Chemistry Reference
In-Depth Information
pyridinum nitrogen atoms allows good extraction from diluted acid. For example
,
log
D
Tc
= 1 for 2 mM 4PyOC4Q in CHCl
3
, and stripping can be achieved with
strongly acidic solutions.
4.5 eXtRACtIon oF ACtInIDes
Three European projects have been devoted to the extraction of the long-lived ele-
ments and in particular of actinides.
16 -18
Initially, the goal of the project was to decat-
egorize the effluents by eliminating cesium, strontium, and actinides with a mixture
of extractants. Then, a much more ambitious project was launched consisting in sepa-
rating selectively the actinides from other elements including lanthanides, contained
in high-activity liquid waste arising from the PUREX process, in only one step,
stimulating the search for extractants based on the calixarenes bearing one or several
ligands. For more information on the separation of actinides from lanthanides, it is
recommended to refer to Chapter 3 of this topic, dedicated to this subject.
Organophosphorus extractants have an exceptional ability to extract hard cat-
ions, particularly actinides and lanthanides, but monodentate organophosphorus
ligands, even the most powerful ones such as alkylphosphine oxides (the most used
is trioctyl phosphine oxide (TOPO)), only extract actinides(IV) and (VI) and to a
lesser extent (V) from low acidity media. Due to their relatively low charge densi-
ties, actinides(III) and lanthanides usually show a weak complexing ability with
most chelating agents in nitric acid solution. Some bidentate neutral ligands have
been developed as useful extractants for actinides, for example, dihexyl-
N,N
- d i e t
hylcarbamoylmethylphosphonate (DHDECMP). Horwitz et al. synthesized and
studied several carbamoylmethylphosphine oxide derivatives.
146 -151
In carbamoyl-
methylphosphine oxides (CMPOs), the C = O and P = O groups act as the ligating
functions, and compounds bearing numerous residues at the nitrogen (R
1
, R
2
) and
phosphorus (R
3
, R
4
) atoms in various combinations have been tested. Among them,
diphenyl-
N,N
-diisobutyl carbamoyl methyl phosphine oxide (DΦCMPO) and finally
octyl(phenyl)-
N,N
-diisobutylcarbamoylmethylphosphine oxide (OΦCMPO) were
chosen to remove actinides, whatever their oxidation states, from acidic medium
activity waste (TRUEX Process).
These compounds, tested in NPHE at Cadarache, were used as reference com-
pounds for the extraction of actinides by functionalized calixarenes (see below). The
distribution ratios for neptunium mainly at the oxidation state (V), plutonium at the
oxidation state (IV), and americium (III) are shown in Table 4.21 for OΦCMPO. They
were also used as references for the americium over europium selectivity (Table 4.22).
tAbLe 4.21
Distribution Ratios for np, Pu, and Am From Aqueous solutions 4 M
nano
3
, 1 M Hno
3
into a nPHe solution of of
Φ
D(ib) CMPo (10
−
2
M)
o
Φ
CMPo
237
np
239
Pu
241
Am
0.85
22
1.2
