Separation of cobalt, nickel and copper with task-specific amido functionalized glycine-betaine-based ionic liquids

Abstract

Task Specific Ionic Liquids (TSILs) were generated by association between a cationic amido functionalized analogues of glycine-betaine (AGB) and coordinating anions such as dicyanamide (Dca−), 4-chlorosalicylate (ClSal−), saccharinate (Sac−) and weak coordinating one such as bis(trifluorosulfonyl)imide (Tf2N−). Extraction of Cu(II), Ni(II), Co(II), from pure water and salt media was performed with these AGB-ILs at room temperature. The obtained results show that in pure water Clsal based AGB-ILs have a high extraction efficiency towards these metals, whereas dicyanamide based AGB-ILs may extract efficiently Cu(II). In some cases, extraction can be improved by using simple chaotropic salts or intermediate anion such as NO3− or Cl−. Co(II) may be quantitatively extracted by Dca based AGB-ILs in NaCl 4 mol L−1. The rational use of background salts can improve the selectivity of the extraction process and allow the separation and the recovery of the three metals separately from a mixture containing two or three divalent metals. The metal could be back-extracted from the ionic liquid phase with aqueous solution of Na2SO4, limiting the release of ionic liquid cation in aqueous media, thus preserving its integrity. The metal extractability by the Dca based ionic liquids after the stripping is quasi-equivalent to that of the fresh AGB-IL showing that it can be reused for three or four extraction and stripping cycles. A regeneration of Dca based ionic liquids after several extraction cycles is made possible by adding a solution of NaDca which restore their extractive capacity.