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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, aquifers to hydrothermal hot springs and scales, soils, 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 living organisms, 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)〕〔M. Fleischer, G. Y. Chao, A. Kato, ''American Mineralogist'', 60 (1975)〕 with the nominal chemical formula 5Fe2O3•9H2O. 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)〕 Drits ''et al.'', using X-ray diffraction data,〔 proposed a multiphase material with three components: defect-free crystallites (f-phase) with double-hexagonal stacking of oxygen and hydroxyl layers (ABAC sequence) and disordered octahedral Fe occupancies, defective crystallites (d-phase) with a short-range feroxyhite-like (δ-FeOOH) structure, and subordinate ultradisperse hematite (α-Fe2O3). Recently, a new 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)〕 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. ==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.〔http://www.water.city.hiroshima.jp/english/methods.html〕〔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)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ferrihydrite」の詳細全文を読む スポンサード リンク
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