Investigation of liquid-liquid distribution behavior of alkali metal ions in polymer inclusion membrane and extraction separation systems

Fundamental aspects of complexation and transport of alkali metal ions by macrocyclic receptors were addressed in this Dissertation. In the view of the urgent need for new technologies for cleanup of US DOE wastes, cesium-selective crown and calixcrown derivatives were chosen as particularly relevant models for investigation.;Extraction studies were performed using ligands of the tetrabenzo-24-crown-8 family as cesium extractants. The structure of the complex [Cs(tetrabenzo-24-crown-8)(1,2-dichloroethane) 2] [NO3]•H2O was recently shown by X-ray crystallography to involve an unprecedented bidentate coordination of two 1,2-dichloroethane solvent molecules to the Cs+ ion. The complete encapsulation of the Cs+ by the crown ether and two solvent molecules explains the extraction behavior of CsNO3 or CsClO 4 into 1,2-DCE solutions of the alkylated analogs of tetrabenzo-24-crown-8. A thorough investigation of the speciation behavior of the extraction systems, conducted using the program SXLSQI, demonstrated that the cation complex and counterion are present either as ligand-separated ion pairs or as dissociated ions. In agreement with a theoretical treatment of ion pairing, the ion pairs possess unusually low stability in 1,2-DCE and exhibit no discrimination between the anions. It was established that even solvent molecules with exceptionally weak donor-acceptor properties may have a profound impact on the liquid-liquid distribution behavior involving supramolecular assemblies.;In a systematic study of cation transport through polymer inclusion membranes (PIMs) with calixcrown carriers, models that postulate diffusion-limited flux were developed. PIM transport behavior was successfully described for the first time based on equilibrium speciation at the PIM interface, establishing that the transport permeability coefficient is proportional to the square root of the corresponding extraction constant. This correlation facilitates ready prediction of the transport rates when the stability constants of the carrier-metal complexes and the Gibbs energies of ion partitioning between source and PIM phases are known. The described approach was extended to competitive-transport experiments. PIMs demonstrated highly efficient and selective Cs+ transport under competitive conditions employing complex source phase mixtures, including simulants of acidic nuclear wastes found at the Idaho National Engineering and Environmental Laboratory. Calorimetric studies were carried out to obtain thermodynamic parameters for the complexation of bis(dodecyloxy)calix[4]arene-crown-6 (1) with alkali metals in acetonitrile. It was established that the complexation process is exclusively enthalpy driven. The stability constant for Cs•1+ was found to be about 1.5 order of magnitude greater than that of for K•1+.