THE RADIOCHEMISTRY OF PLUTONIUM - Sciencemadness.org

a
ml
0
-1
5
0
4
3
2
-1
-2
-3
~- x
I I
\
\
I
-1 0 1,
Log HN03 CONCENTRATION w)
Fig. 12. Extraction of various actinides into 0.5
—
M HDEHP (isooctane diluent) from
HN03 solutions.238
curve at high acid concentrations is due to disproportionation of Np(V ) into Np(lY ) and
Np(VI), both of which are more extractable than Np(V). The minimum in the Am(lII)
curve at high acid concentrations is probably due to nitrate completing of the extracted
Am species.
Horner and Coleman 187 get a different result for the extraction of Pu(lV ) by
HDEHP. As shown in Fig. 13, the extraction curve is concave downward with increasing
HN03 concentration using 0.01 ~ HDEHP in Amsco 125-82. The magnitude of distribution
coefficients are very much larger than those of Kosyakov ~.,
238 ~ the second
power dependence on the extractant concentration is taken into account. Another dif-
ference is the decreased distribution coefficient at 0.1 ~ acid. Homer and Coleman
ascribe this decrease to hydrolysis of the Pu(IV). Horner and Coleman prepared Pu(IY)
by reduction to Pu(IIf) with hydroxylamine nitrate, and reoxidation and stabilization
238
with sodium nitrite, while Kosyakov et al. dld not state their method of preparation of
Pu(lv).
Dreze and Duyckaerts
\
121 investigated the extraction of Pu(IY) by di - n-butyl
phosphoric acid (HDBP) from nitrate solutions as a function of nitric acid concentration,
nitrate concentration, HDBP concentration, and ionic strength. Representative results
are shown in Figs. 14 and 15. These experimenters were able to invoke the known
stability constants of Pu(IV ) nitrate complexes to fit the various fwctional dependencies.
They consider the extraction reaction to be
PU+4 + 2(N03 )- + 2(HDBP)2(0) - PU(N03)2 (H(DBP)2)2(0) + 2H+ (2)
for which they calculate the equilibrium constant to be (1.7 + 0.3) X 109 (m/1 )2.
43
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