Iron hydroxides in soils: A review of publications |
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| Authors: | Yu N Vodyanitskii |
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| Institution: | 1.Dokuchaev Soil Science Institute,Russian Academy of Agricultural Sciences,Moscow,Russia |
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| Abstract: | Iron hydroxides are subdivided into thermodynamically unstable (ferrihydrite, feroxyhyte, and lepidocrocite) and stable (goethite)
minerals. Hydroxides are formed either from Fe3+ (as ferrihydrite) or Fe2+ (as feroxyhyte and lepidocrocite). The high amount of feroxyhyte in ferromanganic concretions is proved, which points to
the leading role of variable redox conditions in the synthesis of hydroxides. The structure of iron hydroxides is stabilized
by inorganic elements, i.e., ferrihydrite, by silicon; feroxyhyte, by manganese; lepidocrocite, by phosphorus; and goethite,
by aluminum. Ferrihydrite and feroxyhyte are formed with the participation of biota, whereas the abiotic formation of lepidocrocite
and goethite is possible. The iron hydroxidogenesis is more pronounced in podzolic soils than in chernozems, and it is more
pronounced in iron-manganic nodules than in the fine earth. Upon the dissolution of iron hydroxides, iron isotopes are fractioned
with light-weight 54Fe atoms being dissolved more readily. Unstable hydroxides are transformed into stable (hydr)oxides, i.e., feroxyhyte is spontaneously
converted to goethite, and ferrihydrite, to hematite or goethite. |
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