Method of separating and purifying gadolinium-153

Details Method of separating and purifying gadolinium-153 Method of separating and purifying gadolinium-153

1998-11-10

2001-06-12

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Treating mixture to obtain metal containing compound

Radioactive metal

C423S021100

Reexamination Certificate

active

06245305

ABSTRACT:

FIELD OF THE INVENTION
The present invention is a method of separating and purifying gadolinium-153 from irradiated europium containing a mixture of at least gadolinium-153 and europium. More specifically, the present invention is a method for the dissolution, separation and purification of gadolinium-153 from an irradiated target of europium oxide (Eu
2
O
3
) containing isotopes of Eu, Sm and Gd.
As used herein, the term “chemically separating” or “chemically reducing” excludes the use of externally applied voltage to effect a change in valence.
BACKGROUND OF THE INVENTION
Gadolinium-153, with a half-life of 242 days, has been used in the early detection and tracking of osteoporosis. (Osteoporosis is a crippling brittle-bone disease that affects 20 million Americans, mostly women over the age of 45.) Presently it is used as a calibration source for single photon emission computerized tomography (SPECT) cameras. Curie amounts of
153
Gd have been produced in the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory in Oak Ridge, Tenn; at the Fast Flux Test Facility (FFTF) at the DOE Hanford site in Richland, Wash.; and at the Argonne Test Reactor (ATR) at Idaho Falls, Id., by the nuclear reactions:
151
Eu
(n,&ggr;)
→
152
Eu
(−&bgr;)
→
152
Gd
(n,&ggr;)
→
153
Gd.
The isotopic composition of the irradiated Eu target varies with the nuclear reactor properties but is approximately as shown in Table 1.
TABLE 1
Composition of Irradiated Europium (FFTF Reactor)
(Basis: 1 g of target RE oxide at discharge)
Initial Final
Activity
Isotope
Mass(gm)
Mass(gm)
(Ci)
Half-life, days
Eu-150
—
2.00E − 04
330
5.25E − 01
Eu-151
0.47
2.88E − 01
—
Stable
Eu-152
—
7.66E − 02
13.6
4.82E + 03
Eu-152m
—
1.00E − 04
220
3.88E − 01
Eu-153
0.53
2.34E − 01
—
Stable
Eu-154
—
1.99E − 01
53.8
3.12E + 03
Eu-155
—
8.70E − 02
40.3
1.81E + 03
Eu-156
—
7.20E − 03
397.4
1.51E + 01
Sm-150
—
2.00E − 04
—
Stable
Sm-151
—
1.00E − 06
<
3.18E + 04
Sm-152
—
1.46E − 02
—
Stable
Sm-153
—
2.00E − 04
86.7
1.96E + 00
Sm-154
—
1.00E − 04
—
Stable
Gd-151
—
1.00E − 05
0.07
1.20E + 02
Gd-152
—
6.19E − 02
<
1.10E + 14
Gd-153
—
1.90E − 03
6.67
2.42E + 2 
Gd-154
—
7.00E − 04
—
Stable
Gd-155
—
2.00E − 03
—
Stable
Gd-156
—
2.05E − 02
—
Stable
All of the samarium isotopes (Table 1) are either stable, generated in insignificant amounts, or have decayed to zero (i.e. Sm-153); and only Eu-152, Eu-154 and Eu-155 contribute to the gamma dose, if the targets are “cooled” for ~150 days before processing. If the Eu isotopes are 99.999% removed, no additional processing may be required.
Dissolution, separation and purification of Europium from other rare earths including gadolinium has been done as reported by McCoy (1935) and Yost (1946), in which dissolution was in sulfuric acid. Separation began with reducing the Eu
+3
to Eu
+2
with zinc either in the form of zinc dust or as an amalgamated (mercury coated) zinc column in the form of a Jones reductor, followed by precipitating the Eu
+2
fraction as EuSO
4
with the sulfate from the sulfuric acid. Dissolution and separation were in a non-oxidative environment of carbon dioxide (CO
2
).
Marsh (1943) reported an improvement over McCoy by using a sodium amalgam. Marsh further recommended against the use of barium sulphate from which the recovery of europium is troublesome even though a barium amalgam resulted in precipitate including europium. He further recommends against the use of zinc dust for rendering bivalent sulfate precipitates unstable.
Ryabchikov (1970) reports that the more soluble rare earths dissolve in weak acids such as acetic, carbonic, and chromic.
More recently, the Oak Ridge National Laboratory has produced
153
Gd by the neutron irradiation of 5 to 10 g of Eu
2
O
3
