Macrocyclic ligand as ion size selective masking reagent in metal ion separation

The extraction-separation of alkali, alkaline earth, and rare earth metal ions could be improved by using macrocyclic ligands as ion size selective masking reagents. By adding a macrocyclic ligand to the aqueous phase of a conventional chelate extraction system, the extraction of metal ions with larger ionic radii was shifted to a higher pH region. Consequently, the separation among the metal ions was enhanced. Diazapolyoxabicyclic ligands (cryptand) exhibited a prominent separation ability for alkali and alkaline earth metal ions. Quantitative separation systems were successfully developed in the synergistic extraction of alkali and alkaline earth metal ions in the presence of a cryptand. A new type of water-soluble sulfonated crown ethers was prepared. The separability of lanthanide ions was found to improve by adding the sulfonated crown ethers into the aqueous phase. The number of water molecules in the first coordination sphere of the central Eu in the complex was determined by a laser-induced luminescence study. In addition, fluorescence spectra were measured to evaluate the structure of the complexes. The stabilization of the complexes formed is discussed, taking into account an outer-sphere electrostatic attraction between the sulfonic acid group and the metal ion.