Europium binding by fulvic acids

The binding of Eu to fulvic acid (FA) as a function of pH was determined by Schubert's method and by equilibrium dialysis. Data obtained by both methods showed a strong pH dependence, which was reproduced well by the model used to interpret the data (humic ion-binding model VI). The model was also able to account for five other data sets from the literature, and there was reasonable agreement among the values of the characteristic binding parameter for Eu-FA interactions. Data sets investigating the effects of aluminum competition were also explained well by Model VI, The model was used to calculate the speciation of Eu in natural waters as a function of the most-likely competitive solution species (protons, aluminium and calcium). The calculations indicate that under environmentally realistic concentrations both, aluminium and calcium can be significant competitors at low and high pH, respectively, although FA binding appears to dominate Eu speciation under most conditions. (C) 1998 Elsevier Science B.V. All rights reserved.