An emulsion liquid membrane process using tri-n-octylamine (Alamine 300) to extract and separate cobalt from the acidic leach solutions has been presented. Liquid membrane consists of a diluent, a surfactant (ECA 4360J), and an extractant (Alamine 300, Cognis Corp.). Ammonia solutions have been used as the stripping solution. The important parameters governing the permeation of cobalt and their effect on the separation process have been studied. These parameters are membrane type and composition, stirring speed, feed phase pH, surfactant concentration, extractant concentration, stripping phase concentration, phase ratio, and treatment ratio. The optimum conditions have been determined. It is possible to selectively extract 99% of cobalt from the acidic cobalt-nickel leach solutions at the optimum conditions. The separation factors of cobalt with respect to nickel, based on initial feed concentration, have experimentally found to be of as high as 108 for about equimolar Co-Ni feed solutions. However, non-equimolar feed mixtures, Ni in excess, separation factor for cobalt decreases as the nickel concentration in the feed phase increases.