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Iron - Wikipedia

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(Top)

1Characteristics

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1.1Allotropes

1.2Melting and boiling points

1.3Magnetic properties

1.4Isotopes

2Origin and occurrence in nature

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2.1Cosmogenesis

2.2Metallic iron

2.3Mantle minerals

2.4Earth's crust

2.5Oceans

3Chemistry and compounds

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3.1Binary compounds

3.1.1Oxides and sulfides

3.1.2Halides

3.2Solution chemistry

3.3Coordination compounds

3.4Organometallic compounds

3.5Industrial uses

4History

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4.1Development of iron metallurgy

4.1.1Meteoritic iron

4.1.2Wrought iron

4.1.3Cast iron

4.1.4Steel

4.2Foundations of modern chemistry

5Symbolic role

6Production of metallic iron

Toggle Production of metallic iron subsection

6.1Laboratory routes

6.2Main industrial route

6.2.1Blast furnace processing

6.2.2Steelmaking

6.3Direct iron reduction

6.4Thermite process

6.5Molten oxide electrolysis

7Applications

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7.1As structural material

7.1.1Mechanical properties

7.1.2Types of steels and alloys

7.2Catalysts and reagents

7.3Iron compounds

8Biological and pathological role

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8.1Biochemistry

8.2Nutrition

8.2.1Diet

8.2.2Dietary recommendations

8.3Deficiency

8.4Excess

8.5ADHD

8.6Cancer

8.7Marine systems

9See also

10References

11Bibliography

12Further reading

13External links

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Iron

216 languages

AfrikaansAlemannischአማርኛAnarâškielâअंगिकाÆngliscالعربيةAragonésܐܪܡܝܐArmãneashtiঅসমীয়াAsturianuअवधीAvañe'ẽAzərbaycancaتۆرکجهBasa BaliবাংলাBanjarBân-lâm-gúБашҡортсаБеларускаяБеларуская (тарашкевіца)भोजपुरीBikol CentralBislamaБългарскиབོད་ཡིགBosanskiBrezhonegБуряадCatalàЧӑвашлаCebuanoČeštinaChiShonaCorsuCymraegDagbanliDanskالدارجةDeutschދިވެހިބަސްDiné bizaadEestiΕλληνικάЭрзяньEspañolEsperantoEstremeñuEuskaraفارسیFiji HindiFøroysktFrançaisFryskFurlanGaeilgeGaelgGàidhligGalegoГӀалгӀай贛語Gĩkũyũગુજરાતીगोंयची कोंकणी / Gõychi Konknni客家語/Hak-kâ-ngîХальмг한국어Հայերենहिन्दीHrvatskiBahasa HulontaloIdoBahasa IndonesiaInterlinguaInterlingueИронIsiZuluÍslenskaItalianoעבריתJawaKabɩyɛಕನ್ನಡქართულიҚазақшаKernowekKiswahiliКомиKongoKotavaKreyòl ayisyenKriyòl gwiyannenKurdîКыргызчаLadinЛаккуLatinaLatviešuLëtzebuergeschЛезгиLietuviųLigureLimburgsLingálaLingua Franca NovaLivvinkarjalaLa .lojban.LugandaLombardMagyarमैथिलीМакедонскиMalagasyമലയാളംMaltiMāoriमराठीმარგალურიمصرىBahasa Melayuꯃꯤꯇꯩ ꯂꯣꯟMinangkabau閩東語 / Mìng-dĕ̤ng-ngṳ̄МокшеньМонголမြန်မာဘာသာNāhuatlNa Vosa VakavitiNederlandsNedersaksiesनेपालीनेपाल भाषा日本語NapulitanoNordfriiskNorfuk / PitkernNorsk bokmålNorsk nynorskNouormandOccitanଓଡ଼ିଆOromooOʻzbekcha / ўзбекчаਪੰਜਾਬੀPangcahپنجابیပအိုဝ်ႏဘာႏသာႏPapiamentuپښتوPatoisПерем комиPiemontèisPlattdüütschPolskiPortuguêsQaraqalpaqshaRipoarischRomânăRuna SimiРусиньскыйРусскийСаха тылаसंस्कृतम्ᱥᱟᱱᱛᱟᱲᱤSarduScotsSeelterskShqipSicilianuසිංහලSimple EnglishسنڌيSlovenčinaSlovenščinaСловѣньскъ / ⰔⰎⰑⰂⰡⰐⰠⰔⰍⰟSoomaaligaکوردیСрпски / srpskiSrpskohrvatski / српскохрватскиSundaSuomiSvenskaTagalogதமிழ்TaqbaylitТатарча / tatarçaతెలుగుไทยThuɔŋjäŋТоҷикӣᏣᎳᎩತುಳುTürkçeУкраїнськаاردوئۇيغۇرچە / UyghurcheVahcuenghVènetoVepsän kel’Tiếng ViệtVolapükVõroWalon文言West-VlamsWinaray吴语ייִדישYorùbá粵語ZazakiŽemaitėška中文ⵜⴰⵎⴰⵣⵉⵖⵜ ⵜⴰⵏⴰⵡⴰⵢⵜ

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From Wikipedia, the free encyclopedia

This article is about the metallic element. For other uses, see Iron (disambiguation).

Chemical element, symbol Fe and atomic number 26Iron, 26FeIronPronunciation/ˈaɪərn/ Allotropessee Allotropes of ironAppearancelustrous metallic with a grayish tingeStandard atomic weight Ar°(Fe)55.845±0.002[1]55.845±0.002 (abridged)[2]

Iron in the periodic table

Hydrogen

Helium

Lithium

Beryllium

Boron

Carbon

Nitrogen

Oxygen

Fluorine

Neon

Sodium

Magnesium

Aluminium

Silicon

Phosphorus

Sulfur

Chlorine

Argon

Potassium

Calcium

Scandium

Titanium

Vanadium

Chromium

Manganese

Iron

Cobalt

Nickel

Copper

Zinc

Gallium

Germanium

Arsenic

Selenium

Bromine

Krypton

Rubidium

Strontium

Yttrium

Zirconium

Niobium

Molybdenum

Technetium

Ruthenium

Rhodium

Palladium

Silver

Cadmium

Indium

Tin

Antimony

Tellurium

Iodine

Xenon

Caesium

Barium

Lanthanum

Cerium

Praseodymium

Neodymium

Promethium

Samarium

Europium

Gadolinium

Terbium

Dysprosium

Holmium

Erbium

Thulium

Ytterbium

Lutetium

Hafnium

Tantalum

Tungsten

Rhenium

Osmium

Iridium

Platinum

Gold

Mercury (element)

Thallium

Lead

Bismuth

Polonium

Astatine

Radon

Francium

Radium

Actinium

Thorium

Protactinium

Uranium

Neptunium

Plutonium

Americium

Curium

Berkelium

Californium

Einsteinium

Fermium

Mendelevium

Nobelium

Lawrencium

Rutherfordium

Dubnium

Seaborgium

Bohrium

Hassium

Meitnerium

Darmstadtium

Roentgenium

Copernicium

Nihonium

Flerovium

Moscovium

Livermorium

Tennessine

Oganesson

–↑Fe↓Ru

manganese ← iron → cobalt

Atomic number (Z)26Groupgroup 8Periodperiod 4Block  d-blockElectron configuration[Ar] 3d6 4s2Electrons per shell2, 8, 14, 2Physical propertiesPhase at STPsolidMelting point1811 K ​(1538 °C, ​2800 °F) Boiling point3134 K ​(2861 °C, ​5182 °F) Density (near r.t.)7.874 g/cm3when liquid (at m.p.)6.98 g/cm3 Heat of fusion13.81 kJ/mol Heat of vaporization340 kJ/mol Molar heat capacity25.10 J/(mol·K) Vapor pressure

P (Pa)

1

10

100

1 k

10 k

100 k

at T (K)

1728

1890

2091

2346

2679

3132

Atomic propertiesOxidation states−4, −2, −1, 0, +1,[3] +2, +3, +4, +5,[4] +6, +7[5] (an amphoteric oxide)ElectronegativityPauling scale: 1.83 Ionization energies1st: 762.5 kJ/mol 2nd: 1561.9 kJ/mol 3rd: 2957 kJ/mol (more) Atomic radiusempirical: 126 pm Covalent radiusLow spin: 132±3 pmHigh spin: 152±6 pm Van der Waals radius194 [1] pm Spectral lines of ironOther propertiesNatural occurrenceprimordialCrystal structureα-Fe: ​body-centered cubic (bcc) (cI2)Lattice constanta = 286.65 pm (at 20 °C)[6]Crystal structureγ-Fe (912–1394 °C): ​face-centered cubic (fcc) (cF4)Lattice constanta = 364.68 pm (at 916°C)[7]Thermal expansion11.8 µm/(m⋅K) (at 25 °C) Thermal conductivity80.4 W/(m⋅K) Electrical resistivity96.1 nΩ⋅m (at 20 °C) Curie point1043 K Magnetic orderingferromagnetic Young's modulus211 GPa Shear modulus82 GPa Bulk modulus170 GPa Speed of sound thin rod5120 m/s (at r.t.) (electrolytic)Poisson ratio0.29 Mohs hardness4 Vickers hardness608 MPa Brinell hardness200–1180 MPa CAS Number7439-89-6 HistoryDiscoverybefore 5000 BCSymbol"Fe": from Latin ferrumIsotopes of ironve

Main isotopes[8]

Decay

abun­dance

half-life (t1/2)

mode

pro­duct

54Fe

5.85%

stable

55Fe

synth

2.73 y

ε

55Mn

56Fe

91.8%

stable

57Fe

2.12%

stable

58Fe

0.28%

stable

59Fe

synth

44.6 d

β−

59Co

60Fe

trace

2.6×106 y

β−

60Co

 Category: Ironviewtalkedit | references

Iron is a chemical element; it has symbol Fe (from Latin ferrum 'iron') and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust, being mainly deposited by meteorites in its metallic state.

Extracting usable metal from iron ores requires kilns or furnaces capable of reaching 1,500 °C (2,730 °F), about 500 °C (932 °F) higher than that required to smelt copper. Humans started to master that process in Eurasia during the 2nd millennium BC and the use of iron tools and weapons began to displace copper alloys – in some regions, only around 1200 BC. That event is considered the transition from the Bronze Age to the Iron Age. In the modern world, iron alloys, such as steel, stainless steel, cast iron and special steels, are by far the most common industrial metals, due to their mechanical properties and low cost. The iron and steel industry is thus very important economically, and iron is the cheapest metal, with a price of a few dollars per kilogram or pound.

Pristine and smooth pure iron surfaces are a mirror-like silvery-gray. Iron reacts readily with oxygen and water to produce brown-to-black hydrated iron oxides, commonly known as rust. Unlike the oxides of some other metals that form passivating layers, rust occupies more volume than the metal and thus flakes off, exposing more fresh surfaces for corrosion. Chemically, the most common oxidation states of iron are iron(II) and iron(III). Iron shares many properties of other transition metals, including the other group 8 elements, ruthenium and osmium. Iron forms compounds in a wide range of oxidation states, −4 to +7. Iron also forms many coordination compounds; some of them, such as ferrocene, ferrioxalate, and Prussian blue have substantial industrial, medical, or research applications.

The body of an adult human contains about 4 grams (0.005% body weight) of iron, mostly in hemoglobin and myoglobin. These two proteins play essential roles in oxygen transport by blood and oxygen storage in muscles. To maintain the necessary levels, human iron metabolism requires a minimum of iron in the diet. Iron is also the metal at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals.[9]

Characteristics

Allotropes

Main article: Allotropes of iron

Molar volume vs. pressure for α iron at room temperature

At least four allotropes of iron (differing atom arrangements in the solid) are known, conventionally denoted α, γ, δ, and ε.

The first three forms are observed at ordinary pressures. As molten iron cools past its freezing point of 1538 °C, it crystallizes into its δ allotrope, which has a body-centered cubic (bcc) crystal structure. As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered cubic (fcc) crystal structure, or austenite. At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope.[10]

The physical properties of iron at very high pressures and temperatures have also been studied extensively,[11][12] because of their relevance to theories about the cores of the Earth and other planets. Above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into another hexagonal close-packed (hcp) structure, which is also known as ε-iron. The higher-temperature γ-phase also changes into ε-iron, but does so at higher pressure.

Some controversial experimental evidence exists for a stable β phase at pressures above 50 GPa and temperatures of at least 1500 K. It is supposed to have an orthorhombic or a double hcp structure.[13] (Confusingly, the term "β-iron" is sometimes also used to refer to α-iron above its Curie point, when it changes from being ferromagnetic to paramagnetic, even though its crystal structure has not changed.[10])

The inner core of the Earth is generally presumed to consist of an iron-nickel alloy with ε (or β) structure.[14]

Melting and boiling points

Low-pressure phase diagram of pure iron

The melting and boiling points of iron, along with its enthalpy of atomization, are lower than those of the earlier 3d elements from scandium to chromium, showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and more into the inert core by the nucleus;[15] however, they are higher than the values for the previous element manganese because that element has a half-filled 3d sub-shell and consequently its d-electrons are not easily delocalized. This same trend appears for ruthenium but not osmium.[16]

The melting point of iron is experimentally well defined for pressures less than 50 GPa. For greater pressures, published data (as of 2007) still varies by tens of gigapascals and over a thousand kelvin.[17]

Magnetic properties

Magnetization curves of 9 ferromagnetic materials, showing saturation. 1. Sheet steel, 2. Silicon steel, 3. Cast steel, 4. Tungsten steel, 5. Magnet steel, 6. Cast iron, 7. Nickel, 8. Cobalt, 9. Magnetite[18]

Below its Curie point of 770 °C (1,420 °F; 1,040 K), α-iron changes from paramagnetic to ferromagnetic: the spins of the two unpaired electrons in each atom generally align with the spins of its neighbors, creating an overall magnetic field.[19] This happens because the orbitals of those two electrons (dz2 and dx2 −. y2) do not point toward neighboring atoms in the lattice, and therefore are not involved in metallic bonding.[10]

In the absence of an external source of magnetic field, the atoms get spontaneously partitioned into magnetic domains, about 10 micrometers across,[20] such that the atoms in each domain have parallel spins, but some domains have other orientations. Thus a macroscopic piece of iron will have a nearly zero overall magnetic field.

Application of an external magnetic field causes the domains that are magnetized in the same general direction to grow at the expense of adjacent ones that point in other directions, reinforcing the external field. This effect is exploited in devices that need to channel magnetic fields to fulfill design function, such as electrical transformers, magnetic recording heads, and electric motors. Impurities, lattice defects, or grain and particle boundaries can "pin" the domains in the new positions, so that the effect persists even after the external field is removed – thus turning the iron object into a (permanent) magnet.[19]

Similar behavior is exhibited by some iron compounds, such as the ferrites including the mineral magnetite, a crystalline form of the mixed iron(II,III) oxide Fe3O4 (although the atomic-scale mechanism, ferrimagnetism, is somewhat different). Pieces of magnetite with natural permanent magnetization (lodestones) provided the earliest compasses for navigation. Particles of magnetite were extensively used in magnetic recording media such as core memories, magnetic tapes, floppies, and disks, until they were replaced by cobalt-based materials.

Isotopes

Main article: Isotopes of iron

Iron has four stable isotopes: 54Fe (5.845% of natural iron), 56Fe (91.754%), 57Fe (2.119%) and 58Fe (0.282%). Twenty-four artificial isotopes have also been created. Of these stable isotopes, only 57Fe has a nuclear spin (−1⁄2). The nuclide 54Fe theoretically can undergo double electron capture to 54Cr, but the process has never been observed and only a lower limit on the half-life of 3.1×1022 years has been established.[21]

60Fe is an extinct radionuclide of long half-life (2.6 million years).[22] It is not found on Earth, but its ultimate decay product is its granddaughter, the stable nuclide 60Ni.[21] Much of the past work on isotopic composition of iron has focused on the nucleosynthesis of 60Fe through studies of meteorites and ore formation. In the last decade, advances in mass spectrometry have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work is driven by the Earth and planetary science communities, although applications to biological and industrial systems are emerging.[23]

In phases of the meteorites Semarkona and Chervony Kut, a correlation between the concentration of 60Ni, the granddaughter of 60Fe, and the abundance of the stable iron isotopes provided evidence for the existence of 60Fe at the time of formation of the Solar System. Possibly the energy released by the decay of 60Fe, along with that released by 26Al, contributed to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of 60Ni present in extraterrestrial material may bring further insight into the origin and early history of the Solar System.[24]

The most abundant iron isotope 56Fe is of particular interest to nuclear scientists because it represents the most common endpoint of nucleosynthesis.[25] Since 56Ni (14 alpha particles) is easily produced from lighter nuclei in the alpha process in nuclear reactions in supernovae (see silicon burning process), it is the endpoint of fusion chains inside extremely massive stars, since addition of another alpha particle, resulting in 60Zn, requires a great deal more energy. This 56Ni, which has a half-life of about 6 days, is created in quantity in these stars, but soon decays by two successive positron emissions within supernova decay products in the supernova remnant gas cloud, first to radioactive 56Co, and then to stable 56Fe. As such, iron is the most abundant element in the core of red giants, and is the most abundant metal in iron meteorites and in the dense metal cores of planets such as Earth.[26] It is also very common in the universe, relative to other stable metals of approximately the same atomic weight.[26][27] Iron is the sixth most abundant element in the universe, and the most common refractory element.[28]

Photon mass attenuation coefficient for iron

Although a further tiny energy gain could be extracted by synthesizing 62Ni, which has a marginally higher binding energy than 56Fe, conditions in stars are unsuitable for this process. Element production in supernovas greatly favor iron over nickel, and in any case, 56Fe still has a lower mass per nucleon than 62Ni due to its higher fraction of lighter protons.[29] Hence, elements heavier than iron require a supernova for their formation, involving rapid neutron capture by starting 56Fe nuclei.[26]

In the far future of the universe, assuming that proton decay does not occur, cold fusion occurring via quantum tunnelling would cause the light nuclei in ordinary matter to fuse into 56Fe nuclei. Fission and alpha-particle emission would then make heavy nuclei decay into iron, converting all stellar-mass objects to cold spheres of pure iron.[30]

Origin and occurrence in nature

Cosmogenesis

Iron's abundance in rocky planets like Earth is due to its abundant production during the runaway fusion and explosion of type Ia supernovae, which scatters the iron into space.[31][32]

Metallic iron

A polished and chemically etched piece of an iron meteorite, believed to be similar in composition to the Earth's metallic core, showing individual crystals of the iron-nickel alloy (Widmanstatten pattern)

Metallic or native iron is rarely found on the surface of the Earth because it tends to oxidize. However, both the Earth's inner and outer core, which together account for 35% of the mass of the whole Earth, are believed to consist largely of an iron alloy, possibly with nickel. Electric currents in the liquid outer core are believed to be the origin of the Earth's magnetic field. The other terrestrial planets (Mercury, Venus, and Mars) as well as the Moon are believed to have a metallic core consisting mostly of iron. The M-type asteroids are also believed to be partly or mostly made of metallic iron alloy.

The rare iron meteorites are the main form of natural metallic iron on the Earth's surface. Items made of cold-worked meteoritic iron have been found in various archaeological sites dating from a time when iron smelting had not yet been developed; and the Inuit in Greenland have been reported to use iron from the Cape York meteorite for tools and hunting weapons.[33] About 1 in 20 meteorites consist of the unique iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron).[34] Native iron is also rarely found in basalts that have formed from magmas that have come into contact with carbon-rich sedimentary rocks, which have reduced the oxygen fugacity sufficiently for iron to crystallize. This is known as telluric iron and is described from a few localities, such as Disko Island in West Greenland, Yakutia in Russia and Bühl in Germany.[35]

Mantle minerals

Ferropericlase (Mg,Fe)O, a solid solution of periclase (MgO) and wüstite (FeO), makes up about 20% of the volume of the lower mantle of the Earth, which makes it the second most abundant mineral phase in that region after silicate perovskite (Mg,Fe)SiO3; it also is the major host for iron in the lower mantle.[36] At the bottom of the transition zone of the mantle, the reaction γ-(Mg,Fe)2[SiO4] ↔ (Mg,Fe)[SiO3] + (Mg,Fe)O transforms γ-olivine into a mixture of silicate perovskite and ferropericlase and vice versa. In the literature, this mineral phase of the lower mantle is also often called magnesiowüstite.[37] Silicate perovskite may form up to 93% of the lower mantle,[38] and the magnesium iron form, (Mg,Fe)SiO3, is considered to be the most abundant mineral in the Earth, making up 38% of its volume.[39]

Earth's crust

Ochre path in Roussillon

While iron is the most abundant element on Earth, most of this iron is concentrated in the inner and outer cores.[40][41] The fraction of iron that is in Earth's crust only amounts to about 5% of the overall mass of the crust and is thus only the fourth most abundant element in that layer (after oxygen, silicon, and aluminium).[42]

Most of the iron in the crust is combined with various other elements to form many iron minerals. An important class is the iron oxide minerals such as hematite (Fe2O3), magnetite (Fe3O4), and siderite (FeCO3), which are the major ores of iron. Many igneous rocks also contain the sulfide minerals pyrrhotite and pentlandite.[43][44] During weathering, iron tends to leach from sulfide deposits as the sulfate and from silicate deposits as the bicarbonate. Both of these are oxidized in aqueous solution and precipitate in even mildly elevated pH as iron(III) oxide.[45]

Banded iron formation in McKinley Park, Minnesota

Large deposits of iron are banded iron formations, a type of rock consisting of repeated thin layers of iron oxides alternating with bands of iron-poor shale and chert. The banded iron formations were laid down in the time between 3,700 million years ago and 1,800 million years ago.[46][47]

Materials containing finely ground iron(III) oxides or oxide-hydroxides, such as ochre, have been used as yellow, red, and brown pigments since pre-historical times. They contribute as well to the color of various rocks and clays, including entire geological formations like the Painted Hills in Oregon and the Buntsandstein ("colored sandstone", British Bunter).[48] Through Eisensandstein (a jurassic 'iron sandstone', e.g. from Donzdorf in Germany)[49] and Bath stone in the UK, iron compounds are responsible for the yellowish color of many historical buildings and sculptures.[50] The proverbial red color of the surface of Mars is derived from an iron oxide-rich regolith.[51]

Significant amounts of iron occur in the iron sulfide mineral pyrite (FeS2), but it is difficult to extract iron from it and it is therefore not exploited.[52] In fact, iron is so common that production generally focuses only on ores with very high quantities of it.[53]

According to the International Resource Panel's Metal Stocks in Society report, the global stock of iron in use in society is 2,200 kg per capita. More-developed countries differ in this respect from less-developed countries (7,000–14,000 vs 2,000 kg per capita).[54]

Oceans

Ocean science demonstrated the role of the iron in the ancient seas in both marine biota and climate.[55]

Chemistry and compounds

See also: Category:Iron compounds

Oxidation state

Representative compound

−4 (d10s2)

[FeIn6−xSnx][56]

−2 (d10)

Disodium tetracarbonylferrate (Collman's reagent)

−1 (d9)

Fe2(CO)2−8

0 (d8)

Iron pentacarbonyl

1 (d7)

Cyclopentadienyliron dicarbonyl dimer ("Fp2")

2 (d6)

Ferrous sulfate, Ferrocene

3 (d5)

Ferric chloride, Ferrocenium tetrafluoroborate

4 (d4)

Fe(diars)2Cl2+2, FeO(BF4)2

5 (d3)

FeO3−4

6 (d2)

Potassium ferrate

7 (d1)

[FeO4]– (matrix isolation, 4K)

Iron shows the characteristic chemical properties of the transition metals, namely the ability to form variable oxidation states differing by steps of one and a very large coordination and organometallic chemistry: indeed, it was the discovery of an iron compound, ferrocene, that revolutionalized the latter field in the 1950s.[57] Iron is sometimes considered as a prototype for the entire block of transition metals, due to its abundance and the immense role it has played in the technological progress of humanity.[58] Its 26 electrons are arranged in the configuration [Ar]3d64s2, of which the 3d and 4s electrons are relatively close in energy, and thus a number of electrons can be ionized.[16]

Iron forms compounds mainly in the oxidation states +2 (iron(II), "ferrous") and +3 (iron(III), "ferric"). Iron also occurs in higher oxidation states, e.g., the purple potassium ferrate (K2FeO4), which contains iron in its +6 oxidation state. The anion [FeO4]– with iron in its +7 oxidation state, along with an iron(V)-peroxo isomer, has been detected by infrared spectroscopy at 4 K after cocondensation of laser-ablated Fe atoms with a mixture of O2/Ar.[59] Iron(IV) is a common intermediate in many biochemical oxidation reactions.[60][61] Numerous organoiron compounds contain formal oxidation states of +1, 0, −1, or even −2. The oxidation states and other bonding properties are often assessed using the technique of Mössbauer spectroscopy.[62] Many mixed valence compounds contain both iron(II) and iron(III) centers, such as magnetite and Prussian blue (Fe4(Fe[CN]6)3).[61] The latter is used as the traditional "blue" in blueprints.[63]

Iron is the first of the transition metals that cannot reach its group oxidation state of +8, although its heavier congeners ruthenium and osmium can, with ruthenium having more difficulty than osmium.[10] Ruthenium exhibits an aqueous cationic chemistry in its low oxidation states similar to that of iron, but osmium does not, favoring high oxidation states in which it forms anionic complexes.[10] In the second half of the 3d transition series, vertical similarities down the groups compete with the horizontal similarities of iron with its neighbors cobalt and nickel in the periodic table, which are also ferromagnetic at room temperature and share similar chemistry. As such, iron, cobalt, and nickel are sometimes grouped together as the iron triad.[58]

Unlike many other metals, iron does not form amalgams with mercury. As a result, mercury is traded in standardized 76 pound flasks (34 kg) made of iron.[64]

Iron is by far the most reactive element in its group; it is pyrophoric when finely divided and dissolves easily in dilute acids, giving Fe2+. However, it does not react with concentrated nitric acid and other oxidizing acids due to the formation of an impervious oxide layer, which can nevertheless react with hydrochloric acid.[10] High-purity iron, called electrolytic iron, is considered to be resistant to rust, due to its oxide layer.

