Chemistry Reference
In-Depth Information
of Parma (monocrown-calixarenes) and Vicens of l'ECPM of Strasbourg (biscrown-
calixarenes) (
395- 404
). Hot tests with raffinate from reprocessing of MOX fuel were
started at the CARMEN cell at Fontenay-aux-Roses in 1995. Several monocrown-
calixarenes were chosen, and the combinations of extractant/modifier/diluent were opti-
mized. Important factors taken into account were good kinetics, sufficient extraction of
Cs from acidities of the feed solution > 2 M, effective stripping by dilute HNO
3
, TPF,
stability and effect of degradation products, high selectivity, and diluent compatibility
with DIAMEX and PUREX processes. Consequently, the following two systems were
selected as candidates. (1) 0.062 M DOC[4]C6/1.5 M TBP/TPH, and (2) 0.1 M Calix
R14/1 M N-methyloctyl-2-dimethyl-butanamide/TPH (
402, 403
). The flowsheets for
the respective systems were established by using calculation code (
365
). Verification
tests have been conducted at the ATALANTE facility by using genuine raffinate solu-
tion, 4 M HNO
3
-0.2 M oxalic acid, demonstrating recovery yields of 99.8-99.9%
137
Cs.
Only 0.01% of the
137
Cs was found in the final organic solvent. These excellent results
prove their systems as being promising. Rais et al. proposed the solvent DOC[4]C6
dissolved
in
90 vol % 1-
n
-octanol-10 vol % dihexyloctanamide (DHOA) following the
CHON principle (
405
). Researchers at Tsinghua University and BARC used extract-
ants,
i
Pr-C[4]C6 (
406
) and calix[4]arene-bis(naphthocrown-6) (
407
), respectively.
A research group at ORNL developed the CSSX (Caustic-Side Solvent eXtraction)
process for removal of cesium from alkaline waste solutions utilizing a novel ligand,
calix[4]arene-1,3-bis-(
tert
-octylbenzo)-2,4-crown-6 (BOBCalixC6) (
408 - 415
). The
extracting solvent is 0.01 M BOBCalixC6/0.50 M Cs-7SB/0.001 M trioctylamine
(TOA)/Isopal L, where Cs-7SB is a modifier, and TOA is a suppressor added as a
counterion of organophilic anion surfactant-impurities which impair stripping of Cs
(
416
). Although the CSSX process was aiming at the alkaline-waste decontamina-
tion, namely SRS tank waste, the solvent could be regarded as applicable to acidic
waste also (see FPEX process below). However, BOBCalixC6 is susceptible to nitra-
tion and is best replaced by alternative calix-crowns for acid-side use (
410
).
Moyer et al. of ORNL have been exploiting new kinds of calix-crown molecules for
Cs extraction: a calix-crown bearing branched aliphatic groups for greater solubility,
calix[4]arene-bis[4-(2-ethylhexyl)benzo-crown-6] (BEHBCalixC6) (
417, 418
), and
pH-switchable calix-crowns bearing amino functionalities, such as BEHBCalixC6-
NH
2
(
419 - 421
). These efforts open up possibilities for a next generation of extract-
ants, though mostly intended for treatment of alkaline solutions.
Diglycol amides.
TODGA and other diglycol amides displayed an affinity toward
Ca(II) and Sr(II) from 2-3 M HNO
3
solutions (
422
). Thereby, recovery of not only
Ans-Lns but also Sr(II) from spent fuels is contemplated (
279, 422, 423
). The
extracted complexes are represented as [Sr(NO
3
)
2
L
2
(HNO
3
)], where L = TODGA.
1.2.2.2.3.2 Multielement Separation
FPEX process.
During the course of
development of the UREX+ processes, the Fission Product EXtraction (FPEX) pro-
cess, based on a combined solvent containing two extractants, DtBu18C6 (SREX for
Sr) and BOBCalixC6 (CSSX for Cs), has been envisaged (
424- 430
). An interesting
point is that a modifier Cs-7SB, used in the CSSX process, exhibited a synergistic
effect in Sr extraction, and thereby TBP, used as a modifier in the SREX process,
was eliminated in the FPEX process. Also, it had been found in the development of
