BACKGROUND: Supported liquid membranes (SLM) are an alternative technique to remove and recover metals from diluted process solutions and waste-water. In the present work, the removal of Co(II) from a synthetic CoSO4 solution containing initial amounts of cobalt(II) in the range 100-200 ppm (0.1-0.2 g dm(-3)) has been studied on a pilot scale. By performing batch equilibrium experiments, the optimal settings, i.e. the composition of the organic phase, the pH of the feed, the type and concentration of the stripping agent were determined. RESULTS: It is shown that the equilibrium characteristics of a synergistic extractant mixture containing di-2-ethylhexylphosphoric acid (D2EHPA) and 5-dodecylsalicylaidoxime (LIX 860-1) are superior to D2EHPA. Both hydrochloric acid and sulfuric acid have been evaluated as stripping solutions in liquid-liquid extraction tests and as the receiving phase in a SLM configuration. Although equilibrium tests showed no difference in stripping characteristics between both chemicals, it was observed that in a SLM configuration the stability of the system when hydrochloric acid is used is poor. With a commercially available SLM module (Liqui-Cel Extra-Flow 4 x 28) having a surface area of 19 m 2, a steady Co(II) flux of 0.140 gm(-2)h(-1) has been obtained at influent concentrations of cobalt between 100 and 200 ppm with 3 mol dm(-3) sulfuric acid as stripping phase. CONCLUSIONS: The results obtained show that a supported liquid membrane containing a synergistic mixture of LIX 860-1 and D2EHPA gives the possibility of recovering cobalt from dilute solutions. (C) 2008 Society of Chemical Industry