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Reduction Pathway-Dependent Formation of Reactive Fe(II) Sites in Clay Minerals

Lookup NU author(s): Kath Rothwell, Dr Anke Neumann

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

© 2023 The Authors. Published by American Chemical Society. Structural Fe in clay minerals is an important, potentially renewable source of electron equivalents for contaminant reduction, yet our knowledge of how clay mineral Fe reduction pathways and Fe reduction extent affect clay mineral Fe(II) reactivity is limited. Here, we used a nitroaromatic compound (NAC) as a reactive probe molecule to assess the reactivity of chemically reduced (dithionite) and Fe(II)-reduced nontronite across a range of reduction extents. We observed biphasic transformation kinetics for all nontronite reduction extents of ≥5% Fe(II)/Fe(total) regardless of the reduction pathway, indicating that two Fe(II) sites of different reactivities form in nontronite at environmentally relevant reduction extents. At even lower reduction extents, Fe(II)-reduced nontronite completely reduced the NAC whereas dithionite-reduced nontronite could not. Our 57Fe Mössbauer spectroscopy, ultraviolet-visible spectroscopy, and kinetic modeling results suggest that the highly reactive Fe(II) entities likely comprise di/trioctahedral Fe(II) domains in the nontronite structure regardless of the reduction mechanism. However, the second Fe(II) species, of lower reactivity, varies and for Fe(II)-reacted NAu-1 likely comprises Fe(II) associated with an Fe-bearing precipitate formed during electron transfer from aqueous to nontronite Fe. Both our observation of biphasic reduction kinetics and the nonlinear relationship of rate constant and clay mineral reduction potential EH have major implications for contaminant fate and remediation.

Publication metadata

Author(s): Rothwell KA, Pentrak MP, Pentrak LA, Stucki JW, Neumann A

Publication type: Article

Publication status: Published

Journal: Environmental Science and Technology

Year: 2023

Volume: 57

Issue: 28

Pages: 10231-10241

Print publication date: 18/07/2023

Online publication date: 07/07/2023

Acceptance date: 02/06/2023

Date deposited: 09/08/2023

ISSN (print): 0013-936X

ISSN (electronic): 1520-5851

Publisher: American Chemical Society

URL: https://doi.org/10.1021/acs.est.3c01655

DOI: 10.1021/acs.est.3c01655

PubMed id: 37418593

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