Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Radioactive metal
Reexamination Certificate
2000-04-19
2001-10-23
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Radioactive metal
C423S010000, C423S021500, C210S634000, C210S638000, C210S643000
Reexamination Certificate
active
06306355
ABSTRACT:
DESCRIPTION
1. Field of the Invention
This invention involves a process for separation of actinides and lanthanides 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 membrane transport by means of calixarenes.
2. State of the Prior Art
Separation of 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 use 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,
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 ortho-nitrophenoxyalkyl groups.
Membrane Transport
These calixarenes can also be used to extract actinides and/or lanthanides by membrane transport through a microporous membrane of which the pores are filled with an organic phase containing the calixarene(s).
In this organic phase, an orthonitrophenyl alkyl ether such as orthonitrophenyl hexyl ether is used as a diluent for the calixarene(s).
With this process, the actinides and/or lanthanides are recovered in a solution containing a complexing agent such as methylene diphosphonic acid.
The use of such a solution presents the drawback of introducing new organic compounds which can hinder the later operations.
Also, the organic phases used do not allow for good separation of actinides and lanthanides from each other from various solutions.
SUMMARY OF THE INVENTION
This invention precisely involves a process for extraction of actinides and lanthanides by membrane transport using a more advantageous re-extraction solution which also allows for separation of actinides and lanthanides from each other from both acid and saline solutions.
According to the invention, the process for separating at least one metal chosen from among the actinides and lanthanides from a first aqueous solution involves putting the aforesaid aqueous solution into contact with one of the sides of a microporous membrane bearing an immiscible organic phase containing at least one calixarene of 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 to put the other side of the aforesaid microporous membrane into contact with an aqueous re-extraction solution to transfer the metal(s) of the first aqueous solution into to the second aqueous re-extraction solution, the immiscible organic phase being made of a solution of the aforesaid calixarene(s) in an organic diluent, and the second aqueous re-extraction solution being an aqueous solution of a mineral acid having a pH less than or equal to 4, for example a nitric acid concentration of 10
−4
to 10
−1
mol/L.
The use of an aqueous re-extraction solution made from a mineral acid is very advantageous.
This solution is non-complexing, it does not contain a hindering organic compound, it has a very low mineral acid concentration and it is more economical that the aqueous solutions of complexers used in FR-A-2 729 958.
In this aqueous re-extraction solution, the mineral acid can be in particular nitric acid; in this case, a nitric acid concentration of 10
−2
mol/L is particularly advantageous.
A microporous membrane bearing the immiscible organic phase including at least one calixarene of formula (II) is used for the invention process.
The microporous membrane can be made of a polymer, for example polyethylene, polysulphone, polypropylene, polyvinylidene fluoride or polytetrafluoroethylene. A thin membrane with high porosity and small diameter pores is advantageously used. The membrane is generally 25 to 100 &mgr;m thick, for example 25 &mgr;m, with a porosity of 45 to 60%, preferably 45%, and an average pore radius from 20 to 1000 nm, preferably about 40 nm. The microporous membrane used could in particular be that marketed under the CELGARD brand name.
According to the invention, the organic diluent used to form the organic phase borne by the microporous membrane is chosen so as to obtain a stable membrane which allows for efficient transport of the metal(s) into the slightly acidic aqueous re-extraction solution.
For this purpose, the diluent must meet the following criteria:
insoluble in water
non-volatile, and
having a viscosity suitable for transport and a sufficiently high interfacial tension with the aqueous phases, for example at least 4 mN/m.
Appropriate diluents could belong for example to the group of heavy alcohols, having more than 10 carbon atoms and which are insoluble in water, for example 10 to 13 carbon atoms such as isotridecanol, and mixtures of heavy alcohols and alkylbenzenes, for example a mixture of isotridecanol and hexylbenzene. The choice of these organic diluents allows for transport of metals of the lanthanide and actinide groups from a saline or acid solution to an aqueous re-extraction solution.
Nitro phenyl alkyl ethers such as ortho-nitrophenyl hexyl ether can also be used, but in this case a first aqueous saline solution should be used to obtain transport of the actinides and lanthanides into the aqueous re-extraction solution.
In the organic phase, calixarenes selected from those described in FR-A-2 729 958 can be used. Calixarenes of formula (II) in which R
1
and R
2
represent an alkyl group with C
5
to C
18
, and R
3
and R
4
both represent phenyl groups are preferably used.
The formula below gives an example of the calixarenes which can be used:
in which Ph represents the phenyl group.
The calixarene concentration in the organic phase is chosen so as to obtain good selectivity in transport of the various metals.
Calixarene concentrations of 5.10
−3
to 5.10
−4
mol/L are generally appropriate.
The microporous membrane bearing the organic liquid phase is prepared by soaking the membrane in a small quantity of the organic phase or solution using, for example, about 1.2·10
−3
cm
3
of solution per cm
2
of membrane, in a low vacuum, for at least 15 minutes. The surplus organic solution is eliminated after this operation.
In order to apply the invention process, the microporous membrane bearing the organic liquid phase can be put in a chamber so as to separate this chamber into two compartments, the first compartment in contact with one of the sides of the membrane containing the first aqueous solution of the metals to be separated and the second compartment in contact with the other side of the membrane containing the second aqueous re-extraction solution.
The invention process can be used to separate actinides and lanthanides from aqueous solutions from in particular processing of spent nuclear fuels, such as generally acidic solutions and aqueous effluents from these facilities which are often saline media. The invention process can also be
Bohmer Volker
Delmau Laetitia
Dozol Jean-François
Jakobi Ralf A.
Mogck Oliver
Bos Steven
Commissariat A l'Energie Atomique
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Method for separating actinides and lanthanides by membrane... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for separating actinides and lanthanides by membrane..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for separating actinides and lanthanides by membrane... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2582957