In Situ 27Al NMR Spectroscopy of Aluminate in Sodium Hydroxide Solutions above and below Saturation with Respect to Gibbsite

Trent R. Graham; Mateusz Dembowski; Ernesto Martinez-Baez; Xin Zhang; Nicholas R. Jaegers; Jianzhi Hu; Miroslaw S. Gruszkiewicz; Hsiu Wen Wang; Andrew G. Stack; Mark E. Bowden; Calvin H. Delegard; Gregory K. Schenter; Aurora E. Clark; Sue B. Clark; Andrew R. Felmy; Kevin M. Rosso; Carolyn I. Pearce

doi:10.1021/acs.inorgchem.8b00617

In Situ ²⁷Al NMR Spectroscopy of Aluminate in Sodium Hydroxide Solutions above and below Saturation with Respect to Gibbsite

Trent R. Graham, Mateusz Dembowski, Ernesto Martinez-Baez, Xin Zhang, Nicholas R. Jaegers, Jianzhi Hu, Miroslaw S. Gruszkiewicz, Hsiu Wen Wang, Andrew G. Stack, Mark E. Bowden, Calvin H. Delegard, Gregory K. Schenter, Aurora E. Clark, Sue B. Clark, Andrew R. Felmy, Kevin M. Rosso, Carolyn I. Pearce

Geochemistry & Interfacial Science

Research output: Contribution to journal › Article › peer-review

34 Scopus citations

Abstract

Aluminum hydroxide (Al(OH)₃, gibbsite) dissolution and precipitation processes in alkaline environments play a commanding role in aluminum refining and nuclear waste processing, yet mechanistic aspects underlying sluggish kinetics during crystallization have remained obscured due to a lack of in situ probes capable of isolating incipient ion pairs. At a molecular level Al is cycling between tetrahedral (T_d) coordination in solution to octahedral (O_h) in the solid. We explored dissolution of Al(OH)₃ that was used to produce variably saturated aluminate (Al(OH)₄ ^-)-containing solutions under alkaline conditions (pH >13) with in situ ²⁷Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, and interrogated the results with ab initio molecular dynamics (AIMD) simulations complemented with chemical shift calculations. The collective results highlight the overall stability of the solvation structure for T_d Al in the Al(OH)₄ ^- oxyanion as a function of both temperature and Al concentration. The observed chemical shift did not change significantly even when the Al concentration in solution became supersaturated upon cooling and limited precipitation of the octahedral Al(OH)₃ phase occurred. However, subtle changes in Al(OH)₄ ^- speciation correlated with the dissolution/precipitation reaction were found. AIMD-informed chemical shift calculations indicate that measurable perturbations should begin when the Al(OH)₄ ^-⋯Na⁺ distance is less than 6 Å, increasing dramatically at shorter distances, coinciding with appreciable changes to the electrostatic interaction and reorganization of the Al(OH)₄ ^- solvation shell. The integrated findings thus suggest that, under conditions incipient to and concurrent with gibbsite crystallization, nominally expected contact ion pairs are insignificant and instead medium-range (4-6 Å) solvent-separated Al(OH)₄ ^-⋯Na⁺ pairs predominate. Moreover, the fact that these medium-range interactions bear directly on resulting gibbsite characteristics was demonstrated by detailed microscopic and X-ray diffraction analysis and by progressive changes in the fwhm of the O_h resonance, as measured by in situ NMR. Sluggish gibbsite crystallization may arise from the activation energy associated with disrupting this robust medium-range ion pair interaction.

Original language	English
Pages (from-to)	11864-11873
Number of pages	10
Journal	Inorganic Chemistry
Volume	57
Issue number	19
DOIs	https://doi.org/10.1021/acs.inorgchem.8b00617
State	Published - Oct 1 2018

Funding

This work was supported by IDREAM (Interfacial Dynamics in Radioactive Environments and Materials), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES). Materials characterization and NMR measurements were performed using the Environmental Molecular Science Laboratory (EMSL), a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). This research used resources of the Oak Ridge Leadership Computing Facility located in the Oak Ridge National Laboratory, which is supported by the Office of Science within the Department of Energy under Contract No. DE-AC05-00OR22725. The authors thank Chuan Wan and Mary Hu for their assistance with the in situ MAS NMR experiments. T.R.G. is grateful for support from the PNNL-WSU DGRP. PNNL is a multiprogram national laboratory operated for DOE by Battelle Memorial Institute under Contract No. DE-AC06-76RLO-1830.

