Studies on the In Situ Electrooxidation and Selective Permeation of Cerium(IV) across a Bulk Liquid Membrane Containing Tributyl Phosphate as the Ion Transporter

Abstract

The results of experiments carried out to develop a liquid membrane (LM) technique for the extractive permeation of cerium from nitric acid solutions are described. In-situ electrooxidation of Ce3+ to extractable Ce4+ and its transport across bulk LM (BLM) composed of tri-n-butyl phosphate (TBP)/dodecane mixtures was systematically studied under varied hydrodynamical and chemical conditions. The permeability of metal ions across the BLM was dependent on the efficiency of extraction, ionic activity of feed solutions, stirring rate, composition of the receiving phase, etc. The transport rates were found to vary linearly (a log-log correlation) with the cation concentration in feed solutions and concentration of TBP in BLM. A permeation velocity equation for cerium ion through the membrane has been proposed. More than 90% permeation of Ce with a maximum flux of 8.63 × 10−5 mol/m2/s could be accomplished under the experimental conditions: stirring rates at feed and strip solutions were 380 and 300 rpm, respectively; feed was 1 mol·dm−3 of HNO3 containing 0.005 mol·dm−3 Ce(NO3)3; LM contained 30% TBP/dodecane; and the receiving phase was distilled water. Radiochemically pure Ce-144 was partitioned from the Ce–Am mixture obtained by extraction chromatographic fractioning of high level radioactive waste. This also resulted in the purification of Am-241 in the feed solution with a decontamination factor of ∼ 12 from Ce.