Tandem Ion-Exchange Fractionation: New Preparative Mode for Separation of Multicomponent Ionic Mixtures

The paper reports the results on the development of the tandem ion-exchange fractionation (TIEF) concept for separation of n-component (n > 2) ionic mixtures on (n -1) ion-exchange columns. TIEF technique is based on a sequential combination of frontal separation (FS) and reverse frontal separation (RFS) of the mixture components. The appropriate sequence of the FS leads to a stepwise elimination of the number of components, and it allows recovery of all ions under separation in a sufficiently pure state. A practical demonstration of this concept has been carried out by applying it to a typical mixture of metal ions present in nonferrous metal alloys, i.e. Cu2+, Al3+, Zn2+, and Mg2+. The values of the equilibrium separation coefficient, α, for quadri-, tri-, and bicomponent mixtures involving the mentioned metal ions on polyacrylic and iminodiacetic resins have been determined. The increase of α values for, e.g., Zn2+-Mg2+ exchange from 3.3 to 15.8 on reducing of the number of mixture components from four to two has been observed to illustrate the validity of the TIEF concept The preparative separation of a Cu2+, Al3+, Zn2+, and Mg2+ mixture with an equivalent ratio of Cu:Al:Zn:Mg = 1:1:1:1, carried out by applying the TIEF technique, has been shown to yield Mg2+ of around 100% purity and Cu2+, Al3+, and Zn2+ of 96.1%, 98.8%, and 95.1% average purity, respectively, at a reasonably high yield. The differential stripping during the RFS stage improves significantly the purity of the products obtained. The results obtained by applying TIEF to separate and recover Cu2+, Al3+, Zn2+, and Mg2+ from an acidic mine water sample containing nine metal ions as main components confirm the practical merit of me proposed technique.