THERMODYNAMICS OF ALKALI AND ALKALINE-EARTH METAL ION-EXCHANGE ON CERIUM(IV) HYDROGEN PHOSPHATE

Thermodynamics of alkali and alkaline earth metal ions/hydrogen ions exchange on a fibrous cerium(IV) hydrogen phosphate have been investigated. Selectivities for alkali and alkaline earth metal ions increase in the order; Na(+)much less than K+<Rb+<Cs+ and Mg2+<Ca2+<Sr2+<Ba2+, respectively. The enthalpy changes for aIkali metal and Ba2+ ions/H+ exchange are negative, those for the other alkaline earth metal ions/H+ exchange are positive, indicating that the enthalpy changes for monovalent ions are more favorable than those for divalent ions. In comparison with ions of the same valency, the enthalpy change decreases with the atomic number of the metal ion corresponding to a decrease in the entropy change of dehydration in response to enthalpy-entropy compensation.