A novel chromatographic separation technique using tertiary pyridine resin for the partitioning of trivalent actinides and lanthanides

Progress in Nuclear Energy; Vol. Available online at www.sciencedirect.com s =, E N c E ~ )

47, N o . 1-4, pp. 4 5 4 - 4 6 1 , 2 0 0 5 © 2 0 0 5 E l s e v i e r Ltd. A l l r i g h t s r e s e r v e d

o , ~ E c 1- o

ELSEVIER www.elsevier.com/locate/pnucene

P r i n t e d in G r e a t B r i t a i n 0 1 4 9 - 1 9 7 0 / $ - s e e front m a t t e r

doi: 10.1016/j.pnueene.2005.05.076

A NOVEL CHROMATOGRAPHIC SEPARATION TECHNIQUE USING TERTIARY PYRIDINE RESIN FOR THE PARTITIONING OF TRIVALENT ACTINIDES AND LANTHANIDES

ATSