Chemistry Reference
In-Depth Information
1 to 2 and
G
(ethylene) ranged from 0.02 to 0.15 molecule/100 eV, depending on
the irradiation conditions (
76
).
After irradiation with 3.3 MGy of a DCH18C6 solution in 1 mol L
−1
nitric acid
containing 20 g L
−1
of uranyl nitrate, compounds 2 and 4 (presented in Figure 8.15
with their radiolytic yields) were shown to be the main products of radiolysis; never-
theless, 50% of DCH18C6 remained unchanged. In these conditions, the disappear-
ance yield
G
(-DCH18C6) was estimated to be 0.72 molecule/100 eV (
7
).
An increase in the acidity from 1 to 2 mol L
−1
had a very slight influence on
the macrocycle degradation. But the presence of a high concentration of uranium
(250 g L
−1
) in the DCH18C6 solution decreased the radiolysis of DCH18C6 and
changed the distribution of degradation products: the least fragmented product (com-
pound 8) was the main compound (
G
~ 0.16 molecule/100 eV) (
252
).
8.3.5.1.2 Influence of the Diluent
The radiolytic degradation of DCH18C6 was strongly influenced by the nature of
the diluents. An experimental approach with gas chromatography concluded on
the following order of stability: chloroform > cyclohexane >1-octanol > toluene
(
254
). The degradation inhibition in toluene was explained, as for previous extract-
ants, by a lower ionization potential of toluene than that of crown ether. DCH18C6
suffered extensive decomposition in chloroform solution. Moreover, crown ethers
exhibited high affinity toward inorganic chloroform radiolysis products (such as
HCl, C
2
Cl
6
…) resulting in the formation of complexes (
44, 255
).
8.3.5.1.3 Influence on Extraction Behavior
The variation of strontium distribution ratios
D
Sr
from nitric acid solution was inves-
tigated as a function of the irradiation dose. In toluene DCH18C6 solution,
D
Sr
was
minimally affected by radiolysis, but decreased with the absorbed dose in the other
nonaromatic solvents (
254
). Nevertheless, the distribution ratios measured after radi-
olysis were higher than expected, given the remaining extractant concentration, indi-
cating some contribution from the degradation products (e.g., after an
irradiation of
0.84 MGy, 70% of the crown ether was destroyed in chloroform, while the distribu-
tion ratio exhibited a decrease of only 30%) (
254
).
Extraction of U(VI) and Pu(IV) from 1 to 8 mol L
−1
HNO
3
solutions by radiolytically
degraded DCH18C6 in toluene was studied (
256
). A decrease in the distribution ratios for
both U and Pu was observed for irradiation in the range 0.010-0.071 MGy, with a higher
effect for Pu(IV). For 0.2 mol L
−1
DCH18C6-toluene solution in contact with 3 mol L
−1
nitric acid,
D
U
decreased from 0.21 to 0.12 and
D
Pu
from 64.3 to 6.42 after a dose of 0.07
MGy. This behavior was explained by both diluent and extractant degradation.
Some degradation products (compounds 2, 3, and 4, see Figure 8.15) were syn-
thesized to evaluate their influence on extraction (
252, 253
). The simultaneous addi-
tion of these three compounds at a concentration of 2 × 10
−3
mol L
−1
did not modify
the extraction of Pu, U, and Sr (DCH18C6 0.134 mol L
−1
in chloroform -HNO
3
4.9
mol L
−1
), but higher amounts (7.35 × 10
−3
mol L
−1
for each compound) led to a slight
decrease of
D
Pu
, whereas no effect was observed on
D
U
and
D
Sr
.
The radiolytic behavior of a solution of D
t
BuCH18C6 (di-
t
-butylcyclohexano-18-
crown-6) in 1-octanol was assessed by measuring the distribution ratio of strontium
