1394
Chemistry Letters Vol.36, No.11 (2007)
ꢀ
ꢀ
2ꢀ
Highly Selective Extraction of TcO4 , ReO4 , and MoO4 by the New Ligand,
2,20-(Methylimino)bis(N,N-Dioctylacetamide) (MIDOA)
Yuji Sasaki,ꢀ Yoshihiro Kitatsuji, and Takaumi Kimura
Japan Atomic Energy Agency, Tokai, Naka-gun, Ibaraki 319-1195
(Received August 1, 2007; CL-070822; E-mail: sasaki.yuji@jaea.go.jp)
Highly selective extraction of oxonium anions can be
analogue of diglycolamide or thiadiglycolamide.15 A prelimina-
ry investigation using MIDOA for the extraction of Tc, Re, and
Mo is reported in this paper.
achieved by the new ligand, 2,20-(methylimino)bis(N,N-dioctyl-
acetamide) (MIDOA). MIDOA has a high solubility in n-dodec-
ane, any types of diluents can be employed for the solvent ex-
traction. The extraction using MIDOA was performed under
the condition, HNO3 and n-dodecane, considering the chemical
process of high-level radioactive liquid waste. It was obvious
The reagents used for the organic synthesis and the solvent
extraction were commercially available. The synthetic method
of MIDOA was followed by the ordinary way of the diamide
synthesis;15 methyliminodiacetic acid and thionyl chloride were
reacted to produce methyliminodiacetic chloride. The organic
chloride is then reacted with di-n-octylamine in the presence
of triethylamine under the freezing point. After synthesis, the
products were washed by water, sodium hydroxide and hydro-
chloride solutions, and purified repeatedly by passing the solu-
tions through silica-gel columns. Its purity was determined
to be 97% by liquid chromatography. The 1H NMR signals
for MIDOA were found (CDCl3): ꢀ 0.9 (t, –CH3), 1.2–16
(–C6H12–), 2.5 (s, –CH3), 3.3 (t, –CH2–), and 3.5 (s, –CH2–).
The solvent extraction was performed as the following method,
two cm3 of the pre-equilibrated organic phase was taken and
mixed with the same volume of the aqueous phase, spiked with
Tc-99 solution or the non-radioactive metal solution. The mix-
ture was shaken mechanically for 2 h at 25 ꢂ 0:1 ꢃC. After cen-
trifugation and separation of the phases, duplicate 0.50 cm3 ali-
quots for both aqueous and organic phases were measured by a
liquid scintillation counter (Tri-Carb 1600 TR, Packard Instru-
ment Company) for the beta activities of 99Tc in 5 cm3 of the
scintillation cocktail. The amounts of the non-radioactive
metal ions in the sample solutions prepared from the aqueous
and the organic phases were measured by an ICP-AES
(SPS 3100, Seiko Instruments Inc) or an ICP-MS (SPQ 9000,
Seiko-EG&G) spectrometers.
2ꢁ
that the oxonium anions, like TcO4ꢁ, ReO4ꢁ, Cr2O7
,
MoO42ꢁ, and WO42ꢁ, are extracted, and the distribution ratios
(D) decrease with increase of HNO3 concentration.
The separation methods for the long-lived radioactive met-
als, the heat source and the noble metals from high-level radio-
active liquid waste (HLW) has been developing over 5 decades.
Not only actinides but also Sr, Cs, Tc, Pd, Rh, Ru, and Mo are the
aimed elements in this partitioning process, the chemical separa-
tion method to recover Tc, which has a long half life decaying, a
catalytic and a medical use, has been studied intensively.1–5
Among these metals, Tc and Mo behave as an oxonium acid
in the aqueous solution, the specific chemical forms have some
difficulties to extract these metals by the existing neutral and
the acidic extractants. The analytical information up to now sug-
gested that the extraction conditions to exhibit the high D(Tc)
values are out of HNO3–dodecane.6–10 Some monoamides can
extract Tc from HNO3 to hydrocarbons but with D of approxi-
mate or lower than 0.1.11,12 The solvent extraction by CMPO
and TBP, whose condition has been used in PUREX and
TRUEX processes, can give D(Tc) as 1.48 and 2.36,13 these re-
sults indicate that the multi-step extraction is necessary to
achieve the quantitative extraction of Tc. Some reports suggest-
ed that D(Tc) increases according to the concentration of co-ex-
tracted metal,11,14 in this case the calculation for its recovery be-
come difficult. Therefore, the development of the neutral extrac-
tant, which has a high solubility in n-dodecane and shows a high
performance on Tc extraction from nitric acid, is still-required.
The novel extractant, 2,20-(methylimino)bis(N,N-dioctyl-
acetamide) (MIDOA, see Figure 1), has three donors of two car-
bonyl oxygen and one nitrogen in the ether position. MIDOA,
composed of carbon, nitrogen, hydrogen, and oxygen atoms, is
expected to have the strong extractability by tridentation, as an
The solubility of MIDOA into n-dodecane was examined by
observation, the clear solution of 1.66 g/cm3 can be obtained.
This solubility corresponds to approximate 1.1 M (=mol/dm3)
of MIDOA in n-dodecane. The C/O ratio of MIDOA is 18.5,
which considers the very high lipophilic property compared to
other extractants,16,17 this extractant is applicable to HNO3–n-
dodecane extraction system.
2ꢁ
Extraction of oxonium anions, TcO4ꢁ, ReO4ꢁ, Cr2O7
,
MoO42ꢁ, and WO42ꢁ, was performed and Figure 2 indicates
the relation between HNO3 concentration and D(M). Here, other
oxonium ions and some metal cations were hardly extracted. As
shown in Figure 2, D for these metals depend on the HNO3 con-
centration and Tc and Re have remarkably high D values from
0.1 M HNO3 to n-dodecane. The publications for Tc coordina-
tion have introduced the soft donor ligands,18,19 MIDOA has
one N donor in the center of backbone, which suggests N or S
coordination is important for the Tc extraction. Concerning with
this, TODGA (N,N,N0,N0-tetraoctyldiglycolamide), whose ether
oxygen is positioned at N donor of MIDOA, has low D(Tc)
(=2).20 Hard donor coordination may decrease D(Tc). As shown
in Figure 2, D decreases with increase of the HNO3 concentra-
C8H17
C8H17
N
CH2
N
CH3
CH2
C
O
C
C8H17
N
O
C8H17
Figure 1. Structure of MIDOA.
Copyright Ó 2007 The Chemical Society of Japan