Molybdenum, properties of the atom, chemical and physical properties

Molybdenum

- an element of the sixth group (according to the old classification - a secondary subgroup of the sixth group) of the fifth period of the periodic system of chemical elements of D.I. Mendeleev, atomic number 42. Denoted by the symbol
Mo
(lat. Molybdaenum).
The simple substance molybdenum
is a light gray transition metal. Its main application is in metallurgy.

Content

• 1 History and origin of the name
• 2 Occurrence in nature 2.1 Deposits
• 2.2 In space

external reference

• Wikimedia Commons contains a multimedia gallery about molybdenum
  .
• WebElements.com - Molybdenum
• EnvironmentalChemistry.com - Molybdenum
• International Molybdenum Association
• Environment Database
• Molybdenum in nanoclusters for sulfur control

• Datos: Q1053
• Multimedia: Molybdenum

History and origin of the name

It was discovered in 1778 by the Swedish chemist Carl Scheele, who obtained MoO3 by calcining molybdic acid. It was first obtained in the metallic state by P. Ghelm in 1781 by reducing the oxide with coal: he obtained molybdenum contaminated with carbon and molybdenum carbide. Pure molybdenum was obtained in 1817 by J. Berzelius by reducing the oxide with hydrogen.

The name comes from ancient Greek. μόλυβδος, meaning "lead". It is given because of the external similarity of molybdenite (MoS2), the mineral from which molybdenum oxide was first isolated, with lead luster (PbS). Until the 18th century, molybdenite was not distinguished from graphite because of its lead-like luster; these minerals bore the common name “molybdenum.”

Obtaining molybdenum

Molybdenum in its pure form is very difficult to obtain from ores. Therefore, ferromolybdenum, the main raw material for the metallurgical industry, is most often isolated from polymetallic or molybdenum- and tungsten-iron ores.

Analysis of molybdenum containing minerals is carried out in specialized enterprises using organic analysis.

To obtain pure metals, it is fired to form oxides or chlorides and then reduced.

Pure trioxide MoO3 is obtained by sublimation or hydrometallurgically by treating the cinder with ammonia, caustic soda or soda.

Trioxide is reduced to metal with hydrogen, carbon, carbon-containing gases, or metallothermic reduction (aluminum, silicon).

In industrial production, reduction with hydrogen is mainly used to obtain molybdenum powder, which is converted into compact blanks using powder metallurgy or smelting methods.

Molybdenum is also obtained by thermal dissociation of molybdenum disulfide, thermal dissociation and reduction of molybdenum halides, electrolysis of molten media, etc.

Molybdenum is produced in the form of bars, wire, plates, tapes, foil, tin and ingots.

Being in nature

The content in the earth's crust is 3⋅10−4% by weight. Molybdenum is not found in free form. In the earth's crust, molybdenum is distributed relatively evenly. Ultramafic and carbonate rocks contain the least amount of molybdenum (0.4–0.5 g/t). The concentration of molybdenum in rocks increases as SiO2 increases. Molybdenum is also found in sea and river water, in plant ash, in coal and oil. The content of molybdenum in seawater ranges from 8.9 to 12.2 μg/l for different oceans and water areas. What is common is that waters near the shore and the upper layers are less enriched in molybdenum than waters at depth and away from the shore. The highest concentrations of molybdenum in rocks are associated with accessory minerals (magnetite, ilmenite, sphene), but the bulk of it is contained in feldspars and less in quartz. Molybdenum in rocks is found in the following forms: molybdate and sulfide in the form of microscopic and submicroscopic precipitation, isomorphic and dispersed (in rock-forming minerals). Molybdenum has a greater affinity for sulfur than for oxygen, and tetravalent molybdenum sulfide, molybdenite, is formed in ore bodies. A reducing environment and high acidity are most favorable for the crystallization of molybdenite. Under surface conditions, predominantly oxygen compounds MO6+ are formed. In primary ores, molybdenite is found in association with wolframite and bismuthin, with copper minerals (porphyry copper ores), as well as with galena, sphalerite and uranium pitch (in low-temperature hydrothermal deposits). Although molybdenite is considered a stable sulfide with respect to acidic and alkaline solvents, under natural conditions, with prolonged exposure to water and atmospheric oxygen, molybdenite is oxidized, and molybdenum can migrate intensively to form secondary minerals. This can explain the increased concentrations of molybdenum in sedimentary deposits - carbonaceous and siliceous-carbonaceous shales and coals.

