Macrocycle-Mediated Selective Transport of Plutonium(IV) Nitrate through Bulk Liquid and Supported Liquid Membranes Using Dicyclohexano-18-crown-6 as Mobile Carrier

Abstract

Macrocycle-facilitated transport of Pu(IV) against its concentration gradient from aqueous nitric acid solutions across an organic bulk liquid membrane (BLM) and a thin-sheet supported liquid membrane (SLM) containing dicyclohexano-18-crown-6 as the mobile carrier and toluene as the membrane solvent was investigated. Extremely dilute and moderately concentrated plutonium nitrate solutions in about 3 mol/dm³ nitric acid generally constituted the source phase. Plutonium transport appreciably increased with stirring of both the source and recovery phases and also with the carrier concentration in the organic phase up to 0.3 mol/dm³ DC18C6 and then decreasing with higher concentrations of the carrier. Enhanced acidity of the aqueous source phase beyond 4 mol/dm³ HNO₃ seriously affected the stripping of the cation. Among the several reagents tested, dilute sodium carbonate (0.5 mol/dm³) served efficiently as the strippant. Enka Accurel thin flat-sheet polypropylene (PP) films were used as the solid support for SLM. By using both BLM and SLM systems, more than 90% of plutonium could be transported through 0.2 mol/dm³ DC18C6/toluene into dilute sodium carbonate strippant in about 7–8 h. The lack of any contamination from even appreciable amounts of possible fission product contaminants is a notable feature of this novel separation technique.