EXTRACTION OF TERNARY COMPLEXES OF THORIUM(IV) WITH 3-PHENYL-4-BENZOYL-5-ISOXAZOLONE AND NEUTRAL DONORS FROM NITRIC-ACID MEDIUM

The extraction behaviour of thorium(IV) from aqueous nitric acid emplo ying 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) in the presence of tri-n- octyl phosphine oxide (TOPO) as well as tri-n-butyl phosphate (TBP) in xylene medium was investigated. The extraction constant (log k(ex)) f or the binary organic phase species Th(PBI), was determined to be 8.26 which is by far the largest amongst the corresponding values known fo r other beta-diketones. The overall extraction constant (log K) for th e ternary species Th(PBI)4 . TBP and Th(PBI)(4) . 2TOPO were estimated to be 14.96 and 20.96 respectively. An inverse correlation of the add uct formation constant (log K-s) with the pK(a) of the beta-diketones, 2-thenoyltrifluoroacetone, 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone a nd HPBI, was observed. The steric as well as the electronic effects of adduct formation have been discussed. Analytical application of HPBI for the separation of Th-234 radiotracer from natural uranium (99.3% U -238) has been suggested.