Solvent extraction of lanthanum(III), europium(III) and lutetium(III) by bis(4-acyl-5-hydroxypyrazoles) derivatives

The liquid–liquid extraction of some trivalent rare earths Ln(III) (Ln: La, Eu, Lu), performed from 0.1 M NaNO3 aqueous solutions by two bis(4-acyl-5-hydroxypyrazoles), 1,12-bis(1′-phenyl-3′-methyl-5′-hydroxy-4′-pyrazolyl)-dodecane-1,12-dione (HL-10-LH) and 1,6-bis(1′-phenyl-3′-methyl-5′-hydroxy-4′-pyrazolyl)-hexane-1,6-dione (HL-4-LH), in chloroform, has been studied. The processes of extraction have been determined by the slope analysis method and by analyzing a function that allows the simultaneous treatment of all the experimental points obtained in different conditions. With HL-10-LH, the stoichiometries of the extracted species differ for the three lanthanides. The ligands are biscoordinated and tetracoordinated in the extracted complexes of lanthanum and europium, La2(L-10-L)2(L-10-LH)2 and Eun(L-10-L)n(L-10-LH)n (n = 1,2). They are exclusively biscoordinated in the complex of lutetium, Lu(L-10-LH)3. The complex of europium extracted by HL-4-LH at weak extraction yields, Eu(L-4-L)(L-4-LH), and the corresponding extraction constant are comparable to the ones obtained for HL-10-LH, whereas polynuclear species are extracted at high extraction yields. The extraction efficiency with HL-10-LH increases with the ascending atomic number of Ln (La < Eu < Lu). A comparison between HL-10-LH and HPMBP (1-phenyl-3-methyl-4-benzoyl-5-hydroxy-pyrazole) for the same concentration of complexation sites shows that the extraction by HL-10-LH is more effective. Moreover, a better selectivity of extraction was obtained with HL-10-LH.