Mixed-ligand chelate extraction of trivalent lanthanides with 4,4,4-trifluoro-1-phenyl-1,3-butanedione and neutral oxo-donors

Mixed-ligand chelate extraction of trivalent lanthanides such as Nd(III), Eu(III) and Lu(III) into benzene with mixtures of 4,4,4-trifluoro-1-phenyl-1,3-butanedione (HBFA) and bis-2-ethylhexyl sulphoxide (B2EHSO) or triphenylphosphine oxide (TPhPO) from thiocyanate solutions was investigated. The results demonstrate that these metal ions are extracted as Ln(BFA) 3 with HBFA alone and in the presence of a neutral oxo-donor, B2EHSO or TPhPO(S), as Ln(BFA) 3·S and Ln(BFA) 3·2S. The equilibrium constants of the above species increase monotonically with decreasing ionic radii of these metals ions. The addition of a neutral donor to the metal chelate system not only enhances the extraction efficiency but also improves the selectivity among these trivalent lanthanides. Hence this mixed-ligand system may be useful for the extraction and separation of individual lanthanides and also for the separation of lanthanides as a group from other metal ions.