Characteristics of Ferrihydrites Formed by Oxidation of FeCl<sub>2</sub> Solutions Containing Different Amounts of Silica

Karim, Zahurul

doi:10.1346/ccmn.1984.0320304

Cited by 59 publications

(40 citation statements)

References 10 publications

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“…The abundance of phosphate ions on the surface may block the sites needed for crystal growth and prevent recrystallization. The inhibition of ferrihydrite recrystallization by saturation of its surface sites by 4-SiO, has been reported in previous studies (Carlson and Schwertmann 1981;Karim 1984;Zhao et al 1994). Although ferrihydrite is known to convert slowly to hematite or goethite (Schwertmann and Murad 1983;Fisher and Schwertmann 1975;Cornell 1988), the absence of an increase in CDB-extractable Fe to compensate for the disappearance of amorphous Fe undermines the recrystallization mechanism as an explanation for the disappearance of amorphous Fe oxides during burial.…”

Section: Discussionsupporting

confidence: 64%

Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments

Anschutz

Zhong

Sundby

et al. 1998

Limnology & Oceanography

207

137

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We have examined the distributions of phosphorus and iron in sediments from well-oxygenated environments on the Atlantic Canadian and the Portuguese continental margins and from the anoxic region of the Chesapeake Bay. The measurements include total, citrate-dithionite-bicarbonate (CDB) extractable, ascorbate extractable, and dissolved P and Fe; acid volatile sulfide; and pyrite. A surface layer (varying in thickness between 2 and 4 cm) enriched in P and Fe was revealed by both the CDB and the ascorbate extractions in all sediments except those from the Chesapeake Bay. The amount of phosphate extracted by the two reagents was similar, but more iron was extracted by the CDB reagent, probably because of its ability to dissolve crystalline iron oxides. Within the Feand P-enriched surface layer, the Fe : P ratio in the ascorbate extract varied within a narrow range (6-14), as did the soluble-reactive phosphate (SRP) concentration (5-16 PM), suggesting that SRP is in sorption equilibrium with the solid phase. Our data are consistent with a dynamic cycling of P and strong interactions between the cycles of P, Fe, and sulfur in many marine environments. The reductive dissolution of amorphous Fe during burial and the formation of pyrite diminish the capacity of the sediment to sequester P, and only a portion of the P that arrives at the sediment-water interface actually gets buried with the sediment.There is much interest in the ability of sediments to sequester and bury phosphorus because of the effects on the oceanic P budget (Froelich et al. 1982;Howarth et al. 1995; Ruttenberg and Berner 1993) and on the chemistry of the ocean and the atmosphere throughout geologic time (Broecker 1982; Van Cappellen and Ingall 1996). On shorter time scales, P sequestration by sediments affects the trophic state of lakes and the productivity of estuaries (Nixon 198 1; Carace et al. 1990).Both the amount and the form of P sequestered by sediments are affected by diagenesis. Near the sediment-water interface, where most of the freshly deposited organic matter is decomposed, phosphate is rapidly remineralized and released to the sediment pore water from which it can readily escape to the overlying water. Consequently, only a portion 1 Present address: Universite de Bordeaux I,

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Section: Discussionsupporting

confidence: 64%

Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments

Anschutz

Zhong

Sundby

et al. 1998

Limnology & Oceanography

207

137

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“…The results suggest that the texture in Si-100 and Si-300 could comprise a large amount of 2Fh and a small amount of XRD-amorphous silica. Karim [28] reported a similar phase change of Fe oxides by oxidation of FeCl 2 solution containing different amounts of silica: lepidocrocite was formed in the solution having initial atomic Si/Fe ratio = 0, well-crystalized ferrihydrite/some feroxylite/trace lepidocrocite + goethite at Si/Fe ratio=18.0 × 10 . Although Carlson and Schwertmann [29] noted that Si-O-Fe bonds were probably responsible for stability of natural ferrihydrite which always contained some silica, the role of Si in Fe/Si complex in abiotic system has not been well understood.…”

