Extraction Of Uranyl Ion With 3-Phenyl-4-Acetyl 5-Isoxazolone And Neutral Donors From Dilute Nitric Acid Medium

摘要

The extraction behaviour of Uranium (VI) from dilute nitric acid medium was investigated employing 3-phenyl-4-acetyl-5-isoxazolone (HPAI) as the chelating ligand and several amides with varying degrees of branching such as di-2-ethylhexylacetamide (D2EHAA), di-2-ethylhexylpropanamide (D2EHPrA), di-2-ethylhexylisobutylamide (D2EHiBA) and di-2-ethylhexylpivalamide (D2EHPvA) as neutral donors in toluene medium. The two-phase extraction constant (log k_(ex)) for the binary species UO_2(PBI)_2·H_2O was found to be 0.70. The log k_(ex) follows an inverse correlation with the pKa value when compared with several other p-diketones investigated earlier in our laboratory. The overall equilibrium constant (log K) for the ternary species of the type UO_2(PAI)_2·S are estimated to be 5.29 (D2EHAA), 5.02 (D2EHPrA), 4.86 (D2EHiBA) and 4.28 (D2EHPvA) respectively which vary linearly with the basicity of the amides. Steric factors play a dominant role in the co-ordination of the amides to the Uranyl β-diketones where the carbonyl group is a part of the heterocyclic ring. Finally, thermodynamic studies have indicated enthalpy stabilized and entropy destabilized extraction for the ternary system while an opposite effect is observed for the binary extraction system. The synergistic systems are promising with respect to quantitative extraction from acidic solution (> 1M HNO_3) and are distinctly better than commercially available β-diketones like TTA and PMBP.