Iron(III) Oxide-hydroxide
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Iron III Oxide-hydroxide
Iron(III) oxide-hydroxide
Samples of iron(III) oxide-hydroxide monohydrate in a vial, and a spoon
IUPAC name
Iron(III) oxide-hydroxide
Other names
Ferric acid
3D model (JSmol)
ECHA InfoCard 100.039.754 Edit this at Wikidata
EC Number
  • 215-176-6
MeSH Goethite
Appearance Vivid, dark orange, opaque crystals
Odor odorless
Density 4.25 g/cm3
insoluble at pH 7
2.79×10-39 for Fe(OH)3[1]
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
B03AB04 (WHO)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
?Y verify (what is ?Y?N ?)
Infobox references

Iron(III) oxide-hydroxide or ferric oxyhydroxide[2] is the chemical compound of iron, oxygen, and hydrogen with formula .

The compound is often encountered as one of its hydrates, ·n [Rust]. The monohydrate · (CAS 51274-00-1, C.I. 77492) is often referred as iron(III) hydroxide , hydrated iron oxide, yellow iron oxide, or Pigment Yellow 42.

Natural occurrences

Anhydrous ferric oxyhydroxide occurs naturally as four different minerals (polymorphs) denoted by the Greek letters ?, ?, ? and ?.

  • Goethite, ?-FeO(OH), has been used as an ocher pigment since prehistoric times.
  • Akaganeite is the ? polymorph,[3] formed by weathering and noted for its presence in some meteorites and the lunar surface. However, recently it has been determined that it must contain some chloride ions to stabilize its structure, so that its more accurate formula is or .[4]
  • Lepidocrocite, the ? polymorph, is commonly encountered as rust on the inside of steel water pipes and tanks.
  • Feroxyhyte (?) is formed under the high pressure conditions of sea and ocean floors, being thermodynamically unstable with respect to the ? polymorph (goethite) at surface conditions.

Goethite and lepidocrocite, both crystallizing in orthorhombic system, are the most common forms of iron(III) oxyhydroxide and the most important mineral carriers of iron in soils.

Iron(III) oxyhydroxide is the main component of other minerals and mineraloids:


The color of iron(III) oxyhydroxide ranges from yellow through dark-brown to black, depending on the degree of hydration, particle size and shape, and crystal structure.


The crystal structure of ?- (akaganeite) is that of hollandite or . The unit cell is tetragonal with a=1.048 and c=0.3023 nm, and contains eight formula units of FeOOH. Its dimensions are about 500 × 50 × 50 nm. Twinning often produces particles with the shape of hexagonal stars. [2]


On heating, ?- decomposes and recrystallizes as ?- (hematite).[2]


Limonite, a mixture of various hydrates and polymorphs of ferric oxyhydroxide, is one of the three major iron ores, having been used since at least 2500 BCE.[5][6]

Yellow iron oxide, or Pigment Yellow 42, is Food and Drug Administration (FDA) approved for use in cosmetics and is used in some tattoo inks.

Iron oxide-hydroxide is also used in aquarium water treatment as a phosphate binder.[7]

Iron oxide-hydroxide nanoparticles have been studied as possible adsorbents for lead removal from aquatic media.[8]


Iron(III) oxyhydroxide precipitates from solutions of iron(III) salts at pH between 6.5 and 8.[9]. Thus the oxyhydroxide can be obtained in the lab by reacting an iron(III) salt, such as ferric chloride or ferric nitrate, with sodium hydroxide:[10]

+ 3 NaOH -> + 3 NaCl
+ 3 NaOH -> + 3

In fact, when dissolved in water, pure will hydrolyze to some extent, yielding the oxyhydroxide and making the solution acidic:[9]

+ 2 + 3

Therefore, the compound can also be obtained by the decomposition of acidic solutions of iron(III) chloride held near the boiling point for days or weeks:[11]

+ 2 -> (s) + 3 (g)

(The same process applied to iron(III) nitrate or perchlorate solutions yields instead particles of ?-.[11])

Another similar route is the decomposition of iron(III) nitrate dissolved in stearic acid at about 120 °C.[12]

The oxyhydroxide prepared from ferric chloride is usually the ? polymorph (akaganeite), often in the form of thin needles.[11][13]

The oxyhydroxide can also be produced by a solid-state transformation from iron(II) chloride tetrahydrate ·4.[3]

The compound also readily forms when iron(II) hydroxide is exposed to air:

4 + -> 4 + 2

The iron(II) hydroxide can also be oxidized by hydrogen peroxide in the presence of an acid:

2 + -> 2


The risk and safety phrases for iron oxides are R36, R37, R38, S26, and S36.

