Effect of reduction on the stability of Pu(VI) hydrolysis species

Abstract

Plutonium(VI) / Reduction / Hydrolysis / Absorption spectroscopy / Capillary cellSummary. The chemical speciation of aqueous plutonium species has been performed by spectrophotometry. The main focus was concentrated on the effect of Pu(V) produced by the reduction of Pu(VI) on the stability of the Pu(VI) hydrolysis species. In order to detect the trace amounts of PuO 2 + ions, a liquid waveguide capillary cell with an optical path length of 100 cm was connected to a spectrophotometer. As a consequence of the improved detection sensitivity, an absorption band at 569 nm being indicative of Pu(V) was observed within one day after the sample preparation from the pure Pu(VI) solution. The first hydrolysis species was (PuO 2 ) 2 (OH) 2 2+ , at plutonium concentrations of 0.1-0.12 mM and at weak acidic conditions (pH 5-6). The formation constant of (PuO 2 ) 2 (OH) 2 2+ was determined to be log * β 22 = −7.34 ± 0.22 at 0.01 M NaClO 4 . This dinuclear hydroxide species was unstable and disappeared within one month after the sample preparation at the present experimental condition. In the neutral pH range, the second hydrolysis species was formed and remained for over one year. The samples showed different behavior for the reduction of Pu(VI). The time dependent distribution of plutonium species and their characteristic features in the absorption spectra are reported.

Mass spectrometric characterization and quantification of Pu(VI) hydrolysis products

“…As 1 The pe value is the negative decadic logarithm of the electron activity in solution pe = − log a e− . It is linked by E h = −(RT/F) ln a e− to the E h and thus describes the redox potential of the solution.…”

“…Hexavalent plutonium hydrolyzes in the near-neutral pH range [1][2][3]. The hydrolysis leads to formation of small polymers but in contrast to the tetravalent actinides, their number and size is rather limited [4,5].…”

“…Different hydrolysis products are proposed in the literature. While some authors found evidence for only monomeric and dimeric hydrolysis products [1][2][3], also larger polymeric species were suggested by other groups [6,7]. There is a large variety of experimental methods applied for the investigation of ions in solution [8], but the conclusions about the composition of the solution species can often be drawn only indirectly [9].…”

Spectroscopic study on the mononuclear hydrolysis species of Pu(VI) under oxidation conditions

“…The sample preparation was described in detail in the previous report [14]. 242 PuO 2 (99.932%, ORNL) was dissolved Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 5/31/15 3:54 AM with concentrated HNO 3 and a small amount of HF.…”

“…It was emphasized that the formation constants for Pu(VI) hydrolysis species should be determined quickly enough to be attributed to pure Pu(VI) and slowly enough to reach the equilibrium state of hydrolysis of Pu(VI) [3]. In the previous work carried out at the plutonium concentration of 0.1 mM [14], it was difficult to investigate mononuclear hydrolysis species of Pu(VI) due to the formation of polynuclear species and the reduction of Pu(VI). The difficulty also *Author for correspondence (E-mail: hrcho@kaeri.re.kr).…”