Separation of the main metals contained in spent Li-ion batteries has been investigated using a treatment route consisting of the following steps: manual dismantling, acid leaching, precipitation with NH4OH and liquid-liquid extraction using Cyanex 272 [bis(2,4,4-trimethylpentyl) phosphinic acid] as the extractant agent. Aluminium, cobalt, lead and lithium were the main metal species identified in the residue. Lead was found solely in the anode of the battery, so this metal can be separated manually from the other metal species, which were found to predominate in the cathode. The following operational variables were investigated in the acid leaching step: temperature, solid/liquid ratio, H2SO4 concentration and H2O2 concentration which was used as the oxidizing agent. Around 55% of aluminium, 80% of cobalt and 95% of lithium were leached from the cathode when leaching solutions with 11,02 Were carried out. In the precipitation step, NH4OH was added to the leach liquor to raise the pH and aluminium was partially separated from cobalt and lithium at pH 5. After filtration, the aqueous solution was submitted to a purification step by liquid-liquid extraction with Cyanex 272 and around 85% of cobalt was separated. (C) 2007 Elsevier B.V. All rights reserved.