Liquid-liquid extraction studies of gadolinium with N-methyl-N,N,N-trioctyl ammonium-bis-(2-ethylhexyl) phosphonate - Task specific ionic liquid

Novel task specific ionic liquid, namely, N-methyl-N,N,N-trioctyl ammonium-bis-(2-ethylhexyl) phosphonate (MTOABEHP) was synthesized by metathesis route and, its extraction efficiency in n-dodecane was evaluated for Gd(III) using liquid-liquid extraction technique. Extraction kinetics was found to be fast, quantitative uptake was attained within ten minutes of equilibration. Increase in pH of aqueous feed solution resulted in the increase of uptake of Gd(III) up to pH = 4, afterward the extraction decreased significantly. Stoichiometry of the extracted complex was found to be Gd(NO3)3·3MTOABEHP using log-log plot method. Temperature variation studies have shown that the extraction is enthalpy driven (ΔH0 = −27.5 kJ mol−1), showing very strong interactions between the ionic liquid moiety and Gd(III). FT-IR and 31P NMR studies have shown the participation of phosphoryl oxygen of task specific ionic liquid moiety in bond formation with gadolinium ions. Efficient back-extraction could be achieved with 0.1 M Ethylene diaminetetraacetic acid (EDTA) and deionized (DI) water (pH ∼ 7, ⩾50 °C), thus providing the option of recyclability of the extractant.