Ion-exchange equilibria involving complex formation in aqueous solution

Abstract

Ion-exchange equilibria in the Ni 2+/Na + system were studied in aqueous solution in the presence of complexing agents. Both inorganic anions and organic chelating agents were used as complexing agents. Experimental results show that equilibrium nickel uptake in the membrane depends upon the stability of the nickel complexes and decreases with increasing capacity of the chelating agent. Assuming that ion-exchange and complexation reactions occur independently, the thermodynamic equilibrium constant, in terms of the activities of free ions in aqueous phase and membrane phase, gives a good estimate of nickel uptake in the membrane without the kind of chelating agents used having to be considered. The nonideality due to ion association in aqueous solution was corrected by the Brønsted-Guggenheim equation for the individual ionic activity coefficients. The total excess Gibbs free energy of the exchanger phase was correlated with the Wilson equation. The thermodynamic constant for nickel to sodium exchange at 298 K was determined to be 8.94.