A combined FTIR and TPD study on the bulk and surface dehydroxylation and decarbonation of synthetic goethite

Boily, Jean-François; Szanyi, János; Felmy, Andrew R.

doi:10.1016/j.gca.2006.05.013

Cited by 47 publications

(56 citation statements)

References 64 publications

(120 reference statements)

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“…7). On that basis, the assumption made earlier about the presence of more hydroxyl groups in this mineral can be verified, since it is expected that the transmittance intensity in that region of the spectrum is proportional to the concentration of functional groups within the structure [12]. It should also be noted that the spectra shown in figures 6 and 7 exhibit subtle spectral perturbations in the region between 1080 cm -1 and 1125 cm -1 , forming shoulders (Fig.…”

Section: Fourier-transform Infrared Spectroscopy Analysis (Ftir)supporting

confidence: 62%

“…As shown in Figure 3, a significant increase in the slope occurred at temperatures between 300 °C and 450 °C; this increase corresponds to the sustained increase in pressure of the water contained into the mineral micropores, which makes them keep growing and subsequently join together [10]. This behavior continues until around 650 °C, temperature at which the coalescence of micropores generates macroporosities, which will facilitate the complete removal of the remaining water within the mineral particle [10,12]. With the generation of this new area at high temperature, the diffusion effects begin to take preponderance and Fe atoms can migrate, starting to adopt the shared octahedral arrangement that leads to the more condensed crystallographic phase of the hematite [12].…”

Section: Figmentioning

confidence: 95%

“…This behavior continues until around 650 °C, temperature at which the coalescence of micropores generates macroporosities, which will facilitate the complete removal of the remaining water within the mineral particle [10,12]. With the generation of this new area at high temperature, the diffusion effects begin to take preponderance and Fe atoms can migrate, starting to adopt the shared octahedral arrangement that leads to the more condensed crystallographic phase of the hematite [12].…”

Section: Figmentioning

confidence: 99%

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Estudio del proceso de calcinación en dos minerales de hierro limoníticos entre 250 °C y 950 °C

et al. 2017

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The dehydration process of two limonitic ores from Venezuela was studied between 250 °C and 950 °C by means of thermogravimetry, infrared spectroscopy, and x-ray diffraction. These techniques indicated for both minerals that the goethite-to-hematite transformation occurred in the range of 250-350 °C. In addition, the x-ray diffraction showed a structural re-arrangement within the orebody above 350 °C, temperature above which only the hematite structure is recognizable. Finally, infrared spectroscopy revealed that such transformation implies the loss of structural OH-functional groups, characteristic of the limonite.Keywords: Iron Ore; Limonite; Thermal Modification of Minerals. ResumenSe estudió el proceso de deshidratación de dos minerales limoníticos de Venezuela entre 250 °C y 950 °C, usando termogravimetría, espectroscopia infrarroja y difracción de rayos x. Para ambos materiales, estas técnicas indicaron que la transformación de goethita a hematita ocurrió en el rango de 250 °C a 350 °C. Adicionalmente, la difracción de rayos X mostró un rearreglo estructural dentro de la mena a una temperatura por encima de 350 °C; a temperaturas mayores, solo se reconoce la estructura de la hematita. Finalmente, la espectroscopia infrarroja reveló que la transformación de goethita a hematita implica la pérdida de grupos funcionales de OH-estructural característicos de la limonita. Study of the calcination process of two limonitic iron ores between 250 °C and 950 °C ResumoEstudou-se o processo de desidratação de dois minérios limoníticos da Venezuela entre 250 °C e 950 °C, usando termogravimetria, espectroscopia infravermelha e difração de raios x. Para ambos os materiais, estas técnicas indicaram que a transformação de goethita a hematita ocorreu no intervalo de 250 °C a 350 °C. Adicionalmente, a difração de raios X mostrou um rearranjo estrutural dentro do minério a uma temperatura por cima de 350 °C; a temperaturas maiores, só reconhece-se a estrutura da hematita. Finalmente, a espectroscopia infravermelha revelou que a transformação de goetite a hematita implica a perda de grupos funcionais de OH-estrutural característicos da limonita.Palavras chave: Limonita; Mineral de ferro; Modificação térmica de minérios.Cómo citar este artículo: L. Longa-Avello, C. Pereyra-Zerpa, J. A. Casal-Ramos, and P. Delvasto, "Study of the calcination process of two limonitic iron ores between 250 °C and 950 °C," Rev.

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Section: Fourier-transform Infrared Spectroscopy Analysis (Ftir)supporting

confidence: 62%

Section: Figmentioning

confidence: 95%

Section: Figmentioning

confidence: 99%

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Estudio del proceso de calcinación en dos minerales de hierro limoníticos entre 250 °C y 950 °C

et al. 2017

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“…at 1,550-1,515 cm Ϫ1 and 1,375-1,345 cm Ϫ1 were assigned to the 3a and 3b (20)(21)(22). It is rare, however, for calculated harmonic frequencies with the B3LYP functional to underestimate measured frequencies.…”

Section: Vibrational Spectroscopy and Isotope Fractionation Factorsmentioning

confidence: 99%

“…Infrared spectroscopy is the main source of information on the structural state of C 4ϩ in soil minerals (20)(21)(22). Overall, the spectra indicate that C 4ϩ is present in these minerals as a carbonate ion, but with the trigonal symmetry broken as indicated by splitting of the asymmetric stretching frequency.…”

Section: Vibrational Spectroscopy and Isotope Fractionation Factorsmentioning

confidence: 99%

Calculation of site-specific carbon-isotope fractionation in pedogenic oxide minerals

Rustad

Zarzycki²

2008

Proc. Natl. Acad. Sci. U.S.A.

