Molybdenum, abundance

Coveney R. M., Jr, Watney W. L., and Maples C. G. (1991) Contrasting depositional models for Pennsylvanian black shale discerned from molybdenum abundances. Geology 19, 147-150. 

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. 

Uranium, not as rare as once thought, is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. 

Zn, Ni, Cu, and W, yet is the seventh most abundant element overall because Cr is concentrated in the earth s core and mantle (1,2). It has atomic number 24 and belongs to Group 6 (VIB) of the Periodic Table and is positioned between vanadium and manganese. Other Group 6 members are molybdenum and tungsten. On a toimage basis, chromium ranks fourth among the metals and thirteenth of aU mineral commodities in commercial production. 

Chromium, 122 ppm of the earth s crustal rocks, is comparable in abundance with vanadium (136 ppm) and chlorine (126 ppm), but molybdenum and tungsten (both 1.2 ppm) are much rarer (cf. Ho 1.4 ppm, Tb 1.2 ppm), and the concentration in their ores is low. The only ore of chromium of any commercial importance is chromite, FeCr204, which is produced principally in southern Africa (where 96% of the known reserves are located), the former Soviet Union and the Philippines. Other less plentiful sources are crocoite, PbCr04, and chrome ochre, Cr203, while the gemstones emerald and ruby owe their colours to traces of chromium (pp. 107, 242). 

The only example of the trifunctional type (V), known at the time, is the Mo02(P02Cl2) POCI3, in which the molybdenum atom completes its octahedral sphere, in spite of abundant solvent, by aid of a chlorine atom of the bridging dicbloro-phosphate group (.SO) ... 

The average crustal abundance of molybdenum is 1 to 2 parts per million. It occurs most readily in conjunction with silica - as the silica content in the igneous rocks goes up, so does the quantity of molybdenum. It is sometimes also found associated with uranium, as well as with coals and petroleum residues. In its host rock, molybdenum tends to occur in thin, tabular, and hexagonal plate forms, or simply as fine specks. 

Uranium is not a very rare element. It is widely disseminated in nature with estimates of its average abundance in the Earth s crust varying from 2 to 4 ppm, close to that of molybdenum, tungsten, arsenic, and beryllium, but richer than such metals as bismuth, cadmium, mercury, and silver its crustal abundance is 2.7 ppm. The economically usable tenor of uranium ore deposits is about 0.2%, and hence the concentration factor needed to form economic ore deposits is about 750. In contrast, the enrichment factors needed to form usable ore deposits of common metals such as lead and chromium are as high as 3125 and 1750, respectively. 

Murthy VR (1962) Isotopic anomalies of molybdenum in some iron meteorites. J Geophys Res 67 905-907 Murthy VR. 1963. Elemental and isotopic abundances of molybdenum in some meteorites. Geochim. Cosmochim. Acta 27 1171-1178... 

Xanthine oxidase (XO) was the first enzyme studied from the family of enzymes now known as the molybdenum hydroxylases (HiUe 1999). XO, which catalyzes the hydroxylation of xanthine to uric acid is abundant in cow s milk and contains several cofactors, including FAD, two Fe-S centers, and a molybdenum cofactor, all of which are required for activity (Massey and Harris 1997). Purified XO has been shown to use xanthine, hypoxan-thine, and several aldehydes as substrates in the reduction of methylene blue (Booth 1938), used as an electron acceptor. Early studies also noted that cyanide was inhibitory but could only inactivate XO during preincubation, not during the reaction with xanthine (Dixon 1927). The target of cyanide inactivation was identified to be a labile sulfur atom, termed the cyanolyzable sulfur (Wahl and Rajagopalan 1982), which is also required for enzyme activity. 

Molybdenum is the 54th most abundant element on Earth. It is relatively rare and is found in just 126 ppm in the Earth s crust. Its major ore is molybdenite (MoS ), which is mined in Colorado in the United States and is found too in Canada, Chile, China, England, Norway, Sweden, Mexico, and Australia. Moldybdenum is also found in two less important ores wul-fenite (PbMoO ) and powellite ([Ca(MoW)0 ]. These ores are usually found in the same sites along with tin and tungsten ores. 

Rhenium abundance in most rocks is measured in parts per billion or less and minerals in which it is a major constituent are rare. It is similar geochemically to molybdenum, which it commonly accompanies through magmatic and related hydrothermal stages, and is concentrated in molybdenite associated with various types of granite-related deposits. Molybdenites with some of the highest concentrations of rhenium are associated with porphyry Cu and Cu-Au deposits, which are the primary industrial source of rhenium. Rhenium can also be concentrated by low-temperature... 

IVCT). The second e value corresponds to the abundance of 28 Mo centers (see Ref. 5). Using an excitation line within the contour of the 1070-nm band gives rise to a resonance-Raman spectrum showing hve bands in the region between 900 and 200 cm very characteristic for all molybdenum blue species [802 (s), 535 (m), 462 (s), 326 (s), 215 (s) cm ]. 

Estimates of the Mars core composition by the authors listed above suggest it is made of metal plus iron sulfide, the latter varying from 29 to 44 wt.%. Abundances of siderophile (tungsten, phosphorus, cobalt, molybdenum, nickel) and chalcophile (indium, copper) elements in the mantle (Fig. 13.23) are consistent with equilibrium between sulfide, metal, and mantle silicate at high temperature and pressure (Righter and Drake, 1996). 

Although the hypothesis of Egumi may be an oversimplification, it is certainly true that Fe /Feu is widely used in redox systems. Zn " in hydrolysis, esterification, and similar reactions, and molybdenum in nitrogenase. xanthine oxkkise. nitnite reductase, etc Putting abundance aside, discuss the specific chemical properties of these metals this make them well suited for their tasks. 

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