Potential of ion exchange:
There are numerous examples like this. The extremely high selectivity of the quaternary ammonium type anion exchange resins for the metallic anionic complexes is one of the most amazing examples of ion exchange chromatography. The industrial application of cation exchangers for water softening is well-known where mainly the Ca2+, Mg2+ and other heavy metal ions are removed by the sodium form of the exchanger. For complete deionization of water, it is passed through a cation exchanger and then an anion exchanger or a mixed bed of both types of ion exchangers.
The best illustration of potential of ion exchange to separate closely similar metal ions is the separation of rare earths. A cation exchange resin alone can provide separation since the affinities of the lanthanide ions for the resin vary inversely with their hydrated radii and these, in turn, vary inversely with the crystallographic radii. Thus, the order of elution is Lu-La. The similarity of various rare earths necessitates the use of complexing agents to increase the separation factor. The use of carboxylic acidssuch as citric, glycolic and tartartic, adjusted to appropriate pH, as eluting agents markedly enhances the separation. Among the other useful ligands employed as eluting agents are α -hydroxyisobutyric acid, EDTA, and 2-hydroxy-EDTA.