The solvent extraction of trivalent lanthanoids (without Pin) with mixtures of chelating extractant 1-(2-tlienyl)-4,4,4-trifluoro-1,3-butanedione (thenoyltrifluoroacetone, HTTA) or 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-on (HP) and 1-(2-pyridylazo)-2-naphthol (PAN, S) in C6H6 has been studied. It was found that in the presence of 1-(2-pyridylazo)-2-naphthol the lanthanoids have been extracted as Ln(TTA)(3)S and LnP(3)S. On the basis of the experimental data, the values of the equilibrium constants have been calculated. The addition of PAN to the chelating extractant produces synergistic effect which is larger for the heavier lanthanoids. The separation of the larithanoids with synergistic mixtures was higher than those obtained with HTTA or HP alone. Ill the most cases all enhancement of the metal ions separation was observed upon the change of the chelating extractant HP with HTTA. (c) 2005 Elsevier B.V. All rights reserved.