Molybdenum
Encyclopedia
Molybdenum is a Group 6
chemical element
with the symbol Mo and atomic number
42. The name is from Neo-Latin Molybdaenum, from Ancient Greek
, meaning lead, itself proposed as a loanword
from Anatolian
Luvian and Lydian
languages, since its ores were confused with lead ores. The free element, which is a silvery metal
, has the sixth-highest melting point
of any element. It readily forms hard, stable carbide
s, and for this reason it is often used in high-strength steel
alloys. Molybdenum does not occur as a free metal
on Earth, but rather in various oxidation state
s in minerals. Industrially, molybdenum compounds
are used in high-pressure and high-temperature applications, as pigments and catalysts
.
Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from the mineral 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 forms when molybdenum-containing minerals are in contact with oxygen
and water.
Molybdenum-containing enzymes are used as catalysts by some bacteria to break the chemical bond
in atmospheric molecular nitrogen
, allowing biological nitrogen fixation
. 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. Owing 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.
of 5.5. It has a melting point
of 2623 °C (4,753.4 °F); of the naturally occurring elements, only tantalum
, osmium
, rhenium
, tungsten
, and carbon
have higher melting points. Molybdenum burns only at temperatures above 600 °C (1,112 °F). It has one of the lowest coefficients of thermal expansion
among commercially used metals. The 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.
from 83 to 117, as well as four metastable nuclear isomer
s. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. Of these naturally occurring isotopes, only molybdenum-100 is unstable. All unstable isotopes of molybdenum decay into isotopes of niobium
, technetium
, and ruthenium
.
Molybdenum-98 is the most abundant isotope, comprising 24.14% of all molybdenum. Molybdenum-100 has a half-life
of about 1019 y
and undergoes double beta decay
into ruthenium
-100. Molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of approximately 150 ns.
As also noted below, the most common isotopic molybdenum application involves molybdenum-99, which is a fission product. It is a parent radioisotope to the short-lived gamma-emitting daughter radioisotope technetium-99m
, a nuclear isomer
used in various imaging applications in medicine.
In 2008, the Delft University of Technology applied for a patent on the molybdenum-98-based production of technetium-99 http://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&adjacent=true&locale=nl_NL&FT=D&date=20110330&CC=EP&NR=2301041A1&KC=A1
Molybdenum is a transition metal
with an electronegativity
of 1.8 on the Pauling scale and an atomic mass of 95.94 g/mol. It does not visibly react with oxygen or water at room temperature, and the bulk oxidation occurs at temperatures above 790 °C, resulting in molybdenum trioxide:
The trioxide is volatile and sublimates at high temperatures. This prevents formation of a continuous protective oxide layer, which would stop the bulk oxidation of metal. Molybdenum has several oxidation state
s, the most stable being +4 and +6 (bolded in the table). The chemistry and the compounds show more similarity to those of tungsten than that of chromium. An example is the instability of molybdenum(III) and tungsten(III) compounds as compared with the stability of the chromium(III) compounds. The highest oxidation state is common in the molybdenum(VI) oxide
(MoO3), whereas the normal sulfur compound is molybdenum disulfide
MoS2.
Molybdenum(VI) oxide is soluble in strong alkaline
water, forming molybdates (MoO42−). Molybdates are weaker oxidants than chromates, but they show a similar tendency to form complex oxyanion
s by condensation at lower pH
values, such as [Mo7O24]6− and [Mo8O26]4−. Polymolybdates can incorporate other ions into their structure, forming polyoxometalate
s. The dark-blue phosphorus
-containing heteropolymolybdate P[Mo12O40]3− is used for the spectroscopic
detection of phosphorus. The broad range of oxidation state
s of molybdenum is reflected in various molybdenum chlorides:
The structure of the MoCl2 is composed of Mo6Cl84+ clusters with four chloride ions to compensate the charge.
Like chromium
and some other transition metals, molybdenum is able to form quadruple bond
s, such as in Mo2(CH3COO)4. This compound can be transformed into Mo2Cl84−, which also has a quadruple bond.
The oxidation state 0 is possible with carbon monoxide as ligand, such as in molybdenum hexacarbonyl
, Mo(CO)6.
—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
. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant. 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
, meaning lead. Although apparent deliberate alloying of molybdenum with steel in one 14th-century Japanese sword (mfd. ca. 1330) has been reported, that art was never employed widely and was later lost. In 1754, Bengt Andersson Qvist
examined molybdenite and determined that it did not contain lead and was thus not the same as galena.
It was not until 1778 that Swedish
chemist Carl Wilhelm Scheele
realized that molybdena was neither graphite nor lead. 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 by using carbon
and linseed oil
in 1781.
For about a century after its isolation, molybdenum had no industrial use, owing to its relative scarcity, difficulty extracting the pure metal, and the immaturity of the metallurgical subfield. Early molybdenum steel alloys showed great promise in their increased hardness, but efforts were hampered by inconsistent results and a tendency toward brittleness and recrystallization. In 1906, William D. Coolidge filed a patent for rendering molybdenum ductile
, leading to its use as a heating element for high-temperature furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation require that moly be physically sealed or held in an inert gas. In 1913, Frank E. Elmore developed a flotation process
to recover molybdenite
from ores; flotation remains the primary isolation process.
During the first World War
, demand for molybdenum spiked; it was used both in armor plating and as a substitute for tungsten in high speed steel
s. Some British tanks were protected by 75 mm (3 in) manganese steel
plating, but this proved to be ineffective. The manganese steel plates were replaced with 25 mm (1 in) molybdenum-steel plating allowing for higher speed, greater maneuverability, and better protection. After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications. In World War II
, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys.
.png)
The world's largest producers of molybdenum materials are the United States
, China
, Chile
, Peru
and Canada
.
Though molybdenum is found in such mineral
s as wulfenite
(PbMoO4) and powellite
(CaMoO4), the main commercial source of molybdenum is molybdenite
(MoS
2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining. Large mines in Colorado
(such as the Henderson mine
and the now-inactive Climax mine
) 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.
