Complexation and Redox Buffering of Iron(II) by Dissolved Organic Matter

Citations Over TimeTop 10% of 2017 papers

Abstract

Iron (Fe) bioavailability depends upon its solubility and oxidation state, which are strongly influenced by complexation with natural organic matter (NOM). Despite observations of Fe(II)-NOM associations under conditions favorable for Fe oxidation, the molecular mechanisms by which NOM influences Fe(II) oxidation remain poorly understood. In this study, we used X-ray absorption spectroscopy to determine the coordination environment of Fe(II) associated with NOM (as-received and chemically reduced) at pH 7, and investigated the effect of NOM complexation on Fe(II) redox stability. Linear combination fitting of extended X-ray absorption fine structure (EXAFS) data using reference organic ligands demonstrated that Fe(II) was complexed primarily by carboxyl functional groups in reduced NOM. Functional groups more likely to preserve Fe(II) represent much smaller fractions of NOM-bound Fe(II). Fe(II) added to anoxic solutions of as-received NOM oxidized to Fe(III) and remained organically complexed. Iron oxidation experiments revealed that the presence of reduced NOM limited Fe(II) oxidation, with over 50% of initial Fe(II) remaining after 4 h. These results suggest reduced NOM may preserve Fe(II) by functioning both as redox buffer and complexant, which may help explain the presence of Fe(II) in oxic circumneutral waters.

Related Papers

• → Comparison of Fourier-transformed and Wavelet-transformed EXAFS(2023)5 cited
• → The application of extended X-ray absorption fine structure (EXAFS) to highly dispersed metal catalysts(1983)33 cited
• → Adaptation of the methanogenic granules to denitrification in anaerobic-anoxic USSB reactor(2002)7 cited
• → New insight on the local structure of Cu2+ion in the solution of CuBr₂by EXAFS studies(2009)1 cited
• Characterization of EXAFS for quantitative analysis of mixed species(1994)