Kinetic analysis of aluminum complex formation with different soil fulvic acids

A fluorescence technique was used to investigate the complex formation kinetics of aluminum with fulvic acids isolated from different forest soil environments. In the pH range of 2.4–3.6, all of the fulvic acids were found to contain two kinetically distinguishable components, which define two types of average aluminum binding sites. Both of these average sites on all of the fulvic acids conformed to a bidentate chelating binding site kinetic analysis, from which average rate and equilibrium parameters were obtained. Evidence indicated that the difference in reaction rate between the two types of aluminum binding sites on the fulvic acids was due to a steric strain, whereby aluminum was repelled from the slower reacting sites. In comparing this study with a similar kinetic study carried out in acetate buffered solutions, it was found that the presence of buffer changed both the overall mechanism by which aluminum reacted with fulvic acid, and the nature of the sites on fulvic acid that bind aluminum.