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Effect of co-anion on DC18C6-mediated Tl+transport through an emulsion liquid membrane

Journal of Membrane Science
Publication Date
DOI: 10.1016/s0376-7388(00)82201-2


Abstract Emulsion membrane systems consisting of an aqueous thallous salt source phase, a toluene membrane containing the macrocyclic ligand dicyclohexano-18-crown-6 (DC 18C6)(0.02 M), the surfactant Span 80 (sorbitan monooleate) (3% v/v), and an aqueous 0.01 M Li 4P 2O 7 receiving phase were studied with respect to the disappearance of Tl + from the source phase as a function of time. The salts TlOH, Tl 2 CO 3, TlAu(CN) 2, TlSCN, TlClO 4, TlAg(CN) 2, Tl 4 Fe(CN) 6, TlF, Tl 2SO 4, TlBr, CH 2 (COOTl) 2, HCOOTl, TlCl, and TlNO 3 were investigated singly (salts listed in order of decreasing total percentage of Tl + transport observed). In competitive transport experiments using equimolar TlAg(CN) 2 and TlAu(CN) 2, TlAu(CN) 2 was found to transport by a factor of six over TlAg(CN) 2. Attempts are made to explain the co-anion effect on Tl + transport by relating transport inversely to the negative free energy of hydration of the co-anion, directly to the amount of ion pairing of the co-anion with a cationic species present, and directly to the amount of deprotonation of the surfactant.

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