In this paper, the adsorption of europium on a natural bentonite was studied and modelled using the component additivity (CA)
approach of the surface complexation theory. The experimental results were modelled considering the formation of monodentate
species at the edge sites of the bentonite and two exchange reactions at the interlayer sites. The CA approach was compared
to the most common approach of the surface complexation theory (the general composite (GC)), by modelling in a predictive
way, experimental results obtained from the literature. This comparison allowed us to conclude that (i) the CA approach successfully
described the behaviour of europium on montmorillonite on a restricted pH range and on a large range of concentrations, (ii)
five surface stoechiometries for the GC approach were necessary to model the europium sorption versus four surface stoechiometries
for the CA approach, (iii) some improvement of the CA approach are necessary concerning the consideration of impurities.