THE RADIOCHEMISTRY OF PLUTONIUM - Sciencemadness.org

Pu(VI) by the addition of enough H2 SO ~ to 2
—
M HN03 to make the solution O. 1 M in
—
H2S04 was only from 2.6 to 2.2.
Sulfuric acid also decreases the extraction of Pu(lY) into TBP from HC1
solutions.441 A solution 1 ~ in H2S04 lowered Dpu approximately a factor of 10
throughout a change in HC1 concentration of 3-8 M.
—
Other neutral phosphorous compounds. A wide variety of organo-phosphorous
compounds has been studied in an attempt to find other extractants for Pu and U,
Higgins et al. 181 working with the butyl series found the order to be phosphate
(( RO)3PO) < phosphonate (R(RO)2PO) < phosphinate (R2(RO)PO) < phosphine oxide
(R3PO). ThUS the extracting power increases with the number of C-P bonds.
Burger
69, 70
corrfirmed this series and correlated the extracting power with the basisity
of the phosphoryl oxygen as measured by the P-O stretching frequency. Burger,
69, 70
and Petrov et al? 18
found that electronegative substituents in the alkyl chain such as Cl and
phenyl strongly depressed the extraction. Siddal~76 found that increasing the length of
the alkyl chain in the phosphate series made little difference up to 8 carbon atoms for
quadrivalent and hexavalent actinides. The effect of branching the alkyl chain is to in-
crease the extraction of U, Np, and Pu, but to strongly depress that of Th. This effect
is attributed to steric effects and possible tri- solvation of the Th complex at high ex-
tractant concentrations.
The etiraction mechanism of these compounds is generally the same as that for
TBP, but not necessarily with the same solvation number for all elements.
267
Tri-n-
oct ylphosphine oxide (!TOPO) and tri-n-butylphosphine oxide (TBPO) extract Pu(IV ) and
Pu(VI) as the di - solvate.
269, 408
The data of Martin and Ockenden 269. 1s ~ven in Figs. 9 and
10 for extraction of several elements into O. 1 ~ TOPO in cyclohexane from HN03 and
HC1 solutions. Pu(IV) and U(VI) are both extracted well (D = 4-30) from 3 ~ H2S04
by 0.3 ~ TOP0.187 The extraction of Pu(lV ) as a function of nitric acid concentration
is similar to that for TBP, but very much higher, while that for U(VI) and Pu(VI) show
different acid dependencies. White and ROSS427 have written a general review of the
extractive properties of TOPO.
Trace quantities of U have been separated from large amounts of Pu by extracting
the U with TOPO under reducing conditions from 2 ~ HN03. 34
Table IV- 16 is a compilation of data for the extraction of Pu(IV) by a large number
of compounds of this type. The extraction coefficients were converted to 1 M extract-
—
ant by using the “square law, ” that is by assuming that the extracted complex is di-
solvated in every case. The distribution coefficients were taken at 1 ~ HN03 where
possible, but cases in which other ions were present or the acidity was different are
noted. The extractive power relative to TBP was calculated by direct comparison in the
same series of experiments where possible, or by comparison to other TBP data taken
,.i under the same stated conditions. The conversion of the phosphine oxide data to 1 ~
extractant generally required large extrapolations, since the experiments were done at
low extractant concentrations. For this reason the numerical values of the distribution
coefficients and the relative extractive power are only approximate.
35