Binary compounds

Oxides and sulfides

Ferrous or iron(II) oxide, FeOFerric or iron(III) oxide Fe2O3Ferrosoferric or iron(II,III) oxide Fe3O4

Iron forms various oxide and hydroxide compounds; the most common are iron(II,III) oxide (Fe3O4), and iron(III) oxide (Fe2O3). Iron(II) oxide also exists, though it is unstable at room temperature. Despite their names, they are actually all non-stoichiometric compounds whose compositions may vary.[65] These oxides are the principal ores for the production of iron (see bloomery and blast furnace). They are also used in the production of ferrites, useful magnetic storage media in computers, and pigments. The best known sulfide is iron pyrite (FeS2), also known as fool's gold owing to its golden luster.[61] It is not an iron(IV) compound, but is actually an iron(II) polysulfide containing Fe2+ and S2−2 ions in a distorted sodium chloride structure.[65]

Pourbaix diagram of iron

Halides

Hydrated iron(III) chloride (ferric chloride)

The binary ferrous and ferric halides are well-known. The ferrous halides typically arise from treating iron metal with the corresponding hydrohalic acid to give the corresponding hydrated salts.[61]

Fe + 2 HX → FeX2 + H2 (X = F, Cl, Br, I)

Iron reacts with fluorine, chlorine, and bromine to give the corresponding ferric halides, ferric chloride being the most common.[66]

2 Fe + 3 X2 → 2 FeX3 (X = F, Cl, Br)

Ferric iodide is an exception, being thermodynamically unstable due to the oxidizing power of Fe3+ and the high reducing power of I−:[66]

2 I− + 2 Fe3+ → I2 + 2 Fe2+ (E0 = +0.23 V)

Ferric iodide, a black solid, is not stable in ordinary conditions, but can be prepared through the reaction of iron pentacarbonyl with iodine and carbon monoxide in the presence of hexane and light at the temperature of −20 °C, with oxygen and water excluded.[66]Complexes of ferric iodide with some soft bases are known to be stable compounds.[67][68]

Solution chemistry

Comparison of colors of solutions of ferrate (left) and permanganate (right)

The standard reduction potentials in acidic aqueous solution for some common iron ions are given below:[10]

[Fe(H2O)6]2+ + 2 e−

⇌ Fe

E0 = −0.447 V

[Fe(H2O)6]3+ + e−

⇌ [Fe(H2O)6]2+

E0 = +0.77 V

FeO2−4 + 8 H3O+ + 3 e−

⇌ [Fe(H2O)6]3+ + 6 H2O

E0 = +2.20 V

The red-purple tetrahedral ferrate(VI) anion is such a strong oxidizing agent that it oxidizes ammonia to nitrogen (N2) and water to oxygen[66]

4 FeO2−4 + 34 H2O → 4 [Fe(H2O)6]3+ + 20 OH− + 3 O2

The pale-violet hexaquo complex [Fe(H2O)6]3+ is an acid such that above pH 0 it is fully hydrolyzed:[69]

[Fe(H2O)6]3+

⇌ [Fe(H2O)5(OH)]2+ + H+

K = 10−3.05 mol dm−3

[Fe(H2O)5(OH)]2+

⇌ [Fe(H2O)4(OH)2]+ + H+

K = 10−3.26 mol dm−3

2[Fe(H2O)6]3+

⇌ [Fe(H2O)4(OH)]4+2 + 2H+ + 2H2O

K = 10−2.91 mol dm−3

Blue-green iron(II) sulfate heptahydrate

As pH rises above 0 the above yellow hydrolyzed species form and as it rises above 2–3, reddish-brown hydrous iron(III) oxide precipitates out of solution. Although Fe3+ has a d5 configuration, its absorption spectrum is not like that of Mn2+ with its weak, spin-forbidden d–d bands, because Fe3+ has higher positive charge and is more polarizing, lowering the energy of its ligand-to-metal charge transfer absorptions. Thus, all the above complexes are rather strongly colored, with the single exception of the hexaquo ion – and even that has a spectrum dominated by charge transfer in the near ultraviolet region.[69] On the other hand, the pale green iron(II) hexaquo ion [Fe(H2O)6]2+ does not undergo appreciable hydrolysis. Carbon dioxide is not evolved when carbonate anions are added, which instead results in white iron(II) carbonate being precipitated out. In excess carbon dioxide this forms the slightly soluble bicarbonate, which occurs commonly in groundwater, but it oxidises quickly in air to form iron(III) oxide that accounts for the brown deposits present in a sizeable number of streams.[70]

Coordination compounds

Due to its electronic structure, iron has a very large coordination and organometallic chemistry.

The two enantiomorphs of the ferrioxalate ion

Many coordination compounds of iron are known. A typical six-coordinate anion is hexachloroferrate(III), [FeCl6]3−, found in the mixed salt tetrakis(methylammonium) hexachloroferrate(III) chloride.[71][72] Complexes with multiple bidentate ligands have geometric isomers. For example, the trans-chlorohydridobis(bis-1,2-(diphenylphosphino)ethane)iron(II) complex is used as a starting material for compounds with the Fe(dppe)2 moiety.[73][74] The ferrioxalate ion with three oxalate ligands (shown at right) displays helical chirality with its two non-superposable geometries labelled Λ (lambda) for the left-handed screw axis and Δ (delta) for the right-handed screw axis, in line with IUPAC conventions.[69] Potassium ferrioxalate is used in chemical actinometry and along with its sodium salt undergoes photoreduction applied in old-style photographic processes. The dihydrate of iron(II) oxalate has a polymeric structure with co-planar oxalate ions bridging between iron centres with the water of crystallisation located forming the caps of each octahedron, as illustrated below.[75]

Crystal structure of iron(II) oxalate dihydrate, showing iron (gray), oxygen (red), carbon (black), and hydrogen (white) atoms.

Blood-red positive thiocyanate test for iron(III)

Iron(III) complexes are quite similar to those of chromium(III) with the exception of iron(III)'s preference for O-donor instead of N-donor ligands. The latter tend to be rather more unstable than iron(II) complexes and often dissociate in water. Many Fe–O complexes show intense colors and are used as tests for phenols or enols. For example, in the ferric chloride test, used to determine the presence of phenols, iron(III) chloride reacts with a phenol to form a deep violet complex:[69]

3 ArOH + FeCl3 → Fe(OAr)3 + 3 HCl (Ar = aryl)

Among the halide and pseudohalide complexes, fluoro complexes of iron(III) are the most stable, with the colorless [FeF5(H2O)]2− being the most stable in aqueous solution. Chloro complexes are less stable and favor tetrahedral coordination as in [FeCl4]−; [FeBr4]− and [FeI4]− are reduced easily to iron(II). Thiocyanate is a common test for the presence of iron(III) as it forms the blood-red [Fe(SCN)(H2O)5]2+. Like manganese(II), most iron(III) complexes are high-spin, the exceptions being those with ligands that are high in the spectrochemical series such as cyanide. An example of a low-spin iron(III) complex is [Fe(CN)6]3−. Iron shows a great variety of electronic spin states, including every possible spin quantum number value for a d-block element from 0 (diamagnetic) to 5⁄2 (5 unpaired electrons). This value is always half the number of unpaired electrons. Complexes with zero to two unpaired electrons are considered low-spin and those with four or five are considered high-spin.[65]

Iron(II) complexes are less stable than iron(III) complexes but the preference for O-donor ligands is less marked, so that for example [Fe(NH3)6]2+ is known while [Fe(NH3)6]3+ is not. They have a tendency to be oxidized to iron(III) but this can be moderated by low pH and the specific ligands used.[70]

Organometallic compounds

Iron penta-carbonyl

Organoiron chemistry is the study of organometallic compounds of iron, where carbon atoms are covalently bound to the metal atom. They are many and varied, including cyanide complexes, carbonyl complexes, sandwich and half-sandwich compounds.

Prussian blue

Prussian blue or "ferric ferrocyanide", Fe4[Fe(CN)6]3, is an old and well-known iron-cyanide complex, extensively used as pigment and in several other applications. Its formation can be used as a simple wet chemistry test to distinguish between aqueous solutions of Fe2+ and Fe3+ as they react (respectively) with potassium ferricyanide and potassium ferrocyanide to form Prussian blue.[61]

Another old example of an organoiron compound is iron pentacarbonyl, Fe(CO)5, in which a neutral iron atom is bound to the carbon atoms of five carbon monoxide molecules. The compound can be used to make carbonyl iron powder, a highly reactive form of metallic iron. Thermolysis of iron pentacarbonyl gives triiron dodecacarbonyl, Fe3(CO)12, a complex with a cluster of three iron atoms at its core. Collman's reagent, disodium tetracarbonylferrate, is a useful reagent for organic chemistry; it contains iron in the −2 oxidation state. Cyclopentadienyliron dicarbonyl dimer contains iron in the rare +1 oxidation state.[76]

Structural formula of ferrocene and a powdered sample

A landmark in this field was the discovery in 1951 of the remarkably stable sandwich compound ferrocene Fe(C5H5)2, by Pauson and Kealy[77] and independently by Miller and colleagues,[78] whose surprising molecular structure was determined only a year later by Woodward and Wilkinson[79] and Fischer.[80]

Ferrocene is still one of the most important tools and models in this class.[81]

Iron-centered organometallic species are used as catalysts. The Knölker complex, for example, is a transfer hydrogenation catalyst for ketones.[82]

Industrial uses

The iron compounds produced on the largest scale in industry are iron(II) sulfate (FeSO4·7H2O) and iron(III) chloride (FeCl3). The former is one of the most readily available sources of iron(II), but is less stable to aerial oxidation than Mohr's salt ((NH4)2Fe(SO4)2·6H2O). Iron(II) compounds tend to be oxidized to iron(III) compounds in the air.[61]

History

Main article: History of ferrous metallurgy

Development of iron metallurgy

Iron is one of the elements undoubtedly known to the ancient world.[83] It has been worked, or wrought, for millennia. However, iron artefacts of great age are much rarer than objects made of gold or silver due to the ease with which iron corrodes.[84] The technology developed slowly, and even after the discovery of smelting it took many centuries for iron to replace bronze as the metal of choice for tools and weapons.

Meteoritic iron

Iron harpoon head from Greenland. The iron edge covers a narwhal tusk harpoon using meteorite iron from the Cape York meteorite, one of the largest iron meteorites known.

Beads made from meteoric iron in 3500 BC or earlier were found in Gerzeh, Egypt by G.A. Wainwright.[85] The beads contain 7.5% nickel, which is a signature of meteoric origin since iron found in the Earth's crust generally has only minuscule nickel impurities.

Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools.[85] For example, a dagger made of meteoric iron was found in the tomb of Tutankhamun, containing similar proportions of iron, cobalt, and nickel to a meteorite discovered in the area, deposited by an ancient meteor shower.[86][87][88] Items that were likely made of iron by Egyptians date from 3000 to 2500 BC.[84]

Meteoritic iron is comparably soft and ductile and easily cold forged but may get brittle when heated because of the nickel content.[89]

Wrought iron

Main article: Wrought iron

Further information: Ancient iron production

The symbol for Mars has been used since antiquity to represent iron. The iron pillar of Delhi is an example of the iron extraction and processing methodologies of early India.

The first iron production started in the Middle Bronze Age, but it took several centuries before iron displaced bronze. Samples of smelted iron from Asmar, Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 3000 and 2700 BC.[90] The Hittites established an empire in north-central Anatolia around 1600 BC. They appear to be the first to understand the production of iron from its ores and regard it highly in their society.[91] The Hittites began to smelt iron between 1500 and 1200 BC and the practice spread to the rest of the Near East after their empire fell in 1180 BC.[90] The subsequent period is called the Iron Age.

Artifacts of smelted iron are found in India dating from 1800 to 1200 BC,[92] and in the Levant from about 1500 BC (suggesting smelting in Anatolia or the Caucasus).[93][94] Alleged references (compare history of metallurgy in South Asia) to iron in the Indian Vedas have been used for claims of a very early usage of iron in India respectively to date the texts as such. The rigveda term ayas (metal) refers to copper, while iron which is called as śyāma ayas, literally "black copper", first is mentioned in the post-rigvedic Atharvaveda.[95]

Some archaeological evidence suggests iron was smelted in Zimbabwe and southeast Africa as early as the eighth century BC.[96] Iron working was introduced to Greece in the late 11th century BC, from which it spread quickly throughout Europe.[97]

Iron sickle from Ancient Greece

The spread of ironworking in Central and Western Europe is associated with Celtic expansion. According to Pliny the Elder, iron use was common in the Roman era.[85] In the lands of what is now considered China, iron appears approximately 700–500 BC.[98] Iron smelting may have been introduced into China through Central Asia.[99] The earliest evidence of the use of a blast furnace in China dates to the 1st century AD,[100] and cupola furnaces were used as early as the Warring States period (403–221 BC).[101] Usage of the blast and cupola furnace remained widespread during the Tang and Song dynasties.[102]

During the Industrial Revolution in Britain, Henry Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative production systems. In 1783 he patented the puddling process for refining iron ore. It was later improved by others, including Joseph Hall.[103]

Cast iron

Main article: Cast iron

Cast iron was first produced in China during 5th century BC,[104] but was hardly in Europe until the medieval period.[105][106] The earliest cast iron artifacts were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture.[107] During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel.[108]

Coalbrookdale by Night, 1801. Blast furnaces light the iron making town of Coalbrookdale.

Medieval blast furnaces were about 10 feet (3.0 m) tall and made of fireproof brick; forced air was usually provided by hand-operated bellows.[106] Modern blast furnaces have grown much bigger, with hearths fourteen meters in diameter that allow them to produce thousands of tons of iron each day, but essentially operate in much the same way as they did during medieval times.[108]

In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron, replacing charcoal, although continuing to use blast furnaces. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper. Carbon content in iron was not implicated as the reason for the differences in properties of wrought iron, cast iron, and steel until the 18th century.[90]

Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative first iron bridge in 1778. This bridge still stands today as a monument to the role iron played in the Industrial Revolution. Following this, iron was used in rails, boats, ships, aqueducts, and buildings, as well as in iron cylinders in steam engines.[108] Railways have been central to the formation of modernity and ideas of progress[109] and various languages refer to railways as iron road (e.g. French chemin de fer, German Eisenbahn, Turkish demiryolu, Russian железная дорога, Chinese, Japanese, and Korean 鐵道, Vietnamese đường sắt).

Steel

Main article: Steel

See also: Steelmaking

Steel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery. Blacksmiths in Luristan in western Persia were making good steel by 1000 BC.[90] Then improved versions, Wootz steel by India and Damascus steel were developed around 300 BC and AD 500 respectively. These methods were specialized, and so steel did not become a major commodity until the 1850s.[110]

New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This made steel much more economical, thereby leading to wrought iron no longer being produced in large quantities.[111]

Foundations of modern chemistry

In 1774, Antoine Lavoisier used the reaction of water steam with metallic iron inside an incandescent iron tube to produce hydrogen in his experiments leading to the demonstration of the conservation of mass, which was instrumental in changing chemistry from a qualitative science to a quantitative one.[112]

Symbolic role

"Ich gab Gold für Eisen" – "I gave gold for iron". German-American brooch from WWI.

Iron plays a certain role in mythology and has found various usage as a metaphor and in folklore. The Greek poet Hesiod's Works and Days (lines 109–201) lists different ages of man named after metals like gold, silver, bronze and iron to account for successive ages of humanity.[113] The Iron Age was closely related with Rome, and in Ovid's Metamorphoses

The Virtues, in despair, quit the earth; and the depravity of man becomes universal and complete. Hard steel succeeded then.— Ovid, Metamorphoses, Book I, Iron age, line 160 ff

An example of the importance of iron's symbolic role may be found in the German Campaign of 1813. Frederick William III commissioned then the first Iron Cross as military decoration. Berlin iron jewellery reached its peak production between 1813 and 1815, when the Prussian royal family urged citizens to donate gold and silver jewellery for military funding. The inscription Ich gab Gold für Eisen (I gave gold for iron) was used as well in later war efforts.[114]

Production of metallic iron

Iron powder

Laboratory routes

For a few limited purposes when it is needed, pure iron is produced in the laboratory in small quantities by reducing the pure oxide or hydroxide with hydrogen, or forming iron pentacarbonyl and heating it to 250 °C so that it decomposes to form pure iron powder.[45] Another method is electrolysis of ferrous chloride onto an iron cathode.[115]

Main industrial route

See also: Iron ore

Iron production 2009 (million tonnes)[116][dubious – discuss]

Country

Iron ore

Pig iron

Direct iron

Steel

 China

1,114.9

549.4

573.6

 Australia

393.9

4.4

5.2

 Brazil

305.0

25.1

0.011

26.5

 Japan

66.9

87.5

 India

257.4

38.2

23.4

63.5

 Russia

92.1

43.9

4.7

60.0

 Ukraine

65.8

25.7

29.9

 South Korea

0.1

27.3

48.6

 Germany

0.4

20.1

0.38

32.7

World

1,594.9

914.0

64.5

1,232.4

Nowadays, the industrial production of iron or steel consists of two main stages. In the first stage, iron ore is reduced with coke in a blast furnace, and the molten metal is separated from gross impurities such as silicate minerals. This stage yields an alloy – pig iron – that contains relatively large amounts of carbon. In the second stage, the amount of carbon in the pig iron is lowered by oxidation to yield wrought iron, steel, or cast iron.[117] Other metals can be added at this stage to form alloy steels.

Blast furnace processing

Main article: Blast furnace

The blast furnace is loaded with iron ores, usually hematite Fe2O3 or magnetite Fe3O4, along with coke (coal that has been separately baked to remove volatile components) and flux (limestone or dolomite). "Blasts" of air pre-heated to 900 °C (sometimes with oxygen enrichment) is blown through the mixture, in sufficient amount to turn the carbon into carbon monoxide:[117]

2

C

+

O

2

⟶

2

CO

{\displaystyle {\ce {2 C + O2 -> 2 CO}}}

This reaction raises the temperature to about 2000 °C. The carbon monoxide reduces the iron ore to metallic iron[117]

Fe

2

O

3

+

3

CO

⟶

2

Fe

+

3

CO

2

{\displaystyle {\ce {Fe2O3 + 3 CO -> 2 Fe + 3 CO2}}}

Some iron in the high-temperature lower region of the furnace reacts directly with the coke:[117]

2

Fe

2

O

3

+

3

C

⟶

4

Fe

+

3

CO

2

{\displaystyle {\ce {2Fe2O3 + 3C -> 4Fe + 3CO2}}}

The flux removes silicaceous minerals in the ore, which would otherwise clog the furnace: The heat of the furnace decomposes the carbonates to calcium oxide, which reacts with any excess silica to form a slag composed of calcium silicate CaSiO3 or other products. At the furnace's temperature, the metal and the slag are both molten. They collect at the bottom as two immiscible liquid layers (with the slag on top), that are then easily separated.[117] The slag can be used as a material in road construction or to improve mineral-poor soils for agriculture.[106]

Steelmaking thus remains one of the largest industrial contributors of CO2 emissions in the world.[118]

17th century Chinese illustration of workers at a blast furnace, making wrought iron from pig iron[119]

How iron was extracted in the 19th century

Iron furnace in Columbus, Ohio, 1922

Steelmaking

Main articles: Steelmaking and Ironworks

The pig iron produced by the blast furnace process contains up to 4–5% carbon (by mass), with small amounts of other impurities like sulfur, magnesium, phosphorus, and manganese. This high level of carbon makes it relatively weak and brittle. Reducing the amount of carbon to 0.002–2.1% produces steel, which may be up to 1000 times harder than pure iron. A great variety of steel articles can then be made by cold working, hot rolling, forging, machining, etc. Removing the impurities from pig iron, but leaving 2–4% carbon, results in cast iron, which is cast by foundries into articles such as stoves, pipes, radiators, lamp-posts, and rails.[117]

Steel products often undergo various heat treatments after they are forged to shape. Annealing consists of heating them to 700–800 °C for several hours and then gradual cooling. It makes the steel softer and more workable.[120]

This heap of iron ore pellets will be used in steel production.

