In this work, a hydrometallurgical process based on leaching is applied to recover cobalt and lithium from spent lithium ion batteries (LIBs). Citric acid and hydrogen peroxide are introduced as leaching reagents and the leaching of cobalt and lithium with a solution containing C8H8O7 center dot H2O is investigated. When both C6H(8)O(7)center dot H2O and H2O2 are used an effective recovery of Li and Co as their respective citrates is possible. The leachate is characterized by scanning electron micrography (SEM) and X-ray diffraction (XRD). The proposed procedure includes the mechanical separation of metal-containing particles and a chemical leaching process. Conditions for achieving a recovery of more than 90% Co and nearly 100% Li are achieved experimentally by varying the concentrations of leachant, time and temperature of the reaction as well as the starting solid-to-liquid ratio. Leaching with 1.25 M citric acid, 1.0 vol.% hydrogen peroxide and a S:L of 20 g L-1 with agitation at 300 rpm in a batch extractor results in a highly efficient recovery of the metals within 30 min of the processing time at 90 degrees C. This hydrometallurgical process is found to be simple, environmentally friendly and adequate for the recovery of valuable metals from spent LlBs. (C) 2009 Elsevier B.V. All rights reserved.