The formation mechanisms of ferric iron (Fe3+) oxyhydroxides, from Fe3+ monomers into particles with defined structure, are fundamentally and  environmentally important but remain largely unknown. Here, we used  UV-Vis and quick-scanning EXAFS spectroscopy to study time-dependent  evolution of Fe3+ species in 0.2 M Fe3+ nitrate solutions partially neutralized using NaHCO3 (h = [NaHCO3]/[Fe3+]).  When h = 0.5, the neutralized solutions contained only Fe monomers and  �-oxo dimers that remained unchanged in abundance within the studied  time period. When h = 0.7 and 0.8, the initial Fe species included only  monomers and dimers but eventually ferrihydrite particles emerged and  increased in abundance. When h = 1, ferrihydrite particles were present  initially and increased in abundance with time. In all h = 0.7  solutions, dimer abundance increased whereas monomer abundance decreased  over time. No intermediate size Fe species between monomers/dimers and  ferrihydrite particles were observed, suggesting at most, transient  existence.

Ferrihydrite formation: From molecular clusters to nanoparticles

244th National Meeting (2012)

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