Efficient selective leaching of ytterbium and lutetium oxides by new hydrophobic deep eutectic solvents

This research reports the first study of selective leaching of ytterbium-lutetium oxides mixture with hydrophobic deep eutectic solvents (DESs), and high-efficiency and simple-prepared were used to separate and beneficiate lutetium. With hydrophobic DESs, which were formed with hydrophobic salicylic acid (SA) or 3,5-dinitrosalicylic acid (DNS) as the hydrogen bond donor (HBD) and hydrophobic tri-n-octyl phosphine oxide (TOPO) as the hydrogen bond acceptor (HBA), powdered eutectic mixtures of ytterbium-lutetium oxides were leached. The separation factor of ytterbium-lutetium was concluded to reached 2.11 with a solid-liquid (S/L) ratio of 1/50 g/ml, a temperature of 90℃ and a 4 h leaching time, and the experimental conditions, such as the S/L ratio, temperature and reaction time, were explored. The formation of intermolecular hydrogen bonds between the HBD and HBA was revealed through multiple methods, such as IR (disappearance of OH characteristic peaks), 1H NMR (formation of sharp peaks not present for intramolecular hydrogen bonds) and 31P NMR (shift of P = O peaks to higher fields). The lattice energies of the intermolecular hydrogen bonds and the solid oxide lattice energies, which were calculated with Gaussian 16 software (0.87 eV for SA/TOPO = 1:1 and 0.94 eV for DNA/TOPO = 1:1) and the Born–Haber cycle (12957.56 kJ/Mol for Yb2O3 and 12993.59 kJ/Mol for Lu2O3), provided a theoretical illustration of preferential Yb/Lu dissolution leading to separation. The stripping, regeneration and recycling capabilities of the DESs were investigated with stripping and recirculation experiments. Based on these results, the new DES as the leaching agent to separation of ytterbium lutetium oxide is identified as a new efficient mothed with industrialization potential.