Method of separating a trivalent actinide from a trivalent...

Details Method of separating a trivalent actinide from a trivalent... Method of separating a trivalent actinide from a trivalent...

2000-03-16

2001-11-06

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Treating mixture to obtain metal containing compound

Radioactive metal

C423S021500, C252S184000

Reexamination Certificate

active

06312654

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a method of separating trivalent actinides from at least one trivalent lanthanide using an extraction-medium containing an extractant and an extraction synergist.
BACKGROUND OF THE INVENTION
The separation of trivalent actinides like americium or curium, from trivalent lanthanides has long been a problem. The reason for the difficulties in the separation of these elements is the very close chemical properties of the trivalent ions of the lanthanides and actinides. Especially the very similar ionic radii contribute to similar properties of these element groups. Thus numerous investigations have hitherto been undertaken to separate the trivalent ions of the actinides and lanthanides with the highest possible selectivity and increased efficiency.
It is indeed known that extraction agents with mild donor groups like nitrogen or sulphur as complex formers contain structural components which in liquid-liquid extraction have a certain selectivity with respect to trivalent actinides although up to now such separations have been carried out only at relatively high pH values which tend to precipitate formation of the trivalent actinides or require 10 molar LiCl solutions.
In the publication K. L. Nash, Solvent Extr. Ion Exch. 11 (4), 729-768 (1993) the Talspeak process is described and enables selective extraction of lanthanides with the aid of complexing agents which maintain the trivalent actinides in solution. However, this separating process is also carried out at a relatively high pH value of 3-4 and requires the addition of further salts.
A process developed by the Applicant for the extraction of trivalent actinides from aqueous solutions which contain trivalent actinides and trivalent lanthanides, enables a separation at high acid concentrations of 0.01 to 2 mol/liter HNO
3
. Following this process, such an aqueous acid solution which contains a mixture of trivalent lanthanides and actinides is extracted by means of an organic solvent. With this process, because of the low pH value or the high acid concentration, a precipitate formation of the trivalent actinides is hindered and good separation results are obtainable. To evaluate the separation results, characteristic values such as the distribution coefficient D and the separation factor &agr; are considered
D
An(III)
=[An(III)
org
]/[An(III)
w
]  (1)
In formula 1:
D
An(III)
=distribution coefficient for a trivalent actinide (dimensionless)
[An(III)
org
]=concentration of the trivalent actinide in the organic phase (mole/liter)
[An(III)
w
]=concentration of the trivalent actinide in the aqueous phase
D
Ln((III)
=[Ln(III)
org
]/[Ln(III)
w
]  (2)
In formula 2:
D
Ln(III)
=Distribution coefficient for a trivalent lanthanide (dimensionless)
[Ln(III)
org
]=concentration of the trivalent lanthanide in the organic phase (mole/liter)
[Ln(III)
w
]=concentration of the trivalent lanthanide in the aqueous phase.
&agr;=D
An(III)
/D
Ln(III)
&agr;=separating factor (dimensionless) depending upon the process, the use of bis(aryl)dithiophosphonic acid in strongly acid medium can produce separating factors &agr; lying between about 20-50.
OBJECT OF THE INVENTION
It is therefore the object of the invention to provide a method for extraction of trivalent actinides from a solution containing at least one trivalent actinide and at least one trivalent lanthanide, and/or trivalent lanthanum and/or trivalent yttrium and, to provide an extraction agent which enables higher separating factors &agr; to be obtained. It should therefore be possible to carry out the method at lower pH values or higher acid concentrations.
SUMMARY OF THE INVENTION
With the method and extraction agent of the invention it is possible at the same time to achieve a higher separation factor cx while maintaining extraction conditions at lower pH values or higher acid concentrations.
Advantageously further features of the invention are given in the dependent claims.
The invention will be elucidated below by way of example.
An aqueous phase contains trivalent ions of lanthanides (cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pr), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), luthenium (Lu), as well as lanthanum (La) and yttrium (Y) or at least one component of this group and ions of trivalent actinides, like americium (Am) and/or curium (Cm). The aqueous phase has a low pH value which can correspond to a H
+
concentration of a strong acid of 0.01 to 2 mole per liter. As acids, HCl, H
2
SO
4
and especially HNO
3
can be used since HNO
3
forms readily soluble salts. The extraction is carried out by means of an organic solvent which contains as extraction medium bis(aryl)dithiophosphonic acid of the general formula (4)—R
2
PS(SH)
where:
R
1
=phenyl or naphthyl,
R
2
=phenyl or naphthyl, as well as methyl-, ethyl-, propyl-, isopropyl-, cyano-, nitro-, halogenyl- (Cl—, F—, Br—, J—) substituted residues of R
1
and R
2
whereby R
1
and R
2
can be substituted with at least one of the components from the group of methyl, ethyl, propyl, isopropyl, cyano, nitro, halogenyl (Cl, F, Br, I).


REFERENCES:
patent: 4162230 (1979-07-01), Horwitz et al.
patent: 4647438 (1987-03-01), Sabot et al.
patent: 4867951 (1989-09-01), Smith et al.
patent: 5966584 (1999-10-01), Modolo et al.
patent: 0 210 387 A1 (1987-02-01), None
A Review of the Basic Chemistry and Recent Developments in Trivalent Element Separation published in Solvent Extraction 11(4), 729-768 (1993), No month.
The Separation of Trivalent Actinides From Lathanides . . . published in Journal of Alloys and Compounds 271-273 (1998), No month.

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