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. 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
.
by air:
The oxidized ore is then either heated to 1100 °C (2,012 °F) to sublimate the oxide, or leached with ammonia
which reacts with the molybdenum(VI) oxide to form water-soluble molybdates:
Copper, an impurity in molybdenite, is less soluble in ammonia. To completely remove it from the solution, it is precipitated with hydrogen sulfide
.
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
. A common form of ferromolybdenum contains 60% molybdenum.
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. In 2008 the London Metal Exchange
announced that molybdenum would be traded as a commodity on the exchange.
Most high-strength steel alloy
s (example 41xx steel
s) contain 0.25% to 8% molybdenum. Despite such small portions, more than 43,000 tonnes of molybdenum are used as an alloying agent each year in stainless steel
s, tool steel
s, cast iron
s and high-temperature superalloy
s.
Molybdenum is also used in steel alloy
s for its high corrosion
resistance and weldability
. 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.
Because of its lower density and more stable price, molybdenum is sometimes used instead of tungsten. An example is the 'M' series of high-speed steels such as M2, M4 and M42 as substitution for the 'T' steel series which contain tungsten. Molybdenum can be implemented both as an alloying agent and as a flame-resistant coating for other metals. Although its melting point is 2623 °C (4,753.4 °F), molybdenum rapidly oxidizes at temperatures above 760 °C (1,400 °F) making it better-suited for use in vacuum environments.
TZM (Mo (~99%), Ti (~0.5%), Zr (~0.08%) and some C) is a corrosion-resisting molybdenum superalloy that resists molten fluoride salts at temperatures above 1300C. It has about twice the strength of pure Mo, and is more ductile and more weldable, yet in tests it resisted corrosion of a standard eutectic salt (FLiBe
) and salt vapors used in molten salt reactor
s for 1100 hours with so little corrosion that it was difficult to measure.
Other molybdenum-based alloys which do not contain iron have only limited applications. For example, because of the corrosion resistance against molten zinc, both pure molybdenum and the molybdenum/tungsten alloy (70%/30%) are used for piping, stirrers and pump impellers which come into contact with molten zinc.
at the active site in certain enzymes. In nitrogen fixation
in certain bacteria, the nitrogenase
enzyme, which is involved in the terminal step of reducing molecular nitrogen, usually contains molybdenum in the active site (though replacement of Mo with iron or vanadium is also known). The structure of the catalytic center of the enzyme is similar to that in iron-sulfur protein
s: it incorporates a Fe4S3 and multiple MoFe3S3 clusters.
In 2008, evidence was reported that a scarcity of molybdenum in the Earth's early oceans was a limiting factor for nearly two billion years in the further evolution of eukaryotic life
(which includes all plants and animals) as eukaryotes cannot fix nitrogen, and must therefore acquire most of their organic nitrogen from prokaryotic bacteria. The scarcity of molybdenum resulted from the relative lack of oxygen in the early ocean. However, once oxygen dissolved in seawater it helped dissolve molybdenum from minerals on the sea bottom, making it available to nitrogen-fixing bacteria and allowing them to provide more nitrogen for higher forms of life.
Although oxygen once promoted nitrogen fixation via making molybdenum available in water, it also directly poisons nitrogenase
enzymes, so that historically, after oxygen arrived in large quantities in Earth's air and water, organisms which continued to fix nitrogen in aerobic conditions were required to isolate their nitrogen-fixing enzymes in heterocyst
s, or similar structures which protect them from too much oxygen.
Though molybdenum forms compounds with various organic molecules, including carbohydrate
s and amino acid
s, it is transported throughout the human body as MoO42−. At least 50 molybdenum-containing enzymes were known by 2002, mostly in bacteria, and their number is increasing with every year; those enzymes include aldehyde oxidase
, sulfite oxidase
and xanthine oxidase
. In some animals, and in humans, the oxidation of xanthine
to uric acid
, a process of purine
catabolism
, is catalyzed by xanthine oxidase
, a molybdenum-containing enzyme. The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. However, an extremely high concentration of molybdenum reverses the trend and can act as an inhibitor in both purine catabolism and other processes. Molybdenum concentrations also affect protein synthesis, metabolism
and growth.
In animals and plants these enzymes use molybdenum bound at the active site in a tricyclic molybdenum cofactor
. All molybdenum-using enzymes so far identified in nature use this cofactor, save for the phylogenetically ancient molybdenum nitrogenase
s, which fix nitrogen in some bacteria and cyanobacteria. Molybdenum enzymes in plants and animals catalyze the oxidation and sometimes reduction of certain small molecules, as part of the regulation of nitrogen
, sulfur
and carbon cycle
s.
and may help prevent its decay.
The average daily intake of molybdenum varies between 0.12 and 0.24 mg, but it depends on the molybdenum content of the food. Pork, lamb and beef liver each have approximately 1.5 parts per million of molybdenum. Other significant dietary sources include green beans, eggs, sunflower seeds, wheat flour, lentils, cucumbers and cereal grain. Acute toxicity has not been seen in humans, and the toxicity depends strongly on the chemical state. Studies on rats show a median lethal dose (LD50) as low as 180 mg/kg for some Mo compounds. Although human toxicity data is unavailable, animal studies have shown that chronic ingestion of more than 10 mg/day of molybdenum can cause diarrhea, growth retardation, infertility
, low birth weight and gout
; it can also affect the lungs, kidneys and liver. Sodium tungstate
is a competitive inhibitor
of molybdenum. Dietary tungsten reduces the concentration of molybdenum in tissues.
Dietary molybdenum deficiency
from low soil concentration of molybdenum has been associated with increased rates of esophageal cancer
in a geographical band from northern China
to Iran. Compared to the United States, which has a greater supply of molybdenum in the soil, people living in these areas have about 16 times greater risk for esophageal
squamous cell carcinoma
.
Molybdenum deficiency has also been reported as a consequence of non-molybdenum supplemented total parenteral nutrition
(complete intravenous feeding) for long periods of time. It results in high blood levels of sulfite
and urate, in much the same way as molybdenum cofactor deficiency
. However, presumably since pure molybdenum deficiency from this mechanism is seen primarily in adults, the neurological consequences have not been as marked as for the congenital cofactor deficiency.
disease, seen in infants, results in interference with the ability of the body to use molybdenum in enzymes. It causes high levels of sulphite and urate, and neurological damage. The cause is the inability of the body to synthesize molybdenum cofactor
, a heterocyclic molecule which binds molybdenum at the active site in all known human enzymes which use molybdenum.
