The application of membrane extraction in the separation of zinc and cadmium ions

The study involved the transport of cadmium(II) and zinc(II) ions from acidic aqueous solutions using alkyl imidazole derivatives as ion carriers. The polymer inclusion membranes consisted of cellulose triacetate as a support, o-nitrophenyl pentyl ether as a plasticizer, 1-decyl-2-methylimidazole (1), 1-decyl-4-methylimidazole (2) or 1-decyl-2,4-dimethylimidazole (3) as ion carriers were used. The membranes were characterized by means of atomic force microscopy. The initial fluxes were much higher for Zn(II) than for Cd(II) for all investigated carriers. Their values depended on the carrier used and increased in the following order: 2 < 1 < 3 for both transported metal ions. An increase in the carrier concentration in the membrane increased the zinc separation. The highest separation coefficient Zn(II)/Cd(II) (24.7) was obtained using 3 as a carrier. The highest recovery coefficient values were obtained for Zn(II) (87%, 83% and 94% for carriers 1, 2 and 3, respectively). The values of the recovery factor for Cd(II) ions decreased in the following order: 1 > 2 > 3.