THERMODYNAMICS OF ALKALI AND ALKALINE EARTH METAL ION-EXCHANGE ON ZIRCONIUM SULPHOPHOSPHONATES

Abstract
The thermodynamics of alkali and alkaline earth metal ion exchange on a layered zirconium sulphophosphonate having the general composition Zr(O3PC6H4SO3H) ×(HPO4) 2−× yH2O have been investigated. Enthalpy and entropy changes accompanying the M2+ - H+ exchange (M = Na+, Cs+, Mg2+ and Ba2+)were determined by the temperature variation method. For the monovalent ions, Na+ and Cs+, the enthalpy terms favor exchange whereas the entropy terms are unfavorable. In contrast, for the divalent ions, Mg2+ and Ba2+, the exchange is due to highly favorable entropy terms.