3D model (JSmol)
CompTox Dashboard (EPA)
|Appearance||Vivid, dark orange, opaque crystals|
|insoluble at pH 7|
Solubility product (Ksp)
|2.79×10−39 for Fe(OH)3|
|NFPA 704 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
The compound is often encountered as one of its hydrates, FeO(OH)·nH
2O [Rust]. The monohydrate FeO(OH)·H
2O (CAS , C.I. 77492) is often referred as iron(III) hydroxide Fe(OH)
3, hydrated iron oxide, yellow iron oxide, or Pigment Yellow 42.
Anhydrous ferric oxyhydroxide FeOOH occurs naturally as four different minerals (polymorphs) denoted by the Greek letters α, β, γ and δ.
- Goethite, α-FeO(OH), has been used as an ocher pigment since prehistoric times.
- Akaganeite is the β polymorph, 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 FeO
- Lepidocrocite, the γ polymorph, is commonly encountered as rust on the inside of steel water pipes and tanks.
- Feroxyhyte (δ) is formed under the high pressure conditions of sea and ocean floors, being thermodynamically unstable with respect to the α 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:
- Limonite is a commonly occurring mixture of mainly goethite, lepidocrocite, quartz and clay minerals.
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 β-FeOOH (akaganeite) is that of hollandite or BaMn
16. 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.
On heating, β-FeOOH decomposes and recrystallizes as α-Fe
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.
Iron(III) oxyhydroxide precipitates from solutions of iron(III) salts at pH between 6.5 and 8.. 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:
3 + 3 NaOH → Fe(OH)
3 + 3 NaCl
3 + 3 NaOH → Fe(OH)
3 + 3 NaNO
In fact, when dissolved in water, pure FeCl
3 will hydrolyze to some extent, yielding the oxyhydroxide and making the solution acidic:
3 + 2 H
2O ↔ FeOOH + 3 HCl
3 + 2 H
2O → FeOOH(s) + 3 HCl(g)
(The same process applied to iron(III) nitrate Fe(NO
3 or chlorate Fe(ClO
3 solutions yields instead particles of α-Fe
The oxyhydroxide can also be produced by a solid-state transformation from iron(II) chloride tetrahydrate FeCl
The compound also readily forms when iron(II) hydroxide is exposed to air:
2 + O
2 → 4 FeOOH + 2 H
The iron(II) hydroxide can also be oxidized by hydrogen peroxide in the presence of an acid:
2 + H
2 → 2 Fe(OH)
- "Archived copy". Archived from the original on 2015-02-26. Retrieved 2015-02-23.CS1 maint: archived copy as title (link)
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- A. L. Mackay (1962): "β-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
- C. Rémazeilles and Ph. Refait (2007): "On the formation of β-FeOOH (akaganéite) in chloride-containing environments". Corrosion Science, volume 49, issue 2, pages 844-857. doi:10.1016/j.corsci.2006.06.003
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- 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 here on 2008-01-25.
- Iron Oxide Hydroxide (GFO) Phosphate Binders
- Safoora Rahimi, Rozita M. Moattari, Laleh Rajabi, Ali Ashraf Derakhshan, and Mohammad Keyhani (2015): "Iron oxide/hydroxide (α,γ-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
- 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
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- Egon Matijević 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
- 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