Effect of humic matter on metal adsorption onto clay materials: Testing the linear additive model

A commonly used composite approach (linear additive model) was tested for suitability in reconstructing the solid-liquid distribution of Tb in ternary systems (Tb/humic acid/clay) on the basis of data determined for binary subsystems. The model can qualitatively explain the influence of humic acid as a function of pH, but it failed to reproduce our experimental data quantitatively. It appears that the elementary processes (metal adsorption, metal-humate complexation, humic acid adsorption) cannot be considered to be independent of each other. Possible reasons are discussed.