Ferrihydrite: A review of structure, properties and occurrence in relation to soils

Abstract

Ferrihydrite occurs in soils undergoing rapid weathering, and in soils containing soluble silicate or organic anions which inhibit the formation of more crystalline iron oxides. Because of its very high specific surface area and adsorptive capacity (analogous to allophane), ferrihydrite can profoundly influence soil properties, even if present in only low concentrations. Ferrihydrite was recognised as a mineral by the International Mineralogical Association in 1975. Its structure and chemical formula, however, are not yet clearly understood. Most evidence to date indicates hexagonal‐close‐packed layers of O2′, OH, and H2O with Fe(III) occupying octahedral positions and giving a trigonal unit cell (a=0.508 nm; c=0.94 nm). Some samples appear to have only a partially ordered structure and uncertainty exists as to how to name such material. Natural ferrihydrites commonly contain up to about 9% Si and the role and location of silicate are subjects of active research. At concentrations greater than 5‐10%, ferrihydrite in soils can usually be identified by X‐ray diffraction. At lower concentrations, a combination of methods can be indicative. Acid‐oxalate‐extractable iron is a convenient and often useful indicator of the presence and quantity of ferrihydrite in a soil, though it cannot be regarded as a means of positive identification.

Relationships between soil characteristics and productivity of Acacia mangium in South Sumatra

“…Decreases of Fe o content and Fe o /Fe d ratio with depth in all soils might be due to higher crystallization in lower layers probably because of lower organic matter content, w h i c h f u n c t i o n s a s a n i n h i b i t i n g a g e n t a g a i n s t crystallization (Childs 1992). The ratio of Fe o /Fe d was correlated positively with T-C and negatively with clay content, indicating higher clay content and lower T-C content are also related to iron crystallization.…”

Sediment origin and pedogenesis in the former mill pond basin of Turznice (north-central Poland) based on magnetic susceptibility measurements

“…The predominant Fe-mineral which forms in changing redox conditions in a temperate climate is ferrihydrite (Schwertmann 1988;Dąbkowska-Naskręt 2013;Vodyanitskii and Shoba 2016) while goethite is the most widespread iron hydroxide -in particular, in the soils of humid and semi-humid areas (Vodyanitskii 2010). In environments rich in humic substances (such as mill pond sediments) the amorphous Fe-minerals are dominative, as the presence of humic acids may cause complete inhibition of crystal formation (Childs 1992;Porsh et al 2010). In soils with organic carbon content higher than 5%, ferrihydrite could prevail over lepidocrocite and goethite, as is reported for the area of Britain, Belgium and Germany (Schwertmann 1988).…”

Émersion des terres et développement des sols bien drainés au lac Guillaume-Delisle, Québec subarctique

“…La migration vers le bas du profil de complexes organométalliques avec les eaux de percolation serait le principal mode d'enrichissement en fer et en aluminium de l'horizon B dans les sols sableux et bien drainés de la région du lac Wang, 1990 ;Childs, 1992 (Jenny, 1941) qui devient alors le seul facteur responsable de l'évolution d'une propriété du sol. Cependant, les propriétés d'un sol sont plus fréquem-ment le résultat de l'action de plusieurs facteurs (Moore, 1978 ;Bockheim, 1980 La relation marginalement significative entre la concentration en Fe p +Al p et la durée de la pédogenèse a tout de même permis de proposer une première approximation de la durée minimale pour l'obtention d'un horizon B podzolique répon-dant aux critères du Système canadien de classification des sols (Groupe de travail sur la classification des sols, 2002), soit environ 12 400 ans.…”