, producing copper deficiency. Molybdenum prevents plasma proteins from binding to copper, and it also increases the amount of copper that is excreted in urine
. Ruminant
s that consume high amounts of molybdenum develop symptoms including diarrhea
, stunted growth, anemia
and achromotrichia (loss of hair pigment). These symptoms can be alleviated by the administration of more copper into the system, both in dietary form and by injection. The condition, as an effective copper deficiency, can be aggravated by excess sulfur
.
Copper reduction or deficiency can also be deliberately induced for therapeutic purposes by the compound ammonium tetrathiomolybdate
, in which the bright red anion tetrathiomolybdate is the copper-chelating agent. Tetrathiomolybdate was first used therapeutically in the treatment of copper toxicosis in animals. It was then introduced as a treatment in Wilson's disease
, a hereditary copper metabolism disorder in humans; it acts both by competing with copper absorption in the bowel and by increasing excretion. It has also been found to have an inhibitory effect on angiogenesis
, potentially via the inhibition of copper ion dependent membrane translocation process invovling a non-classical secretion pathway. This makes it an interesting investigatory treatment for cancer
, age-related macular degeneration, and other diseases featuring excessive blood vessel deposition.
regulations specify the maximum permissible molybdenum exposure in an 8-hour day as 5 mg/m3. Chronic exposure to 60 to 600 mg/m3 can cause symptoms including fatigue, headaches and joint pains.
Group 6 element
A Group 6 element is one in the series of elements in group 6 in the periodic table, which consists of the transition metals chromium , molybdenum , tungsten , and seaborgium ....
chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
with the symbol Mo and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
42. The name is from Neo-Latin Molybdaenum, from Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
, meaning lead, itself proposed as a loanword
Loanword
A loanword is a word borrowed from a donor language and incorporated into a recipient language. By contrast, a calque or loan translation is a related concept where the meaning or idiom is borrowed rather than the lexical item itself. The word loanword is itself a calque of the German Lehnwort,...
from Anatolian
Anatolian languages
The Anatolian languages comprise a group of extinct Indo-European languages that were spoken in Asia Minor, the best attested of them being the Hittite language.-Origins:...
Luvian and Lydian
Lydian language
Lydian was an Indo-European language spoken in the region of Lydia in western Anatolia . It belongs to the Anatolian group of the Indo-European language family....
languages, since its ores were confused with lead ores. The free element, which is a silvery metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
, has the sixth-highest melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
of any element. It readily forms hard, stable carbide
Carbide
In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by chemical bonding type as follows: salt-like, covalent compounds, interstitial compounds, and "intermediate" transition metal carbides...
s, and for this reason it is often used in high-strength steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
alloys. Molybdenum does not occur as a free metal
Native Metal
A native metal is any metal that is found in its metallic form, either pure or as an alloy, in nature. Metals that can be found as native deposits singly and/or in alloys include aluminium, antimony, arsenic, bismuth, cadmium, chromium, cobalt, indium, iron, nickel, selenium, tantalum, tellurium,...
on Earth, but rather in various oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
s in minerals. Industrially, molybdenum compounds
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
are used in high-pressure and high-temperature applications, as pigments and catalysts
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
.
Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele
Carl Wilhelm Scheele
Carl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
. The metal was first isolated in 1781 by Peter Jacob Hjelm.
Most molybdenum compounds have low solubility
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
in water, but the molybdate ion MoO42− is soluble and forms when molybdenum-containing minerals are in contact with oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and water.
Molybdenum-containing enzymes are used as catalysts by some bacteria to break the chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
in atmospheric molecular nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, allowing biological nitrogen fixation
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
. 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. Owing 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.
Physical properties
In its pure form, molybdenum is a silvery-white metal with a Mohs hardnessMohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...
of 5.5. It has a melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
of 2623 °C (4,753.4 °F); of the naturally occurring elements, only tantalum
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...
, osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
, rhenium
Rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an average concentration of 1 part per billion , rhenium is one of the rarest elements in the Earth's crust. The free element has...
, tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
, and carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
have higher melting points. Molybdenum burns only at temperatures above 600 °C (1,112 °F). It has one of the lowest coefficients of thermal expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
among commercially used metals. The tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
of molybdenum wires increases about 3 times, from about 10 to 30 GPa, when their diameter decreases from ~50–100 nm to 10 nm.
Isotopes
There are 35 known isotopes of molybdenum, ranging in atomic massAtomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....
from 83 to 117, as well as four metastable nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
s. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. Of these naturally occurring isotopes, only molybdenum-100 is unstable. All unstable isotopes of molybdenum decay into isotopes of niobium
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
, technetium
Technetium
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature...
, and ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
.
Molybdenum-98 is the most abundant isotope, comprising 24.14% of all molybdenum. Molybdenum-100 has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of about 1019 y
Year
A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic....
and undergoes double beta decay
Double beta decay
Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted...
into ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
-100. Molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of approximately 150 ns.
As also noted below, the most common isotopic molybdenum application involves molybdenum-99, which is a fission product. It is a parent radioisotope to the short-lived gamma-emitting daughter radioisotope technetium-99m
Technetium-99m
Technetium-99m is a metastable nuclear isomer of technetium-99, symbolized as 99mTc. The "m" indicates that this is a metastable nuclear isomer, i.e., that its half-life of 6 hours is considerably longer than most nuclear isomers that undergo gamma decay...
, a nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
used in various imaging applications in medicine.
