Lead molybdate

Analytical Methods. Molybdenum contents in ore concentrates and technical oxide are most accurately deterrnined gravimetricaHy by precipitating lead molybdate. Molybdenum content is usually not determined on pure compounds or metal. Instead, spectrographic methods are used to measure impurity elements that must be controlled. Carbon and oxygen in metal products are measured by standard gas analysis methods. 

SPECTROPHOTOMETRIC DETERMINATION OF RARE EARTH ELEMENTS IN MONO CRYSTALS AND STARTING LEAD MOLYBDATE RAW MATERIAL... 

From strongly addic solutions benzoin-a-oxime precipitates molybdate and tungstate ions quantitatively chromate, vanadate, niobate, tantalate, and palladium) II) are partially predpitated. The molybdate complex is best ignited at 500-525 °C to Mo03 before weighing alternatively, the predpitate may be dissolved in ammonia solution and the molybdenum predpitated as lead molybdate, in which form it is conveniently weighed. 

Lead materials, in electronic materials packaging, 17 840-841 Lead metaborate, 14 797 Lead metatitanate, 14 797 Lead Molybdate Orange, pigment for plastics, 7 370t... 

Molybdenum does not occur in nature in free elemental form. Its most important ore is molybdenite, M0S2, from which the metal is obtained commercially. Other ores are powellite (calcium tungstomolybdate), Ca(MoW)04, and wuhenite (lead molybdate), PbMo04. The metal is an essential nutrient for plants and is found in trace amounts in some plants such as peas and beans, which absorb it from soil. Also, molybdenum is found in many natural petroleum oils. 

Molybdenum is recovered primarily from its sulfide ore, molybdenite, M0S2. It also is produced, although to a much lesser extent, from the tungsten ore wulfenite, which yields lead molybdate, PbMo04. The first phase of the recovery process generally involves concentration of the ore, because ore coming from the mine is very lean and usually contains less than one percent molybdenum. Molybdenite at first is concentrated by flotation which concentrates the M0S2 over 90%. If wulfenite is used as a source material, concentration is usually done by hydrauhc methods. 

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. 

Molybdenum orange is a solid solution of lead molybdate, lead chromate and often lead sulfate. It is used as a pigment in paints, plastics and printing inks. The pigment is used for red hues in automobile and appliance paints. 

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. 

J. he element columbium (niobium) was discovered in 1801 by the English chemist Charles Hatchett, who was bom in London in 1765. As a young man in his thirties he engaged actively in chemical research, and published in the Philosophical Transactions an analysis o lead molybdate from Carinthia and the results of some experiments on shell and bone (2), and in Nicholson s Journal an analysis of an earth from New South Wales called Sydneia, or Terra Australis (81). 

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. 

Inorganic lead compounds such as PbO, Pb02, Pb304, PbS, lead molybdate and lead perchlorate 2) Lead salts of organic adds such as 2,4-dihydroxy benzoic add, salicylic add, acetyl salicylic add and methoxy propionic add i) Effective with propellants of cal. val. less than 900 cal. g 1 ii) Lead salts of aromatic adds are effective with propellants of higher cal. val. [237]. 

The most important chromate pigments include the lead chromate (chrome yellow) and lead molybdate pigments (molybdate orange and molybdate red) whose colors range from light lemon yellow to reds with a blue hue. Chrome yellow,... 

Lead chromates, lead molybdates, chrome greens, and fast chrome greens are supplied as pigment powders, low-dust or dust-free preparations, or as pastes. For standard specifications, see Table 1. 

The colors of lead molybdate pigments vary from red with a yellow hue to red with a blue hue. Since chrome orange is no longer available (see Section 3.4.3), molybdate orange has become much more important. 

To give the lead molybdate pigments very good stability to fight, weathering, chemical attack, and temperature, the same methods are used as those for the stabilization of chrome yellow pigments (see Section 3.4.1) [3.134]-[3.142],... 

Molybdenum salts used as catalysts include cobalt molybdate for hydrogen treatment of petroleum stocks for desulfurization, and phospho-molybdates to promote oxidation. Compounds used for dyes are sodium, potassium, and ammonium molybdates. With basic dyes, phosphomolyb-dic acid is employed. The pigment known as molybdenum orange is a mixed crystal of lead chromate and lead molybdate. Sodium molybdate, or molybdic oxide, is added to fertilizers as a beneficial trace element. Zinc and calcium molybdate serve as inhibitory pigments in protective coatings arid paint for metals subjected to a corrosive atmosphere. Compounds used to produce better adherence of enamels are molybdenum trioxide and ammonium, sodium, calcium, barium, and lead molybdates. 

The Ho parent activity Is purified as a lead molybdate ppt. The ppt. Is dissolved in a mixture of HCi and tartaric acid In the presence of HeOj carrier. (The tartaric acid forms a complex with Mo and Inhibits Its pptn. by tetraphenylarsonlum chloride.) The soln. Is transferred to a BBchner funnel fitted with a membrane filter and a detachable top. The filter Is placed directly beneath a CM tube. Tetraphenylarsonlum chloride soln. Is added, and the suction Is turned on. As soon as the soln. has drained, the sample Is. counted. 

Cadmium pigments Mercury cadmium pigments Lead chromate yellows Lead molybdate oranges Iron blues Chrome greens Bismuth vanadate... 

Use of red iron oxide in plastics has increased as cadmium reds and lead molybdate oranges have been restricted in their use. In combination with the appropriate organic red toners, red iron oxide can be used to cover some of the same color space formerly occupied by cadmium- or molybdate-containing formulations. The red iron oxide component of the organic-inorganic approach also lowers the cost of the formulation, opacifies the formulation, and offers an increment of UV stability to the formulation. 

From a regulatory prespective, it is the trivalent character of its chromium content that distinguishes chrome titanium yellow from the hexavalent character of the chromium in lead chromate and lead molybdate pigments. 

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