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Distribution of manganese in synthetic goethite

Published online by Cambridge University Press:  09 July 2018

U. G. Gasser
Affiliation:
College of Engineering, Im Grüntal, CH 8820 Wädenswil
R. Nüesch
Affiliation:
Department of Materials, Institute of Polymers, ETH, CH 8092 Zürich, Switzerland
M. J. Singer
Affiliation:
Department of Land, Air and Water Resources, University of California, Davis, CA 95616-8627 USA
E. Jeanroy
Affiliation:
Centre de Pédologie Biologique, U.P.R. 6831 du CNRS, associée à l'Université Henri Poincaré, BP 5, F 54501 Vandæuvre-lès-Nancy, France

Abstract

A series of Mn-goethites was synthesized at highly alkaline conditions. The samples were aged for 15 days at a final [KOH] of 0.3 M. Products were washed free from non-goethite phases using 3 M H2SO4. The bulk mineralogy of the samples was determined by X-ray diffraction and verified on selected individual crystals by electron diffraction. The samples had a relatively low magnetic susceptibility (300≤MS≤400×10-9 m3/kg). As revealed by total acid dissolution, the Mn mole fraction XMn ranged from zero to 0.125. Five samples (XMn: 0.025, 0.050, 0.077, 0.099, 0.125) were selected to investigate the variability of the XMn value in single goethite needles (crystals) by analytical electron microscopy (AEM) using rastered and spot analyses. Linear regressions of both as a function of total Mn yielded unit slopes and zero intercepts, indicating that acid dissolution gave the same results as AEM. Spot AEM, however, revealed significant variation of Mn distribution within individual crystals which argues in favour of Mn zoning in goethite. Inhomogeneous transformation of ferrihydrite to goethite may partly explain the Mn zoning.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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