Aliquat IL336 vs. Cyphos IL101 extractants for the solvent extraction of heavy metals from zinc plants residues.

Hydrometallurgical zinc production generates residues containing valuable but environmentally hazardous metals like cadmium, zinc, cobalt and nickel. This study compares two ionic liquid extractants, Aliquat IL336 and Cyphos IL101, for the recovery of cadmium, zinc, cobalt and nickel from chloride solutions. Dichloromethane was used as the diluent. The metals are extracted via an anion-exchange mechanism as ion-pairs of the form [R⁺]2[MCl2]2- (M = Cd or Zn), where R⁺ is the cation of the ionic liquid extractant. Both extractants showed high selectivity and efficiency for Cd(II) and Zn(II) over Co(II) and Ni(II), which was attributed to the greater stability of their chloro-complexes. Using HCl as the chloride source yielded higher extraction percentages for Cd(II) and Zn(II) with respect to NaCl. The difference was explained by the hydration energies of H⁺ and Na⁺. Efficient back-extraction was achieved using sodium hydroxide for cadmium and ammonia for zinc. Different behavior was observed for the temperature dependency of cadmium and zinc ions by the studied extractants. The results demonstrate the potential of these methods for the separation and recovery of metals from industrial residues.