Spectroscopic identification of tri- n -butyl phosphate adducts with Pu(IV) hydrolyzed species

Abstract

The complex chemistry of plutonium under low nitric acid concentration can significantly affect the extraction of tetravalent plutonium by tri-n-butyl phosphate (TBP) in n-dodecane. At low HNO3 concentrations, the main Pu(IV) species present in the aqueous solution are Pu(OH)3+ and Pu(OH)22+. Moreover, due to the disproportionation reaction of Pu(IV), a mixture of Pu(III), Pu(IV) and Pu(VI) must be considered. Also the colloidal Pu(IV) can be present under certain conditions. Vis-NIR spectroscopy revealed that in 0.1 M nitric acid, the formation of colloids and the disproportionation reaction of Pu(IV) are the main processes responsible for the distribution of plutonium between the organic and aqueous phases. Comparison of absorption spectra of Pu(IV) in TBP extracted from 0.4-10 M nitric acid concentrations confirms presence of two different Pu(IV) species. At lower nitric acid concentration (0.1 M), also colloidal Pu in TBP was observed.