Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Radioactive metal
Patent
1993-07-27
1996-04-23
Ivy, C. Warren
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Radioactive metal
546169, 546323, C01G 5600, C01G 4300, C01F 1700
Patent
active
055100902
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/FR92/01124, filed 2 Dec. 1992. The present invention relates to a process for the selective extraction of (III) actinides by means of amides having a nitrogenous heterocyclic substituent more particularly usable for separating trivalent actinides from trivalent lanthanides.
In irradiated nuclear fuel reprocessing installations, during the initial extraction stages, normally uranium and plutonium are obtained, together with aqueous solutions of fission products containing relatively large quantities of trivalent ions from the lanthanide and actinide series. The aqueous effluents from such installations also contain the same ions.
In view of the very long half-life of actinide elements, it is very important to be able to separate all the (III) actinides from the (III) lanthanides, if it is wished to carry out an extensive reprocessing and eliminate the (VI), (IV) and (III) actinides from all the waste materials.
For the transmutation of the separated actinides, it is necessary to separate the lanthanides, which are poisons during the nuclear reactions used for the transmutation.
Up to now the trivalent actinides have been extracted from the aqueous solutions by using organic extractants and in particular propane-diamides, as described in FR-A-2 537 326 and FR-A-2 585 692. However, these extractants are not completely satisfactory, because they lack selectivity for the trivalent ions of series 4f and 5f, whose ionic radii are in the range 0.09 to 0.11 nm and they consequently simultaneously extract trivalent lanthanides. Thus, the ligands, whose interaction with the trivalent ions of series f is of the purely ionic type, do not selectively complex the trivalent lanthanides or actinides.
In order to carry out such a separation, up to now use has been made of other ligands, e.g. mixtures of ligands, such as the mixture of 2,4,6-tri-(2-pyridyl)1,3,5-triazine and dinonyl naphthalene sulphonic acid described in FR-A-2 509 282 and the mixture of Di-2-ethyl hexyl dithiophosphoric acid and tributyl phosphate or trioctyl phosphine oxide described in EP-A-43 765.
Although these mixtures give good results, research has continued for finding other organic ligands which can be used alone for selectively extracting actinides or lanthanides. This research has led to the finding that amides with a nitrogenous heterocyclic substituent had this property and are suitable for selectively extracting trivalent actinides and for separating them from the trivalent lanthanides.
The present invention therefore relates to a process for the selective extraction of the trivalent actinides present in an aqueous solution, characterized in that it consists of extracting the trivalent actinides by an amide having a nitrogenous heterocyclic substituent of formula: ##STR3## in which R.sup.1, R.sup.2 and R.sup.3, which are the same or different, represent hydrogen atom or an alkyl or alkoxy group and ##STR4## in which R.sup.5 and R.sup.6, which are the same or different, represent a hydrogen atom or an alkyl or alkoxy group.
In the above formulas, the alkyl and alkoxy groups which can be used can be straight or branched and generally have 1 to 24 carbon atoms.
The amides with a nitrogenous heterocyclic substituent according to the above formulas (I) and (II) are complex compounds with oxygen and nitrogen donor atoms.
In these molecules, nitrogen is a weaker donor than the oxygen of the conventional extractants and it can give rise to partly covalent bonds. As the covalency is higher with ions of the 5f series, this leads to a stronger complexing with respect to the actinides than the lanthanides, so that the said actinides can be selectively extracted from a mixture of trivalent lanthanides and actinides.
These amides are of interest, because they are completely incineratable organic molecules, so that it is easily possible to solve the problems of the processing of waste when said amides are used as the solvent in an active medium for actinide - lanthanide separation.
The amides having a nitrogenous heterocycli
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Cuillerdier Christine
Musikas Claude
Commissariat a l''Energie Atomique
Ivy C. Warren
M. Mach D. Margaret
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