A pot of molten iron being used to make steel

Direct iron reduction

Owing to environmental concerns, alternative methods of processing iron have been developed. "Direct iron reduction" reduces iron ore to a ferrous lump called "sponge" iron or "direct" iron that is suitable for steelmaking.[106] Two main reactions comprise the direct reduction process:

Natural gas is partially oxidized (with heat and a catalyst):[106]

2

CH

4

+

O

2

⟶

2

CO

+

4

H

2

{\displaystyle {\ce {2 CH4 + O2 -> 2 CO + 4 H2}}}

Iron ore is then treated with these gases in a furnace, producing solid sponge iron:[106]

Fe

2

O

3

+

CO

+

2

H

2

⟶

2

Fe

+

CO

2

+

2

H

2

O

{\displaystyle {\ce {Fe2O3 + CO + 2 H2 -> 2 Fe + CO2 + 2 H2O}}}

Silica is removed by adding a limestone flux as described above.[106]

Thermite process

Main article: Thermite

Ignition of a mixture of aluminium powder and iron oxide yields metallic iron via the thermite reaction:

Fe

2

O

3

+

2

Al

⟶

2

Fe

+

Al

2

O

3

{\displaystyle {\ce {Fe2O3 + 2 Al -> 2 Fe + Al2O3}}}

Alternatively pig iron may be made into steel (with up to about 2% carbon) or wrought iron (commercially pure iron). Various processes have been used for this, including finery forges, puddling furnaces, Bessemer converters, open hearth furnaces, basic oxygen furnaces, and electric arc furnaces. In all cases, the objective is to oxidize some or all of the carbon, together with other impurities. On the other hand, other metals may be added to make alloy steels.[108]

Molten oxide electrolysis

Molten oxide electrolysis uses an alloy of chromium, iron and other metals that does not react with oxygen and a liquid iron cathode while the electrolyte is a mixture of molten metal oxides into which iron ore is dissolved. The current keeps the electrolyte molten, and reduces the iron oxide. In addition to pure liquid iron, put oxygen is also produced, which can be sold to offset part of the cost. Production cell size is variable and can be much smaller than conventional furnaces. The only cardon dioxide emissions come from the electricity used to heat and reduce the metal.[121]

Applications

Characteristic values of tensile strength (TS) and Brinell hardness (BH) of various forms of iron.[122][123]

Material

TS (MPa)

BH (Brinell)

Iron whiskers

11000

Ausformed (hardened) steel

2930

850–1200

Martensitic steel

2070

600

Bainitic steel

1380

400

Pearlitic steel

1200

350

Cold-worked iron

690

200

Small-grain iron

340

100

Carbon-containing iron

140

40

Pure, single-crystal iron

10

3

As structural material

Iron is the most widely used of all the metals, accounting for over 90% of worldwide metal production. Its low cost and high strength often make it the material of choice to withstand stress or transmit forces, such as the construction of machinery and machine tools, rails, automobiles, ship hulls, concrete reinforcing bars, and the load-carrying framework of buildings. Since pure iron is quite soft, it is most commonly combined with alloying elements to make steel.[124]

Mechanical properties

The mechanical properties of iron and its alloys are extremely relevant to their structural applications. Those properties can be evaluated in various ways, including the Brinell test, the Rockwell test and the Vickers hardness test.

The properties of pure iron are often used to calibrate measurements or to compare tests.[123][125] However, the mechanical properties of iron are significantly affected by the sample's purity: pure, single crystals of iron are actually softer than aluminium,[122] and the purest industrially produced iron (99.99%) has a hardness of 20–30 Brinell.[126] The pure iron (99.9%～99.999%), especially called electrolytic iron, is industrially produced by electrolytic refining.

An increase in the carbon content will cause a significant increase in the hardness and tensile strength of iron. Maximum hardness of 65 Rc is achieved with a 0.6% carbon content, although the alloy has low tensile strength.[127] Because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium.[16]

Types of steels and alloys

See also: Steel

Iron-carbon phase diagram

α-Iron is a fairly soft metal that can dissolve only a small concentration of carbon (no more than 0.021% by mass at 910 °C).[128] Austenite (γ-iron) is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.04% by mass at 1146 °C). This form of iron is used in the type of stainless steel used for making cutlery, and hospital and food-service equipment.[20]

Commercially available iron is classified based on purity and the abundance of additives. Pig iron has 3.5–4.5% carbon[129] and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Pig iron is not a saleable product, but rather an intermediate step in the production of cast iron and steel. The reduction of contaminants in pig iron that negatively affect material properties, such as sulfur and phosphorus, yields cast iron containing 2–4% carbon, 1–6% silicon, and small amounts of manganese.[117] Pig iron has a melting point in the range of 1420–1470 K, which is lower than either of its two main components, and makes it the first product to be melted when carbon and iron are heated together.[10] Its mechanical properties vary greatly and depend on the form the carbon takes in the alloy.[16]

"White" cast irons contain their carbon in the form of cementite, or iron carbide (Fe3C).[16] This hard, brittle compound dominates the mechanical properties of white cast irons, rendering them hard, but unresistant to shock. The broken surface of a white cast iron is full of fine facets of the broken iron carbide, a very pale, silvery, shiny material, hence the appellation. Cooling a mixture of iron with 0.8% carbon slowly below 723 °C to room temperature results in separate, alternating layers of cementite and α-iron, which is soft and malleable and is called pearlite for its appearance. Rapid cooling, on the other hand, does not allow time for this separation and creates hard and brittle martensite. The steel can then be tempered by reheating to a temperature in between, changing the proportions of pearlite and martensite. The end product below 0.8% carbon content is a pearlite-αFe mixture, and that above 0.8% carbon content is a pearlite-cementite mixture.[16]

In gray iron the carbon exists as separate, fine flakes of graphite, and also renders the material brittle due to the sharp edged flakes of graphite that produce stress concentration sites within the material.[130] A newer variant of gray iron, referred to as ductile iron, is specially treated with trace amounts of magnesium to alter the shape of graphite to spheroids, or nodules, reducing the stress concentrations and vastly increasing the toughness and strength of the material.[130]

Wrought iron contains less than 0.25% carbon but large amounts of slag that give it a fibrous characteristic.[129] It is a tough, malleable product, but not as fusible as pig iron. If honed to an edge, it loses it quickly. Wrought iron is characterized by the presence of fine fibers of slag entrapped within the metal. Wrought iron is more corrosion resistant than steel. It has been almost completely replaced by mild steel for traditional "wrought iron" products and blacksmithing.

Mild steel corrodes more readily than wrought iron, but is cheaper and more widely available. Carbon steel contains 2.0% carbon or less,[131] with small amounts of manganese, sulfur, phosphorus, and silicon. Alloy steels contain varying amounts of carbon as well as other metals, such as chromium, vanadium, molybdenum, nickel, tungsten, etc. Their alloy content raises their cost, and so they are usually only employed for specialist uses. One common alloy steel, though, is stainless steel. Recent developments in ferrous metallurgy have produced a growing range of microalloyed steels, also termed 'HSLA' or high-strength, low alloy steels, containing tiny additions to produce high strengths and often spectacular toughness at minimal cost.[131][132][133]

Alloys with high purity elemental makeups (such as alloys of electrolytic iron) have specifically enhanced properties such as ductility, tensile strength, toughness, fatigue strength, heat resistance, and corrosion resistance.

Apart from traditional applications, iron is also used for protection from ionizing radiation. Although it is lighter than another traditional protection material, lead, it is much stronger mechanically. The attenuation of radiation as a function of energy is shown in the graph.[134]

The main disadvantage of iron and steel is that pure iron, and most of its alloys, suffer badly from rust if not protected in some way, a cost amounting to over 1% of the world's economy.[135] Painting, galvanization, passivation, plastic coating and bluing are all used to protect iron from rust by excluding water and oxygen or by cathodic protection. The mechanism of the rusting of iron is as follows:[135]

Cathode: 3 O2 + 6 H2O + 12 e− → 12 OH−

Anode: 4 Fe → 4 Fe2+ + 8 e−; 4 Fe2+ → 4 Fe3+ + 4 e−

Overall: 4 Fe + 3 O2 + 6 H2O → 4 Fe3+ + 12 OH− → 4 Fe(OH)3 or 4 FeO(OH) + 4 H2O

The electrolyte is usually iron(II) sulfate in urban areas (formed when atmospheric sulfur dioxide attacks iron), and salt particles in the atmosphere in seaside areas.[135]

Catalysts and reagents

Because Fe is inexpensive and nontoxic, much effort has been devoted to the development of Fe-based catalysts and reagents. Iron is however less common as a catalyst in commercial processes than more expensive metals.[136] In biology, Fe-containing enzymes are pervasive.[137]

Iron catalysts are traditionally used in the Haber–Bosch process for the production of ammonia and the Fischer–Tropsch process for conversion of carbon monoxide to hydrocarbons for fuels and lubricants.[138] Powdered iron in an acidic medium is used in the Bechamp reduction, the conversion of nitrobenzene to aniline.[139]

Iron compounds

Iron(III) oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding large iron parts (like rails) and purifying ores. Iron(III) oxide and oxyhydroxide are used as reddish and ocher pigments.

Iron(III) chloride finds use in water purification and sewage treatment, in the dyeing of cloth, as a coloring agent in paints, as an additive in animal feed, and as an etchant for copper in the manufacture of printed circuit boards.[140] It can also be dissolved in alcohol to form tincture of iron, which is used as a medicine to stop bleeding in canaries.[141]

Iron(II) sulfate is used as a precursor to other iron compounds. It is also used to reduce chromate in cement. It is used to fortify foods and treat iron deficiency anemia. Iron(III) sulfate is used in settling minute sewage particles in tank water. Iron(II) chloride is used as a reducing flocculating agent, in the formation of iron complexes and magnetic iron oxides, and as a reducing agent in organic synthesis.[140]

Sodium nitroprusside is a drug used as a vasodilator. It is on the World Health Organization's List of Essential Medicines.[142]

Biological and pathological role

Main article: Iron in biology

Iron is required for life.[9][143][144] The iron–sulfur clusters are pervasive and include nitrogenase, the enzymes responsible for biological nitrogen fixation. Iron-containing proteins participate in transport, storage and use of oxygen.[9] Iron proteins are involved in electron transfer.[145]

Simplified structure of Heme B; in the protein additional ligand(s) are attached to Fe.

Examples of iron-containing proteins in higher organisms include hemoglobin, cytochrome (see high-valent iron), and catalase.[9][146] The average adult human contains about 0.005% body weight of iron, or about four grams, of which three quarters is in hemoglobin – a level that remains constant despite only about one milligram of iron being absorbed each day,[145] because the human body recycles its hemoglobin for the iron content.[147]

Microbial growth may be assisted by oxidation of iron(II) or by reduction of iron (III).[148]

Biochemistry

Iron acquisition poses a problem for aerobic organisms because ferric iron is poorly soluble near neutral pH. Thus, these organisms have developed means to absorb iron as complexes, sometimes taking up ferrous iron before oxidising it back to ferric iron.[9] In particular, bacteria have evolved very high-affinity sequestering agents called siderophores.[149][150][151]

After uptake in human cells, iron storage is precisely regulated.[9][152] A major component of this regulation is the protein transferrin, which binds iron ions absorbed from the duodenum and carries it in the blood to cells.[9][153] Transferrin contains Fe3+ in the middle of a distorted octahedron, bonded to one nitrogen, three oxygens and a chelating carbonate anion that traps the Fe3+ ion: it has such a high stability constant that it is very effective at taking up Fe3+ ions even from the most stable complexes. At the bone marrow, transferrin is reduced from Fe3+ and Fe2+ and stored as ferritin to be incorporated into hemoglobin.[145]

The most commonly known and studied bioinorganic iron compounds (biological iron molecules) are the heme proteins: examples are hemoglobin, myoglobin, and cytochrome P450.[9] These compounds participate in transporting gases, building enzymes, and transferring electrons.[145] Metalloproteins are a group of proteins with metal ion cofactors. Some examples of iron metalloproteins are ferritin and rubredoxin.[145] Many enzymes vital to life contain iron, such as catalase,[154] lipoxygenases,[155] and IRE-BP.[156]

Hemoglobin is an oxygen carrier that occurs in red blood cells and contributes their color, transporting oxygen in the arteries from the lungs to the muscles where it is transferred to myoglobin, which stores it until it is needed for the metabolic oxidation of glucose, generating energy.[9] Here the hemoglobin binds to carbon dioxide, produced when glucose is oxidized, which is transported through the veins by hemoglobin (predominantly as bicarbonate anions) back to the lungs where it is exhaled.[145] In hemoglobin, the iron is in one of four heme groups and has six possible coordination sites; four are occupied by nitrogen atoms in a porphyrin ring, the fifth by an imidazole nitrogen in a histidine residue of one of the protein chains attached to the heme group, and the sixth is reserved for the oxygen molecule it can reversibly bind to.[145] When hemoglobin is not attached to oxygen (and is then called deoxyhemoglobin), the Fe2+ ion at the center of the heme group (in the hydrophobic protein interior) is in a high-spin configuration. It is thus too large to fit inside the porphyrin ring, which bends instead into a dome with the Fe2+ ion about 55 picometers above it. In this configuration, the sixth coordination site reserved for the oxygen is blocked by another histidine residue.[145]

When deoxyhemoglobin picks up an oxygen molecule, this histidine residue moves away and returns once the oxygen is securely attached to form a hydrogen bond with it. This results in the Fe2+ ion switching to a low-spin configuration, resulting in a 20% decrease in ionic radius so that now it can fit into the porphyrin ring, which becomes planar.[145] (Additionally, this hydrogen bonding results in the tilting of the oxygen molecule, resulting in a Fe–O–O bond angle of around 120° that avoids the formation of Fe–O–Fe or Fe–O2–Fe bridges that would lead to electron transfer, the oxidation of Fe2+ to Fe3+, and the destruction of hemoglobin.) This results in a movement of all the protein chains that leads to the other subunits of hemoglobin changing shape to a form with larger oxygen affinity. Thus, when deoxyhemoglobin takes up oxygen, its affinity for more oxygen increases, and vice versa.[145] Myoglobin, on the other hand, contains only one heme group and hence this cooperative effect cannot occur. Thus, while hemoglobin is almost saturated with oxygen in the high partial pressures of oxygen found in the lungs, its affinity for oxygen is much lower than that of myoglobin, which oxygenates even at low partial pressures of oxygen found in muscle tissue.[145] As described by the Bohr effect (named after Christian Bohr, the father of Niels Bohr), the oxygen affinity of hemoglobin diminishes in the presence of carbon dioxide.[145]

A heme unit of human carboxyhemoglobin, showing the carbonyl ligand at the apical position, trans to the histidine residue[157]

Carbon monoxide and phosphorus trifluoride are poisonous to humans because they bind to hemoglobin similarly to oxygen, but with much more strength, so that oxygen can no longer be transported throughout the body. Hemoglobin bound to carbon monoxide is known as carboxyhemoglobin. This effect also plays a minor role in the toxicity of cyanide, but there the major effect is by far its interference with the proper functioning of the electron transport protein cytochrome a.[145] The cytochrome proteins also involve heme groups and are involved in the metabolic oxidation of glucose by oxygen. The sixth coordination site is then occupied by either another imidazole nitrogen or a methionine sulfur, so that these proteins are largely inert to oxygen – with the exception of cytochrome a, which bonds directly to oxygen and thus is very easily poisoned by cyanide.[145] Here, the electron transfer takes place as the iron remains in low spin but changes between the +2 and +3 oxidation states. Since the reduction potential of each step is slightly greater than the previous one, the energy is released step-by-step and can thus be stored in adenosine triphosphate. Cytochrome a is slightly distinct, as it occurs at the mitochondrial membrane, binds directly to oxygen, and transports protons as well as electrons, as follows:[145]

4 Cytc2+ + O2 + 8H+inside → 4 Cytc3+ + 2 H2O + 4H+outside

Although the heme proteins are the most important class of iron-containing proteins, the iron–sulfur proteins are also very important, being involved in electron transfer, which is possible since iron can exist stably in either the +2 or +3 oxidation states. These have one, two, four, or eight iron atoms that are each approximately tetrahedrally coordinated to four sulfur atoms; because of this tetrahedral coordination, they always have high-spin iron. The simplest of such compounds is rubredoxin, which has only one iron atom coordinated to four sulfur atoms from cysteine residues in the surrounding peptide chains. Another important class of iron–sulfur proteins is the ferredoxins, which have multiple iron atoms. Transferrin does not belong to either of these classes.[145]

The ability of sea mussels to maintain their grip on rocks in the ocean is facilitated by their use of organometallic iron-based bonds in their protein-rich cuticles. Based on synthetic replicas, the presence of iron in these structures increased elastic modulus 770 times, tensile strength 58 times, and toughness 92 times. The amount of stress required to permanently damage them increased 76 times.[158]

Nutrition

Diet

Iron is pervasive, but particularly rich sources of dietary iron include red meat, oysters, beans, poultry, fish, leaf vegetables, watercress, tofu, and blackstrap molasses.[9] Bread and breakfast cereals are sometimes specifically fortified with iron.[9][159]

Iron provided by dietary supplements is often found as iron(II) fumarate, although iron(II) sulfate is cheaper and is absorbed equally well.[140] Elemental iron, or reduced iron, despite being absorbed at only one-third to two-thirds the efficiency (relative to iron sulfate),[160] is often added to foods such as breakfast cereals or enriched wheat flour. Iron is most available to the body when chelated to amino acids[161] and is also available for use as a common iron supplement. Glycine, the least expensive amino acid, is most often used to produce iron glycinate supplements.[162]

Dietary recommendations

The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for iron in 2001.[9] The current EAR for iron for women ages 14–18 is 7.9 mg/day, 8.1 for ages 19–50 and 5.0 thereafter (post menopause). For men the EAR is 6.0 mg/day for ages 19 and up. The RDA is 15.0 mg/day for women ages 15–18, 18.0 for 19–50 and 8.0 thereafter. For men, 8.0 mg/day for ages 19 and up. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 27 mg/day and, for lactation, 9 mg/day.[9] For children ages 1–3 years 7 mg/day, 10 for ages 4–8 and 8 for ages 9–13. As for safety, the IOM also sets Tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of iron the UL is set at 45 mg/day. Collectively the EARs, RDAs and ULs are referred to as Dietary Reference Intakes.[163]

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 defined the same as in United States. For women the PRI is 13 mg/day ages 15–17 years, 16 mg/day for women ages 18 and up who are premenopausal and 11 mg/day postmenopausal. For pregnancy and lactation, 16 mg/day. For men the PRI is 11 mg/day ages 15 and older. For children ages 1 to 14 the PRI increases from 7 to 11 mg/day. The PRIs are higher than the U.S. RDAs, with the exception of pregnancy.[164] The EFSA reviewed the same safety question did not establish a UL.[165]

Infants may require iron supplements if they are bottle-fed cow's milk.[166] Frequent blood donors are at risk of low iron levels and are often advised to supplement their iron intake.[167]

For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For iron labeling purposes 100% of the Daily Value was 18 mg, and as of May 27, 2016[update] remained unchanged at 18 mg.[168][169] A table of the old and new adult daily values is provided at Reference Daily Intake.

Deficiency

Main article: Iron deficiency

Iron deficiency is the most common nutritional deficiency in the world.[9][170][171][172] When loss of iron is not adequately compensated by adequate dietary iron intake, a state of latent iron deficiency occurs, which over time leads to iron-deficiency anemia if left untreated, which is characterised by an insufficient number of red blood cells and an insufficient amount of hemoglobin.[173] Children, pre-menopausal women (women of child-bearing age), and people with poor diet are most susceptible to the disease. Most cases of iron-deficiency anemia are mild, but if not treated can cause problems like fast or irregular heartbeat, complications during pregnancy, and delayed growth in infants and children.[174]

The brain is resistant to acute iron deficiency due to the slow transport of iron through the blood brain barrier.[175] Acute fluctuations in iron status (marked by serum ferritin levels) do not reflect brain iron status, but prolonged nutritional iron deficiency is suspected to reduce brain iron concentrations over time.[176][177] In the brain, iron plays a role in oxygen transport, myelin synthesis, mitochondrial respiration, and as a cofactor for neurotransmitter synthesis and metabolism.[178] Animal models of nutritional iron deficiency report biomolecular changes resembling those seen in Parkinson's and Huntington's disease.[179][180] However, age-related accumulation of iron in the brain has also been linked to the development of Parkinson's.[181]

Excess

Main article: Iron overload

Iron uptake is tightly regulated by the human body, which has no regulated physiological means of excreting iron. Only small amounts of iron are lost daily due to mucosal and skin epithelial cell sloughing, so control of iron levels is primarily accomplished by regulating uptake.[182] Regulation of iron uptake is impaired in some people as a result of a genetic defect that maps to the HLA-H gene region on chromosome 6 and leads to abnormally low levels of hepcidin, a key regulator of the entry of iron into the circulatory system in mammals.[183] In these people, excessive iron intake can result in iron overload disorders, known medically as hemochromatosis.[9] Many people have an undiagnosed genetic susceptibility to iron overload, and are not aware of a family history of the problem. For this reason, people should not take iron supplements unless they suffer from iron deficiency and have consulted a doctor. Hemochromatosis is estimated to be the cause of 0.3–0.8% of all metabolic diseases of Caucasians.[184]

Overdoses of ingested iron can cause excessive levels of free iron in the blood. High blood levels of free ferrous iron react with peroxides to produce highly reactive free radicals that can damage DNA, proteins, lipids, and other cellular components. Iron toxicity occurs when the cell contains free iron, which generally occurs when iron levels exceed the availability of transferrin to bind the iron. Damage to the cells of the gastrointestinal tract can also prevent them from regulating iron absorption, leading to further increases in blood levels. Iron typically damages cells in the heart, liver and elsewhere, causing adverse effects that include coma, metabolic acidosis, shock, liver failure, coagulopathy, long-term organ damage, and even death.[185] Humans experience iron toxicity when the iron exceeds 20 milligrams for every kilogram of body mass; 60 milligrams per kilogram is considered a lethal dose.[186] Overconsumption of iron, often the result of children eating large quantities of ferrous sulfate tablets intended for adult consumption, is one of the most common toxicological causes of death in children under six.[186] The Dietary Reference Intake (DRI) sets the Tolerable Upper Intake Level (UL) for adults at 45 mg/day. For children under fourteen years old the UL is 40 mg/day.[187]

The medical management of iron toxicity is complicated, and can include use of a specific chelating agent called deferoxamine to bind and expel excess iron from the body.[185][188][189]

ADHD

Some research has suggested that low thalamic iron levels may play a role in the pathophysiology of ADHD.[190] Some researchers have found that iron supplementation can be effective especially in the inattentive subtype of the disorder.[191] One study also showed that iron may be able to decrease the risk of cardiovascular events during treatment with ADHD drugs.[192]

Some researchers in the 2000s suggested a link between low levels of iron in the blood and ADHD. A 2012 study found no such correlation.[193]

Cancer

The role of iron in cancer defense can be described as a "double-edged sword" because of its pervasive presence in non-pathological processes.[194] People having chemotherapy may develop iron deficiency and anemia, for which intravenous iron therapy is used to restore iron levels.[195] Iron overload, which may occur from high consumption of red meat,[9] may initiate tumor growth and increase susceptibility to cancer onset,[195] particularly for colorectal cancer.[9]

Marine systems

Iron plays an essential role in marine systems and can act as a limiting nutrient for planktonic activity.[196] Because of this, too much of a decrease in iron may lead to a decrease in growth rates in phytoplanktonic organisms such as diatoms.[197] Iron can also be oxidized by marine microbes under conditions that are high in iron and low in oxygen.[198]

Iron can enter marine systems through adjoining rivers and directly from the atmosphere. Once iron enters the ocean, it can be distributed throughout the water column through ocean mixing and through recycling on the cellular level.[199] In the arctic, sea ice plays a major role in the store and distribution of iron in the ocean, depleting oceanic iron as it freezes in the winter and releasing it back into the water when thawing occurs in the summer.[200] The iron cycle can fluctuate the forms of iron from aqueous to particle forms altering the availability of iron to primary producers.[201] Increased light and warmth increases the amount of iron that is in forms that are usable by primary producers.[202]

See also

Chemistry portal

Economically important iron deposits include:

Carajás Mine in the state of Pará, Brazil, is thought to be the largest iron deposit in the world.

El Mutún in Bolivia, where 10% of the world's accessible iron ore is located.

Hamersley Basin is the largest iron ore deposit in Australia.

Kiirunavaara in Sweden, where one of the world's largest deposits of iron ore is located

The Mesabi Iron Range is the chief iron ore mining district in the United States.

