A simplified method for representing the disproportionation reactions of plutonium is illustrated. It applies to any N within the range (3 < N < 6) and at any pH that does not introduce precipitation or polymer-forming reactions. Recalculation of recent estimates
of the first hydrolysis constant of the tetravalent plutonium ion improves their precision.
The complexation of tetravalent plutonium in aqueous solutions derives from several sources including counterions, hydrolysis,
additives, and impurities. A quantitative tool accounting for all such effects, known and unknown, is the alpha coefficient.
It can be expressed in six ways by means of the equilibrium fractions of two Pu oxidation states.
Equilibrium-constant expressions for Pu disproportionation reactions traditionally contain three or four terms representing
the concentrations or fractions of the oxidation states. The expressions can be rewritten so that one of the oxidation states
is replaced by a term containing the oxidation number of the plutonium. Experimental estimations of the numerical values of
the constants can then be checked in several ways.
The first hydrolysis constant of tetravalent plutonium can be estimated by two methods that also estimate other solution parameters.
The estimates of the hydrolysis constant compare favorably to the traditional values when the ancillary estimates compare
favorably to the measurements.
There is uncertainty about the numerical value of the first hydrolysis constant of the tetravalent plutonium ion. A new method
for discriminating between the claims is illustrated. It suggests the traditional estimates of that constant are closer to
its true value than a singular result based on a few solvent-extraction experiments. A previously unnoticed multiple point
in aqueous Pu chemistry is illustrated.
An empirical method for preparing a plutonium predominance-region diagram is illustrated by an example. The method estimates
the boundaries of the forbidden, unique, and ambiguous regions as defined by the equilibrium fraction of hexavalent plutonium
and the plutonium oxidation number.
Precipitation and solvent extraction methods have been investigated for the purification of plutonium from silver from the
solution generated during oxidative dissolution of plutonium oxide using Ag(II) ions. Initial experiments have been carried
out using thorium as representative of plutonium. Selecting the optimum conditions, the experiments were repeated with plutonium.
The results revealed that Pu can be purified from silver ions either by precipitating silver as silver chloride or silver
metal followed by Pu(IV) oxalate precipitation or by selective extraction of Pu(IV) into 20% Aliquat-336 or 30% TBP.
The determination of the pH of a plutonium solution has traditionally depended on an electrode or a titration in the presence
of a complexing agent. A new approach uses the equilibrium distribution of the Pu oxidation states to estimate the hydrogen
ion concentration. The method is used to estimate the equilibrium constant of the first hydrolysis reaction of tetravalent
Current literature suggests uncertainty about the numerical values of the hydrolysis constants for tetravalent plutonium.
This letter uses recent data to propose that newer methods for estimating the hydrolysis constants are not necessarily more
accurate than the traditional methods.
Alternative methods for estimating the numerical value of the equilibrium-constant of the first hydrolysis reaction of tetravalent
plutonium are illustrated. They are applied to recent data on Pu oxidation-state distributions in HCl solutions. The new estimates
of the hydrolysis constant typically agree with the traditional values.