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= Molybdenum =
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Introduction
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Molybdenum is a chemical element; it has symbol Mo (from Neo-Latin
'molybdaenum') and atomic number 42. The name derived from Ancient
Greek ', meaning lead, since its ores were confused with lead ores.
Molybdenum minerals have been known throughout history, 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.
Molybdenum does not occur naturally as a free metal on Earth; in its
minerals, it is found only in oxidized states. The free element, a
silvery metal with a grey cast, has the sixth-highest melting point of
any element. It readily forms hard, stable carbides in alloys, and for
this reason most of the world production of the element (about 80%) is
used in steel alloys, including high-strength alloys and superalloys.
Most molybdenum compounds have low solubility in water. Heating
molybdenum-bearing minerals under oxygen and water affords molybdate
ion , which forms quite soluble salts. Industrially, molybdenum
compounds (about 14% of world production of the element) are used as
pigments and catalysts.
are by far the most common bacterial catalysts for breaking the
chemical bond in atmospheric molecular nitrogen in the process of
biological nitrogen fixation. At least 50 molybdenum enzymes are now
known in bacteria, plants, and animals, although only bacterial and
cyanobacterial enzymes are involved in nitrogen fixation. Most
nitrogenases contain an iron-molybdenum cofactor FeMoco, which is
believed to contain either Mo(III) or Mo(IV). By contrast Mo(VI) and
Mo(IV) are complexed with molybdopterin in all other
molybdenum-bearing enzymes. Molybdenum is an essential element for all
higher eukaryote organisms, including humans. A species of sponge,
'Theonella conica', is known for hyperaccumulation of molybdenum.
Physical properties
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In its pure form, molybdenum is a silvery-grey metal with a Mohs
hardness of 5.5 and a standard atomic weight of 95.95 g/mol. It has a
melting point of 2623 °C, sixth highest of the naturally occurring
elements; only tantalum, osmium, rhenium, tungsten, and carbon have
higher melting points. It has one of the lowest coefficients of
thermal expansion among commercially used metals.
Chemical properties
=====================
Molybdenum is a transition metal with an electronegativity of 2.16 on
the Pauling scale. It does not visibly react with oxygen or water at
room temperature, but is attacked by halogens and hydrogen peroxide.
Weak oxidation of molybdenum starts at 300 °C; bulk oxidation occurs
at temperatures above 600 °C, resulting in molybdenum trioxide. Like
many heavier transition metals, molybdenum shows little inclination to
form a cation in aqueous solution, although the Mo3+ cation is known
to form under carefully controlled conditions.
Gaseous molybdenum consists of the diatomic species Mo2. That
molecule is a singlet, with two unpaired electrons in bonding
orbitals, in addition to 5 conventional bonds. The result is a
sextuple bond.
Isotopes
==========
There are 39 known isotopes of molybdenum, ranging in atomic mass from
81 to 119, as well as 13 metastable nuclear isomers. 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.
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. All unstable isotopes
of molybdenum decay into isotopes of niobium, technetium, and
ruthenium. Of the synthetic radioisotopes, the most stable is 93Mo,
with a half-life of 4,839 years.
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 molybdenum-99.
Compounds
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Molybdenum forms chemical compounds in oxidation states −4 and from −2
to +6. Higher oxidation states are more relevant to its terrestrial
occurrence and its biological roles, mid-level oxidation states are
often associated with metal clusters, and very low oxidation states
are typically associated with organomolybdenum compounds. The
chemistry of molybdenum and tungsten show strong similarities. The
relative rarity of molybdenum(III), for example, contrasts with the
pervasiveness of the chromium(III) compounds. The highest oxidation
state is seen in molybdenum(VI) oxide (MoO3), whereas the normal
sulfur compound is molybdenum disulfide MoS2.
