Effect of Chemical Properties of Humic Substances on Iron Complexation in Natural Waters

Abstract

 It is important to understand complexation between humic substances and iron in view of the assessment of iron bioavailability in natural water environment. In this study, iron complexation by humic substances from a variety of origins were investigated by measuring stability constant and complexation capacity using the competitive ligand method. In addition, relationship between such complexation parameters and chemical properties of humic substances was examined. Statistically significant positive correlation between the complexation capacity and amount of aromatic carbons of humic substances (as determined by ¹³C-NMR) was provided. Therefore, functional groups resident in aromatic region are likely responsible for iron coordination. In addition, stability constant has significant correlation with sulfer and nitrogen content of humics (as determined by elemental analysis), suggesting that sulfonic and amino groups bind to iron with higher stability constant.