Chemistry Reference
In-Depth Information
promising extraction propensity of TODGA, not only basic studies but also vari-
ous R&D works for applications have been envisaged and demonstrated (
274-277
).
Tian et al. investigated the distribution equilibria and thermodynamics of U(VI),
Np(V), Pu(IV), Am(III), and TcO
−
with another DGA,
N,N,N
'
,N
'-tet ra
iso-
butyl-3-oxa-
glutaramide (T
i
BOGA) (
278
). The extractability of T
i
TiBOGA in 40/60% (V/V) 1-oc-
tanol/kerosene for the ions follows the order Am(III) >> Pu(IV) > U(VI)
Tc( V I I ) >
Np(V). Mowafy et al. compared the extractability of several diglycolamides having
different alkyl groups with amidic nitrogen, using benzene as diluent (
279
).
TRPO
.
The trialkyl phosphine oxide (TRPO) process was developed at Tsinghua
University in China during the 1990s (
280-282
). TRPO is the trademark of a com-
mercial product in China, consisting of a mixture of phosphine oxides with alkyl
groups of different C number. For the extraction of Ans (and Lns), 30 vol % TRPO
in kerosene was used from an aqueous solution of nitric acid concentration of 0.5-1
M. Ans (and Lns) were stripped with a 5-6 M HNO
3
solution. Technetium(VII) is
also efficiently extracted by the solvent and stripped by water (
283
). When TRPO
degrades radiolytically, polymeric products prevent effective stripping of Pu (
284-
286
). The TRPO process has been tested in China (
287
) and at the ITU in Karlsruhe
(
288, 289
) with genuine HLW; its performance was appraised as being satisfactory.
Recently, from the viewpoint of integration of PUREX and TRPO processes, a sim-
plified TRPO flowsheets has been proposed (
290
).
DIDPA.
Application of di-isodecyl phosphoric acid (DIDPA) to the extraction
of Ans(III) and Lns(III) was initiated at JAEA in the 1970s (
291, 292
). Then it was
fully investigated in the frame of the Partitioning and Transmutation program. For
the extraction of Ans (and Lns), 0.5 M DIDPA-0.1 M TBP in
n
-dodecane was con-
tacted with an aqueous solution of nitric acid concentration of ~0.5 M. In the second
cycle, from the re-extracted Ans and Lns, Ans were stripped by 0.05 M diethylene-
triamine-
N,N,N
'
,N
”
,N
”-pentaacetic acid (DTPA) solution, leaving Lns in the organic
phase in the manner of the Reversed TALSPEAK process (
358
). Lns were stripped
by 4 M HNO
3
. The process was tested in a hot-cell with a genuine HLW solution at
the NUCEF facility of JAEA (
293
) and at the Institute for Transuranium Elements
(ITU) in Karlsruhe (
294
). A recovery yield of 99.99% of Am and Cm was achieved.
The process requires denitration of HLW in adjusting the feed, which produces pre-
cipitates of Mo, Zr, etc. Thus, it could, by filtration, remove most of the Mo and Zr,
which are troublesome in the latter processes (Figure 1.2).
Scrubbing and stripping.
Conditions of scrubbing and stripping are very
important from the viewpoint of process performance, as they determine the purity
and recovery yield of a product. The former selectively removes contaminating
solutes from the main extractable solute in an organic phase. The latter strips the
objective solutes selectively and successively from the organic phase. Scrubbing
and stripping produce aqueous streams to be treated next, as a product or waste.
Therefore, their chemical compositions are carefully determined to minimize the
cost and the wastes. Some examples are shown in Table 1.3. The ligands that extract
Ans usually exhibit affinity for multivalent metal ions, such as Fe(III), Mo(VI),
Zr(IV), Pd(II), and Ru, and they are coextracted with Ans. Thus, most processes
shown in Table 1.3 utilize complexing reagents that hold back the impurity elements
by selective complexation in the aqueous phase. Oxalic acid is commonly used as a