. The resulting europium to gadolinium weight ratio after irradiation in the HFIR approaches 17 (Quinby 1987). To achieve 99.99% radiochemical purity of the
153
Gd product a two step process was used. First, the irradiated europium oxide was dissolved in 1 N sulfuric acid. Second, the solution was placed in an electrochemical cell where 90 to 95% of the energetic (gamma) Eu fraction was removed by electroreduction of Eu(III) to Eu(II) [using zinc electrodes]. Argon was used as a cover gas. High pressure ion exchange was then used to remove additional Eu(III) and sulfuric acid to obtain a gadolinium product of 99.9% purity. This process has the disadvantages of low production (7 g batches of Eu oxide), poor yields (~70%) of
153
Gd, and the need for the high pressure ion exchange.
Also Wheelwright (1986) described a method to separate Eu on a large scale (~60 grams) from the Gd-Sm fraction prior to final purification. During the ‘First Cycle of Chemical Purification’ Eu
2
O
3
targets were dissolved. When dissolution was complete, the Eu(III) was reduced to Eu(II). Further chemical purification by ion exchange was then required to separate the Gd from a trace of Eu and the Sm. This was accomplished by ion exchange band displacement (Wheelwright; 1969, 1973).
After separation of the major fraction of the Eu isotopes, to prevent irradiation damage to the organic ion exchange resin, Campbell (1973) and Elbanowski (1985) suggested the use of high-pressure ion exchange for final purification.
A solvent extraction process in which the Gd was extracted away from the Eu by use of di(2-ethylhexyl)phosphoric acid after the reduction of Eu to the divalent form was also investigated by Posey (1986).
However, there still remains a need in the art of gadolinium separation for a method having a higher production and yield.
BACKGROUND REFERENCES
Campbell, D. O. 1973. “Rapid Rare Earth Separation by Pressurized Ion Exchange Chromatography”,
J. Inorg. Nucl. Chem.,
35, pp. 3911-3919.
Elbanowski, M. and J. Baranowska. 1985. “Preparation of High-Purity Europium Oxide Using Combined Reduction-Ion Exchange Method”,
Journal of Less-Common Metals,
112, pp. 267-270, Elsevier Sequoia/Printed in the Netherlands.
Marsh, J. K., 1943. “Rare-earth Metal Amalgams. Part IV. The Isolation of Europium, J. Chem. Soc., No. 142. pp 531-535.
McCoy, H. N. 1935. “The Separation of Europium from Other Rare Earths”,
Journal of American Chemical Society,
57, p. 1756, New York, N.Y.
Posey, J. C. 1986.
Use of High-Pressure Ion Exchange for the Production of Gadolinium
-153,
Status Report,
ORNL/TM-9988, Oak Ridge National Laboratory, Oak Ridge, Tenn.
Quinby, T. C., D. W. Ramey and M. Petek. 1987.
The Application of Electroreduction of Europium in the Production of Gadolinium
-153, ORNL/TM-10284, Oak Ridge National Laboratory, Oak Ridge, Tenn.
Ryabchikov, D. I., V. A. Ryabukhin,
Analytical Chemistry of Yttrium and the Lanthanide Elements,
1970.
Yost, D. M. and R. M. Cooley. 1946.
Inorganic Synthesis,
69, pp. 69-70, McGraw Hill, New York, N.Y.
Wheelwright, E. J. 1969. “A Comparison of Eluting Agents for the Ion-Exchange Purification of Promethium”,
J. Inorg. Nucl. Chem.,
31, pp. 3287-3293.
Wheelwright, E. J. 1973. “Recovery and Purification of Promethium”, Chapter 2,
Promethium Technology,
ed. E. J. Wheelwright, American Nuclear Society, Hinsdale, Ill.
Wheelwright, E. J. 1986.
Production and Purification of Gadolinium-
153
at Hanford,
PNL-SA-14410, presented at the Osteoporosis Seminar on Oct. 27, 1986 in Seattle, Wash., Pacific Northwest Laboratory, Richland, Wash.
SUMMARY OF THE INVENTION
The present invention is an improvement to the method of separating and purifying gadolinium from a mixture of gadolinium and europium having the steps of (1) dissolving the mixture in an acid; (2) reducing europium+3 to europium+2; (3) precipitating the europium+2 with a sulfate in a superstoichiometric amount; and (4) filtering the precipitated europium+2; wherein the improvement is achieved by using one or more of the following:
(i) the acid is a weak acid;
(ii) the reducing is with zinc metal

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