ferrihydrite

Ferrihydrite only exists as a fine grained and highly defective nanomaterial. The powder X-ray diffraction pattern of Fh contains two scattering bands in its most disordered state, and a maximum of six strong lines in its most crystalline state. The principal difference between these two diffraction end-members, commonly named two-line and six-line ferrihydrites, is the size of the constitutive crystallites.V. A. Drits, B. A. Sakharov, A. L. Salyn, et al. Clay Minerals, 28, 185–208 (1993)A. Manceau A., V. A. Drits, Clay Minerals, 28, 165–184 (1993) The six-line form has been classified as a mineral by the IMA in 1973F. V. Chuckrov, B. B. Zvyagin, A.I. Gorshov, et al. International Geology Review, 16, 1131–1143 (1973) with the nominal chemical formula 5{{chem|Fe|2|O|3}}·9{{chem|H|2|O}}.M. Fleischer, G. Y. Chao, A. Kato (1975): American Mineralogist, volume 60 Other proposed formulas are {{chem|Fe|5|HO|8}}·4{{chem|H|2|O}}Kenneth M Towe and William F Bradley (1967): "Mineralogical constitution of colloidal 'hydrous ferric oxides'". Journal of Colloid and Interface Science, volume 24, issue 3, pages 384–392. {{doi|10.1016/0021-9797(67)90266-4}} and {{chem|Fe|2|O|3}}·2{{chem|FeO(OH)}}·2.6{{chem|H|2|O}}.J. D. Russell (1979): "Infrared spectroscopy of ferrihydrite: evidence for the presence of structural hydroxyl groups". Clay Minerals, volume 14, issue 2, pages 109–114. {{doi|10.1180/claymin.1979.014.2.03}} However, its formula is fundamentally indeterminate as its water content is variable. The two-line form is also called hydrous ferric oxides (HFO).

Due to the nanoparticulate nature of ferrihydrite, the structure has remained elusive for many years and is still a matter of controversy.D. G. Rancourt, J. F. Meunier, American Mineralogist, 93, 1412–1417 (2008)A. Manceau. American Mineralogist, 96, 521–533 (2011)A. Manceau ACS Earth and Space Chemistry, 4, 379–390 (2020). {{doi|10.1021/acsearthspacechem.9b00018}} Drits et al., using X-ray diffraction data, proposed in 1993 a multiphase structure model for six-line ferrihydrite with three components: (1) defect-free crystallites (f-phase) with double-hexagonal stacking of oxygen and hydroxyl layers (ABAC sequence) and disordered octahedral Fe occupancies, (2) defective crystallites (d-phase) with a short-range feroxyhite-like (δ-FeOOH) structure, and (3) subordinate ultradisperse hematite (α-Fe₂O₃). The diffraction model has been confirmed in 2002 by neutron diffraction,E. Jansen, A. Kyek, W. Schafer, U. Schwertmann. Appl. Phys. A: Mater. Sci. Process., 74, S1004–S1006 (2002) and the three components were observed by high-resolution transmission electron microscopy.D.E. Janney, J.M. Cowley, P.R. Buseck. American Mineralogist, 85, 1180–1187 (2000)D.E. Janney, J.M. Cowley, P.R. Buseck. American Mineralogist, 86, 327–335 (2001).A. Manceau. Clay Minerals, 44, 19–34 (2009) A single phase model for both ferrihydrite and hydromaghemiteV. Barron, J. Torrent, E. de Grave American Mineralogist, 88, 1679–1688 (2003) has been proposed by Michel et al.,F. M. Michel, L. Ehm, S. M. Antao, et al. Science, 316, 1726–1729 (2007)F. M. Michel, V. Barron, J. Torrent, et al. PNAS, 107, 2787–2792 (2010) in 2007–2010, based on pair distribution function (PDF) analysis of x-ray total scattering data. The structural model, isostructural with the mineral akdalaite (Al₁₀O₁₄(OH)₂), contains 20% tetrahedrally and 80% octahedrally coordinated iron. Manceau et al. showed in 2014A. Manceau, S. Skanthakumar, S. Soderholm, American Mineralogist, 99, 102–108 (2014). {{doi|10.2138/am.2014.4576}} that the Drits et al. model reproduces the PDF data as well as the Michel et al. model, and he suggested in 2019 that the tetrahedral coordination arises from maghemite and magnetite impurities observed by electron microscopy.X. J. M. Cowley, D. E. Janney, R. C. Gerkin, P. R. Buseck, P. R., Journal of Structural Biology 131, 210–216 (2000)Z D. E. Janney, J. M. Cowley, P. R. Buseck, Clays Clay Miner., 48, 111–119 (200)

