Molybdenite MoS

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. 

M37 Molybdenite MoS in granite from A/S Knaben in Norway. It may have been an ore of this type in which Walter and Ida Noddack discovered the element rhenium. 

Molybdenite, MoS Cobaltite, CoAsS Enargite, Cu AsS Gersdorfite, NiAsS Glaucodote, (Co, Fe)AsS Antimonide... 

Molybdenum occurs naturally in various ores the principal source being molybdenite (MoS ). Molybdenum compounds are used primarily in the production of metal allo). Molybdenum is also considered an essential trace element with the provisional recommended dietary intake of 75-250 pg/day for adults and older children. There is no information available on the acute or subchronic oral toxicity of molybdenum in humans. Subchronic and chronic Reference Concentrations (RfC) for Mo are not available. Information on the inhalation toxicity of Mo in humans following acute and subchronic exposures is also not available. The chronic oral Reference Dose (RfD) for Mo and Mo compounds is 0.005 mg/kg/day, based on biochemical indices in humans. The subchronic RfD is also 0.005 mg/kg/day. Mo is placed in EPA Group D, not classifiable as to carcinogenicity in humans. ... 

The most important ore of molybdenum is the sulphide molybdenite, M0S2, of which the largest known deposit is in Colorado, USA, but it is also found in Canada and Chile. Less important ores are wulfenite, PbMo04, and powellite, Ca(Mo,W)04. 

Trigonal-Prism Radii. In molybdenite and the corresponding tungsten sulfide the metal atom is surrounded by six sulfur atoms at the corners of a right trigonal prism of axial ratio unity, the bond orbitals involved being those discussed in an earlier section. Prom the observed interatomic distances the values 1.37 and 1.44 A are calculated for Mo and IPIV in such crystals (Table XV). 

This is a layer structure similar to the Cdl2 structure except that the pairs of S layers are directly superimposed upon each other, so that the central cation is in trigonal prismatic coordination, not octahedral or tetrahedral. In the structures derived from this S-Mo-S unit, these layers can be stacked like the simple layers in atomic close-packed sequences. The molybdenite ((3-MoS2) structure has these layers in... 

Occurrence. The most important ore of Mo is molybdenite, the sulphide MoS2. Another mineral is wulfenite (PbMo04). The recovery of Mo from spent petroleum catalysts is widely used. 

Efforts to measure Mo isotope variations, using thermal ionization mass spectrometry (TIMS), can be traced back to the early 1960s. Early studies were provocative Murthy (1962 1963) reported that the Mo isotope composition in some iron meteorites deviated from that of others, and from terrestrial Mo, by 10 %o/amu, while Crouch and Tuplin (1964) reported mass dependent variations and mass independent isotopic anomalies among terrestrial molybdenites. As discussed below, Wetherill (1964) subsequently demonstrated isotopic uniformity among iron meteorites to better than 1 %o/amu. It is likely that earlier reports were affected by analytical artifacts due to inadequate correction of Mo isotope fractionation during analysis. 

Figure 6. Summary of existing Mo isotope data from natural samples. Isotopic composition of ocean source is based on mass balance (see text). Data are presented as 5 Mo and S Mo relative to the Rochester JMC standard (5 Mo 2/3 x 5 Mo). References ( ) McManus et al. 2002 (t) Siebert et al. 2003 ( ) Barling et ah 2001 ( ) Arnold et al. 2004. Molybdenite values of Wieser and DeLaeter (2003) are omitted because of standard normalization problems (see text). Data obtained by different research groups using different standards are cross-calibrated by comparing seawater 5 values.

The most significant Mo isotope feature in these settings is their 5 Mo enrichment (Barling et al. 2001 Arnold et al. 2004) in Holocene, organic-rich sediments from both basins, 5 Mo is >l%o heavier than in igneous rocks, molybdenites or ferromanganese sediments. Black Sea Unit I samples are more enriched in heavy isotopes than any other rocks analyzed to date. 

The inherent hydrophobicity once thought to be typical of sulphides (Ravitz and Porter, 1933) is now thought to be restricted to sulphides such as molybdenite (Chander et al., 1975) and other minerals or compound with special structural feature (Gaudin et al, 1957b). Common commercial sulphide minerals, which are needed to recover in flotation, are normally composed of anion (S ) and heavy metal ions such as Cu, Cu, Pb, Zn, Hg, Sb, Bi transitive metal ion such as Fe, Co, Ni and noble and rare metal ions such as Ag, Au, Mo. On the basis of structural pattern or mode of linkage of the atoms or polyhedral imits in space, Povarennyk (1972) introduced a crystallochemical classification of sulphide minerals, which have six major patterns as shown in Table 1.1. 

---