About 20 molybdenum minerals are known. The most important of them are: molybdenite MoS2 (60% Mo), powellite CaMoO4 (48% Mo), molybdite Fe(MoO4)3 nH2O (60% Mo) and wulfenite PbMoO4.

Place of Birth

Large deposits of molybdenum are known in the USA, Mexico, Chile, Canada, Australia, Norway, and Russia. In Russia, molybdenum is produced at the Sorsk ferromolybdenum plant. More than 7% of the world's molybdenum reserves are located in Armenia, with 90% of them concentrated in the Kajaran copper-molybdenum deposit.

In space

An abnormally high molybdenum content is observed in stellar formations consisting of a red giant (or supergiant) with a neutron star inside—Landau-Thorn-Zhitkova objects.

Molybdenum containing minerals

Its content in the earth's crust is 1.1 · 10-4%. About 20 molybdenum minerals are known. Of these, the most common in nature are: molybdenite, powellite CaMoO4, molybdite Fe2 (MoO4)3 x nH2O, wulfenite PbMoO4, molybdoscheelite Ca (W, Mo)O4.

Chillagite Pb(Mo, W)O4, kechlinite Bi2(MoO4)O2, lindgrenite Cu (MoO4)2(OH)2, ilsemanite MoO3 SO3 5H2O, uranomolybdate UO2 UO3 2MoO3, eosite 3PbO x V2O4 MoO3; belonesite MgMoO4 and patersite CoMoO4. Prom. Molybdenite, powellite, molybdite and wulfenite are important.

The molybdenum crystal lattice is body-centered cubic with a period a = 3.1466 A. Atomic radius 1.39 A (for coordination number 12); the ionic radius of Mo+4 is 0.68 A, the ionic radius of Mo+6 is 0.62 A.

Production

Molybdenum deposits and its production by country

Genetic groups and industrial types of deposits

1. Contact-metasomatic (skarns).

2. Hydrothermal.

A. High temperature (greisen). B. Medium temperature. A. quartz-molybdenite. b. quartz-sphalerite-galena-molybdenite. V. quartz-chalcopyrite-molybdenite (porphyry copper ores). pitchblende-molybdenite.

Receiving[ | ]

The industrial production of molybdenum begins with the enrichment of ores by the flotation method. The resulting concentrate is fired until MoO3 oxide is formed:

2 MoS 2 + 7 O 2 ⟶ 2 MoO 3 + 4 SO 2 , {\displaystyle {\ce {2 MoS2 + 7 O2 -> 2 MoO3 + 4 SO2,}}}

which is subjected to additional purification. Next, MoO3 is reduced with hydrogen:

MoO 3 + 3 H 2 ⟶ Mo + 3 H 2 O ⋅ {\displaystyle {\ce {MoO3 + 3 H2 -> Mo + 3 H2O.}}}

The resulting workpieces are processed by pressure (forging, rolling, broaching).

Physical properties

Molybdenum is a light gray metal with a body-centered cubic lattice of the α-Fe type ( a

= 3.14 Å;
z
= 2;
space group Im3m
), paramagnetic, the Mohs scale defines its hardness as 4.5 points. Mechanical properties, as with most metals, are determined by the purity of the metal and previous mechanical and thermal treatment (the purer the metal, the softer it is). Has an extremely low coefficient of thermal expansion. Molybdenum is a refractory metal with a melting point of 2620 °C and a boiling point of 4639 °C.