Iron and steel industry

Iron cycle

Iron nanoparticle

Iron–platinum nanoparticle

Iron fertilization – proposed fertilization of oceans to stimulate phytoplankton growth

Iron-oxidizing bacteria

List of countries by iron production

Pelletising – process of creation of iron ore pellets

Rustproof iron

Steel

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^ Institute of Medicine (US) Panel on Micronutrients (2001). "Iron" (PDF). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Iron. National Academy Press. pp. 290–393. ISBN 0-309-07279-4. PMID 25057538. Archived from the original (PDF) on 9 September 2017. Retrieved 9 March 2017.

^ "Overview on Dietary Reference Values for the EU population as derived by the EFSA Panel on Dietetic Products, Nutrition and Allergies" (PDF). European Food Safety Authority. 2017.

^ "Tolerable Upper Intake Levels For Vitamins And Minerals" (PDF). European Food Safety Authority. 2006.

^ "Iron Deficiency Anemia". MediResource. Archived from the original on 16 December 2008. Retrieved 17 December 2008.

^ Milman, N. (1996). "Serum ferritin in Danes: studies of iron status from infancy to old age, during blood donation and pregnancy". International Journal of Hematology. 63 (2): 103–35. doi:10.1016/0925-5710(95)00426-2. PMID 8867722.

^ "Federal Register May 27, 2016 Food Labeling: Revision of the Nutrition and Supplement Facts Labels. FR page 33982" (PDF).

^ "Daily Value Reference of the Dietary Supplement Label Database (DSLD)". Dietary Supplement Label Database (DSLD). Archived from the original on 7 April 2020. Retrieved 16 May 2020.

^ Centers for Disease Control and Prevention (2002). "Iron deficiency – United States, 1999–2000". MMWR. 51 (40): 897–99. PMID 12418542.

^ Hider, Robert C.; Kong, Xiaole (2013). "Chapter 8. Iron: Effect of Overload and Deficiency". In Astrid Sigel, Helmut Sigel and Roland K.O. Sigel (ed.). Interrelations between Essential Metal Ions and Human Diseases. Metal Ions in Life Sciences. Vol. 13. Springer. pp. 229–94. doi:10.1007/978-94-007-7500-8_8. ISBN 978-94-007-7499-5. PMID 24470094.

^ Dlouhy, Adrienne C.; Outten, Caryn E. (2013). "The Iron Metallome in Eukaryotic Organisms". In Banci, Lucia (ed.). Metallomics and the Cell. Metal Ions in Life Sciences. Vol. 12. Springer. pp. 241–78. doi:10.1007/978-94-007-5561-1_8. ISBN 978-94-007-5560-4. PMC 3924584. PMID 23595675. electronic-book ISBN 978-94-007-5561-1

^ CDC Centers for Disease Control and Prevention (3 April 1998). "Recommendations to Prevent and Control Iron Deficiency in the United States". Morbidity and Mortality Weekly Report. 47 (RR3): 1. Retrieved 12 August 2014.

^ Centers for Disease Control and Prevention. "Iron and Iron Deficiency". Retrieved 12 August 2014.

^ Youdim, M. B.; Ben-Shachar, D.; Yehuda, S. (September 1989). "Putative biological mechanisms of the effect of iron deficiency on brain biochemistry and behavior". The American Journal of Clinical Nutrition. 50 (3 Suppl): 607–615, discussion 615–617. doi:10.1093/ajcn/50.3.607. ISSN 0002-9165. PMID 2773840.

^ Erikson, K. M.; Pinero, D. J.; Connor, J. R.; Beard, J. L. (October 1997). "Regional brain iron, ferritin and transferrin concentrations during iron deficiency and iron repletion in developing rats". The Journal of Nutrition. 127 (10): 2030–2038. doi:10.1093/jn/127.10.2030. ISSN 0022-3166. PMID 9311961.

^ Unger, Erica L.; Bianco, Laura E.; Jones, Byron C.; Allen, Richard P.; Earley, Christopher J. (November 2014). "Low brain iron effects and reversibility on striatal dopamine dynamics". Experimental Neurology. 261: 462–468. doi:10.1016/j.expneurol.2014.06.023. PMC 4318655. PMID 24999026.

^ Ward, Roberta J.; Zucca, Fabio A.; Duyn, Jeff H.; Crichton, Robert R.; Zecca, Luigi (October 2014). "The role of iron in brain ageing and neurodegenerative disorders". The Lancet. Neurology. 13 (10): 1045–1060. doi:10.1016/S1474-4422(14)70117-6. ISSN 1474-4465. PMC 5672917. PMID 25231526.

^ Pino, Jessica M. V.; da Luz, Marcio H. M.; Antunes, Hanna K. M.; Giampá, Sara Q. de Campos; Martins, Vilma R.; Lee, Kil S. (17 May 2017). "Iron-Restricted Diet Affects Brain Ferritin Levels, Dopamine Metabolism and Cellular Prion Protein in a Region-Specific Manner". Frontiers in Molecular Neuroscience. 10: 145. doi:10.3389/fnmol.2017.00145. ISSN 1662-5099. PMC 5434142. PMID 28567002.

^ Beard, John; Erikson, Keith M.; Jones, Byron C. (1 April 2003). "Neonatal Iron Deficiency Results in Irreversible Changes in Dopamine Function in Rats". The Journal of Nutrition. 133 (4): 1174–1179. doi:10.1093/jn/133.4.1174. ISSN 0022-3166. PMID 12672939.

^ Dominic J. Hare; Kay L. Double (April 2016). "Iron and dopamine: a toxic couple". Brain. 139 (4): 1026–1035. doi:10.1093/brain/aww022. PMID 26962053.

^ Ramzi S. Cotran; Vinay Kumar; Tucker Collins; Stanley Leonard Robbins (1999). Robbins pathologic basis of disease. Saunders. ISBN 978-0-7216-7335-6. Retrieved 27 June 2012.

^ Ganz T (August 2003). "Hepcidin, a key regulator of iron metabolism and mediator of anemia of inflammation". Blood. 102 (3): 783–8. doi:10.1182/blood-2003-03-0672. PMID 12663437. S2CID 28909635.

^ Durupt, S.; Durieu, I.; Nové-Josserand, R.; Bencharif, L.; Rousset, H.; Vital Durand, D. (2000). "Hereditary hemochromatosis". Rev Méd Interne. 21 (11): 961–71. doi:10.1016/S0248-8663(00)00252-6. PMID 11109593.

^ a b Cheney, K.; Gumbiner, C.; Benson, B.; Tenenbein, M. (1995). "Survival after a severe iron poisoning treated with intermittent infusions of deferoxamine". J Toxicol Clin Toxicol. 33 (1): 61–66. doi:10.3109/15563659509020217. PMID 7837315.

^ a b "Toxicity, Iron". Medscape. Retrieved 23 May 2010.

^ Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals (PDF), Food and Nutrition Board, Institute of Medicine, National Academies, 2004, archived from the original (PDF) on 14 March 2013, retrieved 9 June 2009

^ Tenenbein, M. (1996). "Benefits of parenteral deferoxamine for acute iron poisoning". J Toxicol Clin Toxicol. 34 (5): 485–89. doi:10.3109/15563659609028005. PMID 8800185.

^ Wu H, Wu T, Xu X, Wang J, Wang J (May 2011). "Iron toxicity in mice with collagenase-induced intracerebral hemorrhage". J Cereb Blood Flow Metab. 31 (5): 1243–50. doi:10.1038/jcbfm.2010.209. PMC 3099628. PMID 21102602.

^ Robberecht, Harry; et al. (2020). "Magnesium, Iron, Zinc, Copper and Selenium Status in Attention-Deficit/Hyperactivity Disorder (ADHD)". Molecules. 25 (19): 4440. doi:10.3390/molecules25194440. PMC 7583976. PMID 32992575.

^ Soto-Insuga, V; et al. (2013). "[Role of iron in the treatment of attention deficit-hyperactivity disorder]". An Pediatr (Barc). 79 (4): 230–235. doi:10.1016/j.anpedi.2013.02.008. PMID 23582950.

^ Parisi, Pasquale; Villa, Maria Pia; Donfrancesco, Renato; Miano, Silvia; Paolino, Maria Chiara; Cortese, Samuele (August 2012). "Could treatment of iron deficiency both improve ADHD and reduce cardiovascular risk during treatment with ADHD drugs?". Medical Hypotheses. 79 (2): 246–249. doi:10.1016/j.mehy.2012.04.049. PMID 22632845.

^ Donfrancesco, Renato; Parisi, Pasquale; Vanacore, Nicola; Martines, Francesca; Sargentini, Vittorio; Cortese, Samuele (May 2013). "Iron and ADHD: Time to Move Beyond Serum Ferritin Levels". Journal of Attention Disorders. 17 (4): 347–357. doi:10.1177/1087054711430712. ISSN 1087-0547. PMID 22290693. S2CID 22445593.

^ Thévenod, Frank (2018). "Chapter 15. Iron and Its Role in Cancer Defense: A Double-Edged Sword". In Sigel, Astrid; Sigel, Helmut; Freisinger, Eva; Sigel, Roland K. O. (eds.). Metallo-Drugs: Development and Action of Anticancer Agents. Vol. 18. Berlin: de Gruyter GmbH. pp. 437–67. doi:10.1515/9783110470734-021. PMID 29394034. {{cite book}}: |journal= ignored (help)

^ a b Beguin, Y; Aapro, M; Ludwig, H; Mizzen, L; Osterborg, A (2014). "Epidemiological and nonclinical studies investigating effects of iron in carcinogenesis--a critical review". Critical Reviews in Oncology/Hematology. 89 (1): 1–15. doi:10.1016/j.critrevonc.2013.10.008. PMID 24275533.

^ Morel, F.M.M., Hudson, R.J.M., & Price, N.M. (1991). Limitation of productivity by trace metals in the sea. Limnology and Oceanography, 36(8), 1742-1755. doi:10.4319/lo.1991.36.8.1742

^ Brezezinski, M.A., Baines, S.B., Balch, W.M., Beucher, C.P., Chai, F., Dugdale, R.C., Krause, J.W., Landry, M.R., Marchi, A., Measures, C.I., Nelson, D.M., Parker, A.E., Poulton, A.J., Selph, K.E., Strutton, P.G., Taylor, A.G., & Twining, B.S.(2011). Co-limitation of diatoms by iron and silicic acid in the equatorial Pacific. Deep-Sea Research Part II: Topical Studies in Oceanography, 58(3-4), 493-511. doi:10.1016/j.dsr2.2010.08.005

^ Field, E. K., Kato, S., Findlay, A. J., MacDonald, D. J., Chiu, B. K., Luther, G. W., & Chan, C. S. (2016). Planktonic marine iron oxidizers drive iron mineralization under low-oxygen conditions. Geobiology, 14(5), 499-508. doi:10.1111/gbi.12189

^ Wells, M.L., Price, N.M., & Bruland, K.W. (1995). Iron chemistry in seawater and its relationship to phytoplankton: a workshop report. Marine Chemistry, 48(2), 157-182. doi:10.1016/0304-4203(94)00055-I

^ Lannuzel, D., Vancoppenolle, M., van der Merwe, P., de Jong, J., Meiners, K.M., Grotti, M., Nishioska, J., & Schoemann. (2016). Iron in sea ice: Review and new insights. Elementa: Science of the Anthropocene, 4 000130.

doi:10.12952/journal.elementa.000130

^ Raiswell, R. 2011. Iron Transport from the Continents to the Open Ocean: The Aging–Rejuvenation Cycle. Elements, 7(2), 101–106. doi:10.2113/gselements.7.2.101

^ Tagliabue, A., Bopp, L., Aumont, O., & Arrigo, K.R. (2009). Influence of light and temperature on the marine iron cycle: From theoretical to global modeling. Global Biogeochemical Cycles, 23.

doi:10.1029/2008GB003214

Bibliography

Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

Weeks, Mary Elvira; Leichester, Henry M. (1968). "Elements known to the ancients". Discovery of the elements. Easton, PA: Journal of Chemical Education. pp. 29–40. ISBN 0-7661-3872-0. LCCN 68-15217.

Further reading

H.R. Schubert, History of the British Iron and Steel Industry ... to 1775 AD (Routledge, London, 1957)

R.F. Tylecote, History of Metallurgy (Institute of Materials, London 1992).

R.F. Tylecote, "Iron in the Industrial Revolution" in J. Day and R.F. Tylecote, The Industrial Revolution in Metals (Institute of Materials 1991), 200–60.

External links

Wikiquote has quotations related to Iron.

Look up iron in Wiktionary, the free dictionary.

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Wikisource has the text of the 1905 New International Encyclopedia article "Iron".

It's Elemental – Iron

Iron at The Periodic Table of Videos (University of Nottingham)

Metallurgy for the non-Metallurgist

Iron by J.B. Calvert

vtePeriodic table

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

1

H

He

2

Li

Be

B

C

N

O

F

Ne

3

Na

Mg

Al

Si

P

S

Cl

Ar

4

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

5

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

6

Cs

Ba

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

7

Fr

Ra

Ac

Th

Pa

U

Np

Pu

Am

Cm

Bk

Cf

Es

Fm

Md

No

Lr

Rf

Db

Sg

Bh

Hs

Mt

Ds

Rg

Cn

Nh

Fl

Mc

Lv

Ts

Og

s-block

f-block

d-block

p-block

vteIron compoundsFe(-II)

H2Fe(CO)4

Na2Fe(CO)4

Fe(0)

Fe(CO)5

Fe2(CO)9

Fe3(CO)12

Fe(CO)3CH3COC2H2C6H6

Fe(I)

FeHOrganoiron(I) compounds

(C5H5FeCO)2(CO)2

Fe(0,II)

Fe3C

Fe(II)

FeH2

Mg2FeH6

FeF2

FeCl2

Fe(ClO4)2

FeBr2

FeI2

FeO

Fe(OH)2

FeS

FeSO4

(NH4)2Fe(SO4)2·6H2O

FeSe

FeSeO4

Fe(NO3)2

Fe3(PO4)2

FeSi2

Fe(BF4)2

FeCr2O4

FeMoO4

FeTiO3

FeCO3

FeC2O4

Fe(C2H3O2)2

Fe(C3H5O3)2

FeC6H6O7

FeC12H22O14

FeI2(CO)4

Organoiron(II) compounds

Fe(C5H5)2

Fe(C5H5)(CO)2I

Fe(C5H4P(C6H5)2)2

C4H4Fe(CO)3

C4H6Fe(CO)3

Fe(0,III)

FeSi

FeGe

Fe(II,III)

Fe3O4

Fe3S4

Fe(III)

FeI3

FeBr3

FeCl3

FeF3

FeP

Fe(NO3)3

Fe(acac)3

FeOCl

[(C2H5)4N][O(FeCl3)2]

FeO(OH)

FePO4

Fe4(P2O7)3

Fe2(CrO4)3

Fe2(C2O4)3

Fe2O3

Fe2(SeO3)3

Fe2S3

Fe2(SO4)3

Fe(N3)3

NH4Fe(SO4)2·12H2O

Organoiron(III) compounds

Fe(C5H5)2BF4

C6H8O7⋅xFe3+⋅yNH3

C54H105FeO6

Fe(IV)

FeF4

Fe(VI)

K2FeO4

BaFeO4

Purported

Hemolithin (protein)

Authority control databases National

Spain

France

BnF data

Germany

Israel

United States

Japan

Czech Republic

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Historical Dictionary of Switzerland

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Iron | Element, Occurrence, Uses, Properties, & Compounds | Britannica

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Also known as: Fe, ferrum

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JSPL declared as preferred bidder for Kasia iron ore mine by Odisha govt

iron (Fe), chemical element, metal of Group 8 (VIIIb) of the periodic table, the most-used and cheapest metal.Element Propertiesatomic number26atomic weight55.847melting point1,538 °C (2,800 °F)boiling point3,000 °C (5,432 °F)specific gravity7.86 (20 °C)oxidation states+2, +3, +4, +6electron configuration[Ar]3d64s2 Occurrence, uses, and properties Study how iron ore is mined with explosives and crushed and concentrated with remote-controlled machinesIron ore mining at Kiruna, Sweden.(more)See all videos for this articleIron makes up 5 percent of Earth’s crust and is second in abundance to aluminum among the metals and fourth in abundance behind oxygen, silicon, and aluminum among the elements. Iron, which is the chief constituent of Earth’s core, is the most abundant element in Earth as a whole (about 35 percent) and is relatively plentiful in the Sun and other stars. In the crust the free metal is rare, occurring as terrestrial iron (alloyed with 2–3 percent nickel) in basaltic rocks in Greenland and carbonaceous sediments in the United States (Missouri) and as a low-nickel meteoric iron (5–7 percent nickel), kamacite. Nickel-iron, a native alloy, occurs in terrestrial deposits (21–64 percent iron, 77–34 percent nickel) and in meteorites as taenite (62–75 percent iron, 37–24 percent nickel). (For mineralogical properties of native iron and nickel-iron, see native elements [table].) Meteorites are classified as iron, iron-stone, or stony according to the relative proportion of their iron and silicate-mineral content. Iron is also found combined with other elements in hundreds of minerals; of greatest importance as iron ore are hematite (ferric oxide, Fe2O3), magnetite (triiron tetroxide, Fe3O4), limonite (hydrated ferric oxide hydroxide, FeO(OH)∙nH2O), and siderite (ferrous carbonate, FeCO3). Igneous rocks average about 5 percent iron content. The metal is extracted by smelting with carbon (coke) and limestone. (For specific information on the mining and production of iron, see iron processing.)

Iron ore

country

mine production 2006 (metric tons)*

% of world mine production

demonstrated reserves 2006 (metric tons)*, **

% of world demonstrated reserves

*Estimated.

**Iron content.

***Detail does not add to total given because of rounding.

Source: U.S. Department of the Interior, Mineral Commodity Summaries 2007.

China

520,000,000

30.8

15,000,000,000

8.3

Brazil

300,000,000

17.8

41,000,000,000

22.8

Australia

270,000,000

16.0

25,000,000,000

13.9

India

150,000,000

8.9

6,200,000,000

3.4

Russia

105,000,000

6.2

31,000,000,000

17.2

Ukraine

73,000,000

4.3

20,000,000,000

11.1

United States

54,000,000

3.2

4,600,000,000

2.6

South Africa

40,000,000

2.4

1,500,000,000

0.8

Canada

33,000,000

2.0

2,500,000,000

1.4

Sweden

24,000,000

1.4

5,000,000,000

2.8

Iran

20,000,000

1.2

1,500,000,000

0.8

Venezuela

20,000,000

1.2

3,600,000,000

2.0

Kazakhstan

15,000,000

0.9

7,400,000,000

4.1

Mauritania

11,000,000

0.7

1,000,000,000

0.6

Mexico

13,000,000

0.8

900,000,000

0.5

other countries

43,000,000

2.5

17,000,000,000

9.4

world total

1,690,000,000

100***

180,000,000,000

100***

The average quantity of iron in the human body is about 4.5 grams (about 0.004 percent), of which approximately 65 percent is in the form of hemoglobin, which transports molecular oxygen from the lungs throughout the body; 1 percent in the various enzymes that control intracellular oxidation; and most of the rest stored in the body (liver, spleen, bone marrow) for future conversion to hemoglobin. Red meat, egg yolk, carrots, fruit, whole wheat, and green vegetables contribute most of the 10–20 milligrams of iron required each day by the average adult. For the treatment of hypochromic anemias (caused by iron deficiency), any of a large number of organic or inorganic iron (usually ferrous) compounds are used. Iron, as commonly available, nearly always contains small amounts of carbon, which are picked up from the coke during smelting. These modify its properties, from hard and brittle cast irons containing up to 4 percent carbon to more malleable low-carbon steels containing less than 0.1 percent carbon.

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Three true allotropes of iron in its pure form occur. Delta iron, characterized by a body-centred cubic crystal structure, is stable above a temperature of 1,390 °C (2,534 °F). Below this temperature there is a transition to gamma iron, which has a face-centred cubic (or cubic close-packed) structure and is paramagnetic (capable of being only weakly magnetized and only as long as the magnetizing field is present); its ability to form solid solutions with carbon is important in steelmaking. At 910 °C (1,670 °F) there is a transition to paramagnetic alpha iron, which is also body-centred cubic in structure. Below 773 °C (1,423 °F), alpha iron becomes ferromagnetic (i.e., capable of being permanently magnetized), indicating a change in electronic structure but no change in crystal structure. Above 773 °C (its Curie point), it loses its ferromagnetism altogether. Alpha iron is a soft, ductile, lustrous, gray-white metal of high tensile strength. Pure iron is quite reactive. In a very finely divided state metallic iron is pyrophoric (i.e., it ignites spontaneously). It combines vigorously with chlorine on mild heating and also with a variety of other nonmetals, including all of the halogens, sulfur, phosphorus, boron, carbon, and silicon (the carbide and silicide phases play major roles in the technical metallurgy of iron). Metallic iron dissolves readily in dilute mineral acids. With nonoxidizing acids and in the absence of air, iron in the +2 oxidation state is obtained. With air present or when warm dilute nitric acid is used, some of the iron goes into solution as the Fe3+ ion. Very strongly oxidizing mediums—for example, concentrated nitric acid or acids containing dichromate—passivate iron (i.e., cause it to lose its normal chemical activity), however, much as they do chromium. Air-free water and dilute air-free hydroxides have little effect on the metal, but it is attacked by hot concentrated sodium hydroxide.

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Natural iron is a mixture of four stable isotopes: iron-56 (91.66 percent), iron-54 (5.82 percent), iron-57 (2.19 percent), and iron-58 (0.33 percent).

Iron compounds are amenable to study by taking advantage of a phenomenon known as the Mössbauer effect (the phenomenon of a gamma ray being absorbed and reradiated by a nucleus without recoil). Although the Mössbauer effect has been observed for about one-third of the elements, it is particularly for iron (and to a lesser extent tin) that the effect has been a major research tool for the chemist. In the case of iron the effect depends on the fact that the nucleus of iron-57 can be excited to a high energy state by the absorption of gamma radiation of very sharply defined frequency that is influenced by the oxidation state, electron configuration, and chemical environment of the iron atom and can thus be used as a probe of its chemical behaviour. The marked Mössbauer effect of iron-57 has been used in studying magnetism and hemoglobin derivatives and for making a very precise nuclear clock.

IRON中文(简体)翻译：剑桥词典

IRON中文(简体)翻译：剑桥词典

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英语-中文（简体）

iron 在英语-中文（简体）词典中的翻译

ironnoun uk

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/aɪən/ us

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/aɪrn/

iron noun

(METAL)

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B1 [ U ] (symbol Fe) a chemical element that is a common greyish-coloured metal. It is strong, used in making steel, and exists in very small amounts in blood.

铁

Iron rusts easily.

铁易生锈。

Liver is a particularly rich source of dietary iron.

肝脏中含有特别丰富的可食用铁质。

iron ore

铁矿

an iron deficiency

铁质缺乏

更多范例减少例句A heavy iron chain was clamped around his wrists.The earth's core is a hot, molten mix of iron and nickel.The roof is made from sheets of corrugated iron.The autopsy revealed that his murderer had struck him on the head with an iron bar.Working iron requires higher temperatures than bronze.

iron noun

(FOR CLOTHES)

B1 [ C ] a piece of equipment for making clothes flat and smooth that has a handle and a flat base and is usually heated with electricity

熨斗

a steam iron

蒸汽熨斗

a travel iron

旅行用熨斗

更多范例减少例句I'll have to go back to the house - I think I've left the iron on.I'm not particularly what you would call a New Man, but I do know how to use an iron.The iron was too hot and he scorched the shirt.The hot iron left a singe mark on my dress.I picked up a new steam iron at the sale - it makes the ironing so much quicker and easier.

iron noun

(GOLF)

[ C ] a stick that has an iron or steel part at the end that is used to hit the ball in golf

（高尔夫球运动中的）铁头球杆，铁杆

He'll probably use a 2 or 3 iron for the shot.

