Metal Separations Using Emulsion Liquid Membranes

Abstract

Emulsion membrane systems consisting of an aqueous metal salt source phase, a toluene membrane containing the macrocyclic ligand dicyclohexano-18-crown-6 (DC18C6) (0.02 M) and the surfactant sorbitan monooleate (3% v/v), and an aqueous 0.05 M Li₄P₂O₇ receiving phase were studied with respect to the disappearance of metal from the source phase as a function of time. The salts Pb(NO₃)₂, Sr(NO₃)₂, TINO₃, and LiNO₃ were studied both singly and in mixtures of Pb(NO₃)₂ with each of the other salts. In all mixtures studied, Pb²⁺ was transported first, followed by the second cation (except Li⁺ which was not transported). An excess of a second salt with a common anion enhanced the transport of Pb²⁺. Modeling of these systems was discussed. Source phases containing basic (pH 11) KAl(OH)₄] solutions were studied using the same membrane and a 0.15 M H₃PO₄ receiving phase. K⁺ and Al(III) (as aluminate anion) were both found to transport in this system, but no transport of Al(III) and little transport of K⁺ were detected when DC18C6 was absent.