Extraction of Alkaline Earth Metal Ions with TODGA in the Presence of Ionic Liquids

Abstract

The extraction of microquantities of Ca(II), Sr(II), and Ba(II) from aqueous solutions into the organic phase containing a diglycolamide ligand N,N,N′,N′- tetraoctyl-3-oxapentane diamide (TODGA) and ionic liquids (ILs) 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C₄mim][Tf₂N]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant and IL concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes and conditional extraction constants of alkaline earth metal ions have been determined. A considerable synergistic effect was observed in the presence of ILs in the organic phase containing diglycolamide ligands. This effect is connected with the hydrophobic nature of the IL anion. The partition of ILs between the equilibrium organic and aqueous phases can govern the extractability of alkaline earth metal ions in TODGA - IL systems.

Keywords:

• Diglycolamide ligands
• ionic liquids
• alkaline earth metal ions
• extraction

ACKNOWLEDGMENTS

We are grateful to T.A. Orlova and A.E. Lezhnev for their assistance in ICP-MS measurements.