他这一击很可能要用2号或3号铁头球杆。

iron noun

(CHAINS)

 irons [ plural ] literary

chains tied around someone to prevent them from escaping or moving: It was common practice for the prisoners to be clapped in irons (= tied with chains).

通常会用镣铐铐住犯人。

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习语

have a few, several, etc. irons in the fire

ironverb [ I or T ] uk

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/aɪən/ us

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/aɪrn/

B1 to make clothes flat and smooth using an iron

熨（衣），烫平

It takes about five minutes to iron a shirt properly.

熨好一件衬衣大约需要5分钟。

同义词

press

短语动词

iron something out

ironadjective [ before noun ] uk

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/aɪən/ us

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/aɪrn/

very strong physically, mentally, or emotionally

极强壮的；强硬坚定的

I think you have to have an iron will to make some of these decisions.

我认为你得有钢铁般的意志才能作出这些决定。

习语

an iron hand/fist in a velvet glove

rule something with an iron hand/fist

(iron在剑桥英语-中文（简体）词典的翻译 © Cambridge University Press)

iron的例句

iron

The matter has to be ironed out and specific arrangements detailed and spelt out.

来自 Hansard archive

该例句来自Hansard存档。包含以下议会许可信息开放议会许可v3.0

Why did the legal quibble have to be ironed out before the students were allowed to make their contribution?

来自 Hansard archive

该例句来自Hansard存档。包含以下议会许可信息开放议会许可v3.0

With growing operating experience, most of the problems are progressively being ironed out.

来自 Hansard archive

该例句来自Hansard存档。包含以下议会许可信息开放议会许可v3.0

There are serious anomalies to be ironed out.

来自 Hansard archive

该例句来自Hansard存档。包含以下议会许可信息开放议会许可v3.0

Ironing out our differences will make an important contribution to both economies.

来自 Europarl Parallel Corpus - English

There are still many defects to be ironed out.

来自 Europarl Parallel Corpus - English

Over what period of time does he envisage redeployment ironing out these differences between regions?

来自 Hansard archive

该例句来自Hansard存档。包含以下议会许可信息开放议会许可v3.0

The change of course does, however, mean that we need to have different irons in the fire.

来自 Europarl Parallel Corpus - English

示例中的观点不代表剑桥词典编辑、剑桥大学出版社和其许可证颁发者的观点。

B1,B1,B1

iron的翻译

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金屬, 鐵, 衣服…

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hierro, plancha, hierro de golf…

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एक रासायनिक मूलद्रव्य जे एक सामान्य राखाडी रंगाचे धातू आहे. हे मजबूत आहे, स्टील बनविण्यासाठी वापरले जाते आणि रक्तात खूप कमी प्रमाणात अस्तित्वात आहे, लोखंड…

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ஒரு வேதியியல் தனிமம், இது ஒரு பொதுவான சாம்பல் நிற உலோகமாகும். இது வலுவானது, எஃகு தயாரிக்கப் பயன்படுகிறது…

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jern, jern-, strygejern…

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besi, seterika, pemukul golf…

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jern [neuter], strykejern [neuter], stryke…

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فولاد, لوہا, آہن…

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залізо, праска, гольф-клуб типу “айрон”…

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железо, утюг, гладить…

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ఇనుము/ ఒక రసాయన మూలకం ఇది సాధారణ బూడిద-రంగు లోహం. ఇది బలమైనది, ఉక్కు తయారీలో ఉపయోగించబడుతుంది మరియు రక్తంలో చాలా తక్కువ మొత్తంలో ఉంటుంది., ఇస్త్రీ పెట్టె / ఒక చేతిపిడి…

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حَديد, مِكْواة, يَكْوي…

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železo, železný, žehlička…

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besi, seterikaan, pemukul golf…

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เหล็ก, เตารีด, ไม้ตีกอล์ฟที่ส่วนหัวทำด้วยเหล็ก…

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sắt, bàn là, một hình thức câu lạc bộ gôn…

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żelazo, żelazko, prasować…

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철, 다리미, 다림질하다…

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ferro, ferro da stiro, stirare…

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在英语词典中查看 iron 的释义

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Irishwoman

irk

irksome

IRL

iron

Iron Age

iron box

iron lung

iron man

iron更多的中文(简体)翻译

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Iron Age

iron box

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cast iron

cast-iron

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词组动词

iron something out

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惯用语

pump iron idiom

rule something with an iron hand/fist idiom

strike while the iron is hot idiom

an iron hand/fist in a velvet glove idiom

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“每日一词”

veggie burger

UK

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/ˈvedʒ.i ˌbɜː.ɡər/

US

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/ˈvedʒ.i ˌbɝː.ɡɚ/

a type of food similar to a hamburger but made without meat, by pressing together small pieces of vegetables, seeds, etc. into a flat, round shape

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英语-中文（简体） 

Noun 

iron (METAL)

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irons

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Iron - Health Professional Fact Sheet

Iron - Health Professional Fact Sheet

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Home > Health Information > Dietary Supplement Fact Sheets > Iron > Iron - Health Professional

Iron

Fact Sheet for Health Professionals

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Table of Contents

Introduction

Recommended Intakes

Sources of Iron

Iron Intakes and Status

Iron Deficiency

Groups at Risk of Iron Inadequacy

Iron and Health

Health Risks from Excessive Iron

Interactions with Medications

Iron and Healthful Diets

References

Disclaimer

This is a fact sheet intended for health professionals. For a general overview, see our consumer fact sheet.

Introduction

Iron is a mineral that is naturally present in many foods, added to some food products, and available as a dietary supplement. Iron is an essential component of hemoglobin, an erythrocyte (red blood cell) protein that transfers oxygen from the lungs to the tissues [1]. As a component of myoglobin, another protein that provides oxygen, iron supports muscle metabolism and healthy connective tissue [2]. Iron is also necessary for physical growth, neurological development, cellular functioning, and synthesis of some hormones [2,3].

Dietary iron has two main forms: heme and nonheme [1]. Plants and iron-fortified foods contain nonheme iron only, whereas meat, seafood, and poultry contain both heme and nonheme iron [2]. Heme iron, which is formed when iron combines with protoporphyrin IX, contributes about 10% to 15% of total iron intakes in western populations [3-5].

Most of the 3 to 4 grams of elemental iron in adults is in hemoglobin [2]. Much of the remaining iron is stored in the form of ferritin or hemosiderin (a degradation product of ferritin) in the liver, spleen, and bone marrow or is located in myoglobin in muscle tissue [1,5]. Transferrin is the main protein in blood that binds to iron and transports it throughout the body. Humans typically lose only small amounts of iron in urine, feces, the gastrointestinal tract, and skin. Losses are greater in menstruating women because of blood loss. Hepcidin, a circulating peptide hormone, is the key regulator of both iron absorption and the distribution of iron throughout the body, including in plasma [1,2,6].

The assessment of iron status depends almost entirely on hematological indicators [7]. However, these indicators are not sensitive or specific enough to adequately describe the full spectrum of iron status, and this can complicate the diagnosis of iron deficiency. A complementary approach is to consider how iron intakes from the diet and dietary supplements compare with recommended intakes.

Iron deficiency progresses from depletion of iron stores (mild iron deficiency), to iron-deficiency erythropoiesis (erythrocyte production), and finally to iron deficiency anemia (IDA) [8,9]. With iron-deficiency erythropoiesis (also known as marginal iron deficiency), iron stores are depleted and transferrin saturation declines, but hemoglobin levels are usually within the normal range. IDA is characterized by low hemoglobin concentrations, and decreases in hematocrit (the proportion of red blood cells in blood by volume) and mean corpuscular volume (a measure of erythrocyte size) [2,10].

Serum ferritin concentration, a measure of the body's iron stores, is currently the most efficient and cost-effective test for diagnosing iron deficiency [11-13]. Because serum ferritin decreases during the first stage of iron depletion, it can identify low iron status before the onset of IDA [7,9,14]. A serum ferritin concentration lower than 30 mcg/L suggests iron deficiency, and a value lower than 10 mcg/L suggests IDA [15]. However, serum ferritin is subject to influence by inflammation (due, for example, to infectious disease), which elevates serum ferritin concentrations [16].

Hemoglobin and hematocrit tests are the most commonly used measures to screen patients for iron deficiency, even though they are neither sensitive nor specific [5,7,17]. Often, hemoglobin concentrations are combined with serum ferritin measurements to identify IDA [7]. Hemoglobin concentrations lower than 11 g/dL in children under 10 years of age, or lower than 12 g/dL in individuals age 10 years or older, suggest IDA [8]. Normal hematocrit values are approximately 41% to 50% in males and 36% to 44% in females [18].

Recommended Intakes

Intake recommendations for iron and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine (IOM) of the National Academies (formerly National Academy of Sciences) [5]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender, include the following:

Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals

Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA

Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals

Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects

Table 1 lists the current iron RDAs for nonvegetarians. The RDAs for vegetarians are 1.8 times higher than for people who eat meat. This is because heme iron from meat is more bioavailable than nonheme iron from plant-based foods, and meat, poultry, and seafood increase the absorption of nonheme iron [5].

For infants from birth to 6 months, the FNB established an AI for iron that is equivalent to the mean intake of iron in healthy, breastfed infants.

Table 1: Recommended Dietary Allowances (RDAs) for Iron [5]

Age

Male

Female

Pregnancy

Lactation

Birth to 6 months

0.27 mg*

0.27 mg*

7–12 months

11 mg

11 mg

1–3 years

7 mg

7 mg

4–8 years

10 mg

10 mg

9–13 years

8 mg

8 mg

14–18 years

11 mg

15 mg

27 mg

10 mg

19–50 years

8 mg

18 mg

27 mg

9 mg

51+ years

8 mg

8 mg

* Adequate Intake (AI)

Sources of Iron

Food

The richest sources of heme iron in the diet include lean meat and seafood [19]. Dietary sources of nonheme iron include nuts, beans, vegetables, and fortified grain products. In the United States, about half of dietary iron comes from bread, cereal, and other grain products [2,3,5]. Breast milk contains highly bioavailable iron but in amounts that are not sufficient to meet the needs of infants older than 4 to 6 months [2,20].

In the United States, Canada, and many other countries, wheat and other flours are fortified with iron [21,22]. Infant formulas are fortified with 12 mg iron per liter [20].

Heme iron has higher bioavailability than nonheme iron, and other dietary components have less effect on the bioavailability of heme than nonheme iron [3,4]. The bioavailability of iron is approximately 14% to 18% from mixed diets that include substantial amounts of meat, seafood, and vitamin C (ascorbic acid, which enhances the bioavailability of nonheme iron) and 5% to 12% from vegetarian diets [2,4]. In addition to ascorbic acid, meat, poultry, and seafood can enhance nonheme iron absorption, whereas phytate (present in grains and beans) and certain polyphenols in some nonanimal foods (such as cereals and legumes) have the opposite effect [4]. Unlike other inhibitors of iron absorption, calcium might reduce the bioavailability of both nonheme and heme iron. However, the effects of enhancers and inhibitors of iron absorption are attenuated by a typical mixed western diet, so they have little effect on most people’s iron status.

Several food sources of iron are listed in Table 2. Some plant-based foods that are good sources of iron, such as spinach, have low iron bioavailability because they contain iron-absorption inhibitors, such as polyphenols [23,24].

Table 2: Iron Content of Selected Foods [25]

Food

Milligrams (mg)

per serving

Percent DV*

Breakfast cereals, fortified with 100% of the DV for iron, 1 serving

18

100

Oysters, eastern, cooked with moist heat, 3 ounces

8

44

White beans, canned, 1 cup

8

44

Beef liver, pan fried, 3 ounces

5

28

Lentils, boiled and drained, ½ cup

3

17

Spinach, boiled and drained, ½ cup

3

17

Tofu, firm, ½ cup

3

17

Chocolate, dark, 45%–69% cacao solids, 1 ounce

2

11

Kidney beans, canned, ½ cup

2

11

Sardines, Atlantic, canned in oil, drained solids with bone, 3 ounces

2

11

Chickpeas, boiled and drained, ½ cup

2

11

Tomatoes, canned, stewed, ½ cup

2

11

Beef, braised bottom round, trimmed to 1/8" fat, 3 ounces

2

11

Potato, baked, flesh and skin, 1 medium potato

2

11

Cashew nuts, oil roasted, 1 ounce (18 nuts)

2

11

Green peas, boiled, ½ cup

1

6

Chicken, roasted, meat and skin, 3 ounces

1

6

Rice, white, long grain, enriched, parboiled, drained, ½ cup

1

6

Bread, whole wheat, 1 slice

1

6

Bread, white, 1 slice

1

6

Raisins, seedless, ¼ cup

1

6

Spaghetti, whole wheat, cooked, 1 cup

1

6

Tuna, light, canned in water, 3 ounces

1

6

Turkey, roasted, breast meat and skin, 3 ounces

1

6

Nuts, pistachio, dry roasted, 1 ounce (49 nuts)

1

6

Broccoli, boiled and drained, ½ cup

1

6

Egg, hard boiled, 1 large

1

6

Rice, brown, long or medium grain, cooked, 1 cup

1

6

Cheese, cheddar, 1.5 ounces

0

0

Cantaloupe, diced, ½ cup

0

0

Mushrooms, white, sliced and stir-fried, ½ cup

0

0

Cheese, cottage, 2% milk fat, ½ cup

0

0

Milk, 1 cup

0

0

* DV = Daily Value. The U.S. Food and Drug Administration (FDA) developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for iron is 18 mg for adults and children age 4 years and older [26]. FDA requires food labels to list iron content. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.

The U.S. Department of Agriculture’s (USDA’s) FoodData Central [25] lists the nutrient content of many foods and provides a comprehensive list of foods containing iron arranged by nutrient content and by food name.

Dietary supplements

Iron is available in many dietary supplements. Multivitamin/mineral supplements with iron, especially those designed for women, typically provide 18 mg iron (100% of the DV). Multivitamin/mineral supplements for men or seniors frequently contain less or no iron. Iron-only supplements usually deliver more than the DV, with many providing 65 mg iron (360% of the DV).

Frequently used forms of iron in supplements include ferrous and ferric iron salts, such as ferrous sulfate, ferrous gluconate, ferric citrate, and ferric sulfate [3,27]. Because of its higher solubility, ferrous iron in dietary supplements is more bioavailable than ferric iron [3]. High doses of supplemental iron (45 mg/day or more) may cause gastrointestinal side effects, such as nausea and constipation [5]. Other forms of supplemental iron, such as heme iron polypeptides, carbonyl iron, iron amino-acid chelates, and polysaccharide-iron complexes, might have fewer gastrointestinal side effects than ferrous or ferric salts [27].

The different forms of iron in supplements contain varying amounts of elemental iron. For example, ferrous fumarate is 33% elemental iron by weight, whereas ferrous sulfate is 20% and ferrous gluconate is 12% elemental iron [27]. Fortunately, elemental iron is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of iron supplied by various forms of iron supplements.

Approximately 14% to 18% of Americans use a supplement containing iron [28,29]. Rates of use of supplements containing iron vary by age and gender, ranging from 6% of children age 12 to 19 years to 60% of women who are lactating and 72% of pregnant women [28,30].

Calcium might interfere with the absorption of iron, although this effect has not been definitively established [4,31]. For this reason, some experts suggest that people take individual calcium and iron supplements at different times of the day [32].

Iron Intakes and Status

People in the United States usually obtain adequate amounts of iron from their diets, but infants, young children, teenage girls, pregnant women, and premenopausal women are at risk of obtaining insufficient amounts [28,33-35]. The average daily iron intake from foods is 11.5–13.7 mg/day in children age 2–11 years, 15.1 mg/day in children and teens age 12–19 years, and 16.3–18.2 mg/day in men and 12.6–13.5 mg/day in women older than 19 [28]. The average daily iron intake from foods and supplements is 13.7–15.1 mg/day in children age 2–11 years, 16.3 mg/day in children and teens age 12–19 years, and 19.3–20.5 mg/day in men and 17.0–18.9 mg/day in women older than 19. The median dietary iron intake in pregnant women is 14.7 mg/day [5].

Rates of iron deficiency vary by race and other sociodemographic factors. Six percent of White and Black toddlers age 1 to 3 years in the United States are iron deficient (defined as at least two abnormal results for the child’s age and gender on transferrin saturation, free erythrocyte protoporphyrin, and/or serum ferritin tests), compared with 12% of Hispanic toddlers [36]. Deficiency (including IDA) is more common among children and adolescents in food-insecure households than in food-secure households [36,37]. Among pregnant women, deficiency based on depleted iron stores is more common in Mexican American (23.6%) and non-Hispanic Black women (29.6%) than in non-Hispanic White women (13.9%) [38].

Some groups are at risk of obtaining excess iron. Individuals with hereditary hemochromatosis, which predisposes them to absorb excessive amounts of dietary iron, have an increased risk of iron overload [39]. One study suggests that elderly people are more likely to have chronic positive iron balance and elevated total body iron than iron deficiency. Among 1,106 elderly White adults age 67 to 96 years in the Framingham Heart Study, 13% had high iron stores (serum ferritin levels higher than 300 mcg/L in men and 200 mcg/L in women), of which only 1% was due to chronic disease [40]. The authors did not assess genotypes, so they could not determine whether these results were due to hemochromatosis [40].

Iron Deficiency

Iron deficiency is not uncommon in the United States, especially among young children, women of reproductive age, and pregnant women. Because iron deficiency is associated with poor diet, malabsorptive disorders, and blood loss, people with iron deficiency usually have other nutrient deficiencies [2]. The World Health Organization (WHO) estimates that approximately half of the 1.62 billion cases of anemia worldwide are due to iron deficiency [41]. In developing countries, iron deficiency often results from enteropathies and blood loss associated with gastrointestinal parasites [2].

Iron depletion and deficiency progresses through several stages [8-10]:

Mild deficiency or storage iron depletion: Serum ferritin concentrations and levels of iron in bone marrow decrease.

Marginal deficiency, mild functional deficiency, or iron-deficient erythropoiesis (erythrocyte production): Iron stores are depleted, iron supply to erythropoietic cells and transferrin saturation decline, but hemoglobin levels are usually within the normal range.

IDA: Iron stores are exhausted; hematocrit and levels of hemoglobin decline; and the resulting microcytic, hypochromic anemia is characterized by small red blood cells with low hemoglobin concentrations.

In 2002, the WHO characterized IDA as one of the 10 leading risk factors for disease around the world [42]. Although iron deficiency is the most common cause of anemia, deficiencies of other micronutrients (such as folate and vitamin B12) and other factors (such as chronic infection and inflammation) can cause different forms of anemia or contribute to their severity.

The functional deficits associated with IDA include gastrointestinal disturbances; weakness; fatigue; difficulty concentrating; and impaired cognitive function, immune function, exercise or work performance, and body temperature regulation [15,43]. In infants and children, IDA can result in psychomotor and cognitive abnormalities that, without treatment, can lead to learning difficulties [2,43]. Some evidence indicates that the effects of deficiencies early in life persist through adulthood [2]. Because iron deficiency is often accompanied by deficiencies of other nutrients, the signs and symptoms of iron deficiency can be difficult to isolate [2].

Groups at Risk of Iron Inadequacy

The following groups are among those most likely to have inadequate intakes of iron.

Pregnant women

During pregnancy, plasma volume and red cell mass expand due to dramatic increases in maternal red blood cell production [2]. As a result of this expansion and to meet the needs of the fetus and placenta, the amount of iron that women need increases during pregnancy. Iron deficiency during pregnancy increases the risk of maternal and infant mortality, premature birth, and low birthweight [44].

Infants and young children

Infants—especially those born preterm or with low birthweight or whose mothers have iron deficiency—are at risk of iron deficiency because of their high iron requirements due to their rapid growth [34,45]. Full-term infants usually have sufficient iron stores and need little if any iron from external sources until they are 4 to 6 months old [2]. However, full-term infants have a risk of becoming iron deficient at 6 to 9 months unless they obtain adequate amounts of solid foods that are rich in bioavailable iron or iron-fortified formula.

Women with heavy menstrual bleeding

Women of reproductive age who have menorrhagia, or abnormally heavy bleeding during menstruation, are at increased risk of iron deficiency. At least 10% of menstruating women are believed to have menorrhagia, but the percentage varies widely depending on the diagnostic criteria used [46-48]. Women with menorrhagia lose significantly more iron per menstrual cycle on average than women with normal menstrual bleeding [49]. Limited evidence suggests that menorrhagia might be responsible for about 33% to 41% of cases of IDA in women of reproductive age [50,51].

Frequent blood donors

Frequent blood donors have an increased risk of iron deficiency [5]. In the United States, adults may donate blood as often as every 8 weeks, which can deplete iron stores. About 25%–35% of regular blood donors develop iron deficiency [52]. In a study of 2,425 blood donors, men who had given at least three and women who had given at least two whole-blood donations in the previous year were more than five times as likely to have depleted iron stores as first-time donors [53]. A clinical trial of iron supplementation found that of 215 adults who had donated a unit of blood within the past 3–8 days, those randomized to take an iron supplement (37.5 mg/day elemental iron from ferrous gluconate) for 24 weeks recovered their lost hemoglobin and iron in less than half the time of those not given the supplement [52]. Without iron supplementation, two-thirds of the donors had not recovered the iron they lost, even after 24 weeks.

People with cancer

Up to 60% of patients with colon cancer have iron deficiency at diagnosis, probably due to chronic blood loss [54]. The prevalence of iron deficiency in patients with other types of cancer ranges from 29% to 46%. The main causes of iron deficiency in people with cancer are anemia of chronic disease (discussed in the Iron and Health section below) and chemotherapy-induced anemia. However, chronic blood loss and deficiencies of other nutrients (due, for example, to cancer-induced anorexia) can exacerbate iron deficiency in this population.

People who have gastrointestinal disorders or have had gastrointestinal surgery

People with certain gastrointestinal disorders (such as celiac disease, ulcerative colitis, and Crohn’s disease) or who have undergone certain gastrointestinal surgical procedures (such as gastrectomy or intestinal resection) have an increased risk of iron deficiency because their disorder or surgery requires dietary restrictions or results in iron malabsorption or blood loss in the gastrointestinal tract [55-57]. The combination of low iron intake and high iron loss can lead to a negative iron balance; reduced production of hemoglobin; or microcytic, hypochromic anemia [58].

People with heart failure

Approximately 60% of patients with chronic heart failure have iron deficiency and 17% have IDA, which might be associated with a higher risk of death in this population [59,60]. Potential causes of iron deficiency in people with heart failure include poor nutrition; malabsorption; defective mobilization of iron stores; cardiac cachexia; and use of aspirin and oral anticoagulants, which might result in the loss of some blood in the gastrointestinal tract [61].

Iron and Health

This section focuses on the role of iron in IDA in pregnant women, infants, and toddlers as well as in anemia of chronic disease.

Iron deficiency anemia in pregnant women

Insufficient iron intakes during pregnancy increase a woman’s risk of IDA [62-65]. Low intakes also increase her infant’s risk of low birthweight, premature birth, low iron stores, and impaired cognitive and behavioral development.

An analysis of 1999–2006 data from the National Health and Nutrition Examination Survey (NHANES) found that 18% of pregnant women in the United States had iron deficiency [38]. Rates of deficiency were 6.9% among women in the first trimester,14.3% in the second trimester, and 29.7% in the third trimester.

