Lamellar inorganic ion exchangers. H+/Cs+ ion exchange in γ-titanium phosphate

Abstract

The H⁺/Cs⁺ ion-exchange process in γ-titanium phosphate (γ-Tip) was studied. Exchange isotherms and titration and hydrolysis curves were obtained at 25.0, 40.0, and 55.0 (± 0.1)°C by using CsCl + HCI and CsCl + CsOH solutions. The ion-exchange process and the thermal behaviour of the exchanged solids were followed by X-ray diffraction. In acidic media the easy retention of the Cs⁺ by γ-Tip led to the formation of the crystalline phase [graphic omitted]·2H₂O (11.6 Å) without hydrolysis of the exchanger. The elution of Cs⁺ and the regeneration of the γ-Tip were achieved by treatment with solutions of HCl. Equilibrium constants, and the free energy, enthalpy, and entropy of the exchange reaction were determined. Conversions higher than 25% with partial decomposition of γ-Tip and precipitation of TiO₂·nH₂O were obtained by using CsCl + CsOH solutions. The hydrolysis increased with temperature. The results are compared to those obtained in the study of other alkali-metal cations. A structural model for γ-Tip is proposed on the basis of its ion-exchange properties.