Oxidative alkaline leaching has been proposed to pretreat the high‐level nuclear waste sludges to remove some of the problematic (eg, Cr) and/or nonradioactive (eg, Na, Al) constituents before vitrification It is critical to understand the behavior of actinides, americium and plutonium in particular, in oxidative alkaline leaching We have studied the leaching behavior of americium from four different sludge simulants (BiPO4, BiPO4 modified, Redox, PUREX) using potassium permanganate and potassium persulfate in alkaline solutions Up to 60% of americium sorbed onto the simulants is leached from the sludges by alkaline persulfate and permanganate The percentage of americium leached increases with [NaOH] (between 10 and 50 M) The initial rate of americium leaching by potassium persulfate increases in the order BiPO4 sludge<Redox sludge<PUREX sludge The data are most consistent with oxidation of Am3+ in the sludge to either AmO2 + or AmO2 2+ in solution Though neither of these species is 

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Oxidative Alkaline Leaching of Americium from Simulated High‐Level Nuclear Waste Sludges

Fundamental investigations on preparation of Am(VI) in nitric acid solutions of various concentrations were carried out in order to develop a partitioning method for americium from high level liquid waste generated from the reprocessing of spent fuel. A mixture of ammonium peroxodisulfate and silver nitrate was used as oxidizing reagent. The yields of Am(VI) were determined as a function of the concentrations of nitric acid (0.01—2 M) and oxidizing reagent (0.1—2M) and temperature (55–85°C). The yield of Am(VI) decreased with increasing concentration of nitric acid. In 1 M nitric acid solution, increasing the concentration of ammonium peroxodisulfate resulted in increased of Am(VI) yield. When 1.5 M ammonium peroxodisulfate and 0.01 M silver nitrate were used, 90% of the americium in 1M nitric acid solution was oxidized to the hexavalent state at 85°C.

https://www.tandfonline.com/doi/pdf/10.1080/18811248.1995.9731773

Preparation of Hexavalent Americium in Nitric Acid Solution

Published data on homogeneous catalytic redox reactions involving U, Np, Pu, and Am ions in acidic and alkaline media are summarized. The kinetic data and possible reaction mechanisms are discussed.

Homogeneous catalysis in actinide chemistry

The platinum metals part i: ruthenium, osmium, rhodium and iridium

The properties and stability of the S2O82– ion and mechanisms of its reaction with ions of f-elements in aqueous solutions in a wide range of pH values are considered. S2O82– are converted to SO4 ion radicals. The decomposition is accelerated by Н+, ОН–, Ag+, Co2+ ions, and others. The decomposition in solutions with [H+] > 0.5 or [OH–] > 0.5 M yields monoperoxysulfuric acid, with its hydrolysis generating Н2О2. The SO4– radicals oxidize ions of f-elements and convert ОН– and СО32– ions to oxidizing radicals ОН and СО3– and transform H2PO4– and NO3– ions into reducing compounds. In aerated alkaline solutions, the ОН radicals are transformed to ion-radicals О3–,which oxidize Np(VI), Pu(VI), and Am(VI) to the heptavalent state. In weakly acidic solutions of heteropolycompounds, SO4– radicals transform Tb(III), Am(III), Cm(III), Cf(III) to the tetravalent state. The mixture of Ag+ and S2O82– is used to oxidize Np(VI) to Np(VII) in an alkaline medium, Pu4+ to PuO22+ in acid solutions, Am(III) to Am(IV) in Н3РО4 solutions and in the presence of heteropolycompounds in 5 M HNO3 or 3 M H2SO4 solutions, Am3+ to AmO22+ in acid solutions. The decomposition of S2O82– into radicals occurs under exposure to light or radiation. The reactions of oxidation of f-element ions by SO4– radicals occur by the zeroth-order rate law. To one more group of reactions belongs the interaction of S2O82– with NpO2+, Pu3+, Am3+ ions. The reactions occur with a first-order rate with respect to the f-ion. In the case of U4+, Np4+ in acid media and, Pu(IV) in a solution of K2СО3, complexes of these ions with S2O82– are formed. The complexes decompose by the first-order rate law. Studies are planned of studying reactions involving S2O82– and ions of f-elements, including those in fluoride solutions containing actinides and fission products, and reactions of SO4– radicals at low temperatures to give actinides in higher oxidation state.

