Arsenite Binding to Natural Organic Matter: Spectroscopic Evidence for Ligand Exchange and Ternary Complex Formation
- Hoffmann, Martin
- Mikutta, Christian
- Kretzschmar, Ruben
DOIAbstract
The speciation of As in wetlands is often controlled by natural organic matter (NOM), which can form strong complexes with Fe(III). Here, we elucidated the molecular-scale interaction of arsenite (As(III)) with Fe(III)–NOM complexes under reducing conditions. We reacted peat (40–250 μm size fraction, 1.0 g Fe/kg) with 0–15 g Fe/kg at pH <2, removed nonreacted Fe, and subsequently equilibrated the Fe(III) complexes formed with 900 mg As/kg peat at pH 7.0, 8.4, and 8.8. The solid-phase speciation of Fe and As was studied by electron paramagnetic resonance (Fe) and X-ray absorption spectroscopy (As, Fe). Our results show that the majority of Fe in the peat was present as mononuclear Fe(III) species (RFe–C = 2.82–2.88 Å), probably accompanied b...
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