Evaluation of amide functionalized carbon nanotubes for efficient and selective removal of neptunium: understanding isotherm, kinetics, stripping and radiolytic stability

Solid-phase extraction of neptunium in pentavalent and hexavalent oxidation states from the acidic aqueous medium was investigated. The extraction of neptunium, carried out using N,N-dihexylamide functionalized multiwalled carbon nanotubes (MWCNT-DHA) showed high K d values. The sorption was found to follow Freundlich isotherm via chemical interaction between the amide functionality and neptunium. The time-dependent sorption study showed that the kinetics followed pseudo second order rate constants. MWCNT-DHA was found radiolytically stable up to 1000 kGy. The selectivity of MWCNT-DHA for the sorption of Np ion was found to be satisfactory. Citric acid was evaluated as the best strippants.