The properties of six newly synthesized reagents for extraction of metal ions [Co(II), Ni(II) and Mn(II)] in chloride media were investigated, and the results with the standard extractants such as Cyanex 272, Cyanex 301, Ionquest 801 (DE2HPA) were compared. From these experimental results, a physicochemical model was developed to calculate the extraction curves of Co(II), Ni(II) and Mn(II). This model describes perfectly the extraction curves providing that extraction of M 2+ and MCl + (M=Co 2+ , Ni 2+ or Mn 2+) as well as saponification and aggregation of extractants (dimer and trimer formation) were taken into account. Extraction constants of M 2+ and MCl + as well as speciation diagrams in the extraction solvent as a function of pH were deduced from this model.