A comparative study of membrane extraction of copper using LIX54- or LIX84-impregnated supported liquid membrane (SLM) systems was carried out in this work to remove copper from ammoniacal wastewater. Experimental and computational characterizations of LIX54/Cu(II) and LIX84/Cu(II) complexes were performed and the results agreed well in the reaction mechanisms, complex geometries, and copper extraction strengths of these two carriers. Copper transmembrane fluxes at different conditions were compared and LIX54 was found to have slightly higher copper transmembrane flux in ammoniacal solution but much poorer copper loading in acidic media. Much higher selective separation performances of Cu(II) over Zn(II) and Cd(II) and no ammonia carryover provide LIX54 significant advantages over LIX84 for the treatment of ammoniacal copper solutions. In this work, an impedance spectroscopy technique and initial flux measurement were used to study the long-term stabilities of both LIX54- and LIX84-impregnated vertical flat membrane systems. The results reveal that the membrane stability of both LIX54-and LIX84-impregnated SLM in ammoniacal copper solutions is promising for practical industrial applications. (c) 2006 American Institute of Chemical Engineers.