Isotopes

Main article: Isotopes of molybdenum

Natural molybdenum consists of seven isotopes: 92Mo (15.86% by weight), 94Mo (9.12%), 95Mo (15.70%), 96Mo (16.50%), 97Mo (9.45%), 98Mo (23.75%) and 100Mo (9.62%). Six of them are stable, 100Mo is weakly radioactive (half-life 8.5⋅1018 years, which is a billion times greater than the age of the Universe). Of the artificial isotopes, the most stable is 93Mo, with a half-life of 4 thousand years; the half-life of other isotopes does not exceed 3 days.

Notes[ | ]

1. Michael E. Wieser, Norman Holden, Tyler B. Coplen, John K. Böhlke, Michael Berglund, Willi A. Brand, Paul De Bièvre, Manfred Gröning, Robert D. Loss, Juris Meija, Takafumi Hirata, Thomas Prohaska, Ronny Schoenberg, Glenda O'Connor, Thomas Walczyk, Shige Yoneda, Xiang-Kun Zhu.
   Atomic weights of the elements 2011 (IUPAC Technical Report) // Pure and Applied Chemistry. — 2013. — Vol. 85, no. 5. - P. 1047-1078. - doi:10.1351/PAC-REP-13-03-02.
2. Chemical encyclopedia: in 5 volumes / Editorial Board: Knunyants I. L. (chief editor). - Moscow: Soviet Encyclopedia, 1992. - T. 3. - P. 125. - 639 p. — 50,000 copies. — ISBN 5—85270—039—8.
3. Emsley, John.
   Nature's Building Blocks: an A–Z guide to the elements. - Oxford University Press, 2001. - ISBN 978-0-19-850341-5.
4. Berzelius J.
   Gewicht der elementaren Maafstheile usw (German) // Journal für Chemie und Physik. - Schrag'schen Buchhnadlung, 1818. - Bd. XXII. - S. 51-53.
5. JP Riley, Skirrow G.
   Chemical Oceanography, V. 1, 1965.
6. Results of activities of Zangezur Copper-Molybdenum Combine CJSC (Armenia) in the first quarter of 2005.
7. The existence of a supergiant with a neutron star inside has been confirmed.
8. InfoMine research group. Association of independent experts in the field of mineral resources, metallurgy and chemical industry. https://minerals.usgs.gov/minerals/pubs/commodity/molybdenum/mcs-2016-molyb.pdf.
9. Povarennykh A.S.
   Hardness of minerals. - Academy of Sciences of the Ukrainian SSR, 1963. - P. 197-208. — 304 p.
10. Gurevich Yu. G.
    The mystery of the damask pattern. - M.: Knowledge, 1985. - 192 p. - pp. 15-19.
11. Molybdenum-99 - current state of affairs. Report from the USA.
12. Molybdenum // Encyclopedic Dictionary of a Young Chemist. 2nd ed. / Comp. V. A. Kritsman, V. V. Stanzo. - M.: Pedagogy, 1990. - P. 147-148. — ISBN 5-7155-0292-6.
13. Exchange prices for molybdenum - Metal Torg.Ru.
14. Lopina O. D., Vorobyova R. S., Ovdienko N. I.
    Molybdenum // Great Medical Encyclopedia: in 30 volumes / ch. ed. B.V. Petrovsky. — 3rd ed. - Moscow: Soviet Encyclopedia, 1981. - T. 15. Melanoma - Mudrov. — 576 p. — 150,600 copies.

Chemical properties

At room temperature in air, molybdenum is stable. Begins to oxidize at 400 °C. Above 600 °C it quickly oxidizes to MoO3 trioxide. This oxide is also obtained by the oxidation of molybdenum disulfide MoS2 and the thermolysis of ammonium molybdate (NH4)6Mo7O24·4H2O.

