Selective Extraction of Metals from Chloride Solutions with the Tetraoctylphosphonium Oleate Ionic Liquid

The solvent extraction behavior of a series of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, In3+, La3+, Nd3+, Sm3+, Dy3+, Er3+, Yb3+) from an aqueous chloride feed solution by the nonfluorinated fatty acid-based ionic liquid (IL) tetraoctylphosphonium oleate [P8888][oleate] has been investigated as a function of the pH. The possibility to extract metal chlorides from an aqueous stream via the anion or cation of the hydrophobic, low-viscous water-saturated [P8888][oleate] IL has been exploited. [P8888][oleate] can be considered as a bifunctional or binary IL. At high pH values (pH > 5), all metals are extracted via the oleate anion, whereas some transition metals are extracted at high HCl concentrations and thus low pH values as anionic chloro complexes in combination with [P8888] cations. A difference of one pH unit is observed between the extraction curves (%E as a function of the pH) of the transition metals and those of the rare earth metals. Rare earths are not extracted a...