Extraction of Several Rare-Earth Metal Ions Using isoBu-BTP/［C₂mim］［NTf₂］ System

Hydrophobic ionic liquids are promising extraction media in solvent extraction separation of metal ions. In current research, the extraction behavior of several rare-earth metals(Y, Nd, Eu, Dy) from nitric acid solution was studied using a novel extracting system based on hydrophobic ionic liquid. The novel extracting system is made up of 2,6-bis(5,6-dibutyl-1,2,4-triazin-3-yl)pyridine(isoBu-BTP), which acted as extractant, can separate lanthanides and minor actinides effectively in nitric acid solution. 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (［C₂mim］［NTf₂］), which acted as extraction medium, shows a great solubility against isoBu-BTP. The influence of the concentration of nitric acid, the concentration of extractant and the stripping condition was investigated in detail. It was found that the isoBu-BTP/［C₂mim］［NTf₂］ extracting system is favorable to extract rare-earth metals at low acidity condition (<0.1 mol/L), and back-extract at high acidity condition (>3 mol/L). In addition, Dy was found to be selectively extracted in current extracting system. The extraction mechanism for the extraction of Dy³⁺ was also discussed. A lg-lg plot of the D(Dy） values versus isoBu-BTP concentration gave a straight line with a slope of 2.4. It is suggested that most Dy from aqueous phase was extracted by BTP, which can form a 3∶1 molar complex with Dy³⁺; while a small quantity of Dy was extracted by ionic liquid itself. The cation exchange and co-extraction, which induced from ionic liquid, functioned to extraction and resulted into such stoichiometry mentioned above.