Funders	Funder number
DOE Office of Biological and Environmental Research
Energy Frontier Research Center
IDREAM
PNNL-WSU DGRP
U.S. Department of Energy
Battelle
Office of Science
Basic Energy Sciences
Pacific Northwest National Laboratory

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Cite this

Graham, T. R., Dembowski, M., Martinez-Baez, E., Zhang, X., Jaegers, N. R., Hu, J., Gruszkiewicz, M. S., Wang, H. W., Stack, A. G., Bowden, M. E., Delegard, C. H., Schenter, G. K., Clark, A. E., Clark, S. B., Felmy, A. R., Rosso, K. M., & Pearce, C. I. (2018). In Situ ²⁷Al NMR Spectroscopy of Aluminate in Sodium Hydroxide Solutions above and below Saturation with Respect to Gibbsite. Inorganic Chemistry, 57(19), 11864-11873. https://doi.org/10.1021/acs.inorgchem.8b00617

@article{fd78ae7d4df44abd926cededb9e2dd16,

title = "In Situ 27Al NMR Spectroscopy of Aluminate in Sodium Hydroxide Solutions above and below Saturation with Respect to Gibbsite",

abstract = "Aluminum hydroxide (Al(OH)3, gibbsite) dissolution and precipitation processes in alkaline environments play a commanding role in aluminum refining and nuclear waste processing, yet mechanistic aspects underlying sluggish kinetics during crystallization have remained obscured due to a lack of in situ probes capable of isolating incipient ion pairs. At a molecular level Al is cycling between tetrahedral (Td) coordination in solution to octahedral (Oh) in the solid. We explored dissolution of Al(OH)3 that was used to produce variably saturated aluminate (Al(OH)4 -)-containing solutions under alkaline conditions (pH >13) with in situ 27Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, and interrogated the results with ab initio molecular dynamics (AIMD) simulations complemented with chemical shift calculations. The collective results highlight the overall stability of the solvation structure for Td Al in the Al(OH)4 - oxyanion as a function of both temperature and Al concentration. The observed chemical shift did not change significantly even when the Al concentration in solution became supersaturated upon cooling and limited precipitation of the octahedral Al(OH)3 phase occurred. However, subtle changes in Al(OH)4 - speciation correlated with the dissolution/precipitation reaction were found. AIMD-informed chemical shift calculations indicate that measurable perturbations should begin when the Al(OH)4 -⋯Na+ distance is less than 6 {\AA}, increasing dramatically at shorter distances, coinciding with appreciable changes to the electrostatic interaction and reorganization of the Al(OH)4 - solvation shell. The integrated findings thus suggest that, under conditions incipient to and concurrent with gibbsite crystallization, nominally expected contact ion pairs are insignificant and instead medium-range (4-6 {\AA}) solvent-separated Al(OH)4 -⋯Na+ pairs predominate. Moreover, the fact that these medium-range interactions bear directly on resulting gibbsite characteristics was demonstrated by detailed microscopic and X-ray diffraction analysis and by progressive changes in the fwhm of the Oh resonance, as measured by in situ NMR. Sluggish gibbsite crystallization may arise from the activation energy associated with disrupting this robust medium-range ion pair interaction.",

author = "Graham, {Trent R.} and Mateusz Dembowski and Ernesto Martinez-Baez and Xin Zhang and Jaegers, {Nicholas R.} and Jianzhi Hu and Gruszkiewicz, {Miroslaw S.} and Wang, {Hsiu Wen} and Stack, {Andrew G.} and Bowden, {Mark E.} and Delegard, {Calvin H.} and Schenter, {Gregory K.} and Clark, {Aurora E.} and Clark, {Sue B.} and Felmy, {Andrew R.} and Rosso, {Kevin M.} and Pearce, {Carolyn I.}",

note = "Publisher Copyright: {\textcopyright} 2018 American Chemical Society.",

year = "2018",

month = oct,

day = "1",

doi = "10.1021/acs.inorgchem.8b00617",

language = "English",

volume = "57",

pages = "11864--11873",

journal = "Inorganic Chemistry",

issn = "0020-1669",

publisher = "American Chemical Society",

number = "19",

}

Graham, TR, Dembowski, M, Martinez-Baez, E, Zhang, X, Jaegers, NR, Hu, J, Gruszkiewicz, MS, Wang, HW, Stack, AG, Bowden, ME, Delegard, CH, Schenter, GK, Clark, AE, Clark, SB, Felmy, AR, Rosso, KM & Pearce, CI 2018, 'In Situ ²⁷Al NMR Spectroscopy of Aluminate in Sodium Hydroxide Solutions above and below Saturation with Respect to Gibbsite', Inorganic Chemistry, vol. 57, no. 19, pp. 11864-11873. https://doi.org/10.1021/acs.inorgchem.8b00617

TY - JOUR

T1 - In Situ 27Al NMR Spectroscopy of Aluminate in Sodium Hydroxide Solutions above and below Saturation with Respect to Gibbsite

AU - Graham, Trent R.

AU - Dembowski, Mateusz

AU - Martinez-Baez, Ernesto

AU - Zhang, Xin

AU - Jaegers, Nicholas R.

