Selective heavy rare earth element extraction from dilute solutions using ultrasonically synthesized Cyanex 572 oil droplets and Cyanex 572-impregnated resin

[Display omitted] •Ultrasonically synthesized Cyanex 572 oil droplets introduce a high surface area.•Surfactant showed a significant impact on ζ-potential and droplet size distribution.•Surfactant markedly changed REE removal trend due to the electrostatic interaction.•FTIR showed that the cation-exchange mechanism is involved in removing REE ions.•EM showed very fast selective HREE extraction compared to that of CIR and SX. The extraction of heavy rare earth elements (HREE) from a dilute leach solution using current routes poses crucial challenges including solvent loss, high solvent consumption, and phase disengagement difficulties for rare earth industry. This study proposes the selective extraction of HREE from dilute solutions using the ultrasonically-generated Cyanex 572 oil droplets (UGCOD) and Cyanex 572-impregnated resin (CIR). Oil/water (O/W) emulsion (EM) is a colloidal suspension, which is composed of micron and sub-micron sized oil droplets introducing a very high interfacial surface area in the aqueous solution. Sodium dodecyl sulfate (SDS) and hexadecyl trimethyl ammonium bromide (HTAB)-coated Cyanex 572 oil droplets were synthesized to investigate the impact of surfactant dosage on the zeta potential of EM, droplet size distribution, and extent of selective HREE extraction. Fourier transform infrared (FTIR) results clearly showed that the cation-exchange mechanism is involved in rare earth elements (REE) ions extraction by Cyanex 572 oil droplets. However, the addition of cationic and anionic surfactants markedly changed the REE extraction trend, which was due to the electrostatic interaction between REE ions and the outer charged layer formed at the surface of droplets. EM showed very fast HREE extraction compared to that of CIR and solvent extraction (SX).