Plutonium potential diagram

In the remaining sections, we focus on the chemistries of thorium and uranium (the actinoids for which the most extensive chemistries have been developed) and plutonium. Potential diagrams for Np, Pu and Am are included in Figure 24.6. 

Fig. 4 Potential-pH diagram of the plutonium-water system at 298 K with SnC>2 conduction band edge overlaid. Dissolved plutonium activity=0.01...

What are the relative concentrations of trivalent, tetravalent, and hexavalent plutonium when a small amount of PuOj is dissolved in a large excess of 1 V HNO3 Repeat for 3 N HNO3. Assume that activities are proportional to molarities. For oxidation-reduction potentials use Fig. 9.1, sixth diagram from the top. 

Based on the redox diagrams in Figure 16.6, estimate the reduction potentials for the one-electron step in the following series of plutonium species in acid solution Pu(IIl), Pu(TV), Pu(V), and Pu(VI). 

In principle, the calculation of the oxidation states of plutonium requires knowledge of the redox potential. Eh, of the aqueous phase. However, the Eh measured with a certain type of electrode may not be the potential for the particular redox couple with which the plutonium reacts. One of the reasons for this is that the Eh-electrode usually catalyses the reaction rate for its specific redox couple. For example, in surface sea water, the measured Eh is about 0.8 V and is due to the O2/H2O couple. In the log Eh versus pH diagram,... 

Mikheev (1988,1989,1992) has obtained extensive evidence through cocrystallization that almost all the tripositive lanthanide (except for Sm, Eu, Tm and Yb) and actinide ions (U, Np, Pu, Cm, Bk) can be reduced and have (M /M ) in the neighborhood of — 2.5 to — 2.9 V. The lanthanide potentials are not consistent with the experimentally confirmed generalized f electron energetics scheme developed by Nugent (1975). The potentials are not consistent with potentials inferred from pulse-radiolysis studies (Sullivan et al. 1976,1983,1988). If the potentials (M /M ) proposed by Mikheev for uranium, —2.54 V, and plutonium, —2.59 V, at macroscopic concentrations (Mikheev etal. 1991) were correct, phase diagram studies and electrochemistry ih molten salts should have revealed the ions and Pu ", but no evidence other than cocrystallization has been presented. In fact, the crystal chemistry of the reduced uranium halide NaUjCl (Schleid and Meyer 1989) is consistent with ions and metallic electrons. The cocrystallization model (Mikheev and Merts 1990) may not be transferable to aqueous solution and thus Mikheev s (M /M ) potentials are not cited in table 5. 

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