Interaction between europium ions and selected size fractions of humic acids

The interaction between humic acids and europium shows significant variations with the molecular size of the humic acids. Results presented in this paper show that the complexing capacity, defined as the number of millimoles of metal per gramme of humic material, increases with decreasing molecular size of the humic material. However, because higher molecular weight humics are present in greater concentration, most of the metal is to be found associated with the higher molecular weight fractions. Results show that >98% of europium is associated with humic species larger than 10.000 Daltons and over 50% of europium is associated with humics within the 10.000 – 30.000 dalton range. The effect of humic acids on the mobility of metal ions in the environment is discussed.