Effect of an acidic chelating agent in the synergic extraction systems of rare earth(III)β-diketones-2,2′-bipyridine

Abstract

The extraction of rare earth elements (RE), La(m), Sm(III), Tb(III), Tm(III) and Lu(III), with four β-diketoncs (HA), hexafluoroacetylacetone (Hhfa), pivaloyltrifluoroacetone (Hpta), benzoyl- acetone (Hba) and acetylacetone (Hacac), in the presence or absence of 2,2′-bipyridine (bpy) in benzene was studied. The extraction constants ( K ex) for RE(III) with Hhfa, Hpta and Hacac were determined and compared with each other. The order of K ex is Hacac < Hpta < Hhfa. The synergic enhancement observed in the presence of bpy is attributed to the 1:1 adduct formation such as RE(A) 3bpy, except for the La(III)-Hhfa system, in which La- (hfa) 3(bpy) 2 was also observed. The adduct formation constant, β s,1, tor the β-diketones was in the order of Hacac < Hba < Hpta < Hhfa, which is in the same order as their acid dissociation constants. The trend of β s,1 with the atomic number of RE is obviously different with different β-diketones; the β s,1 for Hacac and Hba tends to decrease with increasing atomic numbers of RE, but those for Hpta and Hhfa increase.