Exchange of Some Divalent Metal Cations and Their Effect on the Dissociation of Iron(III) Phosphate

Abstract

Potentiometric titrations of iron(III) phosphate have shown an apparently weak monobasic acid behaviour towards alkali, alkaline earth and divalent transition metal ions. The selectivity sequence and dissociation of the exchanger was found to increase in the order Cu²⁺ > Zn²⁺ > Ni²⁺ > Ca²⁺ > K⁺. The dissociation constants of iron(III) phosphate have been determined from Potentiometric titration data in the temperature range 303–323 K. In addition, the exchange of Cu²⁺, Zn²⁺ and Co²⁺ on iron(III) phosphate and the effect of these ions on dissociation were also studied as a function of concentration, temperature and solution pH value. The thermodynamic parameters ΔH⁰, ΔS⁰ and ΔG⁰ for the dissociation of iron(III) phosphate are also presented.