The biogeochemical cycles of iron and dissolved organic matter (DOM) are strongly associated, especially at the redox interfaces. However, the role of iron minerals with various redox mineralogies in DOM preservation has not been clearly characterized at the molecular level. In this study, we employed Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to investigate the molecular fractionation of DOM by adsorption onto four model iron minerals with different oxidation states (ferrihydrite, hematite, troilite, and pyrite). The sorption capacity (normalized to per gram adsorbent) to DOM was in the order of ferrihydrite &gt; troilite &gt; hematite &gt; pyrite. After normalization by specific surface area, the sorption capacity of troilite was also considerably higher than hematite and pyrite. The sorptive fractionation of DOM was significant for ferrihydrite and troilite but was not obvious for pyrite. Compounds high in unsaturation and nominal oxidation state of carbon or rich in oxygen were preferentially bound to ferrihydrite and troilite, leaving compounds low in unsaturation or poor in oxygenated groups in solution. This sorptive fractionation was dependent upon DOM concentration. These findings would provide new insights into the stability of aromatic and aliphatic carbon with various oxygenated groups coupled to redox iron transformation in soils.

Preferential molecular fractionation of dissolved organic matter by iron minerals with different oxidation states

2019 Spring National Meeting

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