The present work describes the mechanism of active transport of copper(II) through an immobilized liquid membrane (ILM) containing LIX 54 (beta-diketone) dissolved in Iberfluid as mobile carrier. An uphill transport model has been described and equations have been derived taking into account aqueous boundary layer diffusion and liquid membrane diffusion as simultaneous controlling factors. In the present model, various cases were discussed using the carrier LIX 54 and different chemical species; the diffusional membrane resistance for lower and higher concentrations of extractant was evaluated. The diffusion coefficients were observed to decrease with increase in the extractant concentration, ranging from 4.1 x 10(-3) to 1.65 x 10(-2) mol dm(-3) Plotting [Cu](0)-[Cu](t) vs time resulted in a slope of [HR](0)A/2 Delta(org)V taking into account the complex species, CuR2, in the membrane. The mass transfer coefficient (Delta(org)(-1)), the diffusion coefficient of the metal carrier species (D-org) and the thickness of the aqueous boundary layer were calculated from the proposed model for LIX 54. More than 90% of the Cu(II) could be separated using LIX 54 in the presence of various metals such as Ni, Co(II) and Zn.