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atmospheric carbon dioxide ͉ electronic structure calculations ͉ paleosols ͉ goethite ͉ gibbsite T he paleosol carbon-isotope method is one of the major techniques for reconstructing the composition of the ancient atmosphere (1, 2). The depth-dependent mixing of respirative CO 2 from soil ( 13 C-depleted) with atmospheric CO 2 ( 13 Cenriched) can be preserved in soil minerals and has been used to infer atmospheric PCO 2 and respiration rates in paleosols (3). The idea was directed originally at soil carbonate minerals (4) and later applied to the CO 2 component of pedogenic goethite (␣-FeOOH) (5-7) and gibbsite (Al(OH) 3 ) (8, 9). The fractionation between mineral-dissolved CO 2 [CO 2 (m)] and CO 2 (g) is a key factor in the technique because it determines how the respired CO 2 vs. atmospheric CO 2 mixing profile is imprinted onto the soil mineralogy. Direct measurements of the CO 2 (m)-CO 2 (g) fractionation factors for (oxy)hydroxide soil minerals have thus far been elusive. The small values (0 to ϩ2.5 per mil) that have been provisionally implied are surprising because, by analogy with carbonate minerals, a 13 C-enriched fractionation factor (close to ϩ10 per mil) might be expected (10,11).In carbonate minerals with the calcite and aragonite structure, the overwhelming majority of carbonate ions are in a single crystallographic site that governs the equilibrium isotope fractionation. In contrast, occlusion of CO 2 in oxide soil minerals at trace concentrations could involve multiple sites with varying populations, possibly depending on the kinetics and conditions of soil formation. For goethite, it has commonly been assumed that the open pseudochannels parallel to the c crystallographic axis are the major host for CO 2 (m) (12), but this has not been definitively demonstrated, and it is possible that other types of sites could be involved in the uptake of CO 2 (m). An important question is then whether the various kinds of CO 2 (m) sites would have large differences in their equilibrium 12/13 C isotope fractionation factors. Little attention has been given to the possibility of heterogeneous chemical speciation of CO 2 (m) within the host mineral. Site heterogeneity would complicate the interpretation of the carbon isotope records preserved in these minerals. At the same time, a better understanding of the crystal chemistry of CO 2 (m) defects in oxide/oxhydroxide minerals and their isotopic fractionations could serve as a foundation for a much more sensitive paleoclimate indicator than would be possible with knowledge of only the overall isotopic composition. Knowledge of site-specific isotopic signatures in minerals could have much wider applicability than the CO 2 -Fe,Al(oxy)hydroxide system.Although the experimental difficulties of sampling these individual sites might be daunting, accurate theoretical calculation of the potential fractionations is now feasible by using methods of quantum chemistry. During the last several years, there has been notable success in first-principles calculation of equilibriu...

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Control Over the Crystallinity and Defect Chemistry of YVO₄ Nanocrystals for Optimum Photocatalytic Property

Yang

Zhao

et al. 2011

Eur J Inorg Chem

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This work reports on the kinetic control over the crystallinity and defect chemistry of YVO 4 nanoparticles for the optimization of their photocatalytic performance. YVO 4 nanoparticles were prepared at room temperature via a precipitation method and then annealed in air at selected temperatures Յ 500°C to tune their crystallinity and defect features. By systematic evaluation of the sample characterizations, it has been found that the as-prepared samples crystallized in a pure tetragonal zircon-type structure, and the surfaces of the particles are hydrated. Upon annealing, all YVO 4 nanoparticles became dehydrated, which increased the crystallite sizes and improved the crystallinity of the samples. In con-

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A combined FTIR and TPD study on the bulk and surface dehydroxylation and decarbonation of synthetic goethite

Cited by 47 publications

References 64 publications

Estudio del proceso de calcinación en dos minerales de hierro limoníticos entre 250 °C y 950 °C

Estudio del proceso de calcinación en dos minerales de hierro limoníticos entre 250 °C y 950 °C

Calculation of site-specific carbon-isotope fractionation in pedogenic oxide minerals

Control Over the Crystallinity and Defect Chemistry of YVO₄ Nanocrystals for Optimum Photocatalytic Property

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A combined FTIR and TPD study on the bulk and surface dehydroxylation and decarbonation of synthetic goethite

Cited by 47 publications

References 64 publications

Estudio del proceso de calcinación en dos minerales de hierro limoníticos entre 250 °C y 950 °C

Estudio del proceso de calcinación en dos minerales de hierro limoníticos entre 250 °C y 950 °C

Calculation of site-specific carbon-isotope fractionation in pedogenic oxide minerals

Control Over the Crystallinity and Defect Chemistry of YVO4 Nanocrystals for Optimum Photocatalytic Property

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Product

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About

Control Over the Crystallinity and Defect Chemistry of YVO₄ Nanocrystals for Optimum Photocatalytic Property