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Incorporation of Mo6+ in ferrihydrite, goethite, and hematite

DOI: 10.1007/s42860-021-00116-x DOI Help

Authors: Marcel G. Görn (Friedrich-Schiller-University Jena) , Ralph M. Bolanz (Friedrich-Schiller-University) , Stephen Parry (Diamond Light Source) , Jörg Göttlicher (Karlsruhe Institute of Technology (KIT)) , Ralph Steininger (Karlsruhe Institute of Technology (KIT)) , Juraj Majzlan (Friedrich-Schiller-University Jena)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Clays And Clay Minerals , VOL 44

State: Published (Approved)
Published: May 2021
Diamond Proposal Number(s): 13606

Open Access Open Access

Abstract: Among all iron oxides, hematite (α-Fe2O3), goethite (α-FeOOH), and ferrihydrite (FeOOH⋅nH2O) are the most common mineral species. While immobilization of Mo6+ by surface adsorption on ferric oxides has been studied extensively, the mechanisms of incorporation in their structure have been researched little. The objective of this study was to investigate the relation between Mo content and its structural incorporation in hematite, goethite, and six-line ferrihydrite by a combination of X-ray absorption spectroscopy (XAS), powder X-ray diffraction (pXRD), and inductively-coupled plasma optical emission spectrometry (ICP-OES). Synthesized in the presence of Mo, the hematite, goethite, and six-line ferrihydrite phases incorporated up to 8.52, 0.03, and 17.49 wt. % Mo, respectively. For hematite and goethite, pXRD analyses did not indicate the presence of separate Mo phases. Refined unit-cell parameters correlated with increasing Mo concentration in hematite and goethite. The unit-cell parameters indicated an increase in structural disorder within both phases and, therefore, supported the structural incorporation of Mo in hematite and goethite. Analysis of pXRD measurements of Mo-bearing six-line ferrihydrites revealed small amounts of coprecipitated akaganéite. X-ray absorption near edge structure (XANES) measurements at the Mo L3-edge indicated a strong distortion of the MoO6 octahedra in all three phases. Fitting of extended X-ray absorption fine structure (EXAFS) spectra of the Mo K-edge supported the presence of such distorted octahedra in a coordination environment similar to the Fe position in the investigated specimen. Incorporation of Mo6+ at the Fe3+-position for both hematite and goethite resulted in the formation of one Fe vacancy in close proximity to the newly incorporated Mo6+ and, therefore, charge balance within the hematite and goethite structures.

Journal Keywords: EXAFS; Ferrihydrite; Goethite; Hematite; Iron oxides; Molybdenum; XANES; XAS

Subject Areas: Earth Science, Chemistry


Instruments: B18-Core EXAFS

Other Facilities: SUL-X at Karlsruhe Research Accelerator (KARA)

Added On: 11/05/2021 09:48

Documents:
Görn2021_Article_INCORPORATIONOFMo6INFERRIHYDRI.pdf

Discipline Tags:

Earth Sciences & Environment Mineralogy Geology Geochemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS)