Extraction equilibrium of uranium(VI) with dicyclohexano-18-crown-6 and its application for separating uranium and thorium

Abstract

The extraction of uranium with dicyclohexano-18-crown-6 (mixed isomers) has been described(1). The extraction equilibrium of uranium(VI) from aqueous hydrochloric acid solution with dicyclohexano-18-crown-6 isomer A (I_a) and isomer B (I_b) in 1,2-dichloroethane is presented in this paper. The extracted species are found to be 1:2 (metal/crown) for I_a and 2:3 for I_b from slope analysis and direct determination of extracted complexes. The extraction equilibrium constants (K_ex) have been determined at 25°C and are equal to 29.5 for the former and 0.208 for the latter. It is concluded that I_a has a stronger coordination ability for uranium than I_b. The different orientation of the lone pairs of the oxygen atoms in both isomers will be taken into account for interpreting the above results. The extraction of uranium(VI) with dicyclohexano-18-crown-6 (mixed isomers) or I_a from aqueous hydrochloric acid solution is effective and selective. In 0.1M crown ether-1,2-dichloroethane- 6N HCl system, the separation factor U(VI)/Th(IV) exceeds 1000. The result can be used for separating uranium and thorium.