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The effectiveness of the ligand 4-hexadecyloxybenzyliminodiacetic acid (C 16 BIDA) for the selective removal of Cu 2+ from aqueous solutions using Ugand-modified micellar-enhanced ultrafiltration (LM-MEUF) has been investigated. The cationic surfactant N-hexadecylpyridinium chloride (CPC) was used as the added colloid. Stirred cell ultrafiltration (UF) and semi-equilibrium dialysis (SED) methods were used to determine the effects of solution composition on the rejection of copper ions. The parameters studies include the concentrations of Cu 2+ , ligand, Ca 2+ , surfactant, and NaCl in the initial (feed) solution for UF and SED experiments and the applied pressure in the UF experiments. In solutions containing 100 mM CPC at pH 5.5, predominately 1:2 metal-ligand complexes are formed. Rejections of copper of up to 99.8% are observed, with almost no rejection of calcium, demonstrating the excellent selectivity and separation efficiency of C16BIDA in LM-MEUF. SED experiments showed that the ligand can be recovered for recycling by acid-stripping at pH 2.Surfactant-based separation processes are a class of chemical engineering separations that have great potential for removal and/or recovery of heavy metals and organic pollutants from water streams (7,2). Surfactant-based separation processes can require less energy, be less expensive, and have less environmental impact than traditional separation methods.Micellar-enhanced ultrafiltration (MEUF) is a surfactant-based separation technique that can be used to remove metal ions and/or dissolved organics from aqueous streams. In MEUF, the surfactant is present at a concentration well above its critical micelle concentration (CMC), so most of the surfactant is present as micelles. The micelles are roughly spherical aggregates containing about 50 to 150 surfactant molecules (3). The hydrocarbon chains of the surfactant fill the micelle interior making this core hydrophobic, and the hydrophilic portions of the surfactant are situated at the micelle surface. Cationic multivalent metal ions adsorb or bind to the surface of negatively charged micelles of an anionic surfactant while organic solutes tend to Corresponding author. 280