Metal Separations Using Emulsion Liquid Membranes

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 Li 4 P 2 O 7 receiving phase were studied with respect to the disappearance of metal from the source phase as a function of time. The salts Pb(NO 3 ) 2 , Sr(NO 3 ) 2 , TINO 3 , and LiNO 3 were studied both singly and in mixtures of Pb(NO 3 ) 2 with each of the other salts. In all mixtures studied, Pb 2+ 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 Pb 2+ . Modeling of these systems was discussed. Source phases containing basic (pH 11) K[Al(OH) 4 ] solutions were studied using the same membrane and a 0.15 M H 3 PO 4 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.