Structural features and Fe(II)-Binding capacities of humic acids from reservoir sediments

Reservoirs frequently require dredging to remove accumulated sediment. This sediment is currently unused, but represents a possible source of humic acids (HAs) that have potential as iron-binding supplements in fertilizers. In order to evaluate the utility of these materials, we investigated the structural features and Fe(ll)-binding constants or capacities of some HAs obtained from reservoir sediments. The histidine content in the HAs was correlated to the Freundlich binding constant for an Fe(ll)-HA complex, indicating that indole moieties in histidine function as strong binding sites for Fe(ll). The binding capacities (2.2-3.2 mmolg ^-1) indicated that the HAs have the capacity to be loaded with 12-18% Fe(ll), comparable to the iron content of previously reported Fe fertilizers that employ HAs from other sources (2-17%). The Fe(ll)-binding capacities were positively correlated with the content of phenolic hydroxyl groups. In addition, the positive correlation between Fe(ll)-binding capacity and vanillyl moieties in the HAs indicates that 3,4-dihydroxyben-zene and/or benzoic acid derivatives also serve as Fe(ll) binding sites.