See also


  1. ^ "Archived copy". Archived from the original on 2015-02-26. Retrieved .CS1 maint: archived copy as title (link)
  2. ^ a b c A. L. Mackay (1960): "?-Ferric Oxyhydroxide". Mineralogical Magazine (Journal of the Mineralogical Society), volume 32, issue 250, pages 545-557. doi:10.1180/minmag.1960.032.250.04
  3. ^ a b A. L. Mackay (1962): "?-Ferric oxyhydroxide--akaganéite", Mineralogical Magazine (Journal of the Mineralogical Society), volume 33, issue 259, pages 270-280 doi:10.1180/minmag.1962.033.259.02
  4. ^ C. Rémazeilles and Ph. Refait (2007): "On the formation of ?-FeOOH (akaganéite) in chloride-containing environments". Corrosion Science, volume 49, issue 2, pages 844-857. doi:10.1016/j.corsci.2006.06.003
  5. ^ MacEachern, Scott (1996): "Iron Age beginnings north of the Mandara Mountains, Cameroon and Nigeria". In In Pwiti, Gilbert and Soper, Robert (editors) (1996) Aspects of African Archaeology: Proceedings of the Tenth Pan-African Congress University of Zimbabwe Press, Harare, Zimbabwe, ISBN 978-0-908307-55-5, pages 489-496. Archived here on 2012-03-11.
  6. ^ Diop-Maes, Louise Marie (1996): "La question de l'Âge du fer en Afrique" ("The question of the Iron Age in Africa"). Ankh, volume4/5, pages 278-303. Archived on 2008-01-25.
  7. ^ Iron Oxide Hydroxide (GFO) Phosphate Binders
  8. ^ Safoora Rahimi, Rozita M. Moattari, Laleh Rajabi, Ali Ashraf Derakhshan, and Mohammad Keyhani (2015): "Iron oxide/hydroxide (?,?-FeOOH) nanoparticles as high potential adsorbents for lead removal from polluted aquatic media". Journal of Industrial and Engineering Chemistry, volume 23, pages 33-43. doi:10.1016/j.jiec.2014.07.039
  9. ^ a b Tim Grundl and Jim Delwiche (1993): "Kinetics of ferric oxyhydroxide precipitation". Journal of Contaminant Hydrology, volume 14, issue 1, pages 71-87. doi:10.1016/0169-7722(93)90042-Q
  10. ^ K. H. Gayer and Leo Woontner (1956): "The Solubility of Ferrous Hydroxide and Ferric Hydroxide in Acidic and Basic Media at 25°". Journal of Physical Chemistry, volume 60, issue 11, pages 1569-1571. doi:10.1021/j150545a021
  11. ^ a b c Egon Matijevi? and Paul Scheiner (1978): "Ferric hydrous oxide sols: III. Preparation of uniform particles by hydrolysis of Fe(III)-chloride, -nitrate, and -perchlorate solutions". Journal of Colloid and Interface Science, volume 63, issue 3, pages 509-524. doi:10.1016/S0021-9797(78)80011-3
  12. ^ Dan Li, Xiaohui Wang, Gang Xiong, Lude Lu, Xujie Yang and Xin Wang (1997): "A novel technique to prepare ultrafine via hydrated iron(III) nitrate". Journal of Materials Science Letters volume 16, pages 493-495 doi:10.1023/A:1018528713566
  13. ^ Donald O. Whittemore and Donald Langmuir (1974): "Ferric Oxyhydroxide Microparticles in Water". Environmental Health Perspective, volume 9, pages 173-176. doi:10.1289/ehp.749173

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