THE RADIOCHEMISTRY OF PLUTONIUM - Sciencemadness.org

In this section
coefficient D, which
D.
the data will most often be given in terms of the distribution
is defined by the equation
concentration of the solute in the or~anic phase
concentration of the solute in the aqueous phase
To save space, the notation “Dx” for “the distribution coefficient of species x“ will
be used in the text.
Organo Phosphorous Compounds
This large and important class of extract ants includes the neutral and
acidic esters of ortho phosphoric acid and related compounds, the phosphonates,
phosphinates and phosphine oxides. The class dividea naturally into neutral and
acidic compounds by the differences in extraction mechanism. The neutral compounds
extract by solvation of a neutral complex in the organic phase by the phosphoryl
oxygen, while the acidic compoumds, in general, operate by an ion-exchange reaction
to form an extractable species. Further solvation may occur in the organic phase in
some extraction systems of this type.
Neutral Compounds
Tri-n-butylphosphate (TBP), (C4H90)3P0, will serve as the typical
compound of this type. A complete survey of the literature on TBP extraction of Pu
is beyond the scope of this review. The more recent papers will be emphasized,
although earlier project work will necessarily be included. A summary of early work
on TBP has been given by Geary. 143 The physical and chemical p~5~rties of TBP
as an extracting agent have been summarized by McKay and Healy. The TBP-nitrate
system will be discussed first, followed by other aqueous systems, and finally other
neutral organo-phosphorous compounds.
TBP-nitrate systems. Hesford and McKay 178 have formulated the ex-
traction reaction of metal nitrates into TBP as
M+p + p N03- + q TBP(0) = M (N03)P “ q TBP(0)
where p is the charge on the metal ion and q is the number of TBP molecules solvating
the nitrate molecule in the organic phase. The subscript (o) refers to species in the
organic phase, and species withofit subscripts are in the aqueous phase. The equilib-
rium constant, neglecting activity coefficients, is then
and the distribution coefficient
Under constant aqueous conditions, and at a sufficient dilution of TBP in an inert
diluent to make Eq. (2) valid, the distribution will be proportional to the qth power of
29
(1)
(2)
(3)