A detailed study of the transformation of ferrihydrite to hematite in an aqueous medium at 92°C

Johnston, James H.; Lewis, G. Malcolm

doi:10.1016/0016-7037(83)90200-4

Cited by 100 publications

(70 citation statements)

References 12 publications

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“…Many researchers (Murad and Schwertmann, 1980;Childs and Johnston, 1980;Johnston and Lewis, 1983;Cardile, 1988;Murad, 1988) have reported similar doublets for both natural and synthetic ferrihydrite samples. No magnetically split hyperfine component lines are observed because of the small particle size of the ferrihydrite and its correspondingly low magnetic ordering temperature, in the range 115-25 K depending on crystallite size (Murad and Johnston, 1987;Murad et aL, 1988).…”

Section: Mb'ssbauer Spectroscopymentioning

confidence: 79%

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Studies of the Reactivity of the Ferrihydrite Surface by Iron Isotopic Exchange and Mössbauer Spectroscopy

Rea

Davis

Waychunas

1994

Clays and clay miner.

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Abstract--Two-line ferrihydrite is an important adsorbent of many toxics in natural and anthropogenic systems; however, the specific structural sites responsible for the high adsorption capacity are not well understood. A combination of chemical and spectroscopic techniques have been employed in this study to gain further insight into the structural nature of sites at the ferrihydrite surface. The kinetics of iron isotopic exchange demonstrated that there are at least two types of iron sites in ferrihydrite. One population of sites, referred to as labile sites, approached iron isotopic equilibrium within 24 hr in 59Fe-NTA solutions, while the second population of sites, referred to as non-labile, exhibited a much slower rate of isotopic exchange. Adsorbed arsenate reduced the degree of exchange by labile sites, indicating that the anion blocked or greatly inhibited the rate of exchange of these sites. Mtssbauer spectra were collected from a variety of samples including 56Fe-ferrihydrite samples with 57Fe in labile sites, samples containing STFe throughout the structure, and samples with 5VFe in non-labile sites. The spectra showed characteristic broad doublets signifying poor structural order. Refined fits of the spectra indicated that labile sites have larger quadrupole splitting, hence more local distortion, than non-labile sites. In all cases, the spectra demonstrated some degree of asymmetry, indicating a distribution of Fe environments in ferrihydrite. Overall spectral findings, combined with recent EXAFS results , indicate that labile sites likely are more reactive (with respect to iron isotopic exchange) because they have fewer neighboring Fe octahedra and are therefore bound less strongly to the ferrihydrite structure. The labile population of sites probably is composed of end sites of the dioctahedral chain structure of 2-line ferrihydrite, which is a subset of the entire population of surface sites. Mtssbauer spectra of samples containing adsorbed arsenate indicated that the anion may slightly decrease the distortion of labile sites and stabilized the structure as a whole by bidentate bonding.

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Section: Mb'ssbauer Spectroscopymentioning

confidence: 79%

“…3 Six-line ferrihydrite heated for l0 and 30 min. M6ssbauer spectra exhibited no hematite structure (Johnston and Lewis, 1983). " N163, LC31 = "Relatively well-crystallized ferrihydrite"; LC2 = "Extremely poorly-crystallized ferrihydrite" (Murad et al, 1988).…”

Section: Description Of Fe Sites Of the Labile Fractionmentioning

confidence: 99%

Studies of the Reactivity of the Ferrihydrite Surface by Iron Isotopic Exchange and Mössbauer Spectroscopy

Rea

Davis

Waychunas

1994

Clays and clay miner.

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“…Several authors have shown that 6-line ferrihydrite may convert to hematite with heat treatment (Johnston and Lewis 1983;Stanjek and Weidler 1992;Weidler 1995). Implied but not documented is that 6-line ferrihydrite may be an intermediate or metastable structure in the conversion of 2-line ferrihydrite to hematite.…”

Section: +mentioning

confidence: 99%

Transformation of 2-line ferrihydrite to 6-line ferrihydrite under oxic and anoxic conditions

Kukkadapu

Zachara

Fredrickson

et al. 2003

American Mineralogist

120

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“…In nature, most ferrihydrite transforms to goethite (Lewis and Schwertmann, 1980;Cornell and Giovanoli, 1985), to hematite (Johnston and Lewis, 1983;Combes et al, 1990), or to mixtures of the two phases (Schwertmann and Murad, 1983). The most likely reaction pathway of the transformation to goethite is thought to be dissolution of ferrihydrite and subsequent reprecipitation as goethite.…”

Section: Introductionmentioning

confidence: 99%

The Use of Color to Quantify the Effects of pH and Temperature on the Crystallization Kinetics of Goethite under Highly Alkaline Conditions

Nagano

Nakashima

Nakayama

et al. 1994

Clays and clay miner.

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Abstract--The crystallization kinetics of goethite were studied colorimetrically under highly alkaline conditions (pH 10. l-12.2) at temperatures from 40 ~ to 85~ Color changes during crystallization from fresh precipitates, plotted on a*-b* colorimetric diagrams, were used to discriminate between pure goethite and mixtures of goethite and hematite. Only the b* value increased as goethite crystallization proceeded, and even a minor increase in the a* value revealed the existence of hematite. The rate of goethite crystallization, estimated from the b* value, could be modeled by a pseudo-first-order rate law. This rate depended both on pH and on temperature. Apparent activation energies for the reactions of 56.1 k.J/mol at pH 11.7 and 48.2 kJ/mol at pH 12.2 were estimated from Arrhenius plots.

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A detailed study of the transformation of ferrihydrite to hematite in an aqueous medium at 92°C

Cited by 100 publications

References 12 publications

Studies of the Reactivity of the Ferrihydrite Surface by Iron Isotopic Exchange and Mössbauer Spectroscopy

Studies of the Reactivity of the Ferrihydrite Surface by Iron Isotopic Exchange and Mössbauer Spectroscopy

Transformation of 2-line ferrihydrite to 6-line ferrihydrite under oxic and anoxic conditions

The Use of Color to Quantify the Effects of pH and Temperature on the Crystallization Kinetics of Goethite under Highly Alkaline Conditions

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