On the mechanism of ion exchange in crystalline zirconium phosphates - IV potassium ion exchange of α-zirconium phosphate

The ion exchange behavior of α-zirconium phosphate crystals titrated with potassium ion and the behavior of the potassium-exchanged forms titrated with HCl has been examined. The replacement of protons by potassium ion takes place in two stages. In the first stage, the α-ZrP crystals are converted to Zr(KPO₄)(HPO₄)·H₂O and this reaction is followed by replacement of the second proton to yield Zr(KPO₄)₂·3H₂O. The reactions are not reversible as solid solutions of hydrogen ion in the potassium phases are formed on addition of dilute hydrochloric acid to the potassium-exchanged phases. The dehydration behavior of the exchanged forms was also determined. It is also shown that the approach to equilibrium is very slow and explanations for this behavior are presented.