Mo forms molybdenum(IV) oxide MoO2 and a number of oxides intermediate between MoO3 and MoO2.

Mo forms a number of compounds with halogens in different oxidation states. When molybdenum powder or MoO3 reacts with F2, molybdenum hexafluoride MoF6, a colorless, low-boiling liquid, is obtained. Mo (+4 and +5) forms solid halides MoHal4 and MoHal5 (Hal = F, Cl, Br). Only molybdenum diiodide MoI2 is known with iodine. Molybdenum forms oxyhalides: MoOF4, MoOCl4, MoO2F2, MoO2Cl2, MoO2Br2, MoOBr3 and others.

When molybdenum is heated with sulfur, molybdenum disulfide MoS2 is formed, and with selenium, molybdenum diselenide of the composition MoSe2 is formed. The known molybdenum carbides Mo2C and MoC are crystalline high-melting substances and molybdenum silicide MoSi2.

A special group of molybdenum compounds is molybdenum blues. When reducing agents - sulfur dioxide, zinc dust, aluminum or others - act on weakly acidic (pH=4) suspensions of molybdenum oxide, bright blue substances of variable composition are formed: Mo2O5·H2O, Mo4O11·H2O and Mo8O23·8H2O.

Mo forms molybdates, salts of weak molybdic acids not isolated in the free state, xH2O MoO3 (ammonium paramolybdate 3(NH4)2O 7MoO3 zH2O; CaMoO4, Fe2(MoO4)3 - found in nature). Molybdates of metals of groups I and III contain tetrahedral groups [MoO4].

When aqueous solutions of normal molybdates are acidified, MoO3OH− ions are formed, then polymolybdate ions: hepta-, (para-) Mo7O266−, tetra-(meta-) Mo4O132−, octa-Mo8O264− and others. Anhydrous polymolybdates are synthesized by sintering MoO3 with metal oxides.

There are double molybdates, which contain two cations at once, for example, M+1M+3(MoO4)2, M+15M+3(MoO4)4. Oxide compounds containing molybdenum in lower oxidation states are molybdenum bronzes, for example, red K0.26MoO3 and blue K0.28MoO3. These compounds have metallic conductivity and semiconductor properties.

Oxidation of molybdenum with acids and alkalis

Hydrochloric and sulfuric acids in a cold state do not act on molybdenum; the reaction begins at a temperature of 110 ° C. Nitric acid and “regia vodka” act already in a cold state, quickly when heated.

Sodium and potassium hydroxides in the cold state do not react with molybdenum; in the molten state they dissolve it slowly in air, and quickly in the presence of oxidizing agents.

In most industrial In molybdenum deposits, the molybdenite content does not exceed 1%. Molybdenum ores are enriched mainly by flotation, bringing the MoS2 content to 85-90%.

The decomposition of molybdenum concentrates can be carried out by oxidation with oxygen under pressure in an alkaline solution, nitric acid, sodium hypochlorite solutions, chlorination, etc.

The main industrial method is oxidative roasting. The cinder containing MoO3 serves as the starting material for the smelting of ferromolybdenum.

Molybdenum reacts with acids: it dissolves in aqua regia, hot concentrated hydrochloric, sulfuric and nitric, as well as in oxidative-alkaline melts (for example, in a mixture of NaOH and KOH).

Water slowly oxidizes powdered molybdenum into a complex mixture of hydrated oxides - "molybdenum blue"

Molybdenum reacts with nonmetals under significant heating, forming strong carbides, silicides, sulfides, halides and a number of oxides, the most stable of which are higher MoO3.

They correspond to the Na2MoO4 salt of molybdic acid. In an acidic environment, the anions of these salts are capable of condensation, and a series of polymolybdic acids are formed. The composition of solutions of molybdates and tungstates strongly depends on the pH of the medium.

