The selective separation of cobalt from acidic media, containing both equimolar and nonequimolar mixtures of cobalt and nickel. was examined by supported liquid membranes using Alamine 336 as mobile carrier dissolved in various diluents. The membrane support was microporous hydrophobic polypropylene Celgard 2500 (25 mu m thick, 0.209 x 0.054 mu m pore size and 55% porosity). Acetic acid-Na acetate buffer was used for the adjustment of the feed pH which was critical. Various parameters were experimentally studied and the optimum conditions were determined. (C) 2009 Elsevier B.V. All rights reserved.