Sorption of trivalent plutonium onto UO₂and the effect of the solid phase on the Pu oxidation state

Abstract

SummaryA problem with plutonium in sorption studies is its tendency to occur in a mix of oxidation states. This work was a study of the sorption of plutonium on the solid phase UOA comparison is made between the sorption of Th(IV), Pu(III) and Co(II) on UO

Biogenic nanoparticulate UO2: Synthesis, characterization, and factors affecting surface reactivity

“…Olsson et al (2005) measured Co(II), Pu(III), and Th(IV) uptake on bulk UO 2 and observed an increase in sorption loading as pH was increased from pH 1 to 7. In these experiments, the slope of the sorption curves was a function of the charge of the sorbing ion as well as of the surface charge, suggesting that uptake is dominated by electrostatic interactions.…”

“…Nanoparticulate UO 2 may act as a significant carrier of U(IV) in various environments, including emissions from coal-fired power plants (Utsunomiya et al, 2002), U mine sediments (Suzuki et al, 2003), and systems that have undergone U bioremediation (Kelly et al, 2008). Many of the physical and chemical properties of bulk UO 2 are well characterized, including its stoichiometry (Janeczek and Ewing, 1992a), particle surface area (Narayana et al, 1994), solubility and dissolution rates (Parks and Pohl, 1988;Janeczek and Ewing, 1992;Casas et al, 1998), the presence of particle surface coatings (Janeczek and Ewing, 1992a;Janeczek et al, 1993), and particle surface reactivity with respect to metal sorption (Dewiere et al, 2004;Olsson et al, 2005). However, it is not clear if the properties determined for bulk uraninite are the same as those for nanoparticulate UO 2 .…”

Neptunium interaction with uranium dioxide in aqueous solution

“…This is the case in our study but Np(IV) is readily sorbs onto UO 2 and only small fraction is found in solution. The reduction of Np(V) to Np(IV) and Pu(IV) to Pu(III) by freshly washed UO 2 under anoxic conditions and a subsequent sorption was suggested earlier [17,19]. In our case, at pH 4-5.5, two possible redox scenarios are conceivable: (1) oxidation of Np(IV) and stabilization of Np(V) in the presence of U(VI) in solution, and (2) precipitation of U(VI) solids from solution onto the UO 2 surface, thus negating surface reduction of Np(V).…”

“…The sorption has a minimum near neutral pH values: this is not typical for cation sorption onto oxides or oxyhydroxides. The sorption of plutonium and neptunium onto UO 2 was studied extensively in Chalmers University of Technology [15][16][17]. However, a difference in radionuclide sorption to UO 2 used in this study is expected due to its different degree of surface oxidation.…”

Radioactivity, Geochemistry, and Health

“…UO 2 strongly sorbs Np(V), which is partially reduced to Np(IV) on the mineral surface, and is strongly, perhaps irreversibly bound (Kazakovskaya et al, 2010). At low pH, Pu(IV) is reduced to trivalent Pu and is strongly retained on the UO 2 surface (Olsson et al, 2005). Th can be also sequestered by sorption/coprecipitation at low pH, a process that may be important in reducing repository settings if radiolytic dissolution of SNF is followed by distal reprecipitation of UO 2 (Rousseau et al, 2002).…”