BACKGROUND: Regulatory controls to limit mercury emissions in waters have impacted on the development of membrane extraction-based methodologies for its separation. The specific advantages (effective carrier immobilization, easy preparation, versatility, and good mechanical properties) of polymer inclusion membranes (PIMs) make them suitable for this purpose. In this work a novel procedure using PIMs for mercury separation with a commercial available extractant (Cyanex 471 X) is described and evaluated through the determination of the efficiency parameters (permeability, selectivity, stability) and membrane characterization. RESULTS: Using a membrane composed of 30% cellulose triacetate (CTA), 60% 2-nitrophenyl octyl ether (NPOE), and 10% w/w Cyanex 471X a 0.1 mmol dm(-3) Hg(II) solution prepared in 0.01 mol dm(-3) HCI was transported to a 0.05 mol dm(-3) NaCl solution at pH 12.3 with permeability values in the feed and strip phases of 0.25 and 0.15 cm min(-1), respectively. A diffusive Fickian-type mechanism was inferred from the results. High separation factors ranging between 2 and 5900, less than 11% of competing metal ions transported, active transport of the metal ion and a successful reuse of the PIM were achieved. CONCLUSION: Optimized PIMs using Cyanex 471 X represent an interesting alternative for Hg(II) removal from waters showing high efficiency factors and easy implementation. (c) 2009 Society of Chemical Industry