Extracting Cu(II) from aqueous solutions with hydrophobic room-temperature ionic liquid in the presence of a pyridine-based ionophore to attempt Cu recovery: A laboratory study

Extraction of Cu(II) from neutral aqueous solutions with the hydrophobic room-temperature ionic liquid (IL) N-butyl-N-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide (BMP-TFSI) in the presence of the pyridine-based ionophore N1,N1,N4,N4-tetrakis(2-(pyridin-2-yl)ethyl)butane-1,4-diamine (C4N2Py4) is demonstrated in this study. Although the distribution coefficients, DM, of Cu(II) extraction depend on the concentration of Cu(II) in aqueous solutions, all values were higher than 200, indicating extremely high extraction efficiency. Based on spectrophotometric, electrochemical, and X-ray crystallography studies, the coordination number of the C4N2Py4-coordinated Cu(II) ions was determined as 2. The voltammetric behavior of Cu(I), Cu(II), and their C4N2Py4 complex ions were also studied. The recovery of Cu from the IL was conducted by washing the IL phase containing the extracted Cu(II) complex with an acidic aqueous phase or by controlled-potential electrolysis. The IL containing C4N2Py4 was employed for two complete rounds and a decrease in extraction efficiency was only observed when higher concentration of Cu(II) was used.