Title: Coupled Multimodal Dynamics of Hydrogen-Containing Ion Networks in Water-Deficient, Sodium Hydroxide-Aluminate Solutions

Abstract

Sodium aluminate electrolytes are of industrial and geochemical importance as intermediates in the Bayer process for aluminum refining and high-level nuclear waste processing. We utilized quasi-elastic neutron scattering (QENS) and proton nuclear magnetic resonance spectroscopy (¹H NMR) to investigate the picosecond (ps) to microsecond (ms) timescale motions of H-bearing species (Al(OH)₄^- monomers and Al-clusters, OH- and H₂O) in extremely concentrated sodium aluminate solutions. Variable temperature, elastic window scans demonstrated that the addition of Al solutes to NaOH solutions resulted in more gradual changes in the elastic line profiles when compared to a pure (Al-free) NaOH solution, where a sharp liquidus-solidus transition was observed. The QENS signal was analyzed by applying a two-Lorentzian fitting function. No short-time translational diffusion was observed but two types of stochastic localized motions were found: (A) local backbone tumbling of large hydrated ion clusters on the order of 40-100 ps at 293 K; and (B) much slower, complex, collective dynamics of the ensemble of H-bearing species on the order of 350 – 1400 ps at 293 K. Variable temperature, pulsed field gradient, diffusion ordered NMR was used to quantify the ensemble translation of the H-species, along with NMR relaxometry to calculate rotational correlation coefficients and complementarymore » molecular dynamics to consider the overall solution structure. The ensemble rotational correlation times were on the order of 184-300 ps from ¹H NMR, which is in agreement with the timescale of the fast and slow QENS components. Understanding the mobility of the H-bearing entities in these industrially-relevant, concentrated sodium aluminate electrolytes is critical to predict their behavior during processing for aluminum recovery and nuclear waste retrieval. These results can also be extended to other important concentrated electrolytes.« less

Authors:

Graham, Trent R.  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-8907-8004"

Semrouni, David ^[2]; Mamontov, Eugene  ^[3];

• Search DOE PAGES for author "Mamontov, Eugene"
• Search DOE PAGES for ORCID "0000-0002-5684-2675"

Ramirez-Cuesta, Anibal J. ^[3]; Page, Katharine  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-9071-3383"

Clark, Aurora  ^[4];

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• Search DOE PAGES for ORCID "0000-0001-9381-721X"

Schenter, Gregory K. ^[1]; Pearce, Carolyn I.  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-3098-1615"

Stack, Andrew G.  ^[3];

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• Search DOE PAGES for ORCID "0000-0003-4355-3679"

Wang, Hsiu-Wen  ^[3]

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• Search DOE PAGES for ORCID "0000-0002-2802-4122"

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+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Washington State Univ., Pullman, WA (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. Washington State Univ., Pullman, WA (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Publication Date:

Thu Nov 08 00:00:00 EST 2018

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Interfacial Dynamics in Radioactive Environments and Materials (IDREAM); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1490569

Alternate Identifier(s):

OSTI ID: 1496832

Report Number(s):

PNNL-SA-138723
Journal ID: ISSN 1520-6106

Grant/Contract Number:  

AC05-00OR22725; AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

Additional Journal Information:

Journal Volume: 122; Journal Issue: 50; Journal ID: ISSN 1520-6106

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; NMR, QENS