Redox Reactions between Mn(II) and Hexagonal Birnessite Change Its Layer Symmetry

Huaiyan Zhao, Mengqiang Zhu, Wei Li, Evert J. Elzinga, Mario Villalobos, Fan Liu, Jing Zhang, Xionghan Feng, Donald L. Sparks

Research output: Contribution to journalArticlepeer-review

73 Scopus citations

Abstract

Birnessite, a phyllomanganate and the most common type of Mn oxide, affects the fate and transport of numerous contaminants and nutrients in nature. Birnessite exhibits hexagonal (HexLayBir) or orthogonal (OrthLayBir) layer symmetry. The two types of birnessite contain contrasting content of layer vacancies and Mn(III), and accordingly have different sorption and oxidation abilities. OrthLayBir can transform to HexLayBir, but it is still vaguely understood if and how the reverse transformation occurs. Here, we show that HexLayBir (e.g., δ-MnO2 and acid birnessite) transforms to OrthLayBir after reaction with aqueous Mn(II) at low Mn(II)/Mn (in HexLayBir) molar ratios (5-24%) and pH ≥ 8. The transformation is promoted by higher pH values, as well as smaller particle size, and/or greater stacking disorder of HexLayBir. The transformation is ascribed to Mn(III) formation via the comproportionation reaction between Mn(II) adsorbed on vacant sites and the surrounding layer Mn(IV), and the subsequent migration of the Mn(III) into the vacancies with an ordered distribution in the birnessite layers. This study indicates that aqueous Mn(II) and pH are critical environmental factors controlling birnessite layer structure and reactivity in the environment.

Original languageEnglish (US)
Pages (from-to)1750-1758
Number of pages9
JournalEnvironmental Science and Technology
Volume50
Issue number4
DOIs
StatePublished - Feb 16 2016

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Environmental Chemistry

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