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XRD and TEM studies on nanophase manganese oxides in freshwater ferromanganese nodules from Green Bay, Lake Michigan

Seungyeol Lee and Huifang Xu
XRD and TEM studies on nanophase manganese oxides in freshwater ferromanganese nodules from Green Bay, Lake Michigan
Clays and Clay Minerals (October 2016) 64 (5): 523-536

Abstract

Freshwater ferromanganese nodules (FFN) from Green Bay, Lake Michigan have been investigated by X-ray powder diffraction (XRD), micro X-ray fluorescence (XRF), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and scanning transmission electron microscopy (STEM). The samples can be divided into three types: Mn-rich nodules, Fe-Mn nodules, and Fe-rich nodules. The manganese-bearing phases are todorokite, birnessite, and buserite. The iron-bearing phases are feroxyhyte, goethite, 2-line ferrihydrite, and proto-goethite (intermediate phase between feroxyhyte and goethite). The XRD patterns from nodule cross sections suggest the transformation of birnessite to todorokite. The TEM-EDS spectra show that todorokite is associated with Ba, Co, Ni, and Zn; birnessite is associated with Ca and Na; and buserite is associated with Ca. The todorokite has an average chemical formula of Ba (super 2+) (sub 0.28) (Zn (super +2) (sub 0.14) Co (super 3+) (sub 0.05) Ni (super 2+) (sub 0.02) )(Mn (super 4+) (sub 4.99) Mn (super 3+) _ (sub 0.82) Fe (super 3+) (sub 0.12) Co (super 3+) (sub 0.05) Ni (super 2+) (sub 0.02) )O (sub 12) .nH (sub 2) O. Barium is the main cation in the structural tunnels of the todorokite. The average chemical formula of birnessite and Ca-buserite are: Na (super +) (sub 0.14) Ca (super 2+) (sub 0.19) (Mn (super 4+) (sub 1.48) Mn (super 3+) (sub 0.52) )O (sub 4) .nH (sub 2) O and Ca (super 2+) (sub 0.27) (Mn (super 4+) (sub 1.46) Mn (super 3+) (sub 0.54) )O (sub 4) .nH (sub 2) O, respectively. Most nodules have a concretionary structure of alternating Fe/Mn layers, commonly with a core of reddish feldspar containing phyllosilicates and hematite micro-crystals. Other cores consist of goethite, cristobalite, tridymite, hercynite, hematite-bearing quartz, coal, and chlorite-bearing rock fragments. The hexagonal or hexagonal-like structures of hematite micro-crystals and clay minerals in the cores may serve as heterogeneous nucleation sites for the Mn-oxides and Fe-(oxyhydr)oxides. The alternating Fe/Mn layers in FFNs might be caused by oscillatory redox condition fluctuations at the sediment-water interface due to changes in water level.


ISSN: 0009-8604
EISSN: 1552-8367
Coden: CLCMAB
Serial Title: Clays and Clay Minerals
Serial Volume: 64
Serial Issue: 5
Title: XRD and TEM studies on nanophase manganese oxides in freshwater ferromanganese nodules from Green Bay, Lake Michigan
Affiliation: University of Wisconsin at Madison, Department of Geoscience, Madison, WI, United States
Pages: 523-536
Published: 201610
Text Language: English
Publisher: Clay Minerals Society, Chantilly, VA, United States
References: 49
Accession Number: 2017-014425
Categories: General geochemistrySedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N45°22'36" - N45°22'36", W87°22'40" - W87°22'40"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Clay Minerals Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201710
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