!Oxidation state !Example
−4
−2
−1
0 6}
|-
| +1||Cyclopentadienylmolybdenum tricarbonyl
|-
| +2||Molybdenum(II) chloride
|-
| +3||Molybdenum(III) bromide
|-
| +4||Molybdenum disulfide
|-
| +5||Molybdenum(V) chloride
|-
| +6||Molybdenum(VI) fluoride
|}
From the perspective of commerce, the most important compounds are
molybdenum disulfide () and molybdenum trioxide (). The black
disulfide is the main mineral. It is roasted in air to give the
trioxide:
:2 + 7 → 2 + 4
The trioxide, which is volatile at high temperatures, is the precursor
to virtually all other Mo compounds as well as alloys. Molybdenum has
several oxidation states, the most stable being +4 and +6 (bolded in
the table at left).
Molybdenum(VI) oxide is soluble in strong alkaline water, forming
molybdates (MoO42−). Molybdates are weaker oxidants than chromates.
They tend to form structurally complex oxyanions by condensation at
lower pH values, such as [Mo7O24]6− and [Mo8O26]4−. Polymolybdates can
incorporate other ions, forming polyoxometalates. The dark-blue
phosphorus-containing heteropolymolybdate P[Mo12O40]3− is used for the
spectroscopic detection of phosphorus.
The broad range of oxidation states of molybdenum is reflected in
various molybdenum chlorides:
* Molybdenum(II) chloride MoCl2, which exists as the hexamer Mo6Cl12
and the related dianion [Mo6Cl14]2-.
* Molybdenum(III) chloride MoCl3, a dark red solid, which converts to
the anion trianionic complex [MoCl6]3-.
* Molybdenum(IV) chloride MoCl4, a black solid, which adopts a
polymeric structure.
* Molybdenum(V) chloride MoCl5 dark green solid, which adopts a
dimeric structure.
* Molybdenum(VI) chloride MoCl6 is a black solid, which is monomeric
and slowly decomposes to MoCl5 and Cl2 at room temperature.
The accessibility of these oxidation states depends quite strongly on
the halide counterion: although molybdenum(VI) fluoride is stable,
molybdenum does not form a stable hexachloride, pentabromide, or
tetraiodide.
Like chromium and some other transition metals, molybdenum forms
quadruple bonds, such as in Mo2(CH3COO)4 and [Mo2Cl8]4−. The Lewis
acid properties of the butyrate and perfluorobutyrate dimers,
Mo2(O2CR)4 and Rh2(O2CR) 4, have been reported.
The oxidation state 0 and lower are possible with carbon monoxide as
ligand, such as in molybdenum hexacarbonyl, Mo(CO)6.
History
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Molybdenite--the principal ore from which molybdenum is now
extracted--was previously known as molybdena. Molybdena was confused
with and often utilized 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 the common lead ore PbS (now called galena); the name
comes from Ancient Greek ', meaning 'lead'. (The Greek word itself
has been proposed as a loanword from Anatolian Luvian and Lydian
languages).
Although (reportedly) molybdenum was deliberately alloyed with steel
in one 14th-century Japanese sword (mfd. ), that art was never
employed widely and was later lost. In the West in 1754, Bengt
Andersson Qvist examined a sample of molybdenite and determined that
it did not contain lead and thus was not galena.
By 1778 Swedish chemist Carl Wilhelm Scheele stated firmly that
molybdena was (indeed) neither galena nor graphite. Instead, Scheele
correctly proposed that molybdena was an ore of a distinct new
element, named 'molybdenum' for the mineral in which it resided, and
from which it might be isolated. Peter Jacob Hjelm successfully
isolated molybdenum using carbon and linseed oil in 1781.
For the next century, molybdenum had no industrial use. It was
relatively scarce, the pure metal was difficult to extract, and the
necessary techniques of metallurgy were immature. Early molybdenum
steel alloys showed great promise of increased hardness, but efforts
to manufacture the alloys on a large scale were hampered with
inconsistent results, a tendency toward brittleness, and
recrystallization. In 1906, William D. Coolidge filed a patent for
rendering molybdenum ductile, leading to applications as a heating
element for high-temperature furnaces and as a support for
tungsten-filament light bulbs; oxide formation and degradation require
that molybdenum be physically sealed or held in an inert gas. In 1913,
Frank E. Elmore developed a froth flotation process to recover
molybdenite from ores; flotation remains the primary isolation
process.
