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In-Depth Information
An(III) + Ln(III) fraction with 5.5 M HNO
3
, two stages for the second scrub with
0.6 M oxalic acid, four stages for stripping the Np + Pu fraction with 0.6 M oxalic
acid, and finally four stages for stripping U with 5% Na
2
CO
3
. It involved a mixture
of trialkyl(C
6
-C
8
) phosphine oxides (TRPO) dissolved at 30% in
n
-dodecane as
the organic solvent and a genuine PUREX raffinate (obtained from reprocessing
commercial spent (light water reactor) LWR fuel) denitrated to 0.7 M HNO
3
as
the aqueous feed. Despite the fact that this preceding denitration of the high-level
liquid waste (HLLW) with formic acid might have implied a risk of precipita-
tion and hence losses of minor actinides, the DFs obtained for the raffinate (in
the extraction section) and for the organic solvent (in the stripping section) were,
respectively, higher than 800 and equal to 730 for Am(III), and higher than 200
and equal to 780 for Cm(III). The overall recovery yields for Am(III) and Cm(III)
were 99.7 and 99%, respectively. Losses of the trivalent minor actinides in the
Np + Pu fraction (~0.13%) and in the U output (0.14% for Am(III) and 0.35% for
Cm(III)) were higher than in the spent solvent (0.03% for Am(III) and 0.09% for
Cm(III)) (
95, 96
).
3.3.1.1.3 Bidentate Neutral Organophosphorus Compounds
3.3.1.1.3.1 CMPO: The TRUEX Process
The TRUEX (TRansUranium EXtraction)
process (
97, 98
), developed at the Argonne National Laboratory (ANL) in the 1980s
to decontaminate Cold War legacy transuranic waste (arising from plutonium produc-
tion for nuclear weapon manufacturing), uses a mixture of TBP and CMPO (Figure
3.1) that allows all minor actinides (and the lanthanides) to be extracted from acidic
media (up to 5 M nitric acid). However, it requires a PUREX (or similar) process as
its front-end.
The TRUEX solvent ([CMPO] = 0.2 M + [TBP] = 1.4 M in
n
-dodecane) was
employed to decontaminate samples of sludge arising from the concentration
(by evaporation of water) and neutralization (with caustic) of the acidic waste of
Melton Valley Storage Tank W-25 at the Oak Ridge National Laboratory. The
sludge was quantitatively (~80%) dissolved in concentrated nitric acid after caus-
tic leaching treatment (
99
). Two campaigns of batch liquid-liquid extraction tests
(at 2.9 and 1.6 M HNO
3
, respectively) were successfully carried out, although gel
formation disturbed the experiments. More than 95% of Eu, Pu, Cm, Th, and U
were removed in only one step from the aqueous feeds. Mercury and vanadium
also appeared to be extracted. The analytical results were in good agreement with
i(C
4
H
9
)
C
8
H
17
N
P
i(C
4
H
9
)
O
O
FIGURe 3
.
1
n
-Octyl-phenyl-
N,N
′-di(
iso
)butyl-carbamoyl-methyl phosphine oxide (CMPO)
used in the TRUEX process.