==Porosity and environmental absorbent potential==

Because of the small size of individual nanocrystals, Fh is nanoporous yielding large surface areas of several hundred square meters per gram.T. Hiemstra, W. H. Van Riemsdijk, Geochimica et Cosmochimica Acta, 73, 4423–4436 (2009) In addition to having a high surface area to volume ratio, Fh also has a high density of local or point defects, such as dangling bonds and vacancies. These properties confer a high ability to adsorb many environmentally important chemical species, including arsenic, lead, phosphate, and organic molecules (e.g., humic and fulvic acids).A. L. Foster, G. E. Brown, T. N. Tingle, et al. American Mineralogist, 83, 553–568 (1998)A. H. Welch, D. B. Westjohn, D. R. Helsel, et al. Ground Water, 38, 589–604 (2000)M. F. Hochella, T. Kasama, A. Putnis, et al. American Mineralogist, 90, 718–724 (2005)D. Postma, F. Larsen, N. T. M. Hue, et al. Geochimica et Cosmochimica Acta, 71, 5054–5071 (2007) Its strong and extensive interaction with trace metals and metalloids is used in industry, at large-scale in water purification plants, as in North Germany and to produce the city water at Hiroshima, and at small scale to clean wastewaters and groundwaters, for example to remove arsenic from industrial effluents and drinking water.P. A. Riveros J. E. Dutrizac, P. Spencer, Canadian Metallurgical Quarterly, 40, 395–420 (2001)O. X. Leupin S. J. Hug, Water Research, 39, 1729–1740 (2005)S. Jessen, F. Larsen, C. B. Koch, et al. Environmental Science & Technology, 39, 8045–8051 (2005)A. Manceau, M. Lanson, N. Geoffroy, Geochimica et Cosmochimic Acta, 71, 95–128 (2007)D. Paktunc, J. Dutrizac, V. Gertsman, Geochimica et Cosmochimica Acta, 72, 2649–2672 Its nanoporosity and high affinity for gold can be used to elaborate Fh-supported nanosized Au particles for the catalytic oxidation of CO at temperatures below 0 °C.N. A. Hodge, C. J. Kiely, R. Whyman, et al. Catalysis Today, 72, 133–144 (2002) Dispersed six-line ferrihydrite nanoparticles can be entrapped in a vesicular state to increase their stability.L. Gentile, Journal of Colloid and Interface Science, https://doi.org/10.1016/j.jcis.2021.09.192 (2021) Presence of ferrihydrite can enhance growth of certain microbes, eg. Dissulfuribacter thermophilus, by scavenging sulfide, a waste product of their metabolism.{{Cite journal |last=Slobodkin |first=A. I. |last2=Reysenbach |first2=A.-L. |last3=Slobodkina |first3=G. B. |last4=Kolganova |first4=T. V. |last5=Kostrikina |first5=N. A. |last6=Bonch-Osmolovskaya |first6=E. A. |date=2013-06-01 |title=Dissulfuribacter thermophilus gen. nov., sp. nov., a thermophilic, autotrophic, sulfur-disproportionating, deeply branching deltaproteobacterium from a deep-sea hydrothermal vent |url=https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.046938-0 |journal=International Journal of Systematic and Evolutionary Microbiology |language=en |volume=63 |issue=Pt_6 |pages=1967–1971 |doi=10.1099/ijs.0.046938-0 |issn=1466-5026|url-access=subscription }}

Ferrihydrite is a metastable mineral. It is known to be a precursor of more crystalline minerals like hematite and goethiteU. Schwertmann, E. Murad, Clays Clay Minerals, 31, 277 (1983)U. Schwertmann, J. Friedl, H. Stanjek, Journal of Colloid and Interface Science, 209, 215–223 (1999)U. Schwertmann, H. Stanjek, H.H. Becher, Clay Miner. 39, 433–438 (2004){{cite journal|author = Y. Cudennec, A. Lecerf|title = The transformation of ferrihydrite into goethite or hematite, revisited|journal = Journal of Solid State Chemistry |volume = 179 |pages = 716–722 |year = 2006|doi = 10.1016/j.jssc.2005.11.030 | issue=3|bibcode = 2006JSSCh.179..716C | s2cid=93994327 |url = https://hal.archives-ouvertes.fr/hal-02495178/file/fe2o3jssc_ferrihydrite.pdf}} by aggregation-based crystal growth.W. R. Fischer, U. Schwertmann, Clays and Clay Minerals, 23, 33 (1975)J. F. Banfield, S. A. Welch, H. Z. Zhang, et al. Science, 289, 751–754 (2000) However, its transformation in natural systems generally is blocked by chemical impurities adsorbed at its surface, for example silica as most of natural ferrihydrites are siliceous.L. Carlson, U. Schwertmann, Geochimica et Cosmochimica Acta, 45, 421-429 (1981)

Under reducing conditions as those found in gley soils, or in deep environments depleted in oxygen, and often with the assistance of microbial activity, ferrihydrite can be transformed in green rust, a layered double hydroxide (LDH), also known as the mineral fougerite. However, a short exposure of green rust to atmospheric oxygen is sufficient to oxidize it back to ferrihydrite, making it a very elusive compound.

File:Ferrihydrite precipitate.jpg|Ferrihydrite precipitate from coal mine water

File:Spring in the Zillertaler Alps.jpg|Spring in the Zillertaler Alps with Fh precipitate

File:Seepage of iron-rich water.jpg|Seepage of iron-rich water

File:Ferrihydrite to goethite.jpg|Transformation of ferrihydrite (top) to goethite (bottom)

File:Sand filter.jpg|Water treatment plant using the slow sand filter technology to treat raw water

File:Qtz coating_rAsgFebMn.jpg| Tricolor (RGB) X-ray fluorescence image of the distribution of As (red), Fe (green), and Mn (blue) in coated quartz grains from a water treatment sand bed

Better crystallized and less hydrated iron oxy-hydroxides are amongst others:

• Akaganéite
• Feroxyhyte
• Goethite
• Hematite
• Lepidocrocite
• Limonite
• Maghemite
• Magnetite

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Category:Iron(III) minerals

Category:Iron oxide pigments

Category:Hydroxide minerals

Category:Hexagonal minerals

Category:Minerals in space group 186