During World War I, demand for molybdenum spiked; it was used both in
armor plating and as a substitute for tungsten in high-speed steels.
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 much lighter molybdenum steel plates allowing for
higher speed, greater maneuverability, and better protection. The
Germans also used molybdenum-doped steel for heavy artillery, like in
the super-heavy howitzer Big Bertha, because traditional steel melts
at the temperatures produced by the propellant of the one ton shell.
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.
Occurrence and production
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Molybdenum is the 54th most abundant element in the Earth's crust with
an average of 1.5 parts per million 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 Soviet Luna 24 mission
discovered a molybdenum-bearing grain (1 × 0.6 μm) in a pyroxene
fragment taken from Mare Crisium on the Moon. The comparative rarity
of molybdenum in the Earth's crust is offset by its concentration in a
number of water-insoluble ores, often combined with sulfur in the same
way as copper, with which it is often found. Though molybdenum is
found in such minerals as wulfenite (PbMoO4) and powellite (CaMoO4),
the main commercial source is molybdenite (MoS2). Molybdenum is mined
as a principal ore and is also recovered as a byproduct of copper and
tungsten mining.
The world's production of molybdenum was 250,000 tonnes in 2011, the
largest producers being China (94,000 t), the United States (64,000
t), Chile (38,000 t), Peru (18,000 t) and Mexico (12,000 t). The total
reserves are estimated at 10 million tonnes, and are mostly
concentrated in China (4.3 Mt), the US (2.7 Mt) and Chile (1.2 Mt). By
continent, 93% of world molybdenum production is about evenly shared
between North America, South America (mainly in Chile), and China.
Europe and the rest of Asia (mostly Armenia, Russia, Iran and
Mongolia) produce the remainder.
In molybdenite processing, the ore is first roasted in air at a
temperature of 700 °C. The process gives gaseous sulfur dioxide and
the molybdenum(VI) oxide:
:2MoS2 + 7O2 -> 2MoO3 + 4SO2
The resulting oxide is then usually extracted with aqueous ammonia to
give ammonium molybdate:
:MoO3 + 2NH3 + H2O -> (NH4)2(MoO4)
Copper, an impurity in molybdenite, is separated at this stage by
treatment with hydrogen sulfide. Ammonium molybdate converts to
ammonium dimolybdate, which is isolated as a solid. Heating this solid
gives molybdenum trioxide:
: (NH4)2Mo2O7 -> 2MoO3 + 2NH3 + H2O
Crude trioxide can be further purified by sublimation at 1100 °C.
Metallic molybdenum is produced by reduction of the oxide with
hydrogen:
:MoO3 + 3H2 -> Mo + 3H2O
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 had 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 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.
Mining
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The Knaben mine in southern Norway, opened in 1885, was the first
dedicated molybdenum mine. Closed in 1973 but reopened in 2007, it now
produces of molybdenum disulfide per year. Large mines in Colorado
(such as the Henderson mine and the 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.
Alloys
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About 86% of molybdenum produced is used in metallurgy, with the rest
used in chemical applications. The estimated global use is structural
steel 35%, stainless steel 25%, chemicals 14%, tool & high-speed
steels 9%, cast iron 6%, molybdenum elemental metal 6%, and
superalloys 5%.
Molybdenum can withstand extreme temperatures without significantly
expanding or softening, making it useful in environments of intense
heat, including military armor, aircraft parts, electrical contacts,
industrial motors, and supports for filaments in light bulbs.
Most high-strength steel alloys (for example, 41xx steels) contain
0.25% to 8% molybdenum. Even in these small portions, more than 43,000
tonnes of molybdenum are used each year in stainless steels, tool
steels, cast irons, and high-temperature superalloys.
