THE RADIOCHEMISTRY OF PLUTONIUM - Sciencemadness.org

The extraction of Pu(IV ) from nitric acid solutions was investigated by
Cunninghsme and Miles 110’ 111 using CC14 and benzene as solvents primarily, al -
though other chlorinated hydrocarbons were used also. They find that, by neglecting
aqueous phase nitrate completing of the Pu, the equilibrium can be expressed by the
equation
c = DPU(IV)
4
‘HN03
‘PuT4
(HT)4 f~T
They derive the f‘ s from the TTA concentration dependence of the distribution co-
efficient, and find that C is close to 1 X 10+5 over the range from 1 to 10 ~ HN03 for
tracer Pu. Heisig and Hicks, 173 m a very extensive study of the kinetics of the ex-
traction of Pu(IV ) from nitric acid solutions by TTA, in sec-butyl benzene, determined
that the rate of transfer of Pu chelate across the organic aqueous boundary controls
the forward and reductive back extraction rates. They find that at low nitric acid
concentrations (O. 5 ~) the extracted species is PuT4, while at 4.9 M total nitrate con-
—
centration some partially nitrated complex such as PuN03T3 exists.
Heisig and Hicks 174 found that for Pu(VI) extractions into TTA-benzene from
nitric acid solutions the dependencies are direct second-power on the TTA concentra-
tion and inverse second-power on the hydrogen ion concentration, indicating that Eq.
(1) represents the reaction. These authors measured the distribution coefficients for
the Pu(III) obtained by reduction with 0.005 Mferrous perchlorate — 0.01 ~ sulfuric acid as
—
a function of nitric acid and TTA concentrations. They obtained a direct 2.3 power dependency
on TTA concentration and an inverse 2.6 power dependency on hydrogen ion. These solutions
were never stabilized in the presence of TTA, however. Since the distribution co-
efficient increased with time, extrapolations to time zero were made, and the extrap-
olated values were used. Plots of the distribution coefficients for Pu(IIT) and Pu(VI)
obtained by Heisig and Hicks are shown in Fig. 36.
Cunningham and Miles 111 determined the extraction properties of a number of
possible impurities in the development of a batch process for separating Pu from ir-
radiated U. Their results are shown in Fig. 37. Their procedure, which should be
easily adaptable to the laboratory scale, is to pre-extract the Zr from 0.5 ~ HN03
while the Pu is reduced to Pu(III) with hydroxylamine, oxidize to Pu(lY) with NaN02,
extract with 0.2 ~ TTA-benzene, scrub with dilute HN03, and back-extract the Pu into
8 ~ HN03. They report a 99.4% Pu recovery on a l-gram scale with decontamination
factors from Zr and U of 3000 and 667, respectively.
Other reports on the use of TTA for processing irradiated uranium for Pu are
those of Crandall _et al. and Culler.lOg
105
An interesting variation is the use of U(IV)
to strip Pu from TTA solutions by reduction to Pu(III) or a combination of reduction
342
and displacement. The application of TTA to analytical and radiochemical pro-
cedures for Pu has been reported many times, either as the only purification
287,50,356
step for rapid analysis (see for example, Procedure 2, Section VIII) or in
combination with co-precipitation steps involving LaF3, 136’351’50’284 BiP04,
341, 237
chemisorption on a CaF2 suspension,
352
or other separation steps. 332,315,168,261
67
(5)