Interaction of Pu(IV,VI) hydroxides/oxides with metal hydroxides/oxides in alkaline media

Abstract

SummaryThe interactions of Pu(N) and Pu(VI) in alkaline media with some metal hydroxides and oxides commonly found in Hanford Site tank wastes were studied. The properties of mixed hydroxide systems of Pu(IV) with various metal ions mi@), Fe(III), C o o , Al(m), Cr(m>, Zr(IV), La(IlI), and U(VI)] were investigated at variable component ratios using physicalchemical methods. The interactions of P u O with Al(lII), Fe(III), and Cr(IlI) also were studied.It was shown by infrared (IR) spectroscopy that, except for the system Pu(IV)-Ni(II), Pu(IV) interacts with all the listed metal ions and affects their interatomic bonding. The locations of IR absorption bands of the mixed hydroxides change irregularly compared with the spectra of pure components, with change in the Pu:metal mole ratio of from 1:lO to 1O:l. The changes occur both for the valent and deformation vibration bands of hydroxyl ions and water at 3600 to 3100 and 1750 to 1250 cm-' and for the vibrations of metal-oxygen (M-0) bridging bonds in the range of 1050 to 850 cm-'. In the Pu(IV)/Ni(II) system, the IR spectra are equivalent to the sum of the individual components precipitated separately from alkaline solution.The separate precipitation of h(N) hydrous oxide and Ni(OH), upon adding NaOH solution to acidic solution containing both Pu(N) and Ni(II) nitrate was confirmed by studying the dissolution rate of the resulting precipitate in 3 M HCl at 60°C. No difference in plutonium dissolution behavior was found for pure PuO,-xH,O and the products obtained by alkaline precipitation of 1: 1 mole ratio Pu(N):Ni(II) mixtures, aged for 1 hour at 70"C, over a wide range of NaOH concentrations. Similar results were obtained for the Pu(IV)-Al(III) system. Only trace amounts of aluminum were detected in pUO,.xl&O precipitates formed even in relatively dilute NaOH solutions.

Effects of aging on PuO2·xH2O particle size in alkaline solution

“…Formation of the neutral Pu(OH) 4 (aq) complex from the PuO 2 (am,hydr) or PuO 2 ·xH 2 O solid phase is the first step in the subsequent solution equilibria needed to create the anionic hydroxide-complexed Pu(IV) and Pu(V) species that have been postulated to exist in strongly alkaline solution (e.g., Pu(OH) 5 − and PuO 2 (OH) 4 3− , respectively, [23]). These species sharply enhance total plutonium concentration in alkaline solution displayed in Fig.…”

“…As noted, formation of the neutral Pu(OH) 4 (aq) complex is the first step in the subsequent dissolution equilibria needed to form the anionic hydroxide-complexed Pu(IV) and Pu(V) species that have been postulated to form in strongly alkaline solution (e.g., Pu(OH) 5 − or PuO 2 (OH) 4 3− , respectively [23]). The influences of the subsequent hydroxide complexation and oxidation steps in the plutonium solute species equilibria are fixed for a given hydroxide chemical activity (NaOH concentration) and redox potential (established in Hanford tank waste by influences such as nitrate and nitrite concentration and radiolysis).…”

Ostwald Ripening and Its Effect on PuO2 Particle Size in Hanford Tank Waste

“…In the presence of only sodium hydroxide, or even accompanied by most other anions, dissolved plutonium precipitates from nitric acid solution to form a low-solubility PuO 2 ·xH 2 O solid phase. However, with the more abundant iron and other polyvalent metals also present, plutonium disperses by coprecipitation into the bulk metal (hydr)oxide or hydrous oxide sludges, showing particularly high affinity for the iron phases (Fedoseev et al 1998).…”

Criticality Safety Evaluation of Hanford Site High Level Waste Storage Tanks

“…Interaction of Pu(IV, Vr) Hydroxides/Oxides with Metal Hydroxides/Oxides in Alkaline Media (Fedoseev et al 1998); (Peretrukin et al 1998).…”