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Title: Precipitation pathways for ferrihydrite formation in acidic solutions

In this study, iron oxides and oxyhydroxides form via Fe 3+ hydrolysis and polymerization in many aqueous environments, but the pathway from Fe 3+ monomers to oligomers and then to solid phase nuclei is unknown. In this work, using combined X-ray, UV–vis, and Mössbauer spectroscopic approaches, we were able to identify and quantify the long-time sought ferric speciation over time during ferric oxyhydroxide formation in partially-neutralized ferric nitrate solutions ([Fe 3+] = 0.2 M, 1.8 < pH < 3). Results demonstrate that Fe exists mainly as Fe(H 2O) 6 3+, μ-oxo aquo dimers and ferrihydrite, and that with time, the μ-oxo dimer decreases while the other two species increase in their concentrations. No larger Fe oligomers were detected. Given that the structure of the μ-oxo dimer is incompatible with those of all Fe oxides and oxyhydroxides, our results suggest that reconfiguration of the μ-oxo dimer structure occurs prior to further condensation leading up to the nucleation of ferrihydrite. The structural reconfiguration is likely the rate-limiting step involved in the nucleation process.
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [3] ;  [6] ;  [7]
  1. Univ. of Wyoming, Laramie, WY (United States). Dept. of Ecosystem Science and Management; Lawrence Berkeley National Lab., Berkeley, CA (United States). Earth Sciences Division
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
  3. Technical Univ. of Denmark, Lyngby (Denmark). Dept. of Physics
  4. Univ. of Delaware, Newark, DE (United States). Dept. of Geological Sciences
  5. Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Science
  6. Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Science; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  7. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division
Publication Date:
Report Number(s):
Journal ID: ISSN 0016-7037; R&D Project: LS001
Grant/Contract Number:
SC00112704; AC02-05CH11231; EAR-1529937; AC02-98CH10886; AC02-06CH11357; AC02-76SF00515
Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 172; Journal Issue: C; Journal ID: ISSN 0016-7037
The Geochemical Society; The Meteoritical Society
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); Danish Council for Independent Research (DFF)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1398140; OSTI ID: 1456925