The extraction of cobalt by Winsor II microemulsion system was studied. In the bis (2-ethylhexyl) sulfosuccinate sodium salt
(AOT)/n-pentanol/n-heptane/NaCl system, AOT was used as a anionic surfactant to form microemulsion in n-heptane, n-pentanol was injected in the microemulsion as a cosurfactant. Co(II) was found to be extracted into the microemulsion phase
due to ion pair formation such as Co2+(R–SO3−)Cl. The influence of different parameters such as the volume ratio of aqueous phase to microemulsion, surfactant concentration,
pH of the feed solutions, cosurfactant concentration as well as temperature on the extraction yield (E%) were investigated. The results showed that it was possible to extract 95% of cobalt by the AOT Winsor II microemulsion.