Iron(III) oxide-hydroxide or ferric oxyhydroxideA. L. Mackay (1960): "β-Ferric Oxyhydroxide". ''Mineralogical Magazine'' (''Journal of the Mineralogical Society''), volume 32, issue 250, pages 545-557. is the chemical compound of

iron Iron () is a chemical element with symbol Fe (from la, ferrum) 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, right in ...

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

, and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

with formula . The compound is often encountered as one of its

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

s, ·''n'' ust The monohydrate · is often referred to as iron(III) hydroxide ,CAS , C.I. 77492 hydrated iron oxide, yellow iron oxide, or Pigment Yellow 42.

Natural occurrences

Minerals

Anhydrous ferric hydroxide occurs in the nature as the exceedingly rare mineral bernalite, Fe(OH)₃·''n''H₂O (n=0.0-0.25). Iron oxyhydroxides, , are much more common and occur naturally as structurally different

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

s (polymorphs) denoted by the Greek letters α, β, γ and δ. *

Goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

, α-FeO(OH), has been used as an

ochre Ochre ( ; , ), or ocher in American English, is a natural clay earth pigment, a mixture of ferric oxide and varying amounts of clay and sand. It ranges in colour from yellow to deep orange or brown. It is also the name of the colours produced ...

pigment since prehistoric times. *

Akaganeite Akaganeite, also written as the deprecated Akaganéite,Ernst A.J. Burke (2008):Tidying up Mineral Names: an IMA-CNMNC Scheme for Suffixes, Hyphens and Diacritical marks. ''Mineralogical Record'', volume 39, issue 2. is a chloride-containing ir ...

is the β polymorph,A. L. Mackay (1962): "β-Ferric oxyhydroxide—akaganéite", ''Mineralogical Magazine'' (''Journal of the Mineralogical Society''), volume 33, issue 259, pages 270-280 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 The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...

ions to stabilize its structure, so that its more accurate formula is or .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. *

Lepidocrocite Lepidocrocite (γ-FeO(OH)), also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown ...

, the γ polymorph, is commonly encountered as

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...

on the inside of steel water pipes and tanks. *

Feroxyhyte Feroxyhyte is an oxide/hydroxide of iron, δ-Fe3+O(OH). Feroxyhyte crystallizes in the hexagonal system. It forms as brown rounded to concretionary masses. Feroxyhyte is opaque, magnetic, has a yellow streak, and has a relative density of 4.2. ...

(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

Siderogel Siderogel is an amorphous mineral (a mineraloid) consisting of iron(III) oxide-hydroxide , the same chemical compound as limonite and goethite; or possibly an hydrate of the same •''n''.Sven Köhler (2004): ''Auswahl und Einsatz von eisenhaltigen ...

is a naturally occurring

colloid A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...

al form of iron(III) oxide-hydroxide. 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.

Mineraloids

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

mineraloid A mineraloid is a naturally occurring mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an a ...

s: *

Limonite Limonite () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·H2O, although this is not entirely accurate as the ratio of oxide to hydroxide ...

is a commonly occurring mixture of mainly goethite, lepidocrocite,

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...

and

clay minerals Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minera ...

. *

Ferrihydrite Ferrihydrite (Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hy ...

is an amorphous or

nanocrystal A ''nanocrystal'' is a material particle having at least one dimension smaller than 100 nanometres, based on quantum dots (a nanoparticle) and composed of atoms in either a single- or poly-crystalline arrangement. The size of nanocrystals dist ...

line hydrated mineral, officially •1.8 but with widely variable hydration.

Properties

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.

Structure

The crystal structure of β- (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.

Chemistry

On heating, β- decomposes and recrystallizes as α- (

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

Uses

, a mixture of various hydrates and polymorphs of ferric oxyhydroxide, is one of the three major

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the ...

s, having been used since at least 2500 BC.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, , pages 489-496. Archive
here
on 2012-03-11. Yellow iron oxide, or Pigment Yellow 42, is

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

(FDA) approved for use in

cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protec ...

and is used in some

tattoo A tattoo is a form of body modification made by inserting tattoo ink, dyes, and/or pigments, either indelible or temporary, into the dermis layer of the skin to form a design. Tattoo artists create these designs using several tattooing ...

inks. Iron oxide-hydroxide is also used in

aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...

water treatment as a

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

binder. Iron oxide-hydroxide

nanoparticle A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 10 ...

s have been studied as possible

adsorbent Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...

s for lead removal from aquatic media.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.

Medication

Iron polymaltose is used in treatment of

iron-deficiency anemia Iron-deficiency anemia is anemia caused by a lack of iron. Anemia is defined as a decrease in the number of red blood cells or the amount of hemoglobin in the blood. When onset is slow, symptoms are often vague such as feeling tired, weak, shor ...

Production

Iron(III) oxyhydroxide precipitates from solutions of iron(III) salts at pH between 6.5 and 8.Tim Grundl and Jim Delwiche (1993): "Kinetics of ferric oxyhydroxide precipitation". ''Journal of Contaminant Hydrology'', volume 14, issue 1, pages 71-87. Thus the oxyhydroxide can be obtained in the lab by reacting an iron(III) salt, such as

ferric chloride Iron(III) chloride is the inorganic compound with the formula . Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The col ...

ferric nitrate Iron(III) nitrate, or ferric nitrate, is the name used for a series of inorganic compounds with the formula Fe(NO3)3.(H2O)n. Most common is the nonahydrate Fe(NO3)3.(H2O)9. The hydrates are all pale colored, water-soluble paramagnetic salts. Hy ...

, with

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and al ...

: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. : + 3 NaOH → + 3 NaCl : + 3 NaOH → + 3 In fact, when dissolved in water, pure will

hydrolyze Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis i ...

to some extent, yielding the oxyhydroxide and making the solution acidic: : + 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: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. : + 2 → _(s) + 3 _(g) (The same process applied to

iron(III) nitrate Iron(III) nitrate, or ferric nitrate, is the name used for a series of inorganic compounds with the formula Fe(NO3)3.(H2O)n. Most common is the nonahydrate Fe(NO3)3.(H2O)9. The hydrates are all pale colored, water-soluble paramagnetic salts. Hy ...

or perchlorate solutions yields instead particles of α-.) Another similar route is the decomposition of iron(III) nitrate dissolved in

stearic acid Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a waxy solid and its chemical formula is C17H35CO2H. Its name comes from the Greek word στέαρ "''stéar''", which means ta ...

at about 120 °C.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 The oxyhydroxide prepared from ferric chloride is usually the β polymorph (akaganeite), often in the form of thin needles.Donald O. Whittemore and Donald Langmuir (1974): "Ferric Oxyhydroxide Microparticles in Water". ''Environmental Health Perspective'', volume 9, pages 173-176. The oxyhydroxide can also be produced by a solid-state transformation from

iron(II) chloride Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water a ...

tetrahydrate ·4. The compound also readily forms when

iron(II) hydroxide Iron(II) hydroxide or ferrous hydroxide is an inorganic compound with the formula Fe(OH)2. It is produced when iron(II) salts, from a compound such as iron(II) sulfate, are treated with hydroxide ions. Iron(II) hydroxide is a white solid, but ev ...

is exposed to air: :4 + → 4 + 2 The iron(II) hydroxide can also be oxidized by

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3 ...

in the presence of an acid: :2 + → 2

References

{{Antianemic preparations Iron(III) compounds Hydroxides Transition metal oxides