Ferrihydrite ( Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface,[J. L. Jambor, J.E. Dutrizac, Chemical Reviews, 98, 22549–2585 (1998)][R. M. Cornell R.M., U. Schwertammn, The iron oxides: structure, properties, reactions, occurrences and uses, Wiley–VCH, Weinheim, Germany (2003)] and a likely constituent in extraterrestrial materials.[M. Maurette, Origins of Life and Evolution of the Biosphere, 28, 385–412 (1998)] It forms in several types of environments, from freshwater to marine systems, to hydrothermal and scales, , and areas affected by mining. It can be precipitated directly from oxygenated iron-rich aqueous solutions, or by bacteria either as a result of a metabolic activity or passive sorption of dissolved iron followed by nucleation reactions.[D. Fortin, S. Langley, Earth-Science Reviews, 72, 1–19 (2005)] Ferrihydrite also occurs in the core of the ferritin protein from many , for the purpose of intra-cellular iron storage.[N. D. Chasteen, P. M. Harrison, Journal of Structural Biology, 126, 182–194 (1999)][A. Lewin, G. R. Moore, N. E. Le Brun, Dalton Transactions, 22, 3597–3610 (2005)]
Structure
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 1973
[F. V. Chuckrov, B. B. Zvyagin, A.I. Gorshov, et al. International Geology Review, 16, 1131–1143 (1973)] with the nominal chemical formula 5·9.
[M. Fleischer, G. Y. Chao, A. Kato (1975): American Mineralogist, volume 60 ] Other proposed formulas are ·4
[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. ] and ·2·2.6.
[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. ] 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). ] Drits et al., using X-ray diffraction data,[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 hydromaghemite[V. 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. Alain Manceau et al. showed in 2014[A. Manceau, S. Skanthakumar, S. Soderholm, American Mineralogist, 99, 102–108 (2014). ] that the Drits et al.[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
, 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 acid and
).
[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)][Michael 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
and
, 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
]
(2021) Presence of ferrihydrite can enhance growth of certain microbes, eg.
Dissulfuribacter thermophilus, by scavenging sulfide, a waste product of their metabolism.
Metastability
Ferrihydrite is a
metastable mineral. It is known to be a precursor of more crystalline minerals like
hematite and
goethite[U. 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)] 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 , 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
See also
Better crystallized and less hydrated iron oxy-hydroxides are amongst others:
