Lamellar inorganic ion exchangers. Hydrogen–lithium ion exchange in γ-titanium phosphate

Abstract

The ion-exchange process of H⁺ and Li⁺ 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 LiCl + LiOH solutions. The ion-exchange process and the thermal behaviour of the exchanged solids were monitored by X-ray diffraction. The exchanged phases TiH_1.5Li_0.5(PO₄)₂·2H₂O (interlayer distance 11.0 Å), TiHLi(PO₄)₂·2H₂O (11.3 Å), and TiHLi(PO₄)₂(9.6 Å) were detected. At > 200 °C the TiH_1.5Li_0.5(PO₄)₂·2H₂O phase transformed into mixtures of the Ti(HPO₄)₂(9.1 Å) and TiHLi(PO₄)₂ phases. Extents of conversion higher than 50% with high decomposition of γ-Tip were obtained. The equilibrium constant, free energy, enthalpy, and entropy of the exchange reactions are reported.