Transport of uranium (VI) through a liquid membrane impregnated with phosphonic acid ester

The extraction behavior of U(VI) by 2-ethylhexylphosphonic acid mono-2-ethylhexylester (EHPA; HA) was investigated; the extracted species was found to be UO2(HA2)2. This extractant was employed as a mobile carrier for U transport across a supported liquid membrane (SLM) consisting of EHPA in kerosene impregnated into a microporous polytetrafluoroethylene sheet. Uranium was transported from a feed solution into a sulfuric acid solution (receiving solution) by a large concentration gradient of hydrogen ions between both sides of the SLM. Quantitative stripping became impossible with increasing EHPA concentrations. The addition of 1-decanol to the membrane solution improved the U stripping and contributed further to stabilize the EHPA-membranes without any leaching loss into the aqueous phases. The apparent rate constant of U transport (Kobs) was evaluated from In ([U]f,t/[U]f.o) = -kobst. The values of Kobs varied linearly with pH of the feed solution, and then reached a plateau. The acidity (0.1 ∼ 1 M) of the receiving solution had little effect on Kobs. Uranium in a relatively wide concentration region was quantitatively transported through SLM and concentrated into acidic receiving solutions. (author)