In 2008, the Delft University of Technology applied for a patent on the molybdenum-98-based production of technetium-99 http://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&adjacent=true&locale=nl_NL&FT=D&date=20110330&CC=EP&NR=2301041A1&KC=A1
Compounds and chemistry
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
with an electronegativity
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
of 1.8 on the Pauling scale and an atomic mass of 95.94 g/mol. It does not visibly react with oxygen or water at room temperature, and the bulk oxidation occurs at temperatures above 790 °C, resulting in molybdenum trioxide:
- 2 Mo + 3 → 2
The trioxide is volatile and sublimates at high temperatures. This prevents formation of a continuous protective oxide layer, which would stop the bulk oxidation of metal. Molybdenum has several oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
s, the most stable being +4 and +6 (bolded in the table). The chemistry and the compounds show more similarity to those of tungsten than that of chromium. An example is the instability of molybdenum(III) and tungsten(III) compounds as compared with the stability of the chromium(III) compounds. The highest oxidation state is common in the molybdenum(VI) oxide
Molybdenum(VI) oxide
Molybdenum trioxide is chemical compound with the formula MoO3. This compound is produced on the largest scale of any molybdenum compound. It occurs as the rare mineral molybdite...
(MoO3), whereas the normal sulfur compound is molybdenum disulfide
Molybdenum disulfide
Molybdenum disulfide is the inorganic compound with the formula MoS2. This black crystalline sulfide of molybdenum occurs as the mineral molybdenite. It is the principal ore from which molybdenum metal is extracted. The natural amorphous form is known as the rarer mineral jordisite. MoS2 is less...
MoS2.
Molybdenum(VI) oxide is soluble in strong alkaline
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
water, forming molybdates (MoO42−). Molybdates are weaker oxidants than chromates, but they show a similar tendency to form complex oxyanion
Oxyanion
An oxyanion or oxoanion is a chemical compound with the generic formula AxOyz− . Oxoanions are formed by a large majority of the chemical elements. The formulae of simple oxoanions are determined by the octet rule...
s by condensation at lower pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
values, such as [Mo7O24]6− and [Mo8O26]4−. Polymolybdates can incorporate other ions into their structure, forming polyoxometalate
Polyoxometalate
In chemistry, a polyoxometalate is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form a large, closed 3-dimensional framework....
s. The dark-blue phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
-containing heteropolymolybdate P[Mo12O40]3− is used for the spectroscopic
Ultraviolet-visible spectroscopy
Ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent ranges...
detection of phosphorus. The broad range of oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
s of molybdenum is reflected in various molybdenum chlorides:
- Molybdenum(II) chlorideMolybdenum(II) chlorideMolybdenum dichloride describes chemical compounds with the empirical formula MoCl2. At least two forms are known, and both have attracted much attention from academic researchers because of the unexpected structures seen for these compounds and the fact that they give rise to hundreds of...
MoCl2 (yellow solid) - Molybdenum(III) chloride MoCl3 (dark red solid)
- Molybdenum(IV) chlorideMolybdenum tetrachlorideMolybdenum tetrachloride is the inorganic compound with the empirical formula MoCl4. The material exists as two polymorphs, a polymeric and a hexameric structures, although neither form is soluble in any solvent without degradation...
MoCl4 (black solid) - Molybdenum(V) chlorideMolybdenum(V) chlorideMolybdenum chloride is the inorganic compound with the formula [MoCl5]2. This dark volatile solid is an important starting reagent in the preparation of molybdenum compounds. In the solid state molybdenum pentachloride exists as a dimer with the formula Mo2Cl10, with a structure similar to that...
MoCl5 (dark green solid) - Molybdenum(VI) chloride MoCl6 (brown solid)
The structure of the MoCl2 is composed of Mo6Cl84+ clusters with four chloride ions to compensate the charge.
Like chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
and some other transition metals, molybdenum is able to form quadruple bond
Quadruple bond
A quadruple bond is a type of chemical bond between two atoms involving eight electrons. This bond is an extension of the more familiar types double bonds and triple bonds. Stable quadruple bonds are most common among the middle members transition metal elements such rhenium, tungsten, molybdenum...
s, such as in Mo2(CH3COO)4. This compound can be transformed into Mo2Cl84−, which also has a quadruple bond.
The oxidation state 0 is possible with carbon monoxide as ligand, such as in molybdenum hexacarbonyl
Molybdenum hexacarbonyl
Molybdenum hexacarbonyl is the chemical compound with the formula Mo6. This colorless solid, like its chromium and tungsten analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero oxidation state.-Structure and properties:Mo6 adopts an octahedral geometry consisting...
, Mo(CO)6.
History
MolybdeniteMolybdenite
Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfur atoms...
—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
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant. Even when molybdena was distinguishable from graphite, it was still confused with a common lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
ore (now called galena
Galena
Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...
), which took its name from Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
, meaning lead. Although apparent deliberate alloying of molybdenum with steel in one 14th-century Japanese sword (mfd. ca. 1330) has been reported, that art was never employed widely and was later lost. In 1754, Bengt Andersson Qvist
Bengt Andersson Qvist
Bengt Andersson Qvist Bengt Andersson Qvist Bengt Andersson Qvist (sometimes Benct Qvist or Bengt Quist (21 October 1729 – 14 October 1799) was a Swedish chemist and mineralogist. He was assistant of Sven Rinman and after a visit to steel plants in Britain he built a demonstration plant in...
examined molybdenite and determined that it did not contain lead and was thus not the same as galena.
It was not until 1778 that Swedish
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
chemist Carl Wilhelm Scheele
Carl Wilhelm Scheele
Carl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
realized that molybdena was neither graphite nor lead. 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 by using carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
and linseed oil
Linseed oil
Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant . The oil is obtained by cold pressing, sometimes followed by solvent extraction...
in 1781.
For about a century after its isolation, molybdenum had no industrial use, owing to its relative scarcity, difficulty extracting the pure metal, and the immaturity of the metallurgical subfield. Early molybdenum steel alloys showed great promise in their increased hardness, but efforts were hampered by inconsistent results and a tendency toward brittleness and recrystallization. In 1906, William D. Coolidge filed a patent for rendering molybdenum ductile
Ductility
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...
, leading to its use as a heating element for high-temperature furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation require that moly be physically sealed or held in an inert gas. In 1913, Frank E. Elmore developed a flotation process
Flotation process
Flotation process is a method of separation widely used in the wastewater treatment and mineral processing industries.Various flotation processes include the following:* Dissolved air flotation...
to recover molybdenite
Molybdenite
Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfur atoms...
from ores; flotation remains the primary isolation process.
