The zinc plant purification cake (CINKUR Co., Turkiye) was leached with hydrochloric acid and main acidic leach solution containing Zn(II), Fe(II), Pb(II), AI(III), CU(II), CO(II) and Ni(II) ions was obtained. Except for cadmium, cobalt and nickel, the other metals were precipitated by adding various reagents and adjusting the pH of solution. After this separation process, cadmium was also separated by emulsion liquid membrane (ELM) process. The present investigation deals with carrier-facilitated membrane transport of cobalt from this acidic leach solution containing cobalt and nickel by ELM using as organic reagent 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, PC-88A. The study has highlighted the importance and influence of membrane composition for maximizing the extraction of cobalt. The ELM consists of PC-88A as an extractant, commercial kerosene as a diluent, ECA 4360J as a surfactant and 0.5 M hydrochloric acid solution as a stripping solution. The important factors studied which affect the ELM stability and extraction of cobalt are pH of the acidic leach solution, mixing speed, type and concentration of the stripping solution, extractant and surfactant concentrations, phase ratio and treatment ratio. The parameters mentioned were investigated and optimum conditions were determined. The results showed that it is possible to extract 99% of cobalt by using ELM from the acidic leach solutions, containing Zn(II), Fe(II), Pb(II), AI(III), Cu(II), Co(II) and Ni(II) ions, at the optimum operating conditions. (C) 2008 Elsevier B.V. All rights reserved.