Iron(III) oxide-hydroxide or ferric oxyhydroxide[2] is the chemical compound of iron, oxygen, and hydrogen with formula FeO(OH).
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| Names | |
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| IUPAC name
Iron(III) oxide-hydroxide
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| Other names | |
| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.039.754 |
| EC Number |
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| MeSH | Goethite |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| FeO(OH) | |
| Appearance | Vivid, dark orange, opaque crystals |
| Odor | odorless |
| Density | 4.25 g/cm3 |
| insoluble at pH 7 | |
Solubility product (Ksp)
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2.79×10−39 for Fe(OH)3[1] |
| Hazards | |
| NFPA 704 (fire diamond) | |
| Pharmacology | |
| B03AB04 (WHO) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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The compound is often encountered as one of its hydrates, FeO(OH)·nH
2O [rust]. The monohydrate FeO(OH)·H
2O is often referred to as iron(III) hydroxide Fe(OH)
3,[3] hydrated iron oxide, yellow iron oxide, or Pigment Yellow 42.[3]
Natural occurrences
editMinerals
editAnhydrous ferric hydroxide occurs in the nature as the exceedingly rare mineral bernalite, Fe(OH)3·nH2O (n = 0.0–0.25).[4][5] Iron oxyhydroxides, FeOOH, are much more common and occur naturally as structurally different minerals (polymorphs) denoted by the Greek letters α, β, γ and δ.
- Akaganeite is the β polymorph,[6] 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
0.833(OH)
1.167Cl
0.167 or Fe
6O
5(OH)
7Cl.[7]
- 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.
Non-mineral
editGoethite 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.
Mineraloids
editIron(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.
- Ferrihydrite is an amorphous or nanocrystalline hydrated mineral, officially FeOOH·1.8H
2O but with widely variable hydration.
Properties
editThe 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.
Structure
editThe crystal structure of β-FeOOH (akaganeite) is that of hollandite or BaMn
8O
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. [2]
Chemistry
editOn heating, β-FeOOH decomposes and recrystallizes as α-Fe
2O
3 (hematite).[2]
Uses
editLimonite, 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 BC.[8][9]
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.[10]
Iron oxide-hydroxide nanoparticles have been studied as possible adsorbents for lead removal from aquatic media.[11]
Medication
editIron polymaltose is used in treatment of iron-deficiency anemia.
Production
editIron(III) oxyhydroxide precipitates from solutions of iron(III) salts at pH between 6.5 and 8.[12] 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:[13]
- FeCl
3 + 3 NaOH → Fe(OH)
3 + 3 NaCl - Fe(NO
3)
3 + 3 NaOH → Fe(OH)
3 + 3 NaNO
3
In fact, when dissolved in water, pure FeCl
3 will hydrolyze to some extent, yielding the oxyhydroxide and making the solution acidic:[12]
- FeCl
3 + 2 H
2O ↔ FeOOH + 3 HCl
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:[14]
- FeCl
3 + 2 H
2O → FeOOH(s) + 3 HCl(g)
(The same process applied to iron(III) nitrate Fe(NO
3)
3 or perchlorate Fe(ClO
4)
3 solutions yields instead particles of α-Fe
2O
3.[14])
Another similar route is the decomposition of iron(III) nitrate dissolved in stearic acid at about 120 °C.[15]
The oxyhydroxide prepared from ferric chloride is usually the β polymorph (akaganeite), often in the form of thin needles.[14][16]
The oxyhydroxide can also be produced by a solid-state transformation from iron(II) chloride tetrahydrate FeCl
2·4H
2O.[6]
The compound also readily forms when iron(II) hydroxide is exposed to air:
- 4Fe(OH)
2 + O
2 → 4 FeOOH + 2 H
2O
The iron(II) hydroxide can also be oxidized by hydrogen peroxide in the presence of an acid:
- 2Fe(OH)
2 + H
2O
2 → 2 Fe(OH)
3
See also
edit- Rust
- Iron oxide
- Yellow boy, a yellow precipitate when acidic runoff such as mine waste, is then neutralised
References
edit- ^ "Solubility product constants at 25 oC". Archived from the original on 2015-02-26. Retrieved 2015-02-23.
- ^ a b c A. L. Mackay (1960): "β-Ferric Oxyhydroxide". Mineralogical Magazine (Journal of the Mineralogical Society), volume 32, issue 250, pages 545-557. doi:10.1180/minmag.1960.032.250.04
- ^ a b CAS , C.I. 77492
- ^ "Bernalite".
- ^ "List of Minerals". 21 March 2011.
- ^ a b 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
- ^ 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.
- ^ 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.
- ^ 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
- ^ 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
- ^ 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
- ^ a b c 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
- ^ Dan Li, Xiaohui Wang, Gang Xiong, Lude Lu, Xujie Yang and Xin Wang (1997): "A novel technique to prepare ultrafine Fe
2O
3 via hydrated iron(III) nitrate". Journal of Materials Science Letters volume 16, pages 493–495 doi:10.1023/A:1018528713566 - ^ 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