Chemistry Reference
In-Depth Information
80
DBOA
DiBOA
DBEHA
MBEHA
60
DiBEHA
40
20
0
0
0.5
1
1.5
Dose (MGy)
FIGURe 8.5
Effect of the structure on the radiolytic stability of
N,N
-dialkyl aliphatic
amides in
n
-dodecane: % degraded extractant. Experimental conditions: irradiation with a
2000 Curie
60
Co gamma-irradiator (4.2 kGy h
−1
dose rate) of 0.5 M monoamide in
n
-dodecane
solution pre-equilibrated with 3.5 M HNO
3
. DBOA:
N,N
-dibutyloctanamide, DiBOA:
N,N
-
di-iso-butyloctanamide, DBEHA:
N,N
-dibutyl-2-ethylhexanamide, MBEHA:
N
-methyl,
N
-
butyl-2-ethylhexanamide, DiBEHA:
N,N
-di-iso-butyl-2-ethylhexanamide. (Drawn from
data in Ruikar, P. B., Nagar, M.S., Subramanian, M.S., Gupta, K.K., Varadanajan, N., Singh,
R.K.,
J. Radioanal. Nucl. Chem.
, 1: 171-178, 1995; Ruikar, P.B., Nagar, M.S., Subramanian,
M.S.,
J. Radioanal. Nucl. Chem., Lett.,
176(2): 103-111, 1993; Ruikar, P.B., Nagar, M.S.,
Subramanian, M.S.,
J. Radioanal. Nucl. Chem.,
159(1): 167-173, 1992.)
distribution ratio remaining stable (see Figure 8.6a). This behavior has been attrib-
uted to the decrease of the extractant concentration (
197
) (14-30% at 1 MGy). HNO
3
concentration seemed to have no influence (
187
).
For an irradiation dose of 0.35 MGy, the extent of the decrease in
D
U
was the
same (30-35%) in the case of 0.5 mol L
−1
DEH
i
BA and 5% TBP; but with higher
concentrations of TBP (0.5 or 1 mol L
−1
in dodecane (
191
) and benzene (
194
)), it
must be remembered that
D
U(VI)
systematically increased after gamma irradiation.
In benzene, Mowafi observed some differences between symmetrical amides
RCONR′
2
and unsymmetrical amide RCON(CH
3
)R´. The inluence of the dose on
D
U(VI)
was stronger for
N
-methyl-
N
-alkyl amides (reduction of factor 4 compared to
factor 1.7-1.8 for RCONR′
2
) (
192
), related to the extractant's lower stability.
However, the effect on Pu(IV) extraction was totally different: after a first step,
where the decrease with the dose was very low (factor of 2), the extraction increased
rapidly and then decreased (Figure 8.6b) (
194, 200
). The last two steps have been
explained by authors as:
