Facilitated transport of uranium(VI) across a bulk liquid membrane containing thenoyltrifluoroacetone in the presence of crown ethers as synergistic agents

摘要

A study has been made on carrier-mediated transport of uranium(VI) using a bulk liquid membrane prepared by dissolving equimolar amounts of thenoyltrifluoroacetone (HTTA) and dicyclohexyl-18-crown-6 (DC18C6), as a synergistic agent, in chloroform. The source phase comprised of a solution of UO_2~(2+) in water at pH 2.0, and a solution of 0.2 M hydrochloric acid and 4.0 × 10~(-3) M sodium dodecylsulfate (SDS) served as the receiving phase. While in the presence of 0.02 M HTTA in the membrane phase only 19% of uranyl ion could be transported into the receiving phase, after several hours, the addition of 0.02 M DC18C6, as a suitable synergistic agent, into the membrane phase resulted in the quantitative transport of uranyl ion in 9 h. Various factors influencing the transport process such as the pH of source and receiving phases, the types and concentration of surfactant and carriers concentrations were optimized. The transport efficiency of uranyl ion using different crown ethers followed the order: DC18C6 >DB18C6 >DB24C8 >DB21C7 >DB15C5. Meanwhile, the addition of SDS as a cationic surfactant in acidic receiving phase solution, under optimum conditions, significantly lowered the concentration of acid required and increased the transport efficiency. A kinetic model was also used to describe the U(VI) transport behavior, assuming that it obeys the kinetic laws of two consecutive irreversible first-order processes. The interference from different transition metal ions was found to be negligible. The interference from Th~(4+) and Cu~(2+) could be eliminated by using EDTA as a proper masking agent in the source phase.