431-2 Impact of Dissolved Organic Matter Chemistry on the Fate of Iron(II) in Oxic Environments.
See more from this Division: SSSA Division: Soil ChemistrySee more from this Session: Symposium--Organic Molecule Interactions with Mineral Surfaces As Key Regulators of Soil Processes: I
We studied the interactions of Fe(II) with various types of NOM, including Suwannee River NOM, humic acid and fulvic acid, Leonardite humic acid and DOM extracts from Rifle, CO, at pH 5–7. Oxidation of Fe(II) in anaerobic solutions of NOM indicated the presence of oxidizing functional groups. Consequently, we reduced the NOM solutions with H2(g) in the presence of a Pt catalyst. X-ray absorption spectroscopy (XAS) was used to investigate the molecular structure of Fe complexes formed upon reaction of Fe(II) with reduced and unreduced NOM. X-ray absorption near edge spectroscopy (XANES) and electron paramagnetic resonance (EPR) spectroscopy analyses indicated that under anaerobic conditions the reduced NOM formed stable complexes with iron(II).
Analyses of extended X-ray absorption fine structure (EXAFS) data for the reference NOM types demonstrated that Fe(II) formed mononuclear complexes with NOM functional groups containing oxygen. The EXAFS data for Fe(II) complexes with NOM could be well reproduced by a linear combination of data from Fe(II) reference complexes plus a small amount of Fe(III) complexed by the same NOM material.
Preliminary tests showed that complexed Fe(II) exhibited faster initial kinetics of oxidation by O2 but a fraction of iron(II) was preserved over substantially longer timescales than for organic-free solutions. We hypothesize that both Fe(II) complexation and NOM redox state are key factors controlling the fate of iron in NOM solutions subjected to varying redox conditions.
See more from this Session: Symposium--Organic Molecule Interactions with Mineral Surfaces As Key Regulators of Soil Processes: I