ABSTRACT
Macrocyclic polyether is a class of specific chelating agents capable of forming stable complexes with metal ions in aqueous solutions selectively. According to the principle of soft and hard acids and bases, oxygen-containing legends’ such as crown ethers are hard bases that prefer to associate with hard acids including the alkali metals, the alkaline earth metals, and the f-block elements. This chapter describes promising macrocycle solvent extraction systems for potential nuclear waste management applications. The complex formed by neutral crown ether and a metal cation is naturally charged. Lipophilic counter anions such as picrate, thiocyanate, and organosulfonic acids are often used to neutralize the charges carried by the crown-metal complexes and to facilitate their transport into organic solvents. Reduced forms of technetium are extracted with crown ethers preferentially into polar or mixed solvents. Extraction of technetium from reducing media was studied in the presence of thenoyltrifluoroacetone.
