Solubility and redox reactions of Pu(IV) hydrous oxide: Evidence for the formation of PuO_2+x(s, hyd)

Abstract

The solubility and redox reactions of Pu(IV) hydrous oxide were analyzed by comparing total Pu concentrations, oxidation state distributions and simultaneously measured redox potentials under air and under Ar containing only traces of oxygen. At pH>3 the aqueous Pu concentration is dominated by Pu(V) for both solubility studies under air and argon. Combining all information strongly indicates that PuO

Pu(IV) Intrinsic Colloid Stability in the Presence of Montmorillonite at 25 & 80 C

“…However, the concentration of the Pu colloids with respect to total solution volume (255 mL) is 9.13E-10 M (Table 3-1). This is below the solubility of Pu colloids (Neck et al, 2007), suggesting that the intrinsic colloids should dissolve over time. However, the results presented in Figure 3-3 are inconclusive.…”

“…This is the same method used to prepare amorphous PuO 2 for the solubility studies used by Neck et al (2007). After aging for more than a week, the Pu colloids were centrifuged at an RCF of 9168 for 1 hour, and the supernatant was removed.…”

“…At each temperature, Pu was initially added either as an aqueous phase (to test simple diffusion and sorption of Pu) or as an intrinsic colloid (to test intrinsic colloid dissolution, diffusion and sorption of Pu). The initial Pu concentrations bracketed the PuO 2 (am, hyd) solubility (~5 × 10 -9 M) (Neck et al, 2007). In addition, montmorillonite-free solutions (spiked blanks) with initial Pu concentrations below and near PuO 2 (am, hyd) solubility were used for comparison with sorption experiments and evaluation of Pu loss to container walls and the dialysis membrane.…”

“…The dissolution of PuO 2 intrinsic colloids and sorption of Pu to montmorillonite were examined using three different initial colloidal Pu concentrations (10 -11 , 10 -9 and 10 -7 M) ( Table 3-1) that bracket the range of stability identified in Neck et al (2007). The Pu concentration in the clay suspension is plotted as a function of time and temperature in Figure 3-4.…”

“…Pu can migrate as either an 'intrinsic' colloid or sorbed to a naturally occurring inorganic, organic or microbial species. At high concentrations where actinide ions in solution exceed the solubility product, Pu can hydrolyze to form intrinsic Pu(IV) colloids (or sometimes, eigen-colloids) (Kim, 1991;Neck et al, 2007). As an intrinsic colloid, Pu transport will be controlled by the stability (both physical and chemical) of the Pu(IV) intrinsic colloid.…”