Application

Molybdenum is used to alloy steels as a component of heat-resistant and corrosion-resistant alloys. Molybdenum wire (tape) is used for the manufacture of high-temperature furnaces and electric current inputs in incandescent lamps. Molybdenum compounds - sulfide, oxides, molybdates - are catalysts for chemical reactions, pigments for dyes, and components of glazes. Molybdenum hexafluoride is used when applying metal Mo to various materials, MoS2 is used as a solid high-temperature lubricant. Mo is included in microfertilizers. Radioactive isotopes 93Mo ( T

1/2 = 6.95 h) and 99Mo (
T
1/2 = 66 h) are isotopic indicators.

Molybdenum is one of the few alloying elements that can simultaneously increase the strength, toughness properties of steel and corrosion resistance. Usually, when alloying, along with an increase in hardness, the fragility of the metal also increases. There are known cases of molybdenum being used in the manufacture of edged weapons in Japan in the 11th-13th centuries.

Molybdenum-99 is used to produce technetium-99, which is used in medicine in the diagnosis of cancer and some other diseases. The total world production of molybdenum-99 is about 12,000 curies per week (based on activity on the sixth day), the cost of molybdenum-99 is $46 million per gram ($470 per 1 Ci).

In 2005, world supplies of molybdenum (in terms of pure molybdenum) amounted, according to Sojitz Alloy Division, to 172.2 thousand tons (in 2003 - 144.2 thousand tons). Pure single-crystal molybdenum is used to produce mirrors for high-power gas-dynamic lasers. Molybdenum telluride is a very good thermoelectric material for the production of thermoelectric generators (thermo-emf 780 µV/K). Molybdenum trioxide (molybdenum anhydride) is widely used as a positive electrode in lithium power sources.

Molybdenum is used in high-temperature vacuum resistance furnaces as heating elements and thermal insulation. Molybdenum disilicide is used as heaters in furnaces with an oxidizing atmosphere operating up to 1800 °C.

Hook-holders for the filament body of incandescent lamps, including general-purpose incandescent lamps, are made from molybdenum.

Molybdenum wire with a diameter of 0.05-0.2 mm is used in wire EDM machines for cutting metals with very high accuracy (up to 0.01 mm), including workpieces of large thickness (up to 500 mm). Unlike copper and brass wire, which are used once in such machines, molybdenum wire is reusable (~300-500 meters is enough for 30-80 hours of continuous operation), which somewhat reduces the accuracy of processing, but increases its speed and reduces its cost.

Biological role

The physiological significance of molybdenum for the animal and human body was first demonstrated in 1953, with the discovery of the influence of this element on the activity of the enzyme xanthine oxidase. Molybdenum promotes (makes it more effective) the work of antioxidants, including vitamin C. An important component of the tissue respiration system. Strengthens the synthesis of amino acids, improves nitrogen accumulation. Molybdenum is part of a number of enzymes (aldehyde oxidase, sulfite oxidase, xanthine oxidase, etc.) that perform important physiological functions, in particular, the regulation of uric acid metabolism. Molybdenum enzymes catalyze the hydroxylation of various substrates. Aldehyde oxidase oxidizes and neutralizes various pyrimidines, purines, and pteridines. Xanthine oxidase catalyzes the conversion of hypoxanthines to xanthines, and xanthines to uric acid. Sulfite oxidase catalyzes the conversion of sulfite to sulfate.

A lack of molybdenum in the body is accompanied by a decrease in the content of xanthine oxidase in tissues. With a lack of molybdenum, anabolic processes suffer, and a weakening of the immune system is observed. Ammonium thiomolybdate (soluble molybdenum salt) is a copper antagonist and disrupts its utilization in the body.

Nitrogen cycle

Molybdenum is part of the active site of nitrogenase, an enzyme for fixing atmospheric nitrogen (common in bacteria and archaea).

Microelement

Micro amounts of molybdenum are necessary for the normal development of organisms; it is used as part of microelement nutrition, in particular, for berry crops.

Affects reproduction (in plants).