Persulfate Ion in the Chemistry of f -Elements

Kinetic studies of the americium(III) oxidation have been made in aqueous solutions. The reaction rates are dependent on the concentrations of hydrogen, peroxydisulfate and the silver ion as catalyzers, and on the reaction temperature. The period of induction observed in the initial stage of reaction varies with the concentration of the reactant and with the reaction temperature. The data follow this rate expression:−\fracd[Am(III)]dt=Kh(k1+k2[Ag+])[S2O82−][Am(III)]·1⁄[H+]where Kh is the dissociation constant of hydrogen peroxydisulfate, and where k1 and k2 refer to the silver-ion uncatalyzed and catalyzed paths respectively. The energies of activation were determined to be 28.6 kcal/mol for k1 and 17.4 kcal/mol for k2.

Kinetics of the Reaction of Americium(III) with Peroxydisulfate

The isotopic ligand-exchange reactions of cis-dibromotetraammineruthenium(III) were studied in aqueous and methanol-water solutions in order to distinguish them from those in the case of the monobromocomplex and in order to ascertain the role of the water molecule with respect to the reaction mechanism. In an aqueous solution, the reaction proceeds through the rate-determining aquation step with the SN2 mechanism: Ru(NH3)4Br2++H2O→Ru(NH3)4(H2O)Br2++Br−, Ru(NH3)4(H2O)Br2++*Br−→Ru(NH3)4Br*Br++H2O. This result is similar to that for the monobromocomplex. In the methanol solution (H2O∼1.5%), the exchange reaction proceeds through the SN1 mechanism: Ru(NH3)4Br2+→Ru(NH3)4Br2++Br−, Ru(NH3)4Br2++*Br−→Ru(NH3)4Br*Br+. When the concentration of water becomes very low, the number of solvated water molecules decreases; therefore, the coordinated bromide ion may easily be liberated. When the concentration of water is higher than 10%, the rate constant increases with the increase in the water concentration. Since the el...

Studies of Ruthenium Complexes. IV. The Solvent Effect on the Isotopic Ligand-exchange Reaction of the cis- Dibromotetraammineruthenium(III) Complex

Kinetic studies of isotopic ligand-exchange reactions, [Ru(NH3)5X]2++X*−=[Ru(NH3)5X*]2++X−, where X=Cl, Br, and I, have been made in aqueous solutions. The effects of the hydrogen- and halide-ion concentrations, and of the ionic strength of the aqueous solution on the exchange rate had not been observed under certain definite experimental conditions. The rate constants were determined to be 3.15×10−4 sec−1 for the chloro-pentaammine 3.63×10−4 sec−1 for the bromopentaammine, and 1.1×10−4 sec−1 for the iodopentaammine at 80°C. The energies of activation were 20 kcal/mol (chloropentaammine), 23 kcal/mol (bromopentaamine), and 30 kcal/mol (iodopentaammine). The reactions proceed through the following two steps: [Ru(NH3)5X]2++H2O→[Ru(NH3)5H2O]3++X− [Ru(NH3)5H2O]3++X*−→[Ru(NH3)5X*]2++H2O The first step is regarded as the rate-determining one.

Tetsuo Shinohara

Papers

Kinetics of the Reaction of Americium(III) with Peroxydisulfate

Studies of Ruthenium Complexes. IV. The Solvent Effect on the Isotopic Ligand-exchange Reaction of the cis- Dibromotetraammineruthenium(III) Complex

Studies of Ruthenium Complexes. III. Kinetics of Isotopic Ligand-Exchange Reactions of Halogenopentaammineruthenium(III) Complexes in Aqueous Solution

Studies of ruthenium complexes part 4, the solvent effect on the isotopic ligand-exchange reaction of the cis-dibromotetraammineruthenium(iii) complex

Kinetik der rk. von americium(iii) mit peroxodisulfat