Section: Ed/xrd-results and Crystallinity Of Sheathsmentioning

confidence: 79%

Silicon-Rich, Iron Oxide Microtubular Sheath Produced by an Iron-Oxidizing Bacterium, Leptothrix sp. Strain OUMS1, in Culture

et al. 2014

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This study aimed to manipulate the texture and elemental composition of the novel sheaths produced by the iron-oxidizing bacterium Leptothrix in culture by altering components of the medium. When previously isolated strain OUMS1 was cultured in media (pH 7.0 throughout incubation) containing various levels of Si on a rotary shaker at 20 °C and 70 rpm for 14 days, the strain was able to reproduce in media with up to 300 ppm Si, and the hollow microtubular architecture of the sheath was maintained even at 300 ppm Si. The constitutional iron oxide phase changed from poorly crystalline lepidocrocite at 0 ppm Si to X-ray diffraction (XRD)-amorphous 2-line ferrihydrite at 100-300 ppm via their mixture phase with intermediate Si content . The results strongly indicate that the chemical character and crystallinity of the sheath texture can be regulated by culture conditions, especially components of the medium.

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“…The XRD peaks at 2.4 and 2.2/~ could also be attributed to ferrihydrite (5Fe203.9H20); however, the presence of ferrihydrite is uncertain because of the absence of its other characteristic XRD peaks at 1. 98, 1.73, and 1.51 ~(Chukhrovetal., 1973;Karim, 1984). Further, the formation of ferrihydrite from FeCl: solutions is particularly favored by the presence of Si in the system (Schwertmann and Thalmann, 1976;Karim, 1977).…”

Section: Discussionmentioning

confidence: 99%

Influence of Manganese Oxide Minerals on the Formation of Iron Oxides

Krishnamurti

Huang

1988

Clays and clay miner.

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Abstract--The influence of manganese oxide minerals (cryptomelane, hausmannite, and pyrolusite) on the formation of iron oxides was studied in the FeC12-NH4OH system at different Mn/Fe molar ratios (0, 0.01, 0.1, and 1.0) and pHs (3.0, 4.0, 5.0, and 6.0) by X-ray powder diffraction, infrared absorption, transmission electron microscopic, and chemical analyses. In the absence of Mn minerals, lepidocrocite (3,-FeOOH) precipitated at pHs 5.0 and 6.0; however, no precipitate formed at lower pHs. AH the Mn minerals studied promoted the precipitation of iron oxides and oxyhydroxides. In the presence of Mn oxides, Fe 2 § was oxidized to Fe 3 § which hydrolyzed and precipitated as noncrystalline and/or different crystalline iron oxides and oxyhydroxides, depending on the nature of the Mn oxides present in the system. Simultaneously, Mn 2 § was detected in solution after the reaction by electro'n spin resonance spectroscopy. The presence of cryptomelane and hausmannite resulted in the formation of ~kaganeite (fl-FeOOH) and magnetite (Fe304), respectively. Thus, the effect of Mn oxides on the formation of Fe oxide minerals in the weathering zone merits attention.

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Characteristics of Ferrihydrites Formed by Oxidation of FeCl₂ Solutions Containing Different Amounts of Silica

Cited by 59 publications

References 10 publications

Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments

Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments

Silicon-Rich, Iron Oxide Microtubular Sheath Produced by an Iron-Oxidizing Bacterium, Leptothrix sp. Strain OUMS1, in Culture

Influence of Manganese Oxide Minerals on the Formation of Iron Oxides

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Characteristics of Ferrihydrites Formed by Oxidation of FeCl2 Solutions Containing Different Amounts of Silica

Cited by 59 publications

References 10 publications

Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments

Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments

Silicon-Rich, Iron Oxide Microtubular Sheath Produced by an Iron-Oxidizing Bacterium, Leptothrix sp. Strain OUMS1, in Culture

Influence of Manganese Oxide Minerals on the Formation of Iron Oxides

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Characteristics of Ferrihydrites Formed by Oxidation of FeCl₂ Solutions Containing Different Amounts of Silica