Ion exchange and solvent extraction equilibria in mixed electrolytes

Abstract

The distribution coefficients of 2-thenoyl trifluoroacetone (TTA) between the organic and aqueous phase containing mixtures of ClO4−, NO3−, Cl−, SCN−, and SO42− ions indicate that the activity coefficients of TTA in the aqueous phase are given by ln γ = ΣksiCsi where ksi and Csi are the salting-out parameter and molar concentration of the ith component, respectively. The salting-out effect on TTA follows the usual pattern for a non-electrolyte, i.e. SO42− > Cl− > Br− > ClO4− > SCN− for anions and Li+ > Na+ > H+. In the solvent extraction equilibria, the extraction behavior of the neutral species M(TTA)n may not be similar to that of TTA and thus stability constants determined by this method, wherein there are large changes of anion composition in the aqueous phase to maintain the ionic strength constant, may be in error. The ion exchange equilibria have also been investigated by determining distribution coefficients, D, of metal ions in trace concentrations in mixed electrolyte solutions. The large, poorly hydrated ions are salted into the resin phase in the presence of anions like ClO4− having the property of breaking the water structure. In mixed electrolytes containing perchlorate, nitrate, and chloride ion mixtures, the D values are difficult to rationalize on the basis of the activity coefficients of ions alone. The stability constants for the formation of CaCl+, CaNO3+, BaCl+, and BaNO3+ determined by the ion exchange method at μ = 1 are not in agreement with those obtained by the spectroscopic method.