Modelling the effect of humic substances on the transport of europium through porous media: a comparison of equilibrium and equilibrium/kinetic models

A series of column experiments have been performed, which demonstrate the effect of humic substances on the transport of europium through a sand column. Two approaches have been used to model the results: an approach based on a assumption of local chemical equilibrium, and one which accounts for kinetically hindered reactions. A significant improvement in fit is observed upon the inclusion of kinetics. The model explains the observed behaviour of the europium in terms of two distinct humic bound fractions. One which is exchangeably bound, and interacts with the surface of the column packing, and another, kinetically hindered, which does not.