We report in this paper the solvent extraction separation of cobalt and nickel from synthetic sulphate solutions using TOPS 99 and TIBPS mixtures diluted in kerosene. The feed contains 1.061 g/L Co and 1.187 g/L Ni. Extraction experiments with synergistic mixture of extractants showed highest separation factor of 12,245 with 0.1 M TOPS 99 and 0.05 M TIBPS at pH 1.1. McCabe-Thiele plot for Co extraction with 0.1 M TOPS 99 and 0.05 M TIBPS extractants mixture indicated the necessity of three theoretical stages for >99% Co extraction at an aqueous to organic phase (A/O) ratio of 2. A three stage counter current extraction simulation test conducted at pH 1.1 with 0.1 M TOPS 99 and 0.05 M TIBPS mixture, confirmed Co extraction of 99.5% with Ni co-extraction of 0.02%. The results demonstrated that the addition of TIBPS-TOPS 99 acts as a synergist for Co extraction and antagonist for Ni. (C) 2009 Elsevier Ltd. All rights reserved.