On the mechanism of sodium migration in transition aluminas with calcination

McIntosh, Grant J.; Wijayaratne, Hasini; Chan, Andrew; Perander, Linus; Hyland, Margaret

doi:10.1016/j.actamat.2018.04.049

Cited by 8 publications

(13 citation statements)

References 41 publications

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“…It has been demonstrated that sodium, the largest impurity in Bayer process aluminas, 26 can significantly impact surface chemistry, [27][28][29] textural properties, 30 and even phase transformation. 31 Sodium is observed to surface segregate during calcination, 31,32 consistent with DFT and experimental studies on sodium-doped g-Al 2 O 3 of Digne et al 26 who demonstrated the energetic favourability of sodium in surface sites analogous to protons in hydroxyl groups, relative to bulk incorporation. It has considerable impacts on surface acidity, 27,28 and thus the demand for sodium-free alumina drives the need for acid leaching procedures.…”

Section: Introductionsupporting

confidence: 61%

Probing hydrogen bonding interactions and impurity intercalation in gibbsite using experimental and theoretical XANES spectroscopy

McIntosh

Chan

2018

Phys. Chem. Chem. Phys.

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The Al and O K-edge XANES spectra of Bayer process gibbsite are examined, both experimentally and with plane wave density functional theory, and transition assignments are made. We confirm that the broad transitions in Al K-edge spectra are fundamentally the same as those in more ordered and well-studied corundum, and typical of octahedrally coordinated aluminium. Analysis of O K-edge spectra reveals that while much of the initial edge transition structure (535-548 eV) is due to O 2p hybridization with Al orbitals, the lowest energy region (∼535-539 eV) is particularly influenced by O-H states which are heavily perturbed by hydrogen bonding interactions. We therefore tentatively suggest that an unexplained structure at 539 eV in O K-edge spectra of corundum may be due to surface hydroxylation. Finally, we examined Na K-edge spectra, as sodium is the major impurity in these materials and implicated in perturbation of the evolution of materials properties with calcination through the transition aluminas. Density functional theory calculations find sodium replacement of in-sheet H-atoms is the most thermodynamically stable site for sodium inclusion. We subsequently confirm this assignment spectroscopically, explicitly demonstrating the precise location of Na+ impurities for the first time.

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Section: Introductionsupporting

confidence: 61%

Probing hydrogen bonding interactions and impurity intercalation in gibbsite using experimental and theoretical XANES spectroscopy

McIntosh

Chan

2018

Phys. Chem. Chem. Phys.

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“…Mcintosh et al. reported that sodium accumulated on both the exterior surface and interior of particles during the Bayer process, which affected the calcination kinetics and inhibited conversion to α‐Al 2 O 3 53 . Through use of XPS, nanoSIMS, and NEXAFS analyses, they showed that Na + ions tended to concentrate on the surface of gibbsite particles, which was consistent with thermodynamic considerations.…”

Section: Introductionmentioning

confidence: 59%

Influence of sodium hydroxide on phase transformation of gamma alumina to alpha alumina

Farrokhnemoun,

Sajjadivand,

Parapari

et al. 2023

J Am Ceram Soc.

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Corundum and transition alumina powders are commonly produced through the Bayer process—that is, by digestion of bauxite in a sodium hydroxide solution, followed by gibbsite precipitation, which contains significant amounts of Na+ ions. During the de‐hydroxylation of gibbsite, Na+ is associated with retardation of the structural phase transformations between transition alumina and corundum (α‐Al2O3) phases, although the exact role of Na is unclear. The influence of Na+ ions on the phase transformation of γ‐Al2O3 to α‐alumina was investigated by varying the concentration of NaOH in aqueous γ‐Al2O3 suspensions. The phase transformation behavior of γ‐Al2O3 was monitored through thermal analysis, X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectrometer (XPS), and transmission electron microscope. As the Na concentration in γ‐alumina suspensions increased, the amount of α‐Al2O3 decreased in samples that were heat treated at 1200°C for 2 h. XPS analysis indicated that washing transition alumina powders with NH4OH solutions had decreased the surface concentration of Na+ and facilitated the phase transformation to α‐Al2O3.

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“…The binding energy of Na 1s in RM was 1071.30 eV, which can be assigned to Na species on the surface of RM, while the binding energy of Na in SRM shifted to 1071.9 eV, which is ascribed to Na species in the bulk environments of crystal particles [60] . Sodium can be trapped and incorporated into internal crystallite porosity via bulk cation vacancies during calcination [61] . The bulk Na ions in lattice structures are more stable than the amorphous Na in resistance to water leaching.…”

Section: Resultsmentioning

confidence: 96%

“…[60] Sodium can be trapped and incorporated into internal crystallite porosity via bulk cation vacancies during calcination. [61] The bulk Na ions in lattice structures are more stable than the amorphous Na in resistance to water leaching. Xue et al found the sodium aluminosilicate in RM could react with CO 2 into insoluble silicates and carbonates.…”

Section: Effect On the Mobile Alkalinity Of Red Mudmentioning

confidence: 99%

Upgrading Fast Pyrolysis Oil through Decarboxylation by Using Red Mud as Neutralizing Agent for Ketones Production and Iron Recovery

et al. 2022

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In this work, Red Mud, an alkaline solid waste from alumina production, was used as neutralizing agent to convert carboxylic acids in bio‐oil into ketones. The total acidity of the bio‐oil decreased significantly from 152.60 to 0.63 mg KOH/g, while the high heat value boosted from 17.25 to 29.57 MJ/kg. Meanwhile, the leachable alkalinity of Red Mud declined from 65.34 to 3.02 mg HCl/g, mitigating the harmfulness and perniciousness to the environment. Furthermore, characterizations of XRD, XPS and 57Fe Mössbauer spectroscopy indicated that the weak magnetic iron species in Red Mud was completely transformed into stronger magnetic Fe3O4. With magnetic separation the iron recovery reached up to 91.96 % with iron grade of 65.83 %, which is up to the standard of steelmaking raw material. The findings in this research not only open avenue for valorization of bio‐oil but also help explore the resourceful utilization of Red Mud.

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On the mechanism of sodium migration in transition aluminas with calcination

Cited by 8 publications

References 41 publications

Probing hydrogen bonding interactions and impurity intercalation in gibbsite using experimental and theoretical XANES spectroscopy

Probing hydrogen bonding interactions and impurity intercalation in gibbsite using experimental and theoretical XANES spectroscopy

Influence of sodium hydroxide on phase transformation of gamma alumina to alpha alumina

Upgrading Fast Pyrolysis Oil through Decarboxylation by Using Red Mud as Neutralizing Agent for Ketones Production and Iron Recovery

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