The sorption of ytterbium, nickel, and cesium on magnetite is studied via experiments. The affinity of the magnetite surface is greater for ytterbium, then nickel, and nonexistent for cesium. Three different surface complexation models, with three different electrostatic descriptions of the interface, are used to fit the experiment data. These descriptions are given by the double layer model (DLM), the constant capacitance model (CCM), and a nonelectrostatic model (NEM). The results of fits give the same stoichiometries for the surface reactions for the three tested models in similar surface loading conditions. The values of the surface constants obtained are the same, taking into account the error for DLM and CCM. NEM gives different values, even if the fit quality is comparable.