Extraction of mid-heavy rare earth metal ions from sulphuric acid media by ionic liquid [A336][P507]

• Mid-heavy REs(III) in a simulated ion-adsorbed type rare-earth ore can be effectively recovered by [A336][P507].
• Results show extraction as ion-associates.
• The extractant [A336][P507] was stable after several cycles.
• The stripping efficiency of REs reached nearly 100% at 0.15 mol/L H2SO4.

In the present study, bifunctional ionic liquid extractant (bif-ILE) [A336][P507] was used in the extraction of mid-heavy rare earths metals (REs) from H2SO4 media. The investigation showed that the distribution ratios (D) of REs enhanced with the increase in equilibrium pH, extractant concentration, and the temperature, but decreased with the increase in the concentration of Na2SO4. A possible extraction stoichiometry was obtained. The thermodynamic functions ΔGo, ΔSo and ΔHo were calculated according to Van't Hoff equation. The results from the comparative test showed that the acidity range was different for [A336][P507], Cyanex 923 (mixture of four trialkylphosphine oxides), tributyl phosphate (TBP) and di-(1-methylheptyl)methyl phosphate (P350). The ionic liquid (IL) [A336][P507] had high extractability from solutions of pH 3.5–5.5. This extraction system was used to extract mid-heavy REs in a simulated leach liquor of ion-adsorbed type rare-earth ore. Moreover, there were enhanced effects for REs extraction when NaCl or NaNO3 was added as a salting-out agent of the simulated leach liquor.