The Coordination Numbers and Ion Exchange Behavior of Fe3+ and UO22+-Cl-Complexes in an Anion Exchanger

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The coordination numbers and ion exchange characteristics of Fe3+- Cl- complex ions adsorbed in a porous anion exchanger were measured to study the behavior of complex ions in an ion exchangers. The results demonstrated that the species of Fe3+-Cl- complex ion which had been adsorbed was [FeCl4] -, and that the adsorbed ions were localized in the "Donnan area". Furthermore, the adsorption affinities based on Cl- (Δμ0r) of the adsorbed complex ions were estimated to be 14.3 and 15.8 kJ/ mol respectively for [FeCl4] - and [UO2Cl4] 2-. These values of Δμ0r were much larger than those of common non-complex anions. An analysis of the mechanism of adsorption using the thermodynamic equilibrium constant K indicated the ion exchange reactions were largely controlled by the osmotic pressure of the resin in the exchange of metal complex ions, and by the activity coefficient term in the exchange of Cl- and metal complex ions. These results suggest the peculiar behavior of complex ions adsorbed in an ion exchanger, which is similar to the accelerated rate of the electron exchange reaction shown by adsorbed ions in comparison with that observed with ions in solution.
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