Extraction ability of ionic liquids for Cu(II) and Ni(II)

The extraction ability of hydrophobic ionic liquids such as [Bmim]PF₆, [Hmim]PF₆ and [Omim]PF₆ for Cu(II) and Ni(II)was studied to explore the green technique on the treatment of waste water containing heavy metal ions, and extraction effect of hydrophobic ionic liquids was compared with that of n-butanol for Cu(II) and Ni(II). The results indicate that the extraction efficiencies of both Cu(II) and Ni(II) are very low without chelator. However, the extraction efficiencies are greatly enhanced respectively from 2.31% and 2.18% to 99.89% and 98.64% for Cu(II) and Ni(II) with chelator. The longer of the ionic liquids' carbon bond, the worse for the extraction. Similar to traditional solvent such as n-butanol, ionic liquids have great pH swing effect in extracting heavy metals. When pH<2, the extraction efficiencies for Cu(II) and Ni(II)are almost zero, while for pH>6, the extraction efficiencies are above 90%. The pH swing effect is used to strip the heavy metal ions such as Ni(II) from ionic liquids and recovery and reuse of ionic liquids are realized.