Selective separation of neodymium(III) using dual function DEHPA-menthol deep eutectic solvent

Being a vital component in permanent magnets, the global need for neodymium (Nd) is accelerating, making a recovery of Nd noteworthy due to its scarce resources. This research explored the possibility of using di(2-ethylhexyl)phosphoric acid (DEHPA), a common lanthanide extractant, to prepare a deep eutectic solvent (DES) as an alternative hydrophobic phase to extract Nd(III) from water without additional extractant. Hydrophobic DES obtained from a 1:1 mixture of DEHPA and menthol was used in Nd(III) extraction with NaNO₃ as a salting-out agent. The extraction conditions were studied by varying Nd(III) and NaNO₃ concentrations, solution pH, vortex time, and DES to aqueous phase volume ratio (D:A). An extraction efficiency (%E) of 97.4 ± 0.1 % was obtained using 1 mL DES to extract 10 mL of 10 mM Nd(NO₃)₃ containing 0.5 M NaNO₃ at pH 4 and 2 min vortexing, while a stripping efficiency (%S) of 98.9 ± 0.8 % was acquired using 5 mL of 0.5 M HNO₃. The DES could be used for five cycles without performance loss. Investigation on lanthanide ions from different subgroups showed similar %E but remarkably different %S, leading to a fascinating separation factor for Nd and Dy of 215 using 0.3 M HNO₃. Also, a high purity of Nd(III) (99.6 %) was obtained from the mixture of Nd(III) and Dy(III). This research demonstrates that DEHPA-menthol DES is an attractive solvent that can recover Nd(III) from nitrate medium in a facile, rapid, and economical fashion.