Randomized controlled trials have shown that iron supplementation can prevent IDA in pregnant women and related adverse consequences in their infants [66,67]. A Cochrane Review showed that daily supplementation with 9–90 mg iron reduced the risk of anemia in pregnant women at term by 70% and of iron deficiency at term by 57% [64]. In the same review, use of daily iron supplements was associated with an 8.4% risk of having a low-birthweight newborn compared to 10.2% with no supplementation. In addition, mean birthweight was 31 g higher for infants whose mothers took daily iron supplements during pregnancy compared with the infants of mothers who did not take iron.

Guidelines on iron supplementation during pregnancy vary:

The American College of Obstetricians and Gynecologists (ACOG) states that good and consistent evidence shows that iron supplementation decreases the prevalence of maternal anemia at delivery [68]. However, it acknowledges that only limited or inconsistent evidence shows that IDA during pregnancy is associated with a higher risk of low birthweight, preterm birth, or perinatal mortality. ACOG recommends screening all pregnant women for anemia and treating those with IDA (which it defines as hematocrit levels less than 33% in the first and third trimesters and less than 32% in the second trimester) with supplemental iron in addition to prenatal vitamins [68].

In contrast, the U.S. Preventive Services Task Force (USPSTF) has concluded that the current evidence is insufficient to recommend for or against both screening for IDA in pregnant women and routinely supplementing them with iron to prevent adverse maternal health and birth outcomes [69]. They note, however, that their recommendation does not apply to pregnant women who are malnourished, have symptoms of iron deficiency anemia, or those with special hematologic conditions or nutritional needs that increase iron requirements.

The IOM notes that because the median intake of dietary iron by pregnant women is well below the EAR, pregnant women need iron supplementation [5]. The Dietary Guidelines for Americans advises that women who are pregnant take an iron supplement when recommended by an obstetrician or other health-care provider [19]. It adds that low intakes of iron are a public health concern for pregnant women.

Iron deficiency anemia in infants and toddlers

Approximately 12% of infants age 6 to 11 months in the United States have inadequate iron intakes, and 8% of toddlers have iron deficiency [36,70]. The prevalence of IDA in U.S. toddlers age 12 to 35 months ranges from 0.9% to 4.4% depending on race or ethnicity and socioeconomic status [20]. Full-term infants typically have adequate iron stores for approximately the first 4 to 6 months, but the risk of iron deficiency in low-birthweight and preterm infants begins at birth because of their low iron stores.

IDA in infancy can lead to adverse cognitive and psychological effects, including delayed attention and social withdrawal; some of these effects might be irreversible [2,20]. In addition, IDA is associated with higher lead concentrations in the blood (although the cause of this is not fully understood), which can increase the risk of neurotoxicity [20].

A Cochrane Review of 26 studies in 2,726 preterm and low-birthweight infants found that enteral iron supplementation (at least 1 mg/kg/day) reduces the risk of iron deficiency, but the long-term effects of supplementation on neurodevelopmental outcomes and growth is not clear [71]. Another Cochrane Review of eight trials in 3,748 children younger than 2 in low-income countries showed that home fortification of semi-solid foods with micronutrient powders containing 12.5 mg to 30 mg elemental iron as ferrous fumarate and 4 to 14 other micronutrients for 2 to 12 months reduced rates of anemia by 31% and of iron deficiency by 51% compared with no intervention or placebo but had no effect on any growth measurements [72].

Guidelines vary on dietary iron intakes and possible supplementation to ensure adequate iron status and to prevent or treat IDA in infants and young children:

The Centers for Disease Control and Prevention (CDC) recommends that infants less than 12 months of age who are not exclusively or primarily breastfed drink iron-fortified infant formula [17]. Breastfed infants who were born preterm or with a low birthweight should receive 2–4 mg/kg/day of iron drops (to a maximum of 15 mg/day) from ages 1–12 months. Breastfed infants who receive insufficient iron (less than 1 mg/kg/day) from supplementary foods by age 6 months should receive 1 mg/kg/day of iron drops. The CDC also recommends that infants and preschool children at high risk for IDA (e.g., children from low-income families and migrant children) be screened between age 9–12 months, 6 months later, and annually from age 2–5 years. Treatment for IDA begins with 3 mg/kg/day of iron drops given between meals. (See reference 17 for additional advice from the CDC.)

The American Academy of Pediatrics recommends 1 mg/kg daily iron supplementation for exclusively or primarily breastfed full-term infants from age 4 months until the infants begin eating iron-containing complementary foods, such as iron-fortified cereals [20]. Standard infant formulas containing 10 to 12 mg/L iron can meet the iron needs of infants for the first year of life. The Academy recommends 2 mg/kg/day iron supplementation for preterm infants age 1 to 12 months who are fed breast milk.

The WHO recommends universal supplementation with 2 mg/kg/day of iron in children age 6 to 23 months whose diet does not include foods fortified with iron or who live in regions (such as developing countries) where anemia prevalence is higher than 40% [44].

In a recommendation statement issued in 2015, the USPSTF concluded that the available evidence is insufficient to recommend for or against routine screening for IDA in children age 6 to 24 months who live in the United States and who are asymptomatic for IDA [73]. It added that this recommendation does not apply to severely malnourished children or children who were born prematurely or with low birthweight. Earlier, in 2006, the USPSTF stated that although it found insufficient evidence to recommend routine iron supplementation in asymptomatic infants at average risk of IDA, it did recommend routine iron supplements for children age 6 to 12 months who are at increased risk of IDA (e.g., those who were premature or low birthweight) [74]. The USPSTF's 2015 statement notes that its current recommendation is limited to screening because the widespread use of iron-fortified foods in the United States (including infant formulas and cereals) would likely limit the impact of iron supplementation prescribed by physicians [73].

Some studies have suggested that iron supplementation in young children living in areas where malaria is endemic could increase their risk of malaria [75,76]. However, a Cochrane Review of 33 trials in 13,114 children showed that intermittent supplementation does not appear to have this effect [77]. The WHO therefore recommends 6-month supplementation cycles as follows: children age 24 to 59 months should receive 25 mg iron and those age 5 to 12 years should receive 45 mg every week for 3 months, followed by 3 months of no supplementation [75]. The WHO recommends providing these supplements in malaria-endemic areas in conjunction with measures to prevent, diagnose, and treat malaria.

Anemia of chronic disease

Certain inflammatory, infectious, and neoplastic diseases (such as rheumatoid arthritis, inflammatory bowel disease, and hematologic malignancies) can cause anemia of chronic disease, also known as anemia of inflammation [2,78]. Anemia of chronic disease is the second most common type of anemia after IDA [79]. In people with anemia of chronic disease, inflammatory cytokines upregulate the hormone hepcidin. As a result, iron homeostasis is disrupted and iron is diverted from the circulation to storage sites, limiting the amount of iron available for erythropoiesis.

Anemia of chronic disease is usually mild to moderate (hemoglobin levels 8 to 9.5 g/dL) and is associated with low counts of erythrocytes and decreased erythropoiesis [78]. The condition can be difficult to diagnose because, although low serum ferritin levels indicate iron deficiency, these levels tend to be higher in patients with infection or inflammation [80].

The clinical implications of iron deficiency in people with chronic diseases are not clear. Even mild anemia of chronic disease is associated with an increased risk of hospitalization and mortality in elderly people [81]. Two prospective observational studies found that iron deficiency in patients with objectively measured heart failure was associated with an increased risk of heart transplantation and death, and this association was independent of other well-established prognostic factors for poor outcomes, including anemia [82,83]. However, an analysis of NHANES data on 574 adults with self-reported heart failure found no association between iron deficiency and all-cause or cardiovascular mortality [60].

The main therapy for anemia of chronic disease is treatment of the underlying disease [79]. But when such treatment is not possible, iron supplementation and/or erythropoiesis-stimulating agents (ESAs) are sometimes used. The use of iron supplements—whether oral, intravenous, or parenteral—in this setting is controversial because they might increase the risk of infection and cardiovascular events and could cause tissue damage [79].

Only a few small studies have evaluated the benefits of oral iron supplementation alone or in combination with ESAs to treat anemia of chronic disease. For example, a prospective observational study in 132 patients with anemia and chronic kidney disease who were not on dialysis or ESAs found that oral supplements (130 mg/day elemental iron from ferrous sulfate twice daily) for 1 year resulted in a decline in hemoglobin of only 0.13 g/dL compared with 0.46 g/dL in the placebo group [76,84]. A randomized trial of oral iron supplements (equivalent to 200 mg/day elemental iron, form of iron not specified) taken with an ESA once weekly in 100 patients with cancer-related anemia resulted in a mean increase of 2.4 g/dL hemoglobin after 24 weeks compared with oral supplements only [85]. Iron administered parentally increases hemoglobin levels to a greater extent and is associated with fewer side effects than oral iron supplementation in patients with anemia of chronic disease [86].

Health Risks from Excessive Iron

Adults with normal intestinal function have very little risk of iron overload from dietary sources of iron [2]. However, supplements containing 25 mg iron or more can reduce zinc absorption and plasma zinc concentrations [3,87,88]. High-dose iron supplements can also cause gastrointestinal effects, including gastric upset, constipation, nausea, abdominal pain, vomiting, and diarrhea [5,89]. Taking iron supplements with food can help minimize these adverse effects. Case reports, some involving doses of 130 mg iron, suggest that some people develop even more serious gastrointestinal effects, including gastritis and gastric lesions (along with iron deposits in the gastric mucosa in some cases) [90-93].

Acute intakes of more than 20 mg/kg iron (about 1,365 mg iron for a person weighing 150 lb) from supplements or medicines can lead to corrosive necrosis of the intestine, which might lead to fluid and blood loss, shock, tissue damage, and organ failure, especially if food is not taken at the same time as the iron [89]. In severe cases (e.g., one-time ingestions of 60 mg/kg, or about 4,090 mg iron for a 150-lb person), overdoses of iron can lead to multisystem organ failure, coma, convulsions, and even death [27,94].

Between 1983 and 2000, at least 43 U.S. children died from ingesting supplements containing high doses of iron (36–443 mg iron/kg body weight) [27]. Accidental ingestion of iron supplements caused about a third of poisoning deaths among children reported in the United States between 1983 and 1991.

In 1997, FDA began requiring oral supplements containing more than 30 mg elemental iron per dose to be sold in single-dose packaging with strong warning labels. At the same time, many manufacturers voluntarily replaced the sugar coating on iron tablets with film coatings. Between 1998 and 2002, only one child death due to ingesting an iron-containing tablet was reported [27]. As a result of a court decision, FDA removed its single-dose packaging requirement for iron supplements in 2003 [95]. FDA currently requires that iron-containing dietary supplements sold in solid form (e.g., tablets or capsules but not powders) carry the following label statement: “WARNING: Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6. Keep this product out of reach of children. In case of accidental overdose, call a doctor or poison control center immediately” [96]. In addition, since 1978, the Consumer Product Safety Commission has required manufacturers to package dietary supplements containing 250 mg or more elemental iron per container in child-resistant bottles or packaging to prevent accidental poisoning [97,98].

Hemochromatosis, a disease caused by a mutation in the hemochromatosis (HFE) gene, is associated with an excessive buildup of iron in the body [3,39,99]. About 1 in 10 Whites carry the most common HFE mutation (C282Y), but only 4.4 Whites per 1,000 are homozygous for the mutation and have hemochromatosis [100]. The condition is much less common in other ethnic groups. Without treatment by periodic chelation or phlebotomy, people with hereditary hemochromatosis typically develop signs of iron toxicity by their 30s [3]. These effects can include liver cirrhosis, hepatocellular carcinoma, heart disease, and impaired pancreatic function. The American Association for the Study of Liver Diseases recommends that treatment of hemochromatosis include the avoidance of iron and vitamin C supplements [39].

The FNB has established ULs for iron from food and supplements based on the amounts of iron that are associated with gastrointestinal effects following supplemental intakes of iron salts (see Table 3). The ULs apply to healthy infants, children, and adults. Physicians sometimes prescribe intakes higher than the UL, such as when people with IDA need higher doses to replenish their iron stores [5].

Table 3: Tolerable Upper Intake Levels (ULs) for Iron [5]

Age

Male

Female

Pregnancy

Lactation

Birth to 6 months

40 mg

40 mg

7–12 months

40 mg

40 mg

1–3 years

40 mg

40 mg

4–8 years

40 mg

40 mg

9–13 years

40 mg

40 mg

14–18 years

45 mg

45 mg

45 mg

45 mg

19+ years

45 mg

45 mg

45 mg

45 mg

Interactions with Medications

Iron can interact with certain medications, and some medications can have an adverse effect on iron levels. A few examples are provided below. Individuals taking these and other medications on a regular basis should discuss their iron status with their health care providers.

Levodopa

Some evidence indicates that in healthy people, iron supplements reduce the absorption of levodopa (found in Sinemet and Stalevo), used to treat Parkinson’s disease and restless leg syndrome, possibly through chelation [101-103]. In the United States, the labels for levodopa warn that iron-containing dietary supplements might reduce the amount of levodopa available to the body and, thus, diminish its clinical effectiveness [104,105].

Levothyroxine

Levothyroxine (Levothroid, Levoxyl, Synthroid, Tirosint, and Unithroid) is used to treat hypothyroidism, goiter, and thyroid cancer. The simultaneous ingestion of iron and levothyroxine can result in clinically significant reductions in levothyroxine efficacy in some patients [106]. The labels for some of these products [107,108] warn that iron supplements can reduce the absorption of levothyroxine tablets and advise against administering levothyroxine within 4 hours of iron supplements.

Proton pump inhibitors

Gastric acid plays an important role in the absorption of nonheme iron from the diet. Because proton pump inhibitors, such as lansoprazole (Prevacid) and omeprazole (Prilosec), reduce the acidity of stomach contents, they can reduce iron absorption [3]. Treatment with proton pump inhibitors for up to 10 years is not associated with iron depletion or anemia in people with normal iron stores [109] but patients with iron deficiency taking proton pump inhibitors can have suboptimal responses to iron supplementation [110].

Iron and Healthful Diets

The federal government's 2020–2025 Dietary Guidelines for Americans notes that "Because foods provide an array of nutrients and other components that have benefits for health, nutritional needs should be met primarily through foods. ... In some cases, fortified foods and dietary supplements are useful when it is not possible otherwise to meet needs for one or more nutrients (e.g., during specific life stages such as pregnancy)."

For more information about building a healthy dietary pattern, refer to the Dietary Guidelines for Americans and the USDA's MyPlate.

The Dietary Guidelines for Americans describes a healthy dietary pattern as one that

Includes a variety of vegetables; fruits; grains (at least half whole grains); fat-free and low-fat milk, yogurt, and cheese; and oils.

Many ready-to-eat breakfast cereals are fortified with iron, and some fruits and vegetables contain iron.

Includes a variety of protein foods such as lean meats; poultry; eggs; seafood; beans, peas, and lentils; nuts and seeds; and soy products.

Oysters and beef liver have high amounts of iron. Beef, cashews, chickpeas, and sardines are good sources of iron. Chicken, tuna, and eggs contain iron.

​​​​​​​Limits foods and beverages higher in added sugars, saturated fat, and sodium.

Limits alcoholic beverages.

Stays within your daily calorie needs.

References

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Aggett PJ. Iron. In: Erdman JW, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition. 10th ed. Washington, DC: Wiley-Blackwell; 2012:506-20.

Murray-Kolbe LE, Beard J. Iron. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:432-8.

Hurrell R, Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr 2010;91:1461S-7S. [PubMed abstract]

Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc : a Report of the Panel on Micronutrients. Washington, DC: National Academy Press; 2001.

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Fleming DJ, Jacques PF, Tucker KL, Massaro JM, D'Agostino RB, Sr., Wilson PW, et al. Iron status of the free-living, elderly Framingham Heart Study cohort: an iron-replete population with a high prevalence of elevated iron stores. Am J Clin Nutr 2001;73:638-46. [PubMed abstract]

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Matthews ML. Abnormal uterine bleeding in reproductive-aged women. Obstet Gynecol Clin North Am 2015;42:103-15. 

  [PubMed abstract]

Bitzer J, Heikinheimo O, Nelson AL, Calaf-Alsina J, Fraser IS. Medical management of heavy menstrual bleeding: a comprehensive review of the literature. Obstet Gynecol Surv 2015;70:115-30. [PubMed abstract]

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Napolitano M, Dolce A, Celenza G, Grandone E, Perilli MG, Siragusa S, et al. Iron-dependent erythropoiesis in women with excessive menstrual blood losses and women with normal menses. Ann Hematol 2014;93:557-63. [PubMed abstract]

Vannella L, Aloe Spiriti MA, Cozza G, Tardella L, Monarca B, Cuteri A, et al. Benefit of concomitant gastrointestinal and gynaecological evaluation in premenopausal women with iron deficiency anaemia. Aliment Pharmacol Ther 2008;28:422-30. [PubMed abstract]

Philipp CS, Faiz A, Dowling N, Dilley A, Michaels LA, Ayers C, et al. Age and the prevalence of bleeding disorders in women with menorrhagia. Obstet Gynecol 2005;105:61-6. [PubMed abstract]

Kiss JE, Brambilla D, Glynn SA, Mast AE, Spencer BR, Stone M, et al. Oral iron supplementation after blood donation: a randomized clinical trial. JAMA 2015;313:575-83. [PubMed abstract]

Cable RG, Glynn SA, Kiss JE, Mast AE, Steele WR, Murphy EL, et al. Iron deficiency in blood donors: analysis of enrollment data from the REDS-II Donor Iron Status Evaluation (RISE) study. Transfusion 2011;51:511-22. [PubMed abstract]

Aapro M, Osterborg A, Gascon P, Ludwig H, Beguin Y. Prevalence and management of cancer-related anaemia, iron deficiency and the specific role of i.v. iron. Ann Oncol 2012;23:1954-62. [PubMed abstract]

Bayraktar UD, Bayraktar S. Treatment of iron deficiency anemia associated with gastrointestinal tract diseases. World J Gastroenterol 2010;16:2720-5. [PubMed abstract]

Gasche C, Berstad A, Befrits R, Beglinger C, Dignass A, Erichsen K, et al. Guidelines on the diagnosis and management of iron deficiency and anemia in inflammatory bowel diseases. Inflamm Bowel Dis 2007;13:1545-53. [PubMed abstract]

Bermejo F, Garcia-Lopez S. A guide to diagnosis of iron deficiency and iron deficiency anemia in digestive diseases. World J Gastroenterol 2009;15:4638-43. [PubMed abstract]

Kulnigg S, Gasche C. Systematic review: managing anaemia in Crohn's disease. Aliment Pharmacol Ther 2006;24:1507-23. [PubMed abstract]

Groenveld HF, Januzzi JL, Damman K, van Wijngaarden J, Hillege HL, van Veldhuisen DJ, et al. Anemia and mortality in heart failure patients a systematic review and meta-analysis. J Am Coll Cardiol 2008;52:818-27. [PubMed abstract]

Parikh A, Natarajan S, Lipsitz SR, Katz SD. Iron deficiency in community-dwelling US adults with self-reported heart failure in the National Health and Nutrition Examination Survey III: prevalence and associations with anemia and inflammation. Circ Heart Fail 2011;4:599-606. [PubMed abstract]

Lipsic E, van der Meer P. Erythropoietin, iron, or both in heart failure: FAIR-HF in perspective. Eur J Heart Fail 2010;12:104-5. [PubMed abstract]

Milman N. Iron in pregnancy: How do we secure an appropriate iron status in the mother and child? Ann Nutr Metab 2011;59:50-4. [PubMed abstract]

Pavord S, Myers B, Robinson S, Allard S, Strong J, Oppenheimer C. UK guidelines on the management of iron deficiency in pregnancy. Br J Haematol 2012;156:588-600. [PubMed abstract]

Pena-Rosas JP, De-Regil LM, Dowswell T, Viteri FE. Daily oral iron supplementation during pregnancy. Cochrane Database Syst Rev 2012;12:CD004736. [PubMed abstract]

Scholl TO. Maternal iron status: relation to fetal growth, length of gestation, and iron endowment of the neonate. Nutr Rev 2011;69 Suppl 1:S23-9. [PubMed abstract]

Makrides M, Crowther CA, Gibson RA, Gibson RS, Skeaff CM. Efficacy and tolerability of low-dose iron supplements during pregnancy: a randomized controlled trial. Am J Clin Nutr 2003;78:145-53. [PubMed abstract]

Cogswell ME, Parvanta I, Ickes L, Yip R, Brittenham GM. Iron supplementation during pregnancy, anemia, and birth weight: a randomized controlled trial. Am J Clin Nutr 2003;78:773-81. [PubMed abstract]

American Congress of Obstetrics and Gynecology. ACOG Practice Bulletin No. 95: anemia in pregnancy. Obstet Gynecol 2008;112:201-7. [PubMed abstract]

Siu AL, on behalf of the U.S. Preventive Services Task Force. Screening for iron deficiency anemia and iron supplementation in pregnant women to improve maternal health and birth outcomes: U.S. Preventive Services Task Force Recommendation Statement. Ann Intern Med. doi:10.7326/M15-1707. [PubMed abstract]

Butte NF, Fox MK, Briefel RR, Siega-Riz AM, Dwyer JT, Deming DM, et al. Nutrient intakes of US infants, toddlers, and preschoolers meet or exceed dietary reference intakes. J Am Diet Assoc 2010;110:S27-37. [PubMed abstract]

Mills RJ, Davies MW. Enteral iron supplementation in preterm and low birth weight infants. Cochrane Database Syst Rev 2012;3:CD005095. [PubMed abstract]

De-Regil LM, Suchdev PS, Vist GE, Walleser S, Pena-Rosas JP. Home fortification of foods with multiple micronutrient powders for health and nutrition in children under two years of age (review). Cochrane Database Syst Rev 2011:CD008959. [PubMed abstract]

Siu AL, on behalf of the US Preventive Services Task Force. Screening for iron deficiency anemia in young children: USPSTF recommendation statement. Pediatrics 2015;136:746-52. [PubMed abstract]

U.S. Preventive Services Task Force. Screening for Iron Deficiency Anemia—Including Iron Supplementation for Children and Pregnant Women: Recommendation Statementexternal. Publication No. AHRQ 06-058., 2006.

World Health Organization. Guideline: Intermittent Iron Supplementation in Preschool and School-age Children. Geneva; 2011. [PubMed abstract]

Sazawal S, Black RE, Ramsan M, Chwaya HM, Stoltzfus RJ, Dutta A, et al. Effects of routine prophylactic supplementation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting: community-based, randomised, placebo-controlled trial. Lancet 2006;367:133-43. [PubMed abstract]

De-Regil LM, Jefferds ME, Sylvetsky AC, Dowswell T. Intermittent iron supplementation for improving nutrition and development in children under 12 years of age. Cochrane Database Syst Rev 2011:CD009085. [PubMed abstract]

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Thurnham DI, McCabe LD, Haldar S, Wieringa FT, Northrop-Clewes CA, McCabe GP. Adjusting plasma ferritin concentrations to remove the effects of subclinical inflammation in the assessment of iron deficiency: a meta-analysis. Am J Clin Nutr 2010;92:546-55. [PubMed abstract]

Riva E, Tettamanti M, Mosconi P, Apolone G, Gandini F, Nobili A, et al. Association of mild anemia with hospitalization and mortality in the elderly: the Health and Anemia population-based study. Haematologica 2009;94:22-8. [PubMed abstract]

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Klip IT, Comin-Colet J, Voors AA, Ponikowski P, Enjuanes C, Banasiak W, et al. Iron deficiency in chronic heart failure: An international pooled analysis. Am Heart J 2013;165:575-82 e3. [PubMed abstract]

Kim SM, Lee CH, Oh YK, Joo KW, Kim YS, Kim S, et al. The effects of oral iron supplementation on the progression of anemia and renal dysfunction in patients with chronic kidney disease. Clin Nephrol 2011;75:472-9. [PubMed abstract]

Mystakidou K, Kalaidopoulou O, Katsouda E, Parpa E, Kouskouni E, Chondros C, et al. Evaluation of epoetin supplemented with oral iron in patients with solid malignancies and chronic anemia not receiving anticancer treatment. Anticancer Res 2005;25:3495-500. [PubMed abstract]

Cavill I, Auerbach M, Bailie GR, Barrett-Lee P, Beguin Y, Kaltwasser P, et al. Iron and the anaemia of chronic disease: a review and strategic recommendations. Curr Med Res Opin 2006;22:731-7. [PubMed abstract]

Solomons NW. Competitive interaction of iron and zinc in the diet: consequences for human nutrition. J Nutr 1986;116:927-35. [PubMed abstract]

Whittaker P. Iron and zinc interactions in humans. Am J Clin Nutr 1998;68:442S-6S. [PubMed abstract]

Aggett PJ. Iron. In: Marriott BP, Birt DF, Stallings VA, Yates AA, eds. Present Knowledge in Nutrition. 11th ed. Cambridge, MA: Elsevier; 2020:375-92.

