Talanta 51 (2000) 523 – 530 www.elsevier.com/locate/talanta
The synergistic extraction of thorium(IV) and uranium(VI) with mixtures of 3-phenyl-4-benzoyl-5-isoxazolone and crown ethers S.K. Sahu a, V. Chakravortty a, M.L.P. Reddy b,*, T.R. Ramamohan b a
Department of Chemistry, Utkal Uni6ersity, Bhubaneswar 751 004, India b Regional Research Laboratory (CSIR), Tri6andrum 695 019, India
Received 4 August 1999; received in revised form 30 September 1999; accepted 13 October 1999
Abstract The extraction of thorium(IV) and uranium(VI) from nitric acid solutions has been studied using mixtures of 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and dicyclohexano-18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6 or benzo-15-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 equilibrium constants of the above species have been deduced by non-linear regression analysis. The addition of a CE to the metal chelate system enhances the extraction efficiency and also improves the selectivities between thorium and uranium. IR spectral data of the extracted complexes were used to further 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 DB18C6, steric effects become more important. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Synergistic extraction; Uranium(VI); Thorium(IV); 4-Acyl isoxazolone; Crown ether; Separation factors
1. Introduction The use of tri-n-butylphosphate on a commercial scale for the extraction of uranium(VI) from its ores is well known [1]. However, the selectivity of uranium over thorium is low [2]. Thus it has been a formidable challenge for the separation chemists to develop new extraction systems for the separation of actinides in fewer stages of * Corresponding author. Fax: +91-471-490186. E-mail address: reddy@csrrltrd.ren.nic.in (M.L.P. Reddy)
extraction. Montavon et al. [3] have reported a separation factor of 1000 between thorium(IV) and uranium(VI) with tetracarboxymethyl-p-tertbutyl Calix[4]arene. Synergistic extraction systems have also been applied to these elements and large increases in the extraction efficiency have been reported [4]. The extraction of thorium(IV) and uranium(VI) from nitric acid solution into ligroine solutions of 2-ethylhexyl phenylphosphonic acid, micellar dinonyl naphthalene sulphonic acid and a mixture of the two has been investigated by Otu [5] and reported a synergistic en-
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