AU - Hu, Jianzhi

AU - Gruszkiewicz, Miroslaw S.

AU - Wang, Hsiu Wen

AU - Stack, Andrew G.

AU - Bowden, Mark E.

AU - Delegard, Calvin H.

AU - Schenter, Gregory K.

AU - Clark, Aurora E.

AU - Clark, Sue B.

AU - Felmy, Andrew R.

AU - Rosso, Kevin M.

AU - Pearce, Carolyn I.

PY - 2018/10/1

Y1 - 2018/10/1

N2 - Aluminum hydroxide (Al(OH)3, gibbsite) dissolution and precipitation processes in alkaline environments play a commanding role in aluminum refining and nuclear waste processing, yet mechanistic aspects underlying sluggish kinetics during crystallization have remained obscured due to a lack of in situ probes capable of isolating incipient ion pairs. At a molecular level Al is cycling between tetrahedral (Td) coordination in solution to octahedral (Oh) in the solid. We explored dissolution of Al(OH)3 that was used to produce variably saturated aluminate (Al(OH)4 -)-containing solutions under alkaline conditions (pH >13) with in situ 27Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, and interrogated the results with ab initio molecular dynamics (AIMD) simulations complemented with chemical shift calculations. The collective results highlight the overall stability of the solvation structure for Td Al in the Al(OH)4 - oxyanion as a function of both temperature and Al concentration. The observed chemical shift did not change significantly even when the Al concentration in solution became supersaturated upon cooling and limited precipitation of the octahedral Al(OH)3 phase occurred. However, subtle changes in Al(OH)4 - speciation correlated with the dissolution/precipitation reaction were found. AIMD-informed chemical shift calculations indicate that measurable perturbations should begin when the Al(OH)4 -⋯Na+ distance is less than 6 Å, increasing dramatically at shorter distances, coinciding with appreciable changes to the electrostatic interaction and reorganization of the Al(OH)4 - solvation shell. The integrated findings thus suggest that, under conditions incipient to and concurrent with gibbsite crystallization, nominally expected contact ion pairs are insignificant and instead medium-range (4-6 Å) solvent-separated Al(OH)4 -⋯Na+ pairs predominate. Moreover, the fact that these medium-range interactions bear directly on resulting gibbsite characteristics was demonstrated by detailed microscopic and X-ray diffraction analysis and by progressive changes in the fwhm of the Oh resonance, as measured by in situ NMR. Sluggish gibbsite crystallization may arise from the activation energy associated with disrupting this robust medium-range ion pair interaction.

AB - Aluminum hydroxide (Al(OH)3, gibbsite) dissolution and precipitation processes in alkaline environments play a commanding role in aluminum refining and nuclear waste processing, yet mechanistic aspects underlying sluggish kinetics during crystallization have remained obscured due to a lack of in situ probes capable of isolating incipient ion pairs. At a molecular level Al is cycling between tetrahedral (Td) coordination in solution to octahedral (Oh) in the solid. We explored dissolution of Al(OH)3 that was used to produce variably saturated aluminate (Al(OH)4 -)-containing solutions under alkaline conditions (pH >13) with in situ 27Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, and interrogated the results with ab initio molecular dynamics (AIMD) simulations complemented with chemical shift calculations. The collective results highlight the overall stability of the solvation structure for Td Al in the Al(OH)4 - oxyanion as a function of both temperature and Al concentration. The observed chemical shift did not change significantly even when the Al concentration in solution became supersaturated upon cooling and limited precipitation of the octahedral Al(OH)3 phase occurred. However, subtle changes in Al(OH)4 - speciation correlated with the dissolution/precipitation reaction were found. AIMD-informed chemical shift calculations indicate that measurable perturbations should begin when the Al(OH)4 -⋯Na+ distance is less than 6 Å, increasing dramatically at shorter distances, coinciding with appreciable changes to the electrostatic interaction and reorganization of the Al(OH)4 - solvation shell. The integrated findings thus suggest that, under conditions incipient to and concurrent with gibbsite crystallization, nominally expected contact ion pairs are insignificant and instead medium-range (4-6 Å) solvent-separated Al(OH)4 -⋯Na+ pairs predominate. Moreover, the fact that these medium-range interactions bear directly on resulting gibbsite characteristics was demonstrated by detailed microscopic and X-ray diffraction analysis and by progressive changes in the fwhm of the Oh resonance, as measured by in situ NMR. Sluggish gibbsite crystallization may arise from the activation energy associated with disrupting this robust medium-range ion pair interaction.

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U2 - 10.1021/acs.inorgchem.8b00617

DO - 10.1021/acs.inorgchem.8b00617

M3 - Article

C2 - 30036042

AN - SCOPUS:85054253529

SN - 0020-1669

VL - 57

SP - 11864

EP - 11873

JO - Inorganic Chemistry

JF - Inorganic Chemistry

IS - 19

ER -