Isothermal Oxidation of Magnetite to Hematite in Air and Cyclic Reduction/Oxidation Under Carbon Looping Combustion Conditions

Simmonds, Tegan; Hayes, Peter C.

doi:10.1007/s40553-017-0111-7

Cited by 4 publications

(5 citation statements)

References 11 publications

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“…The third form of hematite observed was in narrow (approximately 2 µm in width) laths in the magnetite. This microstructure, formed at sub solidus temperatures, is consistent with that observed in earlier studies involving the high temperature oxidation of magnetite crystals [16]. In this study, it was demonstrated that these lath structures form by a military transformation propagated through the magnetite along the close packed oxygen planes common to both hematite and magnetite.…”

Section: Mechanisms Of Formation Of Hematite and Magnetitesupporting

confidence: 91%

Measurement of Process Conditions Present in Pilot Scale Iron Ore Sintering

Nicol

Chen

et al. 2019

Minerals

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An improved experimental technique has been developed to measure, concurrently, the oxygen partial pressures and temperatures within a pilot scale iron ore sinter pot as a function of time. The measurements and thermodynamic calculations have demonstrated that the oxygen partial pressure at peak bed temperature and during cooling can be oxidising or reducing relative to hematite. Examples of typical microstructures and phase assemblages observed in product sinters are presented. Potential mechanisms of hematite and magnetite formation at sub-liquidus and sub-solidus conditions are demonstrated. The relative impacts of changes to coke rate and draft pressure drop on the process conditions and proportions of the phases formed in the sinter have been measured. Increasing coke rate was shown to result in a faster sinter heating rates, higher peak bed temperatures and times at peak temperature. Higher draft pressures across the sinter bed resulted in faster sinter heating rates and shorter times at peak temperature.

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Section: Mechanisms Of Formation Of Hematite and Magnetitesupporting

confidence: 91%

Measurement of Process Conditions Present in Pilot Scale Iron Ore Sintering

Nicol

Chen

et al. 2019

Minerals

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“…To confirm this reason, the optical microstructure was observed, as shown in Figure 6. It can be seen that the morphology of the light-color hematite phase transformed from a small-size lath type to a large-size lumpy shape after the re-oxidation process, which is consistent with the results reported by Simmonds and Hayes [34]. Furthermore, the amount of hematite decreased with the increase in MgO adding, which is consistent with the result from the XRD patterns.…”

Section: Effects Of Ganguesupporting

confidence: 91%

Quantitative Investigation of MgO, Al2O3 and SiO2 Effects on Solid-State Formation of Secondary Hematite in Sintering Process of Iron Ore Fines

Chen

Guo

et al. 2022

Minerals

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Secondary hematite (SH) is a serious factor resulting in reduction degradation of iron ore sinter in a blast furnace; however, until now, a quantitative study for SH formation had not been reported. In this work, the effects of gangue composition, including MgO, Al2O3 and SiO2, on the solid-state formation in the sintering process of iron ore fines were investigated quantitatively. It shows that the SH formation decreased from 67.84% to 46.11%, 35.44% and 22.37% after adding 1.0%, 3.0% and 5.0% MgO, respectively, while for Al2O3, the amount increased to 69.38%, 69.98% and 70.56%, respectively. For SiO2, the amount changed to 68.14%, 61.59% and 47.96%, respectively. Simultaneously, the magnetite (magnesioferrite) formation increased from 8.24% to 34.79%, 50.26% and 70.45% after adding 1.0%, 3.0% and 5.0% MgO, respectively. For Al2O3 and SiO2, the amount changed to 8.95%, 8.37%, 7.62% and 7.62%, 11.10%, 18.77%, respectively, compared with no gangue. This indicates that the SH formation increased with decrease in magnesioferrite. It was found that the decrease in SH formation relates to the diffusion of Mg2+ in magnesioferrite, which inhibits the solid-state formation of SH kinetically. A supposition was suggested that a maghemite existed at a high temperature, and decreased with an increase in MgO addition. This would be another reason to improve the degradation performance of iron ore sinter.

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“…The transformation from magnetite to hematite at such an interface would involve only the change from ABCABCA packing of oxygen atoms in magnetite to ABABA in hematite. As pointed out in 16,17) this can be achieved through the relatively rapid cooperative movement of partial dislocations along the common interface rather than the slow long range diffusion of ions and reconstructive processes. At each side of the hematite growth tip, which is typically between 2-5 μm diameter, the hematite product is separated from the magnetite phase by a thin liquid film.…”

Section: Formation Of Fe 2 Omentioning

confidence: 99%

“…From detailed examination of the microstructural changes in the present and previous fundamental studies of magnetite oxidation, three mechanisms have been identified, i) Liquid phase assisted oxidation, as observed in the current study and in, 3) ii) Bulk diffusion of cations through the solid hematite product oxide forming shrinking core microstructures, as in the case of gas/solid reactions, 3,14,15) and iii) Hematite lath growth, also in the case of gas/solid reactions. 16,17) Microstructures characteristic of mechanisms ii) and iii) are not commonly observed in most industrial sinters.…”

Section: Secondary Hematite Formationmentioning

confidence: 99%