Heterogeneous Two-Phase Distribution Analysis of Complexation in Anion Exchangers

HETEROGENEOUS TWO-PHASE DISTRIBUTION ANALYSIS OF COMPLEXATION IN ANION EXCHANGERS 

Since 1961 [20], determination of the composition of complex species present in an anion-exchanger phase has been sought through the analysis of equilibrium distribution measurements between resins and solutions. The distribution ratio of a metal ion, M , defined as the rado of total concentrations of the metal in the two phases of a system containing a monovalent anion as ligand, L, can be represented by 

In systems where the ionic strength of both phases is kept constant, G may be nearly constant. Furthermore, when the change of ligand concentration in the equilibrated solution is very much smaller than in the anion-exchanger phase, Eq. (20) can be simplified to 

With D and [L]r values experimentally accessible, log D is plotted against 1o8[L]r to determine n from the slope. In this case, of course, the assumption that dlog[L]/dlog[L],( is very small must be shown to be reasonably valid before simplified Eqs. (23) or (24) are applied. The reliability of this treatment has been confirmed for the chloro complexes of cobalt(II) and iron(III) [10]. Even if the chloro-complexed species under examination with this treatment exist as H2C0CI4 and HFeCl together with CoCl4 and FeClj, the fact that such species as CoCl and FeCl are presumed to exist in the development of Eqns. [23] and [24] implies that their use does not need to be abandoned. As long as the concentration of ion is kept constant in the course of the D measurements, the resolution of n is similarly valid. 

Examples of this analysis mode are presented in Fig. 5. The slope of the log D versus log[L],i plots for the cobalt(II)-8 M HCl and the Fe(III)-6 M HCl systems indicate the formation of CoClj and FeClj, respectively, as the predominant complexes in the Dowex 1-X8 phase. These results are believed to prove the reliability of this approach, the presence of these complexes in concentrated hydrochloric acid being well documented. The chloride complex of uranium(IV), UClj, v 4iose unique absorption spectrum is shown in Fig. 6 [11], in the HCl, HCIO4 (I = 10 M) 

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