Mercury exchange in zeolites Na-A and Na-Y studied by classical molecular dynamics simulations and ion exchange experiments

Carlos Hernandez-Tamargo, Bright Kwakye-Awuah, Alexander J. O'Malley, Nora H. de Leeuw

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Abstract

Classical molecular dynamics simulations have been employed to study the exchange of Na+ for Hg2+ in zeolite Na-A, with a Si/Al ratio of 1, and zeolite Na-Y, with Si/Al ratios of 2 and 5, in dry and hydrated conditions within the temperature range 330 – 360 K, to understand factors underpinning the performance of zeolites for water decontamination. A classical forcefield based on DFT energies has been developed for the interaction between the Hg2+ ions and the zeolite O atoms. In terms of water diffusion, zeolite Na-A shows the lowest calculated diffusivity, followed by zeolite Na-Y (Si/Al=2) and Na-Y (Si/Al=5), as a consequence of differing pore dimensions and extra-framework ion loadings. In the absence of speciation anions, the Hg2+ ions are consistently adsorbed at the supercage windows in both the LTA and FAU framework types. The reduced pore size of zeolite A leads to an average hydration number per Hg2+ ion of ¡1.0, whilst the wider pore of zeolite Y exerts less steric hindrance, and thus the Hg2+ hydration number reaches values between 1.0 and 2.0 in zeolite Y. These observations might indicate that Hg2+ ions are more strongly immobilized in zeolite A than in zeolite Y. Preliminary measurements of mercury removal using these zeolites, as synthesized from bauxite and kaolin, seem to support these findings.

Original languageEnglish
Article number110903
JournalMicroporous and Mesoporous Materials
Volume315
Early online date21 Jan 2021
DOIs
Publication statusPublished - 28 Feb 2021

Bibliographical note

Funding Information:
The authors acknowledge the UK Engineering and Physical Sciences Research Council [EPSRC grant number: EP/K009567/2] and the UK Natural Environment Research Council [NERC grant number: NE/R009376/1] for funding. This work was performed using the computational facilities of Supercomputing Wales at Cardiff and Swansea Universities. Via our membership in the UK’s HEC Materials Chemistry Consortium, which is funded by EPSRC [grant number: EP/L000202 , EP/R029431 , EP/T022213 ], this work used the ARCHER UK National Supercomputing Service ( http://www.archer.ac.uk ). A.J.O.M. acknowledges Roger and Sue Whorrod for the funding of the Whorrod Fellowship. B.K.A thanks the laboratories of the School of Applied Sciences, University of Wolverhampton, UK for providing the facilities where the characterization of the zeolites was performed. Information on the data underpinning the results presented here, including how to access them, can be found in the Cardif University data catalogue at http://doi.org/10.17035/d.2021.0126616554.

Publisher Copyright:
© 2021 The Authors

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

Keywords

  • Ion exchange
  • Mercury removal
  • Molecular dynamics
  • Zeolites

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials

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