The proton of amorphous titanium(IV) phosphate was exchanged with divalent cations (Zn, Ni, Co, Cu, Cd, Ph, and Hg) in aqueous solution at 298.15 +/- 0.02 K. For these cations, the values for the number of moles exchanged were in the sequence : Hg > Pb > Cu > Co > Ni > Cd > Zn, which is also that of the hydration volume of the cation. A suspension of the exchanger was calorimetrically titrated with a cation solution in a heat-flow microcalorimeter. After subtracting the thermal effect of dilution, the thermodynamic data for this process were calculated. All enthalpies obtained are endothermic in nature; the values were : (Zn) 13.20+/-0.35; (Hg) 6.93+/-0.21; (Cd) 5.36+/-0.21; (Ni) 3.85+/-0.09; (Cu) 3.47+/-0.10; (Cd) 3.41+/-0.07 and (Ph) 1.87+/-0.06 kJ mol(-1), which can be ordered as Zn > Hg > Cd > Ni > Cu > Co > Pb. With the exception of mercury, this sequence of enthalpy is the reverse of that obtained for the number of moles exchanged.