Chemical Species of Plutonium in Hanford Site Radioactive Tank Wastes

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).…”

“…hydr.) solid phase is established by the solubility equilibrium with Pu(OH) 4 (aq) and is not subject to influences of any subsequent dissolved species (e.g., Pu(OH) 5 − or PuO 2 (OH) 4 3− ). …”

“…Most of the plutonium loss streams were in nitric acid solution mixed with much greater concentrations of other metals (e.g., aluminum, bismuth, chromium, iron, uranium, zirconium). When the acid wastes were made alkaline with NaOH before discharge to the mild-steel-lined underground storage tanks and then concentrated by evaporation, sodium nitrate and other sodium salts crystallized and excess sodium hydroxide and dissolved salts remained in solution, while low-solubility polyvalent metal oxide, hydroxide, and hydrated oxide sludges formed with the plutonium largely dispersed on an atomic scale within the precipitated lowsolubility sludges [4]. Plutonium dissolved in nitric acid solution precipitates in sodium hydroxide solution, even when accompanied by most other anions, to form a low-solubility PuO 2 ·xH 2 O solid phase.…”

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

“…Most of the plutonium loss streams were in nitric acid solution mixed with much greater concentrations of other elements (e.g., iron, aluminum, chromium, uranium). When the acid wastes were made alkaline with sodium hydroxide before discharge to the mild steel-lined underground storage tanks and then concentrated by evaporation, dissolved and crystalline sodium nitrate, excess sodium hydroxide solution, and low-solubility metal oxide, hydroxide, and hydrous oxide sludges were formed with the plutonium dispersed on an atomic scale within the low-solubility sludges (Barney and Delegard 1999). 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.…”