Molybdenum is also used in steel alloys for its high corrosion
resistance and weldability. Molybdenum contributes corrosion
resistance to type-300 stainless steels (specifically type-316) and
especially so in the so-called superaustenitic stainless steels (such
as alloy AL-6XN, 254SMO and 1925hMo). Molybdenum increases lattice
strain, thus increasing the energy required to dissolve iron atoms
from the surface. Molybdenum is also used to enhance the corrosion
resistance of ferritic (for example grade 444) and martensitic (for
example 1.4122 and 1.4418) stainless steels.
Because of its lower density and more stable price, molybdenum is
sometimes used in place 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 also be used as a
flame-resistant coating for other metals. Although its melting point
is 2623 °C, molybdenum rapidly oxidizes at temperatures above 760 °C
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 1300 °C. 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 reactors for 1100 hours with so little corrosion
that it was difficult to measure. Due to its excellent mechanical
properties under high temperature and high pressure, TZM alloys are
extensively applied in the military industry. It is used as the valve
body of torpedo engines, rocket nozzles and gas pipelines, where it
can withstand extreme thermal and mechanical stresses. It is also
used as radiation shields in nuclear applications.
Other molybdenum-based alloys that do not contain iron have only
limited applications. For example, because of its resistance to molten
zinc, both pure molybdenum and molybdenum-tungsten alloys (70%/30%)
are used for piping, stirrers and pump impellers that come into
contact with molten zinc.
Pure element applications
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* Molybdenum powder is used as a fertilizer for some plants, such as
cauliflower.
* Elemental molybdenum is used in NO, NO2, NOx analyzers in power
plants for pollution controls. At 350 °C, the element acts as a
catalyst for NO2/NOx to form NO molecules for detection by infrared
light.
* Molybdenum anodes replace tungsten in certain low voltage X-ray
sources for specialized uses such as mammography.
* The radioactive isotope molybdenum-99 is used to generate
technetium-99m, used for medical imaging The isotope is handled and
stored as the molybdate.
Compound applications
=======================
* Molybdenum disulfide (MoS2) is used as a solid lubricant and a
high-pressure high-temperature (HPHT) anti-wear agent. It forms strong
films on metallic surfaces and is a common additive to HPHT greases --
in the event of a catastrophic grease failure, a thin layer of
molybdenum prevents contact of the lubricated parts.
* When combined with small amounts of cobalt, MoS2 is also used as a
catalyst in the hydrodesulfurization (HDS) of petroleum. In the
presence of hydrogen, this catalyst facilitates the removal of
nitrogen and especially sulfur from the feedstock, which otherwise
would poison downstream catalysts. HDS is one of the largest scale
applications of catalysis in industry.
* Molybdenum oxides are important catalysts for selective oxidation of
organic compounds. The production of the commodity chemicals
acrylonitrile and formaldehyde relies on MoO'x'-based catalysts.
* Molybdenum disilicide (MoSi2) is an electrically conducting ceramic
with primary use in heating elements operating at temperatures above
1500 °C in air.
* Molybdenum trioxide (MoO3) is used as an adhesive between enamels
and metals.
* Lead molybdate (wulfenite) co-precipitated with lead chromate and
lead sulfate is a bright-orange pigment used with ceramics and
plastics.
* The molybdenum-based mixed oxides are versatile catalysts in the
chemical industry. Some examples are the catalysts for the oxidation
of carbon monoxide, propylene to acrolein and acrylic acid, the
ammoxidation of propylene to acrylonitrile.
* Molybdenum carbides, nitride and phosphides can be used for
hydrotreatment of rapeseed oil.
* Ammonium heptamolybdate is used in biological staining.
* Molybdenum coated soda lime glass is used in CIGS (copper indium
gallium selenide) solar cells, called CIGS solar cells.
* Phosphomolybdic acid is a stain used in thin-layer chromatography
and trichrome staining in histochemistry.
