tantalum - All these elements have magnetic nuclei occurring at virtually 100% natural abundance, although the high quadrupole moment of tantalum has tended to restrict investigations to those of compounds with highly symmetric coordination around the metal. 

The elements themselves require little comment. Niobium is 10 to 12 times more abundant in the earth s crust than tantalum. The main commercial sources of both are the columbite-tantalite series of minerals, which have the general composition (Fe/Mn)(Nb/Ta)206, with the ratios Fe/Mn and Nb/Ta continuously variable. Niobium is also obtained from pyrochlore, a mixed calcium-sodium niobate. Separation and production of the metals is complex. Both metals are bright, high melting (Nb, 2468°C Ta, 2996°C), and very resistant to acids. They can be dissolved with vigor in an HN03—HF mixture, and very slowly in fused alkalis. 

Flowever, a true catalytic effect is most probably present in transition-metal doped magnesium. A proof of this is the fact that nanostructured catalyst gives enhanced sorption properties compared to its micro-sized counterparts [226-229]. Hanada et al. also showed that after milling the catalyst is homogeneously distributed on a nanometer scale [230]. A possible interpretation of the catalytic effect may be the appearance of ternary magnesium-niobium oxides, which was evidenced by TEM [229, 231] and neutron diffraction [232]. Despite the abundant literature on... 

The refractory component comprises the elements with the highest condensation temperatures. There are two groups of refractory elements the refractory lithophile elements (RLEs)—aluminum, calcium, titanium, beryllium, scandium, vanadium, strontium, yttrium, zirconium, niobium, barium, REE, hafnium, tantalum, thorium, uranium, plutonium—and the refractory siderophile elements (RSEs)—molybdenum, ruthenium, rhodium, tungsten, rhenium, iridium, platinum, osmium. The refractory component accounts for —5% of the total condensible matter. Variations in refractory element abundances of bulk meteorites reflect the incorporation of variable fractions of a refractory aluminum, calcium-rich component. Ratios among refractory lithophile elements are constant in all types of chondritic meteorites, at least to within —5%. 

Niobium. Wade and Wood (2001) have suggested that niobium, potentially the most side-rophile of the RLEs, is depleted in the PM by some extraction into the core. The depletion of niobium estimated from Nb/Ta would be 15 15% (Kamber and Collerson, 2000). As an RLE, niobium would have a mantle abundance of 690 ppb. Considering that 15% is in the core reduces this number to 588 ppm, which is hsted in Table 2. 

Chondritic relative abundances of strongly incompatible RLEs (lanthanum, niobium, tantalum, uranium, thorium) and their ratios to compatible RLEs in the Earth s mantle are more difficult to test. The smooth and complementary patterns of REEs in the continental crust and the residual depleted mantle are consistent with a bulk REE pattern that is flat, i.e., unfractionated when normalized to chondritic abundances. As mentioned earlier, the isotopic compositions of neodymium and hafnium are consistent with chondritic Sm/Nd and Lu/Hf ratios for bulk Earth. Most authors, however, assume that RLEs occur in chondritic relative abundances in the Earth s mantle. However, the uncertainties of RLE ratios in Cl-meteorites do exceed 10% in some cases (see Table 4) and the uncertainties of the corresponding ratios in the Earth are in same range (Jochum et ai, 1989 W eyer et ai, 2002). Minor differences (even in the percent range) in RLE ratios between the Earth and chondritic meteorites cannot be excluded, with the apparent exception of Sm/Nd and Lu/Hf ratios (Blicher-Toft and Albarede, 1997). 

The techniques illustrated in Figures 17 and 18 can be used to establish an approximate compatibility sequence of trace elements for mantle-derived melts. In general, this sequence corresponds to the sequence of decreasing (normalized) abundances in the continental crust shown in Figure 2, but this does not apply to niobium, tantalum, and lead for which the results discussed in the previous section demand rather different positions (see also Hofmann, 1988). Here I adopt a sequence similar to that used by Hofmann (1997), but with slightly modified positions for lead and strontium. 

Rehnements of the Taylor and McLennan (1985) model are provided by McLennan and Taylor (1996) and McLennan (2001b). The latter is a modihcation of several trace-element abundances in the upper crust and as such, should not affect their compositional model for the bulk crust, which does not rely on their upper crustal composition. Nevertheless, McLennan (2001b) does provide modihed bulk-crust estimates for niobium, rubidium, caesium, and tantalum (and these are dealt with in the footnotes of Table 9). McLennan and Taylor (1996) revisited the heat-flow constraints on the proportions of mahc and felsic rocks in the Archean crust and revised the proportion of Archean-aged crust to propose a more evolved bulk crust composition. This revised composition is derived from a mixture of 60% Archean cmst (which is a 50 50 mixture of mahc and felsic end-member lithologies), and 40% average-andesite cmst of Taylor (1977). McLennan and Taylor (1996) focused on potassium, thorium, and uranium, and did not provide amended values for other elements, although other incompatible elements will be higher (e.g., rubidium, barium, LREEs) and compatible elements lower in a cmst composition so revised. 

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