Effect of Cobalt on the Formation of Crystalline Iron Oxides from Ferrihydrite in Alkaline Media

Cornell, R. M.

doi:10.1346/ccmn.1989.0370108

Cited by 55 publications

(24 citation statements)

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“…A major requirement for isomorphous substitution is a reasonable match between the radii and charges of Fe 3+ (radius 0.64 nm) and the substituent ion (Goldschmidt, 1937). Both Mn 2+ and Co 2+ were oxidized before incorporation into the goethite structure (Stiers & Schwertmann, 1985;Cornell & Giovanoli, 1989). The difference between the radii of these ions and that of Fe 3+ is <20% (Table 1).…”

Section: Resultsmentioning

confidence: 99%

Simultaneous incorporation of Mn, Ni and Co in the goethite (α-FeOOH) structure

Cornell

1991

Clay miner.

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The extent of incorporation of metal ions into the structure of iron oxides is of interest to two quite divergent disciplines-soil science and the disposal of radioactive waste. In soils, metal substituted goethites appear to be widespread (Schwertmann & Taylor, 1989): the incorporation of foreign ions is important because it alters the properties of goethite such as its dissolution behaviour (Schwertmann, 1984). In the strongly alkaline (pH 12-13) environment of a repository for radioactive waste, radionuclides released by ground water leaching of the waste may be immobilized in the structures of the iron oxides formed as a result of corrosion of the steel canister enclosing the waste. Laboratory studies of substituted iron oxides have been concerned with the incorporation of a single foreign cation (Schulze & Schwertmann, 1984; Stiers & Schwertmann, 1985; Lim-Nunez & Gilkes, 1987; Schwertmann et a i, 1989). For soils and radioactive waste repositories, however, investigations into the simultaneous uptake of several ions may be of greater relevance. The present study examines the simultaneous incorporation of three divalent ions, Mn, Co and Ni, into the structure of goethite formed from ferrihydrite. These ions are associated with iron oxides in soils and sediments and the effects of individual ions on the kinetics and products of the crystallization of ferrihydrite have already been investigated (Cornell & Giovanoli, 1987, 1989; Cornell, 1988). In the present work the following specific questions were considered: (1) Can all three ions be accommodated simultaneously in the goethite structure? (2) Is there an upper limit on the extent of substitution? (3) Is there a preferential order of substitution and, if so, on what does it depend? Materials and methods Metal substituted goethites were obtained by holding metal-ferrihydrite coprecipitates at pH 12 and 70°C in closed polyethylene flasks for up to 40 days. These reaction conditions were chosen to enable crystalline products to be obtained in a reasonable length of time and to facilitate comparison with earlier studies involving single substituents. The metalferrihydrite (1 g/1) was precipitated with 1 m KOH from a solution of ferric nitrate and Mn, Co and Ni nitrate. All reagents were Analar grade (Fluka). The metal/(Fe + metal) mole fractions were 0*056 and 0*13 for mixtures of three substituting ions, and 0-165 for mixtures of two substituting ions; equal amounts of each substituent were added. These concentrations served to reveal any differences in the extent of incorporation of the different ions. Higher mole fractions were not used because at metal/(Fe + metal) >0*18, a spinel phase as well as goethite may form (Cornell, 1988). After complete transformation of the ferrihydrite, the reaction product was washed, dried at 50°C and X-ray diffraction (X R D) was used to verify that the product was well crystallized goethite. The total amount of Fe, Mn, Ni and Co in the reaction product was determined by dissolving the oxide in 4 m HC1 (70°C, 24 h). All metals...

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Section: Resultsmentioning

confidence: 99%

Simultaneous incorporation of Mn, Ni and Co in the goethite (α-FeOOH) structure

Cornell

1991

Clay miner.

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“…In roasting wastes, Co and Ni are mainly present in the Res fraction (>79%), suggesting that most of sulfide-associated Co and Ni were incorporated into silicates or crystalline Fe-oxides during the roasting. Previous studies also suggested that Co and Ni could be easily incorporated into iron oxides via the formation of strong bonds during thermal treatments [15,42,43]. Moreover, thermodynamic analyses predict that CoFe 2 O 4 , NiO·Fe 2 O 3 , and Fe 2 NiO 4 will be major products of the reactions of Co or Ni with iron oxides [35,40].…”

Section: Cobalt and Nickelmentioning

confidence: 94%

Trace element transformations and partitioning during the roasting of pyrite ores in the sulfuric acid industry

Yang

Chen

Peng

et al. 2009

Journal of Hazardous Materials

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“…Initial values of (Co)/(Co + Fe) × 100 mole ratios (x Co ) were 0, 3, 5, 7, and 10 mol% (samples were named G 0 , G 3, G 5, G 7 , and G 10, respectively). After the aging period, the samples were centrifuged, dried at 40 °C, and the amorphous materials were extracted with 0.4 mol/dm 3 HCl at room temperature (Cornell and Giovanoli 1989). The crystalline solids were washed with doubly distilled water until the conductivity of the filtrated solution was similar to that of doubly distilled water.…”

Section: Methodsmentioning

confidence: 99%

“…Different aspects of Co-substituted goethite obtained in alkaline media have been studied by other authors (Cornell and Giovanoli 1989;Gerth 1990;Cornell 1991;Gasser et al 1996;Iwasaki and Yamamura 2002). Recent studies of Co-goethites obtained from aerial oxidation of both Fe 2+ and Co 2+ solutions were carried out by Pozas et al (2002Pozas et al ( , 2004.…”

Section: Introductionmentioning

confidence: 99%

Structure and reactivity of synthetic Co-substituted goethites

Álvarez

Sileo

Rueda

2008

American Mineralogist

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A set of synthetic goethites were prepared from Fe 3+ -and Co 2+ -nitrate solutions in alkaline media with a Co/(Co + Fe) ratio (x Co ) up to 10 mol%. The structural characterization of the resultant solid phases was carried out by X-ray diffraction (XRD). XRD analyses showed that in preparations with x Co <10 mol%, Co-substituted goethite was the only crystalline phase present. Atomic and cell parameters for the samples synthesized were obtained by the Rietveld refinement of the XRD data, and showed that the unit cell in the goethite-like phase is contracted as a function of x Co . Little deviation from the Vegard rule was observed for all unit-cell parameters. Cobalt substitution produces an increase in the surface area of the goethite, as well as an increment in the dehydroxylation temperature. The acid dissolution of all Co-goethites showed an increase in dissolution rate with the Co content, and a congruent behavior was observed. The activation energy for dissolution was obtained two samples. A modified first-order Kabai equation best describes the dissolution data.

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Effect of Cobalt on the Formation of Crystalline Iron Oxides from Ferrihydrite in Alkaline Media

Cited by 55 publications

References 24 publications

Simultaneous incorporation of Mn, Ni and Co in the goethite (α-FeOOH) structure

Simultaneous incorporation of Mn, Ni and Co in the goethite (α-FeOOH) structure

Trace element transformations and partitioning during the roasting of pyrite ores in the sulfuric acid industry

Structure and reactivity of synthetic Co-substituted goethites

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