The synergistic extraction of thorium(IV) and uranium(VI) with mixtures of3-phenyl-4-benzoyl-5-isoxazolone and crown ethers

The extraction of thorium(IV) and uranium(VI) from nitric acid solutions ha s been studied using mixtures of 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) an d dicyclohexano-18-crown-6, benzo-18-crown-6. dibenzo-18-crown-6 or benzo-1 5-crown-5. The results demonstrate that these metal ions are extracted into chloroform as Th(PBI)(4) and UO2(PBI)(2) with HPBI alone and as Th(PBI)(4) . CE and UO2(PBI)(2). CE in the presence of crown ethers (CE). The equilibr ium constants of the above species have been deduced by non-linear regressi on analysis. The addition of a CE to the metal chelate system enhances the extraction efficiency and also improves the selectivities between thorium a nd uranium. IR spectral data of the extracted complexes were used to furthe r clarify the nature of the complexes. The binding to the CEs by Th(PBI)(4) and UO2(PBI)(2) follows the CE basicity sequence but with DC18C6 and DB18C 6, steric effects become more important. (C) 2000 Elsevier Science B.V. All rights reserved.