Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Radioactive metal
Reexamination Certificate
2000-04-27
2001-11-06
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Radioactive metal
C423S010000, C423S021500, C210S638000, C210S634000
Reexamination Certificate
active
06312653
ABSTRACT:
FIELD OF THE INVENTION
This invention involves a process for separation of actinides and lanthanides from each other from an aqueous solution containing them.
Such solutions could be in particular aqueous solutions from used nuclear fuel treatment facilities, such as fuel dissolving solutions or aqueous effluents.
They could also be aqueous solutions from processing of rare earth, thorium and/or uranium ores.
More precisely, it involves separation of such metals by liquid-liquid extraction by means of calixarenes.
STATE OF THE PRIOR ART
Separation among lanthanides and actinides
In the former technique, liquid-liquid extraction processes were used to separate lanthanides among themselves by means of organic extractors such as di(2-ethylhexyl)phosphoric acid, amines, quaternary ammonium salts and tributyl phosphate, as described in Engineering Techniques J 6630-1 to J6630-8. The most selective extractor is di(2-ethylhexyl)phosphoric acid, which favours extraction of heavy lanthanides with low ionic radii.
Calixarenes substituted by acetamidophosphine oxide groups
The used of macrocyclic ligands such as calixarenes was also considered for extraction of actinides and lanthanides present in aqueous solutions as described in document FR-A-2 729 958.
The calixarenes used in this document have the formula:
in which m is equal to 0 or 1, where
n is a whole number from 2 to 8, with 4·(m+1)×n·8
R
1
and R
2
which can be identical or different, are alkyl or o-nitrophenoxyalkyl groups, and
R
3
and R
4
which can identical or different, are alkyl or aryl groups.
These calixarenes can be used to extract actinides and lanthanides from aqueous solutions from used nuclear fuel processing.
They are functionalised on their upper edges by acetamidophosphine oxide substituents which have good affinity for actinides and lanthanides and they are substituted on the lower edge by alkyl or o-nitrophenoxyalkyl groups.
For liquid-liquid extraction of actinides and lanthanides, these calixarenes are dissolved in an appropriate organic diluent such as nitrophenyl alkyl ethers, such as orthonitrophenyl hexyl ether.
Good extraction rates are obtained with such an organic diluent, but it is impossible to separate the actinides and lanthanides from each other.
Document JP-A-06/228032 describes the use of a mixture of chloroform and another organic solvent such as chlorobenzene or toluene to dissolve a calixarene in order to prepare calixarene films from the somution obtained.
SUMMARY OF THE INVENTION
The invention precisely involves a process for separating actinides and lanthanides by means of such calixarenes, according to which the diluent and the calixarene concentration are chosen in order to obtain a separation of the actinides and lanthanides from each other.
According to the invention, the process for separation of at least one metal M1 chosen in the group of actinides and lanthanides from at least one metal M2 chosen from the same group from an aqueous solution containing M1 and M2, includes the following steps:
a) putting the aqueous solution of the aforesaid metals M1 and M2 into contact with the organic liquid phase including
at least one calixarene with formula:
in which:
R
1
and R
2
which can be identical or different, are alkyl or o-nitrophenoxyalkyl groups, and
R
3
and R
4
which can identical or different, are aryl groups; and
an organic diluent
the aforesaid diluent and the calixarene concentration of the organic phase being chosen so that the distribution coefficient of the metal(s) M1 between this organic phase and the aforesaid aqueous solution is greater than 1 and the distribution coefficient of the metal(s) M2 between this organic phase and the aforesaid aqueous solution is less than 1; and
b) separating the aforesaid aqueous solution from the aforesaid organic phase.
It should be remembered that the distribution coefficient of a metal M such as M1 or M2 is defined by the following formula:
D
M
=
[
M
]
org
,
eq
[
M
]
aq
,
eq
in which [M]
org,eq
corresponds to the concentration of the metal in the organic phase at equilibrium, and [M]
aq,eq
corresponds to the concentration of this same metal in an aqueous solution at equilibrium. For example, the extraction can be monitored by a radioactive tracer. This distribution coefficient D is determined with respect to the activity of the metal in the organic phase and the activity of the metal in the aqueous solution at equilibrium.
When D is greater than 1, the metal goes mostly into the organic phase; when D is less than 1, the metal remains mostly in the aqueous phase.
To separate various actinides and lanthanides by liquid-liquid extraction, the distribution coefficients of metals M1 to be extracted in the organic phase must be high with respect to those of metals M2 which must remain in the aqueous phase.
According to the invention, it was found that by choosing an appropriate organic diluent and by adjusting the calixarene concentration of the organic phase, a coefficient D greater than 1 could be obtained for certain elements and a coefficient D less than 1 for other elements, although this was practically impossible with the diluent used up until now, orthonitrophenyl alkyl ether.
The choice of diluent and calixarene concentration depend not just on the metals to be separated but also on the nature of the starting aqueous solution, as will be seen below.
According to the invention, the choice of organic diluent can in particular be made by determining the distribution coefficient D
Gd
of gadolinium between an organic phase composed of calixarene in solution in the diluent and an aqueous solution of gadolinium. In this case, the diluents which are suitable are those for which the distribution coefficient D
Gd
of gadolinium between the organic phase and the aqueous solution of gadolinium is from 0.5 to 5 when the calixarene concentration of the organic phase is from 10
−4
to 10
−3
mol/L.
Appropriate diluents could belong in particular to the group of heavy alcohols, for example with formula C
n
H
2n
O with n·7, particularly with n from 7 to 13. Octanol and isotridecanol are examples of such alcohols. Chlorinated solvents such as chloroform, dichloromethane and 1,2-dichloroethane can also be used. Mixtures of diluents can also be used.
The calixarenes which can be used in the invention process are to be selected from those described in FR-A-2 729 958. Calixarenes which correspond to formula (II) above must be used, and particularly those of formula (II) in which R
1
and R
2
are alkyl groups of 3 to 18 carbon atoms and R
3
and R
4
are phenyl groups.
The following formula can be given by way of example of calixarenes which can be used:
in which Ph represents a phenyl group.
With the calixarenes used in the invention, the length of chain R
1
can vary because, as was seen, chain length has almost no influence on the extraction capacity of calixarene with respect to element of the lanthanide and actinide groups.
According to the invention, the calixarene concentration of the organic phase depends in particular on the organic diluent used. In general, calixarene concentrations are between 10
−4
and 5·10
−2
mol/L.
The invention process can be used in the following manner.
First, the organic phase, which is immiscible in water, is prepared by dissolving calixarene in the diluent used, then the aqueous solution containing the metals to be separated is mixed in and stirred for at least 10 minutes at a temperature of 10° C. to 35° C. The two phases are then separated by centrifuging of the mixture at a speed of at least 2500 rotations/min, for example 3000 rotations/min, for about 5 minutes.
According to the invention, to improve the yield of extraction of the metal(s) M1 in the organic phase, the organic phase can be put in contact with the aqueous phase in several stages to enrich the organic phase with metal(s) M1 in each stage. After each contact, the organic liquid phase is separated from the aqueous solution. All of the operations can be done in classic liquid-liq
Bohmer Volker
Delmau Laetitia
Dozol Jean-François
Eymard Serge
Gruttner Cordula
Bos Steven
Commissariat A l'Energie Atomique
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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