The residues after cementation were analyzed by electron probe micro-analysis (EPMA) to research mechanism of cobalt removal. The results show a small amount of cadmium is beneficial in terms of the final cobalt concentration. It is an important consideration in purification circuits that removal cadmium completely prior to cobalt cementation, because cadmium can inhibit basic zinc sulphate to adsorb on the surface of zinc dust. To enhance cobalt, the Zn-Co or Zn-Cd alloys must form. The Zn-Co and the Zn-Cd alloys were found to enhance cobalt removal, whereas Zn-Cu and Cu-Cd alloys had an advarse effect on cobalt removal.