Thermodynamics of Ion Exchange on Ammonium 12-Molybdophosphate

Synopsis

Standard free energies, enthalpies and entropies for the exchange of NH₄ ⁺ ions on AMP are reported for eight cationic species. For those ions which are weakly adsorbed (e.g. Li⁺, Na⁺, H₃O ⁺, Ag⁺ and K⁺)ΔG° values are positive, as expected, whereas for reactions involving Rb⁺, Cs⁺ and Tl⁺, ΔG° values are negative. Variations in enthalpy and entropy terms for the various exchange reactions are discussed in terms of the energies required to remove the hydration shells of ingoing ions relative to that of the NH₄ ⁺ ions and the energy term for the electrostatic interaction between the cations and the lattice anions.