Competitive transport experiments involving nickel(II), cobalt(II), zinc(II), cadmium(II), silver(I), chromium(III) and lead(II) metal cations from an aqueous source phase through an organic membrane into an aqueous receiving phase have been carried out using 15-crown-5 and 1,4,8,11-tetraazacyclotetradecane (cyclam) as ionophores present in organic membrane phase. The organic membrane phases include: dichloromethane (DCM), 1,2-dichloroethane (1,2-DCE), nitrobenzene (NB) and chloroform (CHCl3) and also chloroform-dichloromethane (CHCl3-DCM) ,chloroform-nitrobenzene (CHCl3-NB) and dichloromethane-nitrobenzene (DCM-NB) binary mixed solvent solutions. The obtained results show that the selectivity and the efficiency of transport for the heavy metal cations change with the nature of the ligand and also the organic solvents, which were used as liquid membrane in these experiments. 15- crown-5 was a highly selective ionophore for Ag+cation in NB and DCM membrane systems, but the highest transport efficiency for this cation was obtained in NB. But, no transport was observed for these metal cations by cyclam in all used solvents. The sequence of selectivity for silver (I) ion in organic solvents was found to be: NB >DCM > CHCl3> 1,2-DCE. The transport of Ag+ ion in DCM-NB, CHCl3–NB and CHCl3-DCM binary solvents is sensitive to the solvent composition. A non-linear relationship was observed between the transport rate of silver (I) ion and the composition of these binary mixed solvents. The amount of Ag+ transported follows the trend: DCM-NB> CHCl3-NB > CHCl3-DCM in the bulk liquid membrane studies. The influence of the stearic, palmetic and oleic acids as surfactant in the membrane phase on the ion transport was also investigated.

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