Ionic liquid extraction of metal ions by 2-aminothiophenol in 1-butyl-3-methylimidazolium hexafluorophosphate

Abstract

The ionic liquid namely 1-butyl-3-methylimidazolium hexafluorophosphate was synthesized and characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The optimum conditions for the extraction of Ni[superscript 2+], Cu[superscript 2+], and Pb[superscript 2+], in water by liquid-liquid extraction method was investigated using the synthetic ionic liquid combined with 2-aminothiophenol ligand. The results showed that the optimum pH for the extraction of Ni[superscript 2+], and Pb[superscript 2+], were 4-6 and 5, respectively. The percentage extractions of Ni[superscript 2+], Cu[superscript 2+] and Pb[superscript 2+] were about 100, 100, and 80% when using 5 mg L[superscript -1] of metal solution and 56, 76, and 20%, when using 1.0 mM of metal solution, respectively. The extraction of Cu[superscript 2+] is independent of the pH of solution. The extraction equilibria of Ni[superscript 2+], Cu[superscript 2+] and Pb[superscript 2+] were reached within 120, 30 and 30 min. The existence of sodium, calcium, magnesium, sulphate and chloride ions did not significantly affect the extraction efficiency of all metal ions. The stoichiometries of complexes between Ni[superscript 2+], Cu[superscript 2+] and Pb[superscript 2+] and the ligand are 1:3, 1:2 and 1:2, respectively. The extracted Ni[superscript 2+] in ionic liquid phase could be back-transferred into 3% H[subscript 2]O[subscript 2] in 0.5 M HNO[subscript 3] at 20 min of contact time and the extracted Cu[superscript 2+] and Pb[superscript 2+] could be stripped with 1 M HNO[subscript 3] at the contact time of 20 min and 10 min, respectively, with the percentage stripping higher than 95 %. The extraction efficiency of all metal ions with the ligand in the ionic liquid was higher than that obtained in chloroform at the same conditions. The association constants of complexes between Ni[superscript 2+] and Pb[superscript 2+] and the ligand in ionic liquid are 5.47x10[superscript 7] and 51.1, respectively.