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Disclaimer

This fact sheet by the National Institutes of Health (NIH) Office of Dietary Supplements (ODS) provides information that should not take the place of medical advice. We encourage you to talk to your health care providers (doctor, registered dietitian, pharmacist, etc.) about your interest in, questions about, or use of dietary supplements and what may be best for your overall health. Any mention in this publication of a specific product or service, or recommendation from an organization or professional society, does not represent an endorsement by ODS of that product, service, or expert advice.

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June 15, 2023

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Summary

What is iron?

Iron is a mineral that our bodies need for growth and development. Your body uses iron to make hemoglobin, a protein in red blood cells. Hemoglobin carries oxygen from the lungs to all parts of the body. Iron is also important for healthy muscles, bone marrow, and organ function. Your body also needs iron to make some hormones.

How do you get iron?

Iron is found naturally in many foods and is added to some fortified food products. Foods that are high in iron include:

Lean meat, seafood, and poultry

Iron-fortified breakfast cereals and breads

White beans, lentils, spinach, kidney beans, and peas

Nuts and some dried fruits, such as raisins

Iron is available in supplements, either on its own or as part of many multivitamin/mineral supplements.

What causes low iron?

Most people in the United States get enough iron. The amount that you need each day depends on your age, your sex, and whether you consume a mostly plant-based diet.

Sometimes people can have trouble getting enough iron. There can be many causes, including blood loss, a poor diet, or a problem absorbing enough iron from foods. Those who are more likely to have low iron include people who:

Have heavy periods

Are pregnant or breastfeeding

Are infants (especially if they were born premature or low birth weight)

Are frequent blood donors

Have cancer, certain digestive diseases, or heart failure

Are on kidney dialysis

Have trouble absorbing iron because they:

Have a digestive condition such as celiac disease, ulcerative colitis, Crohn's disease, or Helicobacter pylori infection

Had weight loss surgery

What happens if you don't get enough iron?

If you have too little iron, you may develop iron-deficiency anemia. It may not cause symptoms at first, but over time, it can cause fatigue, shortness of breath, and trouble with memory and concentration. Treatment for low iron and iron-deficiency anemia is usually with iron supplements.

What happens if you get too much iron?

Too much iron can damage your body. For example, if you are healthy and take too many iron supplements, you may have symptoms such as constipation, nausea and vomiting, abdominal (belly) pain, and diarrhea. Higher iron levels can cause ulcers. Extremely high levels can lead to organ damage, coma, and death.

A disease called hemochromatosis can cause too much iron to build up in the body. Hemochromatosis is inherited (passed down through families). It is usually treated by removing blood (and iron) from your body on a regular basis.

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Article: Associations of maternal serum concentration of iron-related indicators with birth outcomes...

Article: Iron dysregulation and inflammatory stress erythropoiesis associates with long-term outcome of...

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Iron | The Nutrition Source | Harvard T.H. Chan School of Public Health

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Iron

Iron is an important mineral that helps maintain healthy blood. A lack of iron is called iron-deficiency anemia, which affects about 4-5 million Americans yearly. [1] It is the most common nutritional deficiency worldwide, causing extreme fatigue and lightheadedness. It affects all ages, with children, women who are pregnant or menstruating, and people receiving kidney dialysis among those at highest risk for this condition.

Iron is a major component of hemoglobin, a type of protein in red blood cells that carries oxygen from your lungs to all parts of the body. Without enough iron, there aren’t enough red blood cells to transport oxygen, which leads to fatigue. Iron is also part of myoglobin, a protein that carries and stores oxygen specifically in muscle tissues. Iron is important for healthy brain development and growth in children, and for the normal production and function of various cells and hormones.

Iron from food comes in two forms: heme and non-heme. Heme is found only in animal flesh like meat, poultry, and seafood. Non-heme iron is found in plant foods like whole grains, nuts, seeds, legumes, and leafy greens. Non-heme iron is also found in animal flesh (as animals consume plant foods with non-heme iron) and fortified foods.

Iron is stored in the body as ferritin (in the liver, spleen, muscle tissue, and bone marrow) and is delivered throughout the body by transferrin (a protein in blood that binds to iron). A doctor may sometimes check blood levels of these two components if anemia is suspected.

Recommended Amounts

RDA:  The Recommended Dietary Allowance (RDA) for adults 19-50 years is 8 mg daily for men, 18 mg for women, 27 mg for pregnancy, and 9 mg for lactation. [2] The higher amounts in women and pregnancy are due to blood loss through menstruation and because of the rapid growth of the fetus requiring extra blood circulation during pregnancy. Adolescents 14-18 years actively growing also need higher iron: 11 mg for boys, 15 mg for girls, 27 mg for pregnancy, and 10 mg for lactation. The RDA for women 51+ years drops to 8 mg with the assumption that cessation of menstruation has occurred with menopause. It may be noted that menopause occurs later for some women, so they should continue to follow the RDA for younger women until menopause is confirmed.

UL:  The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health. The UL for iron is 45 mg daily for all males and females ages 14+ years.  For younger ages, the UL is 40 mg.

Food Sources

Meats, poultry, and seafood are richest in heme iron. Fortified grains, nuts, seeds, legumes, and vegetables contain non-heme iron. In the U.S. many breads, cereals, and infant formulas are fortified with iron.

Heme iron is better absorbed by the body than non-heme iron. Certain factors can improve or inhibit the absorption of non-heme iron. Vitamin C and heme iron taken at the same meal can improve the absorption of non-heme iron. Bran fiber, large amounts of calcium particularly from supplements, and plant substances like phytates and tannins can inhibit the absorption of non-heme iron. [3]

Sources of heme iron:

Oysters, clams, mussels

Beef or chicken liver

Organ meats

Canned sardines

Beef

Poultry

Canned light tuna

Sources of non-heme iron: 

Fortified breakfast cereals

Beans

Dark chocolate (at least 45%)

Lentils

Spinach

Potato with skin

Nuts, seeds

Enriched rice or bread

What about iron supplements? Iron is available in supplement form. Some cereals and multivitamin/mineral supplements are fortified with 100% of the RDA for women for iron (18 mg). Over-the-counter high-dosage iron supplements prescribed for those with iron-deficiency anemia or who are at high risk for it may contain 65 mg or more. Commonly reported side effects of using high-dosage iron supplements include constipation and nausea.

Confusion with iron supplements

There are several types of iron available as over-the-counter supplements, e.g., ferrous sulfate, ferrous fumarate, ferrous gluconate. Confusion is also caused by two number amounts listed on the label, a higher number and a lower number. What is the difference among supplement forms and which number should you refer to for the right amount to take?

Elemental versus chemical form of iron. If two iron amounts are listed on the label, the larger number is the chemical compound form because iron is bound to salts (e.g., ferrous sulfate), whereas the smaller number refers only to the amount of iron in the compound, also called the elemental iron. Elemental iron is the more important number because this is the amount available for the body to absorb. However, a physician may not specify in a prescription if the iron amount is the chemical form or the elemental iron. For example, a ferrous sulfate iron supplement may list a total of 325 mg of ferrous sulfate on the front of the label but 65 mg of elemental iron in smaller print on the back. If a physician prescribed 65 mg of iron, would you take five pills to equal 325 mg, or just one pill, assuming the prescription referred to elemental iron?

Different types. All types of supplemental iron help to increase red blood cell production but vary in cost and amounts of elemental iron. Ferrous gluconate is usually sold in liquid form and some clinical studies have shown that it is better absorbed than ferrous sulfate tablets. However, ferrous gluconate contains less elemental iron than ferrous sulfate, so a greater dosage may be needed to correct a deficiency. It is also more expensive than ferrous sulfate. Newer slow-release forms of iron have been introduced, which may help reduce gastrointestinal side effects, but they are more expensive and usually contain less iron.

Any confusion with iron supplement types and amounts can be resolved by asking your doctor to specify both the elemental amount and the chemical compound amount. You can also ask a store pharmacist for assistance in interpreting a doctor’s prescription or to recommend an appropriate amount if you do not have a prescription.

Signs of Deficiency and Toxicity

Deficiency

An iron deficiency is seen most commonly in children, women who are menstruating or pregnant, and those eating a diet lacking in iron.

Iron deficiency occurs in stages. [4] The mild form begins with a decrease in stored iron, usually either from a low-iron diet or from excessive bleeding. If this does not resolve, the next stage is a greater depletion of iron stores and a drop in red blood cells. Eventually this leads to iron-deficiency anemia (IDA) where iron stores are used up and there is significant loss of total red blood cells. Typically, a doctor screens for anemia by first checking a complete blood count (including hemoglobin, hematocrit, and other factors that measure red blood cell volume and size). If this is below normal, ferritin and transferrin levels may be measured to determine if the type of anemia is IDA (there are other forms of anemia not caused specifically by an iron deficiency). All of these measures would decrease with IDA.

Signs of IDA:

Fatigue, weakness

Lightheadedness

Confusion, loss of concentration

Sensitivity to cold

Shortness of breath

Rapid heartbeat

Pale skin

Hair loss, brittle nails

Pica: cravings for dirt, clay, ice, or other non-food items

IDA is usually corrected with oral iron supplements of up to 150-200 mg of elemental iron daily. Those at high risk of IDA may be prescribed 60-100 mg daily. Blood levels should be rechecked periodically, and supplements discontinued or taken at a lower dosage if levels return to normal, as long-term high dosages can lead to constipation or other digestive upset.

Groups at risk for IDA:

Pregnant women—during pregnancy a woman produces much greater amounts of red blood cells for the fetus, increasing the need for additional dietary or supplemental iron. IDA during pregnancy can lead to premature birth or low birth weight so iron is routinely included in prenatal vitamins. The Centers for Disease Control and Prevention recommend that all pregnant women begin taking 30 mg daily of supplemental iron. [3]

Menstruating women—women who experience heavy bleeding during menstruation (lasting longer than 7 days or soaking through tampons or pads once every hour) can develop IDA.

Children—infants and children have high iron needs due to their rapid growth.

Elderly—older ages are associated with a higher risk of poor nutrition and chronic inflammatory diseases that can lead to anemia. [1]

Vegetarians—those who eat a diet without heme iron from meats, fish, and poultry may develop IDA if they do not include adequate non-heme iron foods in the diet. Because non-heme iron is not well-absorbed, either greater quantities of these foods my be required or careful attention is needed in how they are eaten to improve absorption (consuming with vitamin C-rich foods while avoiding eating with calcium-rich foods, calcium supplements, or tea).

Endurance athletes—running can cause trace amounts of gastrointestinal bleeding and a condition called “foot-strike” hemolysis that breaks down red blood cells at a faster rate. Female endurance athletes who are also menstruating are at greatest risk for IDA. [4]

People with chronic kidney failure on dialysis—the kidneys make a hormone called erythropoietin (EPO) that signals the body to make red blood cells. Kidney failure reduces the production of EPO and therefore blood cells. In addition, there is some blood loss during hemodialysis.

What is anemia of chronic disease?

Anemia of chronic disease (AOCD) occurs not from a low iron intake but with conditions that cause inflammation in the body, such as infections, cancer, kidney disease, inflammatory bowel disease, heart failure, lupus, and rheumatoid arthritis. The body may actually contain normal amounts of iron, but levels in the blood are very low. Inflammation changes the body’s immune function, preventing the body from being able to use available stored iron to make red blood cells and also causing blood cells to die out more quickly.

Treatment for AOCD focuses on treating the inflammatory condition. Increasing iron in the diet typically does not help. If the inflammation or condition improves, the anemia will usually decrease as well. In rare severe cases, a blood transfusion can be given to quickly boost the amount of hemoglobin in the blood.

Toxicity

Toxicity is rare because the body regulates iron absorption and will absorb less if iron stores are adequate. [2] Excessive iron occurs most often from taking high-dosage supplements when not needed or from having a genetic condition that stores too much iron.

Common signs:

Constipation

Upset stomach

Nausea, vomiting

Abdominal pain

Some people have a hereditary condition called hemochromatosis that causes an excessive buildup of iron in the body. Treatments are given periodically to remove blood or excess iron in the blood. People with hemochromatosis are educated to follow a low-iron diet and to avoid iron and vitamin C supplements. If left untreated, iron can build up in certain organs so that there is a higher risk of developing conditions like liver cirrhosis, liver cancer, or heart disease. 

Did You Know?

It is possible to obtain enough iron in a vegetarian/vegan diet with careful planning. Try this easy dish that can boost iron levels by combining foods rich in non-heme iron and vitamin C:

In a large bowl, combine cooked beans or lentils with diced fresh tomatoes, raw baby spinach, pumpkin seeds or cashews, and raisins or dried chopped apricots. Drizzle with a simple lemon vinaigrette made from 2 tablespoons lemon juice, ½ teaspoon Dijon mustard, 3 tablespoons olive oil, and 1 teaspoon of honey (optional). Stir ingredients well and allow to sit for at least 15 minutes to incorporate the flavors.

Related

Vitamins and Minerals

References

Le CH. The prevalence of anemia and moderate-severe anemia in the US population (NHANES 2003-2012). PLoS One. 2016 Nov 15;11(11):e0166635.

Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc : a Report of the Panel on Micronutrients. Washington, DC: National Academy Press; 2001.

National Institutes of Health Office of Dietary Supplements: Iron Fact Sheet for Health Professionals https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/. Accessed 9/2/2019.

Powers JM, Buchanan GR. Disorders of Iron Metabolism: New Diagnostic and Treatment Approaches to Iron Deficiency. Hematology/Oncology Clinics. 2019 Jun 1;33(3):393-408.

Last reviewed March 2023

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Iron - Element information, properties and uses | Periodic Table

Iron

- Element information, properties and uses | Periodic Table

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Glossary

Allotropes

Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.

For more information on the Visual Elements image see the Uses and properties section below.

< Move to Manganese

Move to Cobalt >

Iron

Discovery date

approx 3500BC 

Discovered by

- 

Origin of the name

The name comes from the Anglo-Saxon name 'iren'. 

Allotropes

Fe

Iron

26

55.845

Glossary

Group

A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

Period

A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.

Block

Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).

Atomic number

The number of protons in an atom.

Electron configuration

The arrangements of electrons above the last (closed shell) noble gas.

Melting point

The temperature at which the solid–liquid phase change occurs.

Boiling point

The temperature at which the liquid–gas phase change occurs.

Sublimation

The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.

Density (g cm−3)

Density is the mass of a substance that would fill 1 cm3 at room temperature.

Relative atomic mass

The mass of an atom relative to that of carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists, the value given is the abundance weighted average.

Isotopes

Atoms of the same element with different numbers of neutrons.

CAS number

The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems.

Fact box

Fact box

Group

8 

Melting point

1538°C, 2800°F, 1811 K 

Period

4 

Boiling point

2861°C, 5182°F, 3134 K 

Block

d 

Density (g cm−3)

7.87 

Atomic number

26 

Relative atomic mass

55.845

State at 20°C

Solid 

Key isotopes

56Fe 

Electron configuration

[Ar] 3d64s2 

CAS number

7439-89-6 

ChemSpider ID

22368

ChemSpider is a free chemical structure database

Glossary

Image explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.

Appearance

The description of the element in its natural form.

Biological role

The role of the element in humans, animals and plants.

Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

Uses and properties

Uses and properties

Image explanation

The image is of the alchemical symbol for iron. The symbol is shown against a rusty mild steel plate.

Appearance

A shiny, greyish metal that rusts in damp air.

Uses

Iron is an enigma – it rusts easily, yet it is the most important of all metals. 90% of all metal that is refined today is iron. Most is used to manufacture steel, used in civil engineering (reinforced concrete, girders etc) and in manufacturing. There are many different types of steel with different properties and uses. Ordinary carbon steel is an alloy of iron with carbon (from 0.1% for mild steel up to 2% for high carbon steels), with small amounts of other elements. Alloy steels are carbon steels with other additives such as nickel, chromium, vanadium, tungsten and manganese. These are stronger and tougher than carbon steels and have a huge variety of applications including bridges, electricity pylons, bicycle chains, cutting tools and rifle barrels.Stainless steel is very resistant to corrosion. It contains at least 10.5% chromium. Other metals such as nickel, molybdenum, titanium and copper are added to enhance its strength and workability. It is used in architecture, bearings, cutlery, surgical instruments and jewellery.Cast iron contains 3–5% carbon. It is used for pipes, valves and pumps. It is not as tough as steel but it is cheaper. Magnets can be made of iron and its alloys and compounds.Iron catalysts are used in the Haber process for producing ammonia, and in the Fischer–Tropsch process for converting syngas (hydrogen and carbon monoxide) into liquid fuels.

Biological role

Iron is an essential element for all forms of life and is non-toxic. The average human contains about 4 grams of iron. A lot of this is in haemoglobin, in the blood. Haemoglobin carries oxygen from our lungs to the cells, where it is needed for tissue respiration. Humans need 10–18 milligrams of iron each day. A lack of iron will cause anaemia to develop. Foods such as liver, kidney, molasses, brewer’s yeast, cocoa and liquorice contain a lot of iron.

Natural abundance

Iron is the fourth most abundant element, by mass, in the Earth’s crust. The core of the Earth is thought to be largely composed of iron with nickel and sulfur. The most common iron-containing ore is haematite, but iron is found widely distributed in other minerals such as magnetite and taconite. Commercially, iron is produced in a blast furnace by heating haematite or magnetite with coke (carbon) and limestone (calcium carbonate). This forms pig iron, which contains about 3% carbon and other impurities, but is used to make steel. Around 1.3 billion tonnes of crude steel are produced worldwide each year.

Help text not available for this section currently

History

History

Elements and Periodic Table History

Iron objects have been found in Egypt dating from around 3500 BC. They contain about 7.5% nickel, which indicates that they were of meteoric origin.The ancient Hittites of Asia Minor, today’s Turkey, were the first to smelt iron from its ores around 1500 BC and this new, stronger, metal gave them economic and political power. The Iron Age had begun. Some kinds of iron were clearly superior to others depending on its carbon content, although this was not appreciated. Some iron ore contained vanadium producing so-called Damascene steel, ideal for swords.The first person to explain the various types of iron was René Antoine Ferchault de Réaumur who wrote a book on the subject in 1722. This explained how steel, wrought iron, and cast iron, were to be distinguished by the amount of charcoal (carbon) they contained. The Industrial Revolution which began that same century relied extensively on this metal.

Glossary

Atomic radius, non-bonded

Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.

Covalent radiusHalf of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.

Electron affinityThe energy released when an electron is added to the neutral atom and a negative ion is formed.

Electronegativity (Pauling scale)The tendency of an atom to attract electrons towards itself, expressed on a relative scale.

First ionisation energyThe minimum energy required to remove an electron from a neutral atom in its ground state.

Atomic data

Atomic data

Atomic radius, non-bonded (Å)

2.04

Covalent radius (Å)

1.24

Electron affinity (kJ mol−1)

14.569

Electronegativity (Pauling scale)

1.83

Ionisation energies (kJ mol−1) 

1st

762.466

2nd

1561.876

3rd

2957.469

4th

5287.4

5th

7236

6th

9561.7

7th

12058.74

8th

14575.08

Glossary

Common oxidation states

The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.

Isotopes

Atoms of the same element with different numbers of neutrons.

Key for isotopes

Half life

y

years

d

days

h

hours

m

minutes

s

seconds

Mode of decay

α

alpha particle emission

β

negative beta (electron) emission

β+

positron emission

EC

orbital electron capture

sf

spontaneous fission

ββ

double beta emission

ECEC

double orbital electron capture

Oxidation states and isotopes

Oxidation states and isotopes

Common oxidation states

6, 3, 2, 0, -2

Isotopes

Isotope

Atomic mass

Natural abundance (%)

Half life

Mode of decay

54Fe

53.940

5.845

> 3.1 x 1022 y 

EC-EC 

56Fe

55.935

91.754

- 

- 

57Fe

56.935

2.119

- 

- 

58Fe

57.933

0.282

- 

- 

Glossary

Data for this section been provided by the British Geological Survey.

Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.

Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.

Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.

Substitutability

The availability of suitable substitutes for a given commodity.

High = substitution not possible or very difficult.

Medium = substitution is possible but there may be an economic and/or performance impact

Low = substitution is possible with little or no economic and/or performance impact

Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.

Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.

Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.

Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.

Supply risk

Supply risk

Relative supply risk

5.2

Crustal abundance (ppm)

52157

Recycling rate (%)

>30

Substitutability

Medium

Production concentration (%)

41

Reserve distribution (%)

21

Top 3 producers

1) China

2) Australia

3) Brazil

Top 3 reserve holders

1) Australia

2) Brazil

3) Russia

Political stability of top producer

24.1

Political stability of top reserve holder

74.5

Glossary

Specific heat capacity (J kg−1 K−1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.

Young's modulus

A measure of the stiffness of a substance. It provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.

Shear modulus

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.

Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour pressure

A measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

Pressure and temperature data – advanced

Specific heat capacity (J kg−1 K−1)

449

Young's modulus (GPa)

211.4 (soft); 152.3 (cast)

Shear modulus (GPa)

81.6 (soft); 60.0 (cast)

Bulk modulus (GPa)

169.8

Vapour pressure

Temperature (K)

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

Pressure (Pa)

-

-

-

5.54 x 10-9

2.51 x 10-5

0.0104

0.961

32.7

36.8

-

-

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Chemistry in its element: iron (Promo)You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.(End promo)Chris SmithHello, this week we turn to one of the most important elements in the human body. It's the one that makes metabolism possible and don't we just know it. There are iron man challenges, iron fisted leaders and those said to have iron in the soul. But there's a dark side to element number 26 too because its powerful chemistry means that it's also bad news for brain cells as Nobel Laureate Kary Mullis explainsKary MullisFor the human brain, iron is essential yet deadly. It exists on Earth mainly in two oxidation states - FeII and FeIII. FeIII is predominant within a few meters of the atmosphere which about two billion years ago turned 20% oxygen - oxidizing this iron to the plus three state which is virtually insoluble in water. This change from the relatively plentiful and soluble FeII, took a heavy toil on almost everything alive at the time.Surviving terrestrial and ocean-dwelling microbes developed soluble siderophore molecules to regain access to this plentiful, but otherwise inaccessible essential resource, which used hydroxamate or catechol chelating groups to bring the FeIII back into solution. Eventually higher organisms including animals, evolved. And animals used the energy of oxygen recombining with the hydrocarbons and carbohydrates in plant life to enable motion. Iron was essential to this process.But no animal, however, has been able to adequately deal, in the long run - meaning eighty year life spans - with the fact that iron is essential for the conversion of solar energy to movement, but is virtually insoluble in water at neutral pH, and, even worse, is toxic. Carbon, sulfur, nitrogen. calcium, magnesium, sodium, maybe ten other elements are also involved in life, but none of them have the power of iron to move electrons around, and none of them have the power to totally destroy the whole system. Iron does. Systems have evolved to maintain iron in specific useful and safe configurations - enzymes which utilize its catalytic powers, or transferrins and haemosiderins, which move it around and store it. But these are not perfect. Sometimes iron atoms are misplaced, and there are no known systems to recapture iron that has precipitated inside of a cell. In some tissues, cells overloaded with iron can be recycled or destroyed - but this doesn't work for neurons. Neurons sprout thousands of processes during their existence - reaching out to form networks of connections to other neurons. During development of the adult human brain a large percentage of cells are completely eliminated, and some new ones are added. It is a learning process. But once an area of the brain is up and running, there is nothing that can be done biologically, if a large number of its cells stop working for any reason. And the slow creep of precipitating iron over many decades is perhaps most often that reason. In less sophisticated tissues, like the liver, new stem cells can be activated, but in the brain, trained, structurally complex, interconnected neurons are needed, with thousands of projections that are accumulated over a lifetime of learning. So the result is slowly progressive neurodegenerative disease, like Parkinson's and Alzheimer's.This same basic mechanism can result in a variety of diseases. There are twenty or thirty proteins that that deal with iron in the brain - holding iron and passing it from place to place. Every new individual endowed with a new set of chromosomes is endowed with a new set of these proteins. Some combinations will be better than others and some will be dangerous individually and collectively. A mutation in a gene that codes for one of these proteins could disrupt its function - allowing iron atoms to become lost. These atoms that have been lost from the chemical groups that hold them will not always be safely returned to some structure like transferrin or haemoferritin. Some of them will react with water and be lost forever. Only they aren't really lost. They are piling up in the unlucky cell types that were the designated locations for expression of the most iron-leaky proteins. And oxides of iron are not just taking up critical space. Iron is very reactive. The infamous "Reactive Oxygen Species" which have been suspected of causing so many age related illnesses may just derive from various forms of iron.It is time for specialists trained in chemistry, and with an eye to the chemistry of iron, to pay some attention to neurodegenerative disease. Chris SmithKary Mullis telling the story of iron, the element that we can't do without, but which at the same time could hold the key to our neurological downfall. Next time on Chemistry in its Element Johnny Ball will tell the story of Marie Curie and the element that she discovered and then named after her homeland.Johnny BallPitchblende, a uranium bearing ore, seemed to be far too radio active than could be accounted for by the uranium. They sieved and sorted by hand ounce by ounce through tons of pitchblende in a drafty, freezing shed, before eventually tiny amounts of polonium were discovered. Chris SmithSo be radioactive or at least podcast proactive and join us for the mysterious story of Polonium on next week's Chemistry in its Element. I'm Chris Smith, thank you for listening, see you next time.(Promo)Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements.(End promo)

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References

References

Visual Elements images and videos© Murray Robertson 1998-2017. DataW. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.

Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.

J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.

T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954. Uses and propertiesJohn Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.

Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.

Periodic Table of Videos, accessed December 2014. Supply risk dataDerived in part from material provided by the British Geological Survey © NERC. History textElements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017. PodcastsProduced by The Naked Scientists. Periodic Table of Videos

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Iron - Simple English Wikipedia, the free encyclopedia

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1Properties

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1.1Physical properties

1.2Chemical properties

1.3Chemical compounds

1.3.1Iron(II) compounds

1.3.2Mixed oxidation state

1.3.3Iron(III) compounds

2Where iron is found

3Making iron

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4.1As a metal

4.2As compounds

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Iron

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From Simple English Wikipedia, the free encyclopedia

This article is about iron the metal. For the tool called iron, see ironing.

A chunk of iron

Iron is a chemical element and a metal. It is the most common chemical element on Earth (by mass), and the most widely used metal. It makes up much of the Earth's core, and is the fourth most common element in the Earth's crust. Its atomic number is 26, because each atom has 26 protons.

The metal is used a lot because it is strong and cheap. Iron is the main ingredient used to make steel. Raw iron is magnetic (attracted to magnets), and its compound magnetite is permanently magnetic.

In some regions iron was used around 1200 BCE. That event is considered the transition from bronze age to iron age.

Properties[change | change source]

Iron(II) oxideIron(II) sulfate

Iron(III) chloride

Physical properties[change | change source]

Iron is a grey, silvery metal. It is magnetic, though different allotropes of iron have different magnetic qualities. Iron is easily found, mined and smelted, which is why it is so useful. Pure iron is soft and very malleable.

Chemical properties[change | change source]

Iron is reactive. It reacts with most acids like sulfuric acid. It makes ferrous sulfate when it reacts with sulfuric acid. This reaction with sulfuric acid is used to clean metal.

Iron reacts with air and water to make rust. When the rust flakes off, more iron is exposed allowing more iron to rust. Eventually, the whole piece of iron is rusted away. Other metals like aluminum do not rust away. Iron can be alloyed with chromium to make stainless steel, which does not rust under most conditions.

Iron powder can react with sulfur to make iron(II) sulfide, a hard black solid. Iron also reacts with the halogens to make iron(III) halides, like iron(III) chloride. Iron reacts with the hydrohalic acids to make iron(II) halides like iron(II) chloride.

Chemical compounds[change | change source]

Iron makes chemical compounds with other elements. Normally the other element oxidizes iron. Sometimes two electrons are taken and sometimes three. Compounds where iron has two electrons taken are called ferrous compounds. Compounds where iron has three electrons taken are called ferric compounds. Ferrous compounds have iron in its +2 oxidation state. Ferric compounds have iron in its +3 oxidation state. Iron compounds can be black, brown, yellow, green, or purple.

Ferrous compounds are weak reducing agents. Many of them are green or blue. The most common ferrous compound is ferrous sulfate.

Ferric compounds are oxidizing agents. Many of them are brown. The most common ferric compound is ferric oxide, the same thing as rust. One reason why iron rusts is because ferric oxide is an oxidizing agent. It oxidizes iron, rusting it even under paint. That is why if there is a small scratch in the paint, the whole thing can rust.

Iron(II) compounds[change | change source]

Compounds in the +2 oxidation state are weak reducing agents. They are normally light colored. They react with oxygen in air. They are also known as ferrous compounds.

Iron(II) sulfide, a shiny chemical that reacts with acids to release hydrogen sulfide, found in the ground

Iron(II) sulfate, a blue-green crystalline chemical made by reacting sulfuric acid with steel, used to reduce poisons like chromate in concrete

Iron(II) chloride, a pale green crystalline chemical made by reacting hydrochloric acid with steel

Iron(II) hydroxide, a dark green powder made by electrolyzing water with an iron anode, reacts with oxygen and turns brown

Iron(II) oxide, black, flammable, rare

Mixed oxidation state[change | change source]

These compounds are rare; only one is common. They are found in the ground.

Iron(II,III) oxide, a black mineral, used as ore of iron, contains iron in the +2 and +3 oxidation state.

Iron(III) compounds[change | change source]

Compounds in the +3 oxidation state are normally brown. They are oxidizing agents. They are corrosive. They are also known as ferric compounds.

Iron(III) oxide, rust, red-brown, dissolves in acid

Iron(III) chloride, poisonous and corrosive, dissolves in water to make dark brown acidic solution. Made by reacting iron with hydrochloric acid and an oxidizing agent

Iron(III) nitrate, light purple, corrosive, used in etching

Iron(III) sulfate, rare, light brown, dissolves in water. Made by reacting iron with sulfuric acid and an oxidizing agent.

Where iron is found[change | change source]

There is a lot of iron in the universe because it is the end point of the nuclear reactions in large stars. It is the last element to be produced before the violent collapse of a supernova scatters the iron into space.

The metal is the main ingredient in the Earth's core. Near the surface it is found as a ferrous or ferric compound. Some meteorites contain iron in the form of rare minerals. Normally iron is found as hematite ore in the ground, much of which was made in the Great Oxygenation Event. Iron can be extracted from the ore in a blast furnace. Some iron is found as magnetite.

There are iron compounds in meat. Iron is an essential part of the hemoglobin in red blood cells.

Making iron[change | change source]

Blast furnace

Iron is made in large factories called ironworks by reducing hematite with carbon (coke). This happens in large containers called blast furnaces. The blast furnace is filled with iron ore, coke and limestone. A very hot blast of air is blown in, where it causes the coke to burn. The extreme heat makes the carbon react with iron ore, taking off the oxygen from iron oxides, and making carbon dioxide. The carbon dioxide is a gas and it leaves the mix. There is some sand in with the iron. The limestone, which is made of calcium carbonate, turns into calcium oxide and carbon dioxide when the limestone is very hot. The calcium oxide reacts with the sand to make a liquid called a slag. The slag is drained, leaving only the iron. The reaction will leave pure liquid iron in the blast furnace, where it can be shaped and hardened after cooling down. Almost all ironworks are today part of steel mills, and almost all iron is made into steel.

There are many ways to work iron. Iron can be hardened by heating a piece of metal and splashing it into cold water. It can be softened by heating it and allowing it to slowly cool. It can also be stamped by a heavy press. It can be pulled into wires. It can be rolled to make sheet metal.

In the United States, much of the iron was taken from the ground in Minnesota and then sent by ship to Indiana and Michigan where it was made into steel.

Uses[change | change source]

As a metal[change | change source]

A bridge made out of iron

Iron is used more than any other metal. It is strong and cheap. It is used to make buildings, bridges, nails, screws, pipes, girders, and towers.

Iron is not very reactive, so it is both easy and cheap to extract from ores. It is very strong once made into steel, and is used to reinforce concrete.

There are different types of iron. Cast iron is iron made by the way described above in the article. It is hard and brittle. It is used to make things like storm drain covers, manhole covers, and engine blocks (the main part of an engine).

Steel is the most common form of iron. Steels come in several forms. Mild steel is steel with a low percentage of carbon. It is soft and easily bent, but it does not crack easily. It is used for nails and wires. Carbon steel is harder but more brittle. It is used in tools.

There are other types of steel. Stainless steel, because of the chromium content, is rust resistant, and nickel-iron alloys can remain strong at high temperatures. Other steels can be very hard, depending on the alloys added.

Wrought iron is easily shaped and used to make fences and chains.

Very pure iron is soft, and can rust (oxidize) easily. It is also fairly reactive.

As compounds[change | change source]

Iron compounds are used for several things. Iron(II) chloride is used to make water clean. Iron(III) chloride is also used. Iron(II) sulfate is used to reduce chromates in cement. Some iron compounds are used in vitamins.

Nutrition[change | change source]

Iron deficiency is the most common nutritional deficiency in the world.[1][2][3]

Human bodies need iron to help oxygen get to our muscles, because it is at the heart of some essential macromolecules such as hemoglobin. Many cereals have some added iron (the element metal iron).[4][5] It is added to cereal in the form of tiny metal filings. It is even possible to see the slivers sometimes by taking an extremely strong magnet and putting it into the box. The magnet will attract these pieces of iron. Eating these small metal shavings are not harmful to our body.[6]

Iron is most available to the body when added to amino acids – iron in this form is ten to fifteen times more digestible than than it is as an element.[7] Iron is also found in meat, for example steak. Iron provided by diet supplements is in the form of a chemical, such as Iron(II) sulfate, which is cheap and is absorbed well. The body will not take up more iron than it needs, and it usually needs very little. The iron in red blood cells is recycled by a system which breaks down old cells. Loss of blood by injury or parasite infection may be more serious.[8]

Toxicity[change | change source]

Iron is toxic when large amounts are taken into the body. When too many iron pills are taken, people (especially children) get sick. Also, there is a genetic disorder which damages the regulation of iron levels in the body.

Related pages[change | change source]

Allotropes of iron

Iron compounds

Iron Age

References[change | change source]

↑ Centers for Disease Control and Prevention (2002). "Iron deficiency – United States, 1999–2000". MMWR. 51 (40): 897–9. PMID 12418542.

↑ Hider, Robert C.; Kong, Xiaole (2013). "Chapter 8. Iron: Effect of Overload and Deficiency". In Astrid Sigel, Helmut Sigel and Roland K. O. Sigel (ed.). Interrelations between Essential Metal Ions and Human Diseases. Metal Ions in Life Sciences. Vol. 13. Springer. pp. 229–294. doi:10.1007/978-94-007-7500-8_8. PMID 24470094.

↑ Dlouhy, Adrienne C.; Outten, Caryn E. (2013). "Chapter 8.4 Iron Uptake, Trafficking and Storage". In Banci, Lucia (Ed.) (ed.). Metallomics and the Cell. Metal Ions in Life Sciences. Vol. 12. Springer. pp. 241–278. doi:10.1007/978-94-007-5561-1_8. ISBN 978-94-007-5560-4. PMC 3924584. PMID 23595675. electronic-book ISBN 978-94-007-5561-1 ISSN 1559-0836 electronic-ISSN 1868-0402

↑ "Testing the fortitude of iron in cereals". United States Department of Agriculture. Retrieved 2010-01-29.

↑ Adams, Cecil. Return of the Straight Dope. New York: Ballantine Books, 1994

↑ Felton, Bruce. One of a Kind. New York: William Morrow and Co., 1992

↑ Pineda O. & Ashmead H.D. (2001). "Effectiveness of treatment of iron-deficiency anemia in infants and young children with ferrous bis-glycinate chelate". Nutrition. 17 (5): 381–4. doi:10.1016/S0899-9007(01)00519-6. PMID 11377130.

↑ Andrews N.C. 2000. Disorders of iron metabolism. New England Journal of Medicine. Related correspondence, published in NEJM 342:1293-1294.

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Group 8: Transition Metalsd-Block Elements{ Iron_in_Humans : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()" }{ Chemistry_of_Hassium : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", Chemistry_of_Iron : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", Chemistry_of_Osmium : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", Chemistry_of_Ruthenium : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()" }{ "1b_Properties_of_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", Group_03 : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_04:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_05:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_06:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_07:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_08:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_09:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_10:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_11:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()", "Group_12:_Transition_Metals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.b__1]()" }Fri, 30 Jun 2023 23:47:14 GMTChemistry of Iron37203720admin{ }AnonymousAnonymous User2falsefalse[ "article:topic", "catalyst", "Redox", "Titration", "Haber Process", "Redox titration", "authorname:clarkj", "Iron", "showtoc:no", "ferrum", "iron ions", "license:ccbync", "licenseversion:40" ][ "article:topic", "catalyst", "Redox", "Titration", "Haber Process", "Redox titration", "authorname:clarkj", "Iron", "showtoc:no", "ferrum", "iron ions", "license:ccbync", "licenseversion:40" ]https://chem.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FInorganic_Chemistry%2FSupplemental_Modules_and_Websites_(Inorganic_Chemistry)%2FDescriptive_Chemistry%2FElements_Organized_by_Block%2F3_d-Block_Elements%2FGroup_08%253A_Transition_Metals%2FChemistry_of_Iron

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Page ID3720

Jim ClarkTruro School in Cornwall

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IntroductionIron as CatalystReactions of iron ions in solutionReactions of the iron ions with hydroxide ionsReactions of Iron Ions with AmmoniaReactions of the iron ions with carbonate ionsIron(II) ions and carbonate ionsIron(III) ions and carbonate ionsTesting for iron(III) ions with thiocyanate ionsFinding the concentration of iron(II) ions in solution by Redox titrationUsing potassium manganate(VII) solutionUsing potassium dichromate(VI) solutionContributors and Attributions

Iron, which takes its English name from the old Anglo-Saxon and its symbol from the Latin, ferrum, was identified and used in prehistoric times. It is a very common element, fourth most abundant in the earth's crust. In addition, two of the ten most common compounds in the earth's crust are the two common oxides of iron, \(FeO\) and \(Fe_2O_3\).

Introduction

In its pure form, iron is a silvery-white metal, distinguished by its ability to take and retain a magnetic field, and also dissolve small amounts of carbon when molten (thus yielding steel). Commercial refining of iron is based on the heating of \(Fe_2O_3\) or \(Fe_3O_4\) (magnetite) with a mixture of other substances in the high temperature environment of the blast furnace. The oxides are reduced to pure iron. In addition to hardening iron by adding small amounts of carbon and also some other metals to the molten iron, iron castings or forgings can be heat-treated to take advantage of the various physical properties of the different solid phases of iron.

Pure iron reacts readily with oxygen and moisture in the environment and corrodes destructively. Even alloys such as steel need protection by painting or some other coating to prevent structural failure over time.

Iron as Catalyst

The Haber Process combines nitrogen and hydrogen into ammonia. The nitrogen comes from the air and the hydrogen is obtained mainly from natural gas (methane). Iron is used as a catalyst.

\[N_{2(g)} + 3H_{2(g)} \overset{Fe}{\rightleftharpoons} 2NH_{3(g)} \label{1} \]

The reaction between persulfate ions (peroxodisulfate ions), S2O82-, and iodide ions in solution can be catalyzed using either iron(II) or iron(III) ions. The overall equation for the reaction is:

\[ S_2O_8^{2-} + 2I^- \rightarrow 2SO_4^{2-}+ I_2 \label{2} \]

For the sake of argument, we'll take the catalyst to be iron(II) ions. The reaction happens in two stages.

\[ S_2O_8^{2-} + 2Fe^{2+} \rightarrow 2SO_4^{2-}+ 2Fe^{3+} \label{3} \]

\[ 2Fe^{3+} + 2I^- \rightarrow 2Fe^{2+}+ I_2 \label{4} \]

If you use iron(III) ions, the second of these reactions happens first. This is a good example of the use of transition metal compounds as catalysts because of their ability to change oxidation state.

Reactions of iron ions in solution

Free iron ions are compeled with water in aqueous solutions. The simplest of these complex ions are:

the hexaaquairon(II) ion: \([Fe(H_2O)_6]^{2+}\).

the hexaaquairon(III) ion: \([Fe(H_2O)_6]^{3+}\).

They are both acidic ions, but the iron(III) ion is more acidic.

Reactions of the iron ions with hydroxide ions

Hydroxide ions (from, say, sodium hydroxide solution) remove hydrogen ions from the water ligands attached to the iron ions. When enough hydrogen ions have been removed, you are left with a complex with no charge - a neutral complex. This is insoluble in water and a precipitate is formed.

In the iron(II) case:

\[[Fe(H_2O)_6]^{2+} + 2OH^- \rightarrow [Fe(H_2O)_4(OH)_2] + 2H_2O \label{5} \]

In the iron(III) case:

\[[Fe(H_2O)_6]^{3+} + 3OH^- \rightarrow [Fe(H_2O)_3(OH)_3] + 3H_2O \label{6} \]

In the test-tube, the color changes are:

In the iron(II) case:

Iron is very easily oxidized under alkaline conditions. Oxygen in the air oxidizes the iron(II) hydroxide precipitate to iron(III) hydroxide especially around the top of the tube. The darkening of the precipitate comes from the same effect.

In the iron(III) case:

Reactions of Iron Ions with Ammonia

Ammonia can act as both a base and a ligand. In these cases, it simply acts as a base - removing hydrogen ions from the aqua complex.

In the iron(II) case:

\[ [Fe(H_2O)_6]^{2+} + 2NH_3 \rightarrow [Fe(H_2O)_4(OH)_2] + 2NH_4^+ \nonumber \]

The appearance is just the same as in when you add sodium hydroxide solution. The precipitate again changes color as the iron(II) hydroxide complex is oxidized by the air to iron(III) hydroxide. In the iron(III) case:

\[ [Fe(H_2O)_6]^{3+} + 3NH_3 \rightarrow [Fe(H_2O)_3(OH)_3] + 3NH_4^+ \nonumber \]

The reaction looks just the same as when you add sodium hydroxide solution.

Reactions of the iron ions with carbonate ions

There is an important difference here between the behavior of iron(II) and iron(III) ions.

Iron(II) ions and carbonate ions

You simply get a precipitate of what you can think of as iron(II) carbonate.

\[ Fe^{2+} (aq) + CO_3^{2-} \rightarrow FeCO_3(s) \nonumber \]

Iron(III) ions and carbonate ions

The hexaaquairon(III) ion is sufficiently acidic to react with the weakly basic carbonate ion. If sodium carbonate solution is added to a solution of hexaaquairon(III) ions, you get exactly the same precipitate as if you added sodium hydroxide solution or ammonia solution. This time, it is the carbonate ions which remove hydrogen ions from the hexaaqua ion and produce the neutral complex. Depending on the proportions of carbonate ions to hexaaqua ions, you will get either hydrogencarbonate ions formed or carbon dioxide gas from the reaction between the hydrogen ions and carbonate ions. The more usually quoted equation shows the formation of carbon dioxide.

\[2 [Fe(H_2O)_6^{3+} + 3CO_3^{2-} \rightarrow 2[Fe(H_2O)_3(OH)_3] + 3CO_2 + 3H_2O \nonumber \]

Apart from the carbon dioxide, there is nothing new in this reaction:

Testing for iron(III) ions with thiocyanate ions

This provides an extremely sensitive test for iron(III) ions in solution. If you add thiocyanate ions, SCN-, (e.g., from sodium or potassium or ammonium thiocyanate solution) to a solution containing iron(III) ions, you get an intense blood red solution containing the ion [Fe(SCN)(H2O)5]2+.

Finding the concentration of iron(II) ions in solution by Redox titration

You can find the concentration of iron(II) ions in solution by titrating with either potassium manganate(VII) solution or potassium dichromate(VI) solution. The reactions are done in the presence of dilute sulfuric acid. In either case, you would pipette a known volume of solution containing the iron(II) ions into a flask, and add a roughly equal volume of dilute sulfuric acid. What happens next depends on whether you are using potassium manganate(VII) solution or potassium dichromate(VI) solution.

Using potassium manganate(VII) solution

The potassium manganate(VII) solution is run in from a burette. At first, it turns colorless as it reacts. The end point is the first trace of permanent pink in the solution showing a tiny excess of manganate(VII) ions. The manganate(VII) ions oxidize iron(II) to iron(III) ions. The two half-equations for the reaction are:

\[ Fe^{2+} \rightarrow Fe^{3+} + e^- \label{10} \]

\[ MnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O \label{11} \]

These combine to give the ionic equation for the reaction:

\[ 5Fe^{2+} + MnO_4^- + 8H^+\rightarrow Mn^{2+} + 4H_2O + 5Fe^{3+} \label{12} \]

The complete equation shows that 1 mole of manganate(VII) ions react with 5 moles of iron(II) ions. Having got that information, the titration calculations are just like any other ones.

Using potassium dichromate(VI) solution

Potassium dichromate(VI) solution turns green as it reacts with the iron(II) ions, and there is no way you could possibly detect the color change when you have one drop of excess orange solution in a strongly colored green solution. With potassium dichromate(VI) solution you have to use a separate indicator, known as a redox indicator. These change color in the presence of an oxidizing agent. There are several such indicators - such as diphenylamine sulfonate. This gives a violet-blue color in the presence of excess potassium dichromate(VI) solution.

The two half-equations are:

\[ Fe^{2+} \rightarrow Fe^{3+} + e^- \label{13} \]

\[ Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O \label{14} \]

Combining these gives:

\[ Cr_2O_7^{2-} + 14H^+ + 6Fe^{2+} \rightarrow 2Cr^{3+} + + 7H_2O + 6Fe^{3+} \label{15} \]

You can see that the reacting proportions are 1 mole of dichromate(VI) ions to 6 moles of iron(II) ions. Once you have established that, the titration calculation is again going to be just like any other one.

Contributors and Attributions

Jim Clark (Chemguide.co.uk)

Stephen R. Marsden

This page titled Chemistry of Iron is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Jim Clark.

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