Ion-pair extraction of cadmium complex anions from hydrochloric acid media using oxonium ion-dicyclohexyl-18-crown-6 complex

Solvent extraction of cadmium from aqueous hydrochloric acid media (1-11 mol dm−3) into dichloromethane solution of 18-crown-6, dibenzo-18-crown-6 and dicyclohexyl-18-crown-6 (DC18C6) has been studied at 25 °C. The highest extraction abilities have been found by DC18C6 in the range of 6-7 mol dm−3 hydrochloric acid. The conventional log-log plot analysis of the extraction equilibrium data at 3 and 8 mol dm−3 of the acid revealed that the cadmium ions were extracted as ion-pairs [HL+][CdCl3−] and [HL+]2[CdCl42−] (L = DC18C6), respectively. The effect of diluent has been investigated using chloroform, dichloromethane, 1,2-dichloroethane, carbon tetrachloride and toluene. The extraction of the cadmium increased with diluent polarity. The ability of DC18C6 to separate cadmium from binary mixtures of Cd and M (M = Ni, Mn, Co, Zn, Pb and Fe) has been evaluated. The efficiency and selectivity of the method allow to propose it for the recovery of cadmium from consumed Ni-Cd rechargeable batteries.