Authors:S. Thompson, F. Molz, R. Fjeld, and D. Kaplan
A transport velocity of Pu complexed with the siderophore DFOB has been measured in corn to be at least 174 cm/h. Based on
a calculated plant water velocity, a Pu retardation factor of 1–10 was estimated. Dominant Pu species retardation in soil
is typically several orders of magnitude higher than this, implying that plants can be a vector for exceptionally rapid upward
Modern software has made the method of proportional equations easy to use. The method quickly yields oxidation state distributions for plutonium in aqueous solutions, so it serves as a check on the results obtained by other techniques. It is a versatile tool that incorporates mass and charge conservation without specifically starting those two laws.
Disproportionation equations are illustrated for two oxidation numbers (N) and for the general case of any N. The new method illustrates the effect of N on the coefficients in disproportionation equations. An estimate of the equilibrium constant for the first hydrolysis reaction
of tetravalent plutonium is obtained by a new approach. The estimated value agrees with many previous results.
Authors:A. Rykov, N. Andreychuk, V. Vasilev, and V. Ermakov
Plutonium(IV) oxidation has been studied in 1 to 20 mol/1 HNO3 under 1 to 14 W/1 internal alpha-irradiation and at plutonium concentrations from 2 to 100 mmol/1. Curium isotopes have been
used as the basic alpha-irradiation sources. It has been established that in the systems investigated both oxidation of plutonium(IV)
and reduction of plutonium(VI) take place, resulting with time in reaching the equilibrium between plutonium(IV) and plutonium(VI).
The presence of plutonium(IV) enhances the reduction of plutonium(VI). The rate constants for plutonium(IV) oxidation and
plutonium(VI) reduction have been estimated and their dependences upon the concentrations of nitric acid, plutonium(IV) and
plutonium(VI) as well as upon the dose rate investigated. An equation has been derived which permits to calculate the concentrations
of plutonium(IV) and plutonium(VI) at any desired time.
Two predominance-region diagrams for plutonium are illustrated. One diagram plots the pH vs. the equilibrium fraction of hexavalent plutonium. The other diagram plots the equilibrium fraction of tetravalent plutonium vs. the plutonium oxidation number. Both diagrams define the boundaries of the regions where tri-, tetra-, penta-, and hexavalent plutonium are the predominant species. In each diagram, the two principal triple points are located at the intersections of three predominance-region boundary lines.
A predominance-region diagram for aqueous plutonium can be prepared by plotting the equilibrium fractions of tetra- and hexavalent
plutonium. An example illustrates how the triple points can be used to estimate hydrolysis constants.
Separations research at the Rocky Flats Plant /RFP/ has found ways to significantly improve plutonium secondary recovery from nitric acid waste streams generated by plutonium purifications operations. Capacity and break-through studies show anion exchange with Dowex 1×4 /50–100 mesh/ to be superior for secondary recovery of plutonium. Extraction chromatography with TOPO /tri-n-octylphosphine oxide/ on XAD-4 removes the final traces of plutonium, including hydrolytic polymer.
The distribution of plutonium oxidation-states in acid solutions can be estimated if the pH and the fraction of one oxidation
state can be determined. The approach applies to plutonium in laboratory solutions and to plutonium in water of the environment.