Biological role
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Molybdenum, despite its low concentration in the environment, is a
critically important element for Earth's biosphere due to its presence
in the most common nitrogenases. Without molybdenum, nitrogen fixation
would be greatly reduced, and a large part of biosynthesis as we know
it would not occur. Molybdenum is also essential to many individual
organisms as a component of enzymes, particularly as part of the
molybdopterin class of cofactors.
Mo-containing enzymes
=======================
Molybdenum is an essential element in most organisms; a 2008 research
paper speculated that a scarcity of molybdenum in the Earth's early
oceans may have strongly influenced the evolution of eukaryotic life
(which includes all plants and animals).
At least 50 molybdenum-containing enzymes have been identified, mostly
in bacteria. Those enzymes include aldehyde oxidase, sulfite oxidase
and xanthine oxidase. With one exception, Mo in proteins is bound by
molybdopterin to give the molybdenum cofactor. The only known
exception is nitrogenase, which uses the FeMoco cofactor, which has
the formula Fe7MoS9C.
In terms of function, molybdoenzymes catalyze the oxidation and
sometimes reduction of certain small molecules in the process of
regulating nitrogen, sulfur, and carbon. 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. An extremely high concentration
of molybdenum reverses the trend and can inhibit purine catabolism and
other processes. Molybdenum concentration also affects protein
synthesis, metabolism, and growth.
Mo is a component in most nitrogenases. Among molybdoenzymes,
nitrogenases are unique in lacking the molybdopterin. electronic-book
electronic-
Nitrogenases catalyze the production of ammonia from atmospheric
nitrogen:
:
The biosynthesis of the FeMoco active site is highly complex.
Molybdate is transported in the body as MoO42−.
Human metabolism and deficiency
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Molybdenum is an essential trace dietary element. Four mammalian
Mo-dependent enzymes are known, all of them harboring a pterin-based
molybdenum cofactor (Moco) in their active site: sulfite oxidase,
xanthine oxidoreductase, aldehyde oxidase, and mitochondrial amidoxime
reductase. People severely deficient in molybdenum have poorly
functioning sulfite oxidase and are prone to toxic reactions to
sulfites in foods. The human body contains about 0.07 mg of molybdenum
per kilogram of body weight, with higher concentrations in the liver
and kidneys and lower in the vertebrae. Molybdenum is also present
within human tooth enamel and may help prevent its decay.
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.
Low soil concentration of molybdenum in a geographical band from
northern China to Iran results in a general dietary molybdenum
deficiency and is associated with increased rates of esophageal
cancer. Compared to the United States, which has a greater supply of
molybdenum in the soil, people living in those 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. Since pure molybdenum deficiency from this cause
occurs primarily in adults, the neurological consequences are not as
marked as in cases of congenital cofactor deficiency.
A congenital molybdenum cofactor deficiency disease, seen in infants,
is an inability to synthesize molybdenum cofactor, the heterocyclic
molecule discussed above that binds molybdenum at the active site in
all known human enzymes that use molybdenum. The resulting deficiency
results in high levels of sulfite and urate, and neurological damage.
Excretion
===========
Most molybdenum is excreted from the human body as molybdate in the
urine. Furthermore, urinary excretion of molybdenum increases as
dietary molybdenum intake increases. Small amounts of molybdenum are
excreted from the body in the feces by way of the bile; small amounts
also can be lost in sweat and in hair.
Excess and copper antagonism
==============================
High levels of molybdenum can interfere with the body's uptake of
copper, producing copper deficiency. Molybdenum prevents plasma
proteins from binding to copper, and it also increases the amount of
copper that is excreted in urine. Ruminants that consume high levels
of molybdenum suffer from diarrhea, stunted growth, anemia, and
achromotrichia (loss of fur pigment). These symptoms can be alleviated
by copper supplements, either dietary and injection. The 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 by inhibiting the
membrane translocation process that is dependent on copper ions. This
is a promising avenue for investigation of treatments for cancer,
age-related macular degeneration, and other diseases that involve a
pathologic proliferation of blood vessels.
