Extraction of Am(III) from aqueous nitrate solutions into micellar pseudo phase of anionic or non-ionic surfactant and separation by ultrafiltration

Abstract

Recovery of americium(III) from nitric acid solutions using anionic sodium dodecyl sulfate (SDS) and non-ionic polyethylene glycol ether (Tergitol 15-S-9) surfactant micelles was investigated. For the separation of surfactant micelles, polyethersulfone membranes with nominal molecular weight cut-off (NMWCO); 3, 5 and 10 kDa were used in the batch, stirred cell ultrafiltration unit. The effects of NMWCO of the membrane, feed solution conditions such as the concentration of surfactant, organic ligand 2-ethylhexyl phosphonic acid mono-2-ethylheyxl ester (H 2A 2) and metal ions on the efficiency of Am(III) removal and permeate flux were studied. Almost 100% removal of Am(III) was achieved even in the presence of very low concentration (below CMC) of SDS in the aqueous phase with pH > 2 while containing [Am(III)] < 10 −3 mM. It was observed that surfactant micelle of SDS fails to retain Am(III) ions from aqueous phase containing [NaNO 3] > 0.5 M, whereas, micelles of Tergitol containing H 2A 2 could retain Am(III) from aqueous solution containing [NaNO 3] up to 1 M. The retentions of other commonly associated metal ions with Am(III) such as 144Ce, 137Cs, 152,154Eu, 95Nb, 85Sr and 95Zr were also investigated at different pH of the aqueous solution. Repeated use of metal loaded surfactant solutions gave more than 20 times concentration up gradation of Am(III) in the retentate micellar phase. Back extraction of Am(III) from surfactant micelles was achieved by adjusting the acidity of retentate > 0.5 M with the addition of nitric acid.