Role of ferric oxide in abiotic humification enhancement of organic matter

The significance of humification pathway as promoted by metallic oxides has previously been well investigated using a model system containing humus precursors. Metallic oxides, co-existing with organic matter in nature, are capable of promoting humification of organic matter to different degrees. This study is an investigation into the role of ferric oxide in the process of humification, based on the degree of darkening for humus precursors. Glucose (Glu), glycine (Gly) and catechol (Cat) were introduced as humification model precursors, and the role of ferric oxide in different periods of humification was discussed by characterizing humification degree in terms of dissolved organic carbon, ratio of Fulvic acids (FA) to Humic acids (HA), and E600. Valence changes of Fe were analyzed using X-ray photoelectron spectroscopy. The results showed that ferric oxide was effective on the conversion from FA to HA, and the effectiveness grew as the ferric oxide concentration increased. A higher pH value was more conducive to form dark substances. Amounts of Fe with various valences changed remarkably after humification, suggesting that ferric oxide was involved in the humification reaction.