Molybdate minerals

Molybdates. Minerals containing the molybdate radical, M0O4. Tungstates. Minerals containing the tungstate radical. WO4. 

The uranyl molybdate minerals are relatively poorly characterized. The first uranyl molybdate mineral was recognized by Brophy and Kerr, but since then a number of minerals that belong to this group have been described from many different deposits (Table 14). An affinity of uranium and molybdenum, especially in roll-front type deposits, has been known for some time. Initially, only minerals with U were recognized, but the occurrence of such minerals as sedovite shows that U compounds also exist. 

Biomedical Uses. The molybdate ion is added to total parenteral nutrition protocols and appears to alleviate toxicity of some of the amino acid components in these preparations (see Mineral NUTRIENTS) (97). Molybdenum supplements have been shown to reduce iiitrosarnine-induced mammary carcinomas in rats (50). A number of studies have shown that certain heteropolymolybdates (98) and organometaUic molybdenum compounds (99) have antiviral, including anti-AIDS, and antitumor activity (see Antiviral agents Chemotherapeutics, anticancer). 

The effect of other inorganic anions (sulfate, molybdate, silicate), low molecular mass organic ligands (LMMOLs, such as oxalate, malate, citrate, tartrate and succinate), and fulvic or humic acid on the sorption of arsenate and arsenite onto variable charge minerals and soils has been studied (Roy et al. 1986 Grafe et al. 2001 Liu et al. 2001 Violante et al. 2005a,b). 

Huber s reagent analy chem Aqueous solution of ammonium molybdate and potassium ferrocyanide used as a reagent to detect free mineral acid. hyu-barz re,a- 3nt ... 

Transport of contaminants by surface runoff is illustrated in the experimental results of Turner et al. (2004), which deal with the colloid-mediated transfer of phosphorus (P) from a calcareous agricultural land to watercourses. Colloidal molybdate-reactive phosphorus (MRP) was identified by ultrafiltration associated with particles between l am and Inm in diameter. Colloidal P compounds can constitute a substantial component of the filterable MRP in soil solution and include primary and secondary P minerals, P occluded or adsorbed on or within mineral or organic particles, and biocolloids (Kretzschmar et al. 1999). 

Manning, B.A. Goldberg, S. (1996) Modeling competitive adsorption of arsenate with phosphate and molybdate on oxide minerals. Soil Sci. Soc. Am. J. 60 121-131 Manning, B.A. Fendorf S.E. Goldberg, S. (1998) Surface structures and stability of ar-senic(lll) on goethite spectroscopic evidence for inner-sphere complexes. Environ. Sci. Techn. 34 2383-2388... 

Among molybdate salts, sodium and ammonium molybdates have commercial applications. The normal salt, sodium orthomolyhdate, Na2 M0O4, is used in pigments. It also is used as a corrosion inhibitor and as an additive to soil. Lead molybdate, Pb M0O4, occurs in nature as mineral ulfenite, from which molybdenum metal is recovered. 

In 1785 B. Pelletier proved that the ore mineralogists used to call molybdenum is a sulfide of that metal (28). The molybdic acid obtained by Scheele does not exist as such in the mineral, but was produced when he oxidized the molybdenum sulfide with nitric acid. 

Although molybdenite was for several years the only known source of molybdenum, the Abbe F. X. Wulfen in 1785 described a lead mineral from Carinthia which had previously been regarded as lead tungstate, and when M. H. Klaproth analyzed a specimen of it from Bleyberg in 1792-94, he found it to be lead molybdate (76). Two years later, Charles Hatchett examined a larger specimen of it and confirmed Klaproth s conclusion. This mineral is now known as wulfenite. 

Most of his scientific research was done during the decade 1796 to 1806. His first paper in the Philosophical Transactions described his analysis of the Carinthian lead molybdate (4). The celebrated Scheele, said he, in 1778 read before the Academy of Sciences at Stockholm an essay in which he proved. . . that the mineral called Molybdaena was composed of sulfur and a peculiar metallic substance, which, like arsenic and tungsten, was liable by super-oxygenation to be converted into a metallic acid which in its properties differed from any other that had been previously discovered. Hatchett mentioned the confirmatory researches of B. Pelletier, P. J. Hjelm, and Mr. Islmann [J. C. Ilsemann], and added But the existence of this substance was known to be only in that mineral which Scheele had examined. This lead mineral from Carinthia had been described by the Abbe F. X. Wulfen and by N. J. Jacquin. For several years it was believed to be lead tungstate, but Klaproth proved it to be lead molybdate. Since Klaproth had had an insufficient amount of the mineral, Hatchett made a complete analysis of it and investigated the properties of molybdic add. 

Asphaltic Sandstone from Lodeve-Mas Alary, Herault, France. This rock of Permian age contains, together with uraninite, secondary uranium minerals, sulfides, molybdates, etc. (12, 15) (Figure 3). 

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