The complexation properties of a pyrazolone derivative, 3-methyl-1-phenyl-4-(4-trifluoromethylbenzoyl)-pyrazol-5-one (HL), in chloroform were examined and it was found that it possesses improved complexation ability in comparison with 4-benzoyl, 4-(4-methylbenzoyl) and 4-(4-fluorobenzoyl) derivatives. Mixed ligand chelate extractions of trivalent lanthanoids (La, Nd, Eu, Ho and Lu) with HL and 5,11,17,23-tetra-tert-butyl-25,26,27-tris(dimethylphosphinoylpropoxy)-28-hydroxy-calix[4]arene (S1) or 5,11,17,23-tetra-tert-butyl-25,27-bis(dimethylphosphinoylpropoxy)-26,28-dihydroxy-calix[4]arene (S2) as synergistic agents were also carried out in chloride medium at constant ionic strength μ = 0.1 and CHCl₃ as organic phase. The interactions between the extractants in deuterochloroform were studied by ¹H, ¹³C, and ³¹P NMR. The composition of the extracted species was established as LnL₃·HL (L⁻ represents HL anion) with HL as a single extractant, and as LnL₃·S in the presence of the phosphorus-containing calix[4]arene. On the basis of the experimental data, the values of the equilibrium constants were calculated. The influence of the number of PO groups of tert-butyl-calix[4]arene on the extraction process was discussed. The synergistic enhancement and separation factors between metals were evaluated. Finally, the extraction of La(III) and Eu(III) ions was performed by using an ionic liquid, 1-butyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide, as a solvent and varying the type of ligands. By comparison to CHCl₃, the ionic liquid offers increased distribution ratios, at the expense of a levelling off of the separation factors. Reasons for such a phenomenon are discussed.