A new carrier for selective removal of heavy metal ions from aqueous solutions by bulk liquid membranes

The carrier-mediated transport of heavy metal ions through bulk liquid membranes has been examined: toxic Hg2+, Cd2+ and Pb2+ ions were studied, along with Cu2+ ions for comparative purposes. The ability of a new carrier, 2,2'-bis(p-octyloxybenzyl) diethylenetriamine (bis-pODET), to complex and transport all the selected metal ions is reported. Differing affinities of the carrier for the different metal ions and the different experimental conditions required for their release into the receiving phase allowed the selective separation of equimolar binary mixtures. For Hg2+/Cd2+ and Hg2+/Pb2+ mixtures, two different separation methods were performed, while the inefficacy of the separation of Cd2+/Pb2+ and Hg2+/ Cu2+ mixtures was for two different reasons: (i) the carrier is able to extract the metal ions with similar levels of ability, and (ii) the carrier metal ion complexes require the same acidity of the receiving phase to release the metal ions. The capability of the carrier to transport Hg2+ efficiently in consecutive cycles is also reported: over 90% of the metal ions were transferred into the receiving phase for three consecutive processes.