In some grazing livestock, most strongly in cattle, molybdenum excess
in the soil of pasturage can produce scours (diarrhea) if the pH of
the soil is neutral to alkaline; see teartness.
Mammography
=============
Molybdenum targets are used in mammography because they produce X-rays
in the energy range of 17-20 keV, which is optimal for imaging soft
tissues like the breast. The characteristic X-rays emitted from
molybdenum provide high contrast between different types of tissues,
allowing for the effective visualization of microcalcifications and
other subtle abnormalities in breast tissue. This energy range also
minimizes radiation dose while maximizing image quality, making
molybdenum targets particularly suitable for breast cancer screening.
Dietary recommendations
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In 2000, the then U.S. Institute of Medicine (now the National Academy
of Medicine, NAM) updated its Estimated Average Requirements (EARs)
and Recommended Dietary Allowances (RDAs) for molybdenum. If there is
not sufficient information to establish EARs and RDAs, an estimate
designated Adequate Intake (AI) is used instead.
An AI of 2 micrograms (μg) of molybdenum per day was established for
infants up to 6 months of age, and 3 μg/day from 7 to 12 months of
age, both for males and females. For older children and adults, the
following daily RDAs have been established for molybdenum: 17 μg from
1 to 3 years of age, 22 μg from 4 to 8 years, 34 μg from 9 to 13
years, 43 μg from 14 to 18 years, and 45 μg for persons 19 years old
and older. All these RDAs are valid for both sexes. Pregnant or
lactating females from 14 to 50 years of age have a higher daily RDA
of 50 μg of molybdenum.
As for safety, the NAM sets tolerable upper intake levels (ULs) for
vitamins and minerals when evidence is sufficient. In the case of
molybdenum, the UL is 2000 μg/day. Collectively the EARs, RDAs, AIs
and ULs are referred to as Dietary Reference Intakes (DRIs).
The European Food Safety Authority (EFSA) refers to the collective set
of information as Dietary Reference Values, with Population Reference
Intake (PRI) instead of RDA, and Average Requirement instead of EAR.
AI and UL are defined the same as in the United States. For women and
men ages 15 and older, the AI is set at 65 μg/day. Pregnant and
lactating women have the same AI. For children aged 1-14 years, the
AIs increase with age from 15 to 45 μg/day. The adult AIs are higher
than the U.S. RDAs, but on the other hand, the European Food Safety
Authority reviewed the same safety question and set its UL at 600
μg/day, which is much lower than the U.S. value.
Labeling
==========
For U.S. food and dietary supplement labeling purposes, the amount in
a serving is expressed as a percent of Daily Value (%DV). For
molybdenum labeling purposes, 100% of the Daily Value was 75 μg, but
as of May 27, 2016 it was revised to 45 μg. A table of the old and new
adult daily values is provided at Reference Daily Intake.
Food sources
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Average daily intake varies between 120 and 240 μg/day, which is
higher than dietary recommendations. 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.
Precautions
======================================================================
Molybdenum dusts and fumes, 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. OSHA 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. At levels of 5000 mg/m3,
molybdenum is immediately dangerous to life and health.
See also
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* List of molybdenum mines
* Molybdenum mining in the United States
External links
======================================================================
* [
http://www.periodicvideos.com/videos/042.htm Molybdenum] at 'The
Periodic Table of Videos' (University of Nottingham)
* [
http://www.mineral-exploration.com/publications.htm Mineral &
Exploration] - Map of World Molybdenum Producers 2009
* [
https://books.google.com/books?id=td4DAAAAMBAJ&pg=PA63 "Mining
A Mountain" 'Popular Mechanics', July 1935 pp. 63-64]
* [
http://www.imoa.info/ Site for global molybdenum info]
* [
https://www.cdc.gov/niosh/npg/npgd0433.html CDC - NIOSH Pocket
Guide to Chemical Hazards]
License
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Molybdenum
