Cryptomelane formation from nanocrystalline vernadite precursor: a high energy X-ray scattering and transmission electron microscopy perspective on reaction mechanisms

Geochemical Transactions
Sylvain GrangeonBruno Lanson

Abstract

Vernadite is a nanocrystalline and turbostratic phyllomanganate which is ubiquitous in the environment. Its layers are built of (MnO6)(8-) octahedra connected through their edges and frequently contain vacancies and  (or) isomorphic substitutions. Both create a layer charge deficit that can exceed 1 valence unit per layer octahedron and thus induces a strong chemical reactivity. In addition, vernadite has a high affinity for many trace elements (e.g., Co, Ni, and Zn) and possesses a redox potential that allows for the oxidation of redox-sensitive elements (e.g., As, Cr, Tl). As a result, vernadite acts as a sink for many trace metal elements. In the environment, vernadite is often found associated with tectomanganates (e.g., todorokite and cryptomelane) of which it is thought to be the precursor. The transformation mechanism is not yet fully understood however and the fate of metals initially contained in vernadite structure during this transformation is still debated. In the present work, the transformation of synthetic vernadite (δ-MnO2) to synthetic cryptomelane under conditions analogous to those prevailing in soils (dry state, room temperature and ambient pressure, in the dark) and over a time scale of ~10 years was monito...Continue Reading

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Citations

Sep 28, 2016·Inorganic Chemistry·Qian WangMengqiang Zhu
Aug 25, 2020·Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials·Seungyeol LeeXiaoming Sun
Jun 1, 2019·Environmental Science & Technology·Peng YangMengqiang Zhu
Jan 23, 2018·Environmental Science & Technology·Qian WangMengqiang Zhu
Nov 2, 2019·Environmental Science & Technology·Silvan WickAndreas Voegelin

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Methods Mentioned

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X-ray
transmission electron microscopy
electron diffraction

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