Extraction and separation of metal cations in solution by supported liquid membrane using lasalocid A as carrier*

Flat-sheet-supported liquid membranes incorporating lasalocid A (a natural ionophore), were previously shown to be permeable to metal cations (Cd2+ and Zn2+) against a proton gradient (∆pH), which is the driving force of the process [1]. This transport process has been extended to other metal species such as Pb2+, Na+, and Ag+ and also to the case where two metal species compete for transport. A higher transport flux for Pb2+ as compared to Cd2+ and Zn2+ is observed and partly explained by a higher rate of interfacial complexation owing to the smaller hydration shell of this species. This effect is confirmed by the data obtained with Ag+. However, the size of the metal cation in relation to its hydration shell does not appear as the major parameter to take into account for an estimate of the trans-membrane transport efficiency, as the Na+ ions escape to this behavior, which has been considered until now as a general trend for metal cation ionophores.