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Title: A multi-method characterization of natural terrestrial birnessites

Journal Article · · American Mineralogist
 [1];  [2];  [3];  [4];  [5];  [6];  [3]
  1. Pennsylvania State Univ., University Park, PA (United States). Dept. of Geosciences; La Salle Univ., Philadelphia, PA (United States). Dept. of Biology
  2. Smithsonian Institute, Washington, DC (United States). Dept. of Mineral Sciences
  3. Pennsylvania State Univ., University Park, PA (United States). Dept. of Geosciences
  4. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Earth and Environmental Sciences
  5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  6. Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil and Environmental Engineering

With a focus on a large set of natural birnessites collected from terrestrial, freshwater systems, in this study we applied and compared the capabilities of X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) to characterize crystal structure and chemistry. Using XRD, we successfully identified 3 of the 11 natural birnessite samples as hexagonal ranciéite-like phases, but the remaining samples yielded less interpretable “3-line” diffraction patterns with broad, asymmetrical peaks at d-spacings of ~7.2, ~2.4, and ~1.4 Å. EXAFS analysis suggested that many of these samples had characteristics of both triclinic and hexagonal birnessite. However, application of EXAFS to the ranciéite-like phases yielded unreasonably high concentrations of triclinic birnessite as an intergrowth, calling into question the use of synthetic hexagonal H-birnessite as an appropriate standard in the linear combination fitting of EXAFS data for natural birnessites. FTIR spectroscopy of the “3-line” birnessite samples successfully distinguished triclinic and hexagonal constituents, and analyses of peak positions suggested that natural birnessites occur as a full spectrum of triclinic and hexagonal intergrowths. XPS analysis of these samples revealed that higher Mn3+ concentrations relative to Mn2+ and Mn4+ are correlated to increased proportions of triclinic birnessite.

Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF)
Grant/Contract Number:
AC05-76RL01830; AC02-06CH11357
OSTI ID:
1673587
Alternate ID(s):
OSTI ID: 1632888
Report Number(s):
PNNL-SA--149385; {"","Journal ID: ISSN 0003-004X"}
Journal Information:
American Mineralogist, Journal Name: American Mineralogist Journal Issue: 6 Vol. 105; ISSN 0003-004X
Publisher:
Mineralogical Society of AmericaCopyright Statement
Country of Publication:
United States
Language:
English