molybdenum ore - 06

Molybdenum (pronounced /ˌmɒlɪbˈdiːnəm/ MOL-ib-DEE-nəm or /məˈlɪbdɨnəm/ mə-LIB-di-nəm), is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores.[3] The free element, which is a silvery metal, has the sixth-highest melting point of any element. It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys. Molybdenum does not occur as the free metal in nature, but rather in various oxidation states in minerals. Industrially, molybdenum compounds are used in high pressure and high temperature applications, as pigments and catalysts.


Detailed descrption:


Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from minerals salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm.
Most molybdenum compounds have low solubility in water, but the molybdate ion MoO42− is soluble and will form if molybdenum-containing minerals are in contact with oxygen and water. Recent theories suggest that the release of oxygen by early life was important in removing molybdenum from minerals into a soluble form in the early oceans, where it was used as a catalyst by single-celled organisms. This sequence may have been important in the history of life, because molybdenum-containing enzymes then became the most important catalysts used by some bacteria to break into atoms the atmospheric molecular nitrogen, allowing biological nitrogen fixation. This, in turn allowed biologically driven nitrogen-fertilization of the oceans, and thus the development of more complex organisms.
At least 50 molybdenum-containing enzymes are now known in bacteria and animals, though only the bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Due to the diverse functions of the remainder of the enzymes, molybdenum is a required element for life in higher organisms (eukaryotes), though not in all bacteria.

Characteristics
Physical
In its pure form, molybdenum is silvery white metal with a Mohs hardness of 5.5. It has a melting point of 2,623 °C (4,753 °F); of the naturally occurring elements, only tantalum, osmium, rhenium, tungsten and carbon have higher melting points.[3] Molybdenum burns only at temperatures above 600 °C (1,112 °F).[4] It has one of the lowest coefficient of thermal expansion among commercially used metals.[5] Tensile strength of molybdenum wires increases about 3 times from about 10 to 30 GPa when their diameter decreases from ~50–100 nm to 10 nm.[6]

History
Molybdenite—the principal ore from which molybdenum is now extracted—was previously known as molybdena. Molybdena was confused with and often implemented as though it were graphite. Even when molybdena was distinguishable from graphite, it was still confused with a common lead ore (now called galena), which took its name from Ancient Greek Μόλυβδος molybdos, meaning lead [5] In 1754, Bengt Andersson Qvist examined molybdenite and determined that it did not contain lead and was thus not the same as galena.[16]
It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized molybdena was neither graphite nor lead.[17][18] He and other chemists then correctly assumed that it was the ore of a distinct new element, named molybdenum for the mineral in which it was discovered. Peter Jacob Hjelm successfully isolated molybdenum using carbon and linseed oil in 1781.[5][19]
For a long time there was no industrial use for molybdenum. Although apparent deliberate alloying of molybdenum with steel in one 14th century Japanese sword has been reported, that art was never employed widely, and later lost.[20] Upon its rediscovery, the French Schneider Electric company produced the first molybdenum-steel armor plates in 1894. Until World War I, most other armor factories also used molybdenum alloys. In World War I, some British tanks were protected by 75 mm (3 in) manganese steel plating, but this proved to be ineffective. The manganese steel plates were then replaced with 25 mm (1 in) molybdenum-steel plating. These allowed for higher speed, greater maneuverability, and, despite being thinner, better protection.[5] The high demand for molybdenum in World War I and World War II and the steep decrease after the wars had a great influence on prices and production of molybdenum.
Occurrence
Though molybdenum is found in such minerals as wulfenite (PbMoO4) and powellite (CaMoO4), the main commercial source of molybdenum is molybdenite (MoS2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining.[3] Large mines in Colorado (such as the Henderson mine and the now-inactive Climax mine)[24] and in British Columbia yield molybdenite as their primary product, while many porphyry copper deposits such as the Bingham Canyon Mine in Utah and the Chuquicamata mine in northern Chile produce molybdenum as a byproduct of copper mining. The Knaben mine in southern Norway was opened in 1885, making it the first molybdenum mine. It remained open until 1973.[25]
Molybdenum is the 54th most abundant element in the Earth's crust and the 25th most abundant element in the oceans, with an average of 10 parts per billion; it is the 42nd most abundant element in the Universe.[4][5] The Russian Luna 24 mission discovered a molybdenum-bearing grain (1 × 0.6 µm) in a pyroxene fragment taken from Mare Crisium on the Moon.[26]
Production
The molybdenite is first heated to a temperature of 700 °C (1,292 °F) and the sulfide is oxidized into molybdenum(VI) oxide by air:[13]
2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2
The oxidized ore is then either heated to 1,100 °C (2,010 °F) to sublimate the oxide, or leached with ammonia which reacts with the molybdenum(VI) oxide to form water-soluble molybdates:
MoO3 + 2 NH4OH → (NH4)2(MoO4) + H2O
Copper, an impurity in molybdenite, is less soluble in ammonia. To completely remove it from the solution, it is precipitated with hydrogen sulfide.[13]
Pure molybdenum is produced by reduction of the oxide with hydrogen, while the molybdenum for steel production is reduced by the aluminothermic reaction with addition of iron to produce ferromolybdenum. Molybdenum has a value of approximately $30,000 per tonne as of August 2009. It maintained a price at or near $10,000 per tonne from 1997 through 2003, and reached, due to increased demand, a peak of $103,000 per tonne in June 2005.[27] In 2008 the London Metal Exchange announced that molybdenum would be traded as a commodity on the exchange.[28]
Applications
In alloys
The ability of molybdenum to withstand extreme temperatures without significantly expanding or softening makes it useful in applications that involve intense heat, including the manufacture of aircraft parts, electrical contacts, industrial motors and filaments.[5][29]
Most high-strength steel alloys (example 41xx steels) contain 0.25% to 8% molybdenum.[3] Despite such small portions, more than 43,000 tonnes of molybdenum are used as an alloying agent each year in stainless steels, tool steels, cast irons and high-temperature superalloys.[4]
Molybdenum is also used in steel alloys for its high corrosion resistance and weldability.[4][21] Molybdenum contributes further corrosion resistance to "chrome-moly" type-300 stainless steels (high-chromium steels that are corrosion-resistant already due to their chromium content) and especially so in the so-called superaustenitic stainless steels (such as alloy AL-6XN). Molybdenum acts by increasing lattice strain, thus increasing the energy required to dissolve out iron atoms from the surface.