Issue 35, 2022

Concentration dependent interfacial chemistry of the NaOH(aq): gibbsite interface

Abstract

Caustic conditions are often employed for dissolution of a wide variety of minerals, where ion sorption, surface diffusion, and interfacial organization impact surface reactivity. In the case of gibbsite, γ-Al(OH)3, the chemistry at the NaOH(aq) interface is deeply intertwined with industrial processing of aluminum, including metal production and the disposition of Al-containing wastes. To date, little is known about the structure, speciation, and dynamic behavior of gibbsite interfaces (and that of many other minerals) with NaOH(aq)—particularly as a function of ionic strength. Yet concentration-dependent interfacial organization and dynamics are a critical starting point to develop a fundamental understanding of the factors that influence dissolution. This work reports equilibrium molecular dynamics simulations of the γ-Al(OH)3:NaOH(aq) interface, revealing the sorption behavior and speciation of ions from 0.5–10 M [NaOH]. As inner-sphere complexes, Na+ primarily coordinates to the side of the gibbsite hexagonal cavities, while OH accepts hydrogen-bonding from the surface-OH groups. The mobility of inner-sphere Na+ and OH ions is significantly reduced due to a strong surface affinity in comparison to previous reports of NaCl, CaCl2, or BaCl2 electrolytes. At high [NaOH], contact ion pairing that is observed in the bulk solution is partially disrupted upon sorption to the gibbsite surface by the individual ion–surface interactions. The molecular-scale changes to surface speciation and competition between ion–surface vs. ion–ion interactions influence surface characterization of gibbsite and potential dissolution processes, providing a valuable baseline for starting conditions needed within future reactive molecular simulations.

Graphical abstract: Concentration dependent interfacial chemistry of the NaOH(aq): gibbsite interface

Supplementary files

Article information

Article type
Paper
Submitted
02 May 2022
Accepted
12 Aug 2022
First published
17 Aug 2022
This article is Open Access
Creative Commons BY-NC license

Phys. Chem. Chem. Phys., 2022,24, 20998-21008

Concentration dependent interfacial chemistry of the NaOH(aq): gibbsite interface

W. Liu, M. Pouvreau, A. G. Stack, X. Yang and A. E. Clark, Phys. Chem. Chem. Phys., 2022, 24, 20998 DOI: 10.1039/D2CP01997C

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