Strong Complexation in Anion-Exchanger Phase

One of the most remarkable and useful properties of fully dissociated strong-base anion exchangers is their unique tendency to interact selectively with metal ions that are complexed by the exchanger counterions. When metal ion is added to the electrolyte solution equilibrated with the exchanger a portion of the absorption spectrum resolved for the exchanger phase is not matched by the absorption spectrum of the solution phase even when care has been taken to keep the concentration level of counterion in the two phases the same. Advantage of this property has been taken for the development of a number of anion-exchange facilitated separations of metals [6,7,20]. 

A typical example of such different behavior is given in Fig. 3. The absorption spectra of the anion-exchange resin, AG-1-X8, and the 4 M hydrochloric acid solution of Co(II) used to prepare the resin sample for such a comparison are presented in this figure. It is immediately apparent that species exhibiting tetrahedral symmetry, e.g., CoC , or CoCl , pre- 

The fact that the selective uptake of metal ion by the ion exchanger is associated with highly coordinated species undetectable in the solution, even vtiien ligand concentrations in the two phases have been kept similar, has to be attributed to either the immobilization of these species by their interaction with the organic component of the exchanger matrix or to sizable reduction of activity coefficients of ion species in the resin phase because of the lowering of the dielectric constant of the resin phase media. 

Their absence in the solution phase is consistent with both explanations. If species immobilization is involved only the diffusible components of the system can be observable in both phases. The absence of the highly coordinated species in the solution phase can then be attributed to the immobilization phenomenon projected as shown. 

The several peaks in the absorption spectrum obtained with the AG 1-X8 resin equilibrated in a 4 M HCl solution of Co(II) (Fig 3) are con- 

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