What are the main contributions to the total enthalpy of displacement accompanying the adsorption of some multivalent metals at the silica-electrolyte interface?

► Molar integral enthalpy of displacement is measured at constant pH and ionic strength. ► Reliable data are provided to test the thermodynamic models of heavy metal adsorption. ► Displacement is endothermic, irrespective of the nature of the adsorbing metal. ► Cation dehydration during sorption is shown to be responsible for this endothermicity. ► The adsorbed species likely include “free” and hydrolyzed cations.