During the first World War
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, demand for molybdenum spiked; it was used both in armor plating and as a substitute for tungsten in high speed steel
High speed steel
High speed steelMost copyeditors today would tend to choose to style the unit adjective high-speed with a hyphen, rendering the full term as high-speed steel, and this styling is not uncommon . However, it is true that in the metalworking industries the styling high speed steel is long-established...
s. Some British tanks were protected by 75 mm (3 in) manganese steel
Mangalloy
Mangalloy, also called manganese steel or Hadfield steel, is a steel alloy containing an average of around 13% manganese. Mangalloy is known for its high impact strength and resistance to abrasion.-Material properties:...
plating, but this proved to be ineffective. The manganese steel plates were replaced with 25 mm (1 in) molybdenum-steel plating allowing for higher speed, greater maneuverability, and better protection. After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications. In World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys.
Occurrence
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
.
Though molybdenum is found in such mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
s as wulfenite
Wulfenite
Wulfenite is a lead molybdate mineral with the formula PbMoO4. It can be most often found as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be highly variable. In its yellow form it is sometimes called "yellow lead ore".It crystallizes...
(PbMoO4) and powellite
Powellite
Powellite is a calcium molybdate mineral with formula CaMoO4. Powellite crystallizes with tetragonal - dipyramidal crystal structure as transparent adamantine blue, greenish brown, yellow to grey typically anhedral forms. It exhibits distinct cleavage and has a brittle to conchoidal fracture. It...
(CaMoO4), the main commercial source of molybdenum is molybdenite
Molybdenite
Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfur atoms...
(MoS
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining. Large mines in Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
(such as the Henderson mine
Henderson molybdenum mine
The Henderson molybdenum mine is a large underground molybdenum mine west of the town of Empire in Clear Creek County, Colorado, USA. The Henderson mine, which has produced molybdenum since 1976, is owned by Freeport-McMoRan....
and the now-inactive Climax mine
Climax mine
The Climax mine, located in Climax, Colorado, United States, was a major molybdenum mine in Lake and Summit counties, Colorado. In its heyday, the Climax mine was the largest molybdenum mine in the world, and for many years it supplied three-fourths of the world's supply of molbdenum...
) and in British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
yield molybdenite as their primary product, while many porphyry copper deposits such as the Bingham Canyon Mine
Bingham Canyon Mine
The Bingham Canyon Mine, also known as the Kennecott Copper Mine, is an open-pit mining operation extracting a large porphyry copper deposit southwest of Salt Lake City, Utah, USA, in the Oquirrh Mountains. It is the deepest open-pit mine in the world. The mine is owned by Rio Tinto Group, an...
in Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
and the Chuquicamata
Chuquicamata
Chuquicamata, or "Chuqui" as it is more familiarly known, is by digged volume the biggest open pit copper mine in the world, located in the north of Chile, 215 km northeast of Antofagasta and 1,240 km north of the capital, Santiago...
mine in northern Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
produce molybdenum as a byproduct of copper mining.
The Knaben
Knaben
Knaben is a former mining community in the northern part of Kvinesdal municipality, Norway, and currently a popular ski resort. The settlement lies about 630 metres above sea level. The molybdenum mines were operated from 1885 to 1973. Buildings and constructions are still partly intact...
mine in southern Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
was opened in 1885, making it the first molybdenum mine. It remained open until 1973.
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. The Russian Luna 24
Luna 24
-External links:*...
mission discovered a molybdenum-bearing grain (1 × 0.6 µm) in a pyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
fragment taken from Mare Crisium
Mare Crisium
Mare Crisium is a lunar mare located in the Moon's Crisium basin, just northeast of Mare Tranquillitatis. This basin is of the Pre-Imbrian period, 4.55 to 3.85 billion years ago. This mare is in diameter, and 176,000 km2 in area. It has a very flat floor, with a ring of wrinkled ridges...
on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
.
Production
In molybdenite processing, the molybdenite is first heated to a temperature of 700 °C (1,292 °F) and the sulfide is oxidized into molybdenum(VI) oxideMolybdenum(VI) oxide
Molybdenum trioxide is chemical compound with the formula MoO3. This compound is produced on the largest scale of any molybdenum compound. It occurs as the rare mineral molybdite...
by air:
- 2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2
The oxidized ore is then either heated to 1100 °C (2,012 °F) to sublimate the oxide, or leached with ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
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
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
.
Pure molybdenum is produced by reduction of the oxide with hydrogen, while the molybdenum for steel production is reduced by the aluminothermic reaction
Aluminothermic reaction
Aluminothermic reactions are exothermic chemical reactions using aluminium as the reducing agent at high temperature. The most prominent example is the thermite reaction between aluminium and iron oxides:-History:...
with addition of iron to produce ferromolybdenum
Ferromolybdenum
Ferromolybdenum is an important iron molybdenum alloy, with a molybdenum content of 60-70% It is the main source for molybdenum alloying of HSLA steel. The molybdenum is mined and is subsequently transformed into the molybdenum oxide MoO3. This oxide is mixed with iron oxide and aluminium and is...
. A common form of ferromolybdenum contains 60% molybdenum.
Molybdenum has a value of approximately $30,000 per tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
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. In 2008 the London Metal Exchange
London Metal Exchange
The London Metal Exchange is the futures exchange with the world's largest market in options, and futures contracts on base and other metals. As the LME offers contracts with daily expiry dates of up to three months from trade date, along with longer-dated contracts up to 123 months, it also...
announced that molybdenum would be traded as a commodity on the exchange.
Applications
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 armour, aircraft parts, electrical contacts, industrial motors and filaments.Most high-strength steel alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s (example 41xx steel
41xx steel
41xx steel is a family of SAE steel grades, as specified by the Society of Automotive Engineers . Alloying elements include chromium and molybdenum, and as a result these materials are often referred to as chromoly steel or CRMO...
s) contain 0.25% to 8% molybdenum. Despite such small portions, more than 43,000 tonnes of molybdenum are used as an alloying agent each year in stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
s, tool steel
Tool steel
Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures...
s, cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
s and high-temperature superalloy
Superalloy
A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys typically have a matrix with an austenitic face-centered cubic crystal structure. ...
s.
