On the use of imidazolium and ammonium-based ionic liquids as green solvents for the selective recovery of Zn(II), Cd(II), Cu(II) and Fe(III) from hydrochloride aqueous solutions

This work analysed the extraction of Zn(II), Cd(II), Cu(II) and Fe(III) from hydrochloride aqueous solutions using imidazolium and ammonium-based ionic liquids as sole extraction agents. The selective separation of the different species is desired for potential valorization of aqueous effluents in which these ions are involved, for example, in zinc refineries. The influence of parameters affecting the extraction of the target metal ions, such as the ionic liquid composition, metal ion concentrations and hydrochloric acid concentration in the aqueous phase was analysed. It was found that the ionic liquid methyltrioctylammonium chloride [MTOA(+)][Cl-] allowed almost the complete removal of Zn(II), Cd(II) and Fe(III) from the aqueous solutions while the use of 1-methyl-3-octylimidazolium tetrafluoroborate [omim(+)][BF4-] allowed the selective separation of Zn(II) and Cd(II) over Fe(III) and Cu(II). An increase in metal ion concentration decreases the extraction percentage of the assayed metal ions. The initial HCl concentration has also an important effect on the efficiency of the extraction process, founding that an increase in HCl concentration involves a significant increase in the extraction percentages for Zn(II), Cd(II) and Fe(III). This work demonstrates the exciting potential of ionic liquids for use as green extraction agents in liquid/liquid extraction of heavy metal ions. (C) 2012 Elsevier B.V. All rights reserved.