Molybdenum is also used in steel alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s for its high corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
resistance and weldability
Weldability
The weldability, also known as joinability, of a material refers to its ability to be welded. Many metals and thermoplastics can be welded, but some are easier to weld than others...
. 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
AL-6XN
The AL-6XN alloy is a superaustenitic stainless steel which was developed by . It exhibits far greater resistance to chloride pitting, crevice corrosion and stress corrosion cracking than exhibited by the standard 300 series stainless steels, and is less costly than the traditional nickel-base...
). Molybdenum acts by increasing lattice strain, thus increasing the energy required to dissolve out iron atoms from the surface.
Because of its lower density and more stable price, molybdenum is sometimes used instead of tungsten. An example is the 'M' series of high-speed steels such as M2, M4 and M42 as substitution for the 'T' steel series which contain tungsten. Molybdenum can be implemented both as an alloying agent and as a flame-resistant coating for other metals. Although its melting point is 2623 °C (4,753.4 °F), molybdenum rapidly oxidizes at temperatures above 760 °C (1,400 °F) making it better-suited for use in vacuum environments.
TZM (Mo (~99%), Ti (~0.5%), Zr (~0.08%) and some C) is a corrosion-resisting molybdenum superalloy that resists molten fluoride salts at temperatures above 1300C. It has about twice the strength of pure Mo, and is more ductile and more weldable, yet in tests it resisted corrosion of a standard eutectic salt (FLiBe
FLiBe
FLiBe is a mixture of lithium fluoride and beryllium fluoride . As a molten salt it is proposed as a nuclear reactor coolant, and two different mixtures were used in the Molten-Salt Reactor Experiment....
) and salt vapors used in molten salt reactor
Molten salt reactor
A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...
s for 1100 hours with so little corrosion that it was difficult to measure.
Other molybdenum-based alloys which do not contain iron have only limited applications. For example, because of the corrosion resistance against molten zinc, both pure molybdenum and the molybdenum/tungsten alloy (70%/30%) are used for piping, stirrers and pump impellers which come into contact with molten zinc.
Other applications as catalyst and compounds
- Molybdenum-99 is a parent radioisotope to the daughter radioisotope technetium-99mTechnetium-99mTechnetium-99m is a metastable nuclear isomer of technetium-99, symbolized as 99mTc. The "m" indicates that this is a metastable nuclear isomer, i.e., that its half-life of 6 hours is considerably longer than most nuclear isomers that undergo gamma decay...
, which is used in many medical procedures. - Molybdenum disulfideMolybdenum disulfideMolybdenum disulfide is the inorganic compound with the formula MoS2. This black crystalline sulfide of molybdenum occurs as the mineral molybdenite. It is the principal ore from which molybdenum metal is extracted. The natural amorphous form is known as the rarer mineral jordisite. MoS2 is less...
(MoS2) is used as a solid lubricant and a high-pressure high-temperature (HPHT) antiwear agent. It forms strong films on metallic surfaces and is a common additive to HPHT greases—in case of a catastrophic grease failure, thin layer of molybdenum prevents contact of the lubricated parts. It also has semiconducting properties with distinct advantages over traditional silicon or grapheneGrapheneGraphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm, who described single-layer...
in electronics applications. MoS2 is also used as a catalyst in hydrocracking of petroleum fractions which contain nitrogen, sulfur and oxygen. - Molybdenum disilicide (MoSi2) is an electrically conducting ceramicCeramicA ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
with primary use in heating elementHeating elementA heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element....
s operating at temperatures above 1500 °C in air. - Molybdenum trioxide (MoO3) is used as an adhesive between enamelVitreous enamelVitreous enamel, also porcelain enamel in U.S. English, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C...
s and metals. Lead molybdate (wulfenite) co-precipitated with lead chromate and lead sulfate is a bright-orange pigment used with ceramics and plastics. - Molybdenum powder is used as a fertilizer for some plants, such as cauliflower.
- The element is also used in NO, NO2, NOx analyzers in power plants for pollution controls. At 350 °C (662 °F) the element acts as a catalyst for NO2/NOx to form only NO molecules for consistent readings by infrared light.
- Ammonium heptamolybdate is used in biological staining procedures.
Biochemistry
The most important role of the molybdenum in living organisms is as a metal heteroatomHeteroatom
In organic chemistry, a heteroatom is any atom that is not carbon or hydrogen. Usually, the term is used to indicate that non-carbon atoms have replaced carbon in the backbone of the molecular structure...
at the active site in certain enzymes. In nitrogen fixation
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
in certain bacteria, the nitrogenase
Nitrogenase
Nitrogenases are enzymes used by some organisms to fix atmospheric nitrogen gas . It is the only known family of enzymes that accomplish this process. Dinitrogen is quite inert because of the strength of its N-N triple bond...
enzyme, which is involved in the terminal step of reducing molecular nitrogen, usually contains molybdenum in the active site (though replacement of Mo with iron or vanadium is also known). The structure of the catalytic center of the enzyme is similar to that in iron-sulfur protein
Iron-sulfur protein
Iron-sulfur proteins are proteins characterized by the presence of iron-sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states...
s: it incorporates a Fe4S3 and multiple MoFe3S3 clusters.
In 2008, evidence was reported that a scarcity of molybdenum in the Earth's early oceans was a limiting factor for nearly two billion years in the further evolution of eukaryotic life
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
(which includes all plants and animals) as eukaryotes cannot fix nitrogen, and must therefore acquire most of their organic nitrogen from prokaryotic bacteria. The scarcity of molybdenum resulted from the relative lack of oxygen in the early ocean. However, once oxygen dissolved in seawater it helped dissolve molybdenum from minerals on the sea bottom, making it available to nitrogen-fixing bacteria and allowing them to provide more nitrogen for higher forms of life.
Although oxygen once promoted nitrogen fixation via making molybdenum available in water, it also directly poisons nitrogenase
Nitrogenase
Nitrogenases are enzymes used by some organisms to fix atmospheric nitrogen gas . It is the only known family of enzymes that accomplish this process. Dinitrogen is quite inert because of the strength of its N-N triple bond...
enzymes, so that historically, after oxygen arrived in large quantities in Earth's air and water, organisms which continued to fix nitrogen in aerobic conditions were required to isolate their nitrogen-fixing enzymes in heterocyst
Heterocyst
Heterocysts are specialized nitrogen-fixing cells formed by some filamentous cyanobacteria, such as Nostoc punctiforme, Cylindrospermum stagnale and Anabaena sphaerica, during nitrogen starvation. They fix nitrogen from dinitrogen in the air using the enzyme nitrogenase, in order to provide the...
s, or similar structures which protect them from too much oxygen.
Though molybdenum forms compounds with various organic molecules, including carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
s and amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s, it is transported throughout the human body as MoO42−. At least 50 molybdenum-containing enzymes were known by 2002, mostly in bacteria, and their number is increasing with every year; those enzymes include aldehyde oxidase
Aldehyde oxidase
Aldehyde oxidase is an enzyme which generates carboxylic acids from aldehydes. It catalyzes the conversion of an aldehyde in the presence of oxygen and water to an acid and hydrogen peroxide.* an aldehyde + H2O + O2 a carboxylate + H2O2 + H+...
, sulfite oxidase
Sulfite oxidase
Sulfite oxidase is an enzyme in the mitochondria of all eukaryotes. It oxidizes sulfite to sulfate and, via cytochrome c, transfers the electrons produced to the electron transport chain, allowing generation of ATP in oxidative phosphorylation...
and xanthine oxidase
Xanthine oxidase
Xanthine oxidase Xanthine oxidase Xanthine oxidase (XO (sometimes 'XAO'), a form of xanthine oxidoreductase that generates reactive oxygen species. Is an enzyme that catalyzes the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid...
. In some animals, and in humans, the oxidation of xanthine
Xanthine
Xanthine , is a purine base found in most human body tissues and fluids and in other organisms. A number of stimulants are derived from xanthine, including caffeine and theobromine....
to uric acid
Uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates such as ammonium acid urate. Uric acid is created when the body breaks down purine nucleotides. High blood concentrations of uric acid...
, a process of purine
Purine
A purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
catabolism
Catabolism
Catabolism is the set of metabolic pathways that break down molecules into smaller units and release energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides, and amino...
, is catalyzed by xanthine oxidase
Xanthine oxidase
Xanthine oxidase Xanthine oxidase Xanthine oxidase (XO (sometimes 'XAO'), a form of xanthine oxidoreductase that generates reactive oxygen species. Is an enzyme that catalyzes the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid...
, a molybdenum-containing enzyme. The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. However, an extremely high concentration of molybdenum reverses the trend and can act as an inhibitor in both purine catabolism and other processes. Molybdenum concentrations also affect protein synthesis, metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
and growth.
In animals and plants these enzymes use molybdenum bound at the active site in a tricyclic molybdenum cofactor
Molybdenum cofactor
Molybdenum cofactor is a cofactor required for the activity of enzymes such as sulfite oxidase, xanthine oxidoreductase, and aldehyde oxidase. It is a coordination complex formed between molybdopterin and an oxide of molybdenum.Molybdopterins, in turn, are synthesized from guanosine triphosphate...
. All molybdenum-using enzymes so far identified in nature use this cofactor, save for the phylogenetically ancient molybdenum nitrogenase
Nitrogenase
Nitrogenases are enzymes used by some organisms to fix atmospheric nitrogen gas . It is the only known family of enzymes that accomplish this process. Dinitrogen is quite inert because of the strength of its N-N triple bond...
s, which fix nitrogen in some bacteria and cyanobacteria. Molybdenum enzymes in plants and animals catalyze the oxidation and sometimes reduction of certain small molecules, as part of the regulation of nitrogen
Nitrogen cycle
The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This transformation can be carried out by both biological and non-biological processes. Important processes in the nitrogen cycle include fixation, mineralization, nitrification, and denitrification...
, sulfur
Sulfur cycle
The sulfur cycle are the collection of processes by which sulfur moves to and from minerals and living systems. Such biogeochemical cycles are important in geology because they affect many minerals...
and carbon cycle
Carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
s.
Human dietary intake and deficiency
The human body contains about 0.07 mg of molybdenum per kilogram of weight. It occurs in higher concentrations in the liver and kidneys and in lower concentrations in the vertebrae. Molybdenum is also present within human tooth enamelTooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
and may help prevent its decay.
The average daily intake of molybdenum varies between 0.12 and 0.24 mg, but it depends on the molybdenum content of the food. Pork, lamb and beef liver each have approximately 1.5 parts per million of molybdenum. Other significant dietary sources include green beans, eggs, sunflower seeds, wheat flour, lentils, cucumbers and cereal grain. Acute toxicity has not been seen in humans, and the toxicity depends strongly on the chemical state. Studies on rats show a median lethal dose (LD50) as low as 180 mg/kg for some Mo compounds. Although human toxicity data is unavailable, animal studies have shown that chronic ingestion of more than 10 mg/day of molybdenum can cause diarrhea, growth retardation, infertility
Infertility
Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to full term...
, low birth weight and gout
Gout
Gout is a medical condition usually characterized by recurrent attacks of acute inflammatory arthritis—a red, tender, hot, swollen joint. The metatarsal-phalangeal joint at the base of the big toe is the most commonly affected . However, it may also present as tophi, kidney stones, or urate...
; it can also affect the lungs, kidneys and liver. Sodium tungstate
Sodium tungstate
Sodium tungstate, Na2WO4, a tungstate of sodium, is useful as a source of tungsten. It is prepared from tungsten ores used to manufacture tungsten by reducing it....
is a competitive inhibitor
Competitive inhibition
Competitive inhibition is a form of enzyme inhibition where binding of the inhibitor to the active site on the enzyme prevents binding of the substrate and vice versa.-Mechanism:...
of molybdenum. Dietary tungsten reduces the concentration of molybdenum in tissues.
Dietary molybdenum deficiency
Molybdenum deficiency
Molybdenum deficiency refers to the clinical consequences of inadequate supplies of molybdenum in the diet.The amount of molybdenum required is relatively small, and molybdenum deficiency usually doesn't occur in natural settings. However, it can occur in individuals receiving parenteral nutrition....
from low soil concentration of molybdenum has been associated with increased rates of esophageal cancer
Esophageal cancer
Esophageal cancer is malignancy of the esophagus. There are various subtypes, primarily squamous cell cancer and adenocarcinoma . Squamous cell cancer arises from the cells that line the upper part of the esophagus...
in a geographical band from northern China
North China
thumb|250px|Northern [[People's Republic of China]] region.Northern China or North China is a geographical region of China. The heartland of North China is the North China Plain....
to Iran. Compared to the United States, which has a greater supply of molybdenum in the soil, people living in these areas have about 16 times greater risk for esophageal
Esophageal cancer
Esophageal cancer is malignancy of the esophagus. There are various subtypes, primarily squamous cell cancer and adenocarcinoma . Squamous cell cancer arises from the cells that line the upper part of the esophagus...
squamous cell carcinoma
Squamous cell carcinoma
Squamous cell carcinoma , occasionally rendered as "squamous-cell carcinoma", is a histologically distinct form of cancer. It arises from the uncontrolled multiplication of malignant cells deriving from epithelium, or showing particular cytological or tissue architectural characteristics of...
.
Molybdenum deficiency has also been reported as a consequence of non-molybdenum supplemented total parenteral nutrition
Total parenteral nutrition
Parenteral nutrition is feeding a person intravenously, bypassing the usual process of eating and digestion. The person receives nutritional formulae that contain nutrients such as glucose, amino acids, lipids and added vitamins and dietary minerals...
(complete intravenous feeding) for long periods of time. It results in high blood levels of sulfite
Sulfite
Sulfites are compounds that contain the sulfite ion SO. The sulfite ion is the conjugate base of bisulfite. Although the acid itself is elusive, its salts are widely used.-Structure:...
and urate, in much the same way as molybdenum cofactor deficiency
Molybdenum cofactor deficiency
Molybdenum cofactor deficiency is a human disease. Absence of molybdenum cofactor leads to accumulation of toxic levels of sulphite and neurological damage usually leading to death within months of birth, due to the lack of active sulfite oxidase...
. However, presumably since pure molybdenum deficiency from this mechanism is seen primarily in adults, the neurological consequences have not been as marked as for the congenital cofactor deficiency.
Related diseases
A congenital molybdenum cofactor deficiencyMolybdenum cofactor deficiency
Molybdenum cofactor deficiency is a human disease. Absence of molybdenum cofactor leads to accumulation of toxic levels of sulphite and neurological damage usually leading to death within months of birth, due to the lack of active sulfite oxidase...
disease, seen in infants, results in interference with the ability of the body to use molybdenum in enzymes. It causes high levels of sulphite and urate, and neurological damage. The cause is the inability of the body to synthesize molybdenum cofactor
Molybdenum cofactor
Molybdenum cofactor is a cofactor required for the activity of enzymes such as sulfite oxidase, xanthine oxidoreductase, and aldehyde oxidase. It is a coordination complex formed between molybdopterin and an oxide of molybdenum.Molybdopterins, in turn, are synthesized from guanosine triphosphate...
, a heterocyclic molecule which binds molybdenum at the active site in all known human enzymes which use molybdenum.
Copper-molybdenum antagonism
High levels of molybdenum can interfere with the body's uptake of copperCopper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, producing copper deficiency. Molybdenum prevents plasma proteins from binding to copper, and it also increases the amount of copper that is excreted in urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
. Ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s that consume high amounts of molybdenum develop symptoms including diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
, stunted growth, anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
and achromotrichia (loss of hair pigment). These symptoms can be alleviated by the administration of more copper into the system, both in dietary form and by injection. The condition, as an effective copper deficiency, can be aggravated by excess sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
.
Copper reduction or deficiency can also be deliberately induced for therapeutic purposes by the compound ammonium tetrathiomolybdate
Ammonium tetrathiomolybdate
Ammonium tetrathiomolybdate is the chemical compound with the formula [NH4]2MoS4. This bright red ammonium salt is an important reagent in the chemistry of molybdenum and has been used as a building block in bioinorganic chemistry...
, in which the bright red anion tetrathiomolybdate is the copper-chelating agent. Tetrathiomolybdate was first used therapeutically in the treatment of copper toxicosis in animals. It was then introduced as a treatment in Wilson's disease
Wilson's disease
Wilson's disease or hepatolenticular degeneration is an autosomal recessive genetic disorder in which copper accumulates in tissues; this manifests as neurological or psychiatric symptoms and liver disease...
, a hereditary copper metabolism disorder in humans; it acts both by competing with copper absorption in the bowel and by increasing excretion. It has also been found to have an inhibitory effect on angiogenesis
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
, potentially via the inhibition of copper ion dependent membrane translocation process invovling a non-classical secretion pathway. This makes it an interesting investigatory treatment for cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
, age-related macular degeneration, and other diseases featuring excessive blood vessel deposition.
Precautions
Molybdenum dusts and fumes, which can be generated by mining or metalworking, can be toxic, especially if ingested (including dust trapped in the sinuses and later swallowed). Low levels of prolonged exposure can cause irritation to the eyes and skin. Direct inhalation or ingestion of molybdenum and its oxides should be avoided. OSHAOccupational Safety and Health Administration
The United States Occupational Safety and Health Administration is an agency of the United States Department of Labor. It was created by Congress of the United States under the Occupational Safety and Health Act, signed by President Richard M. Nixon, on December 29, 1970...
regulations specify the maximum permissible molybdenum exposure in an 8-hour day as 5 mg/m3. Chronic exposure to 60 to 600 mg/m3 can cause symptoms including fatigue, headaches and joint pains.
External links
- Mineral & Exploration – Map of World Molybdenum Producers 2009
- "Mining A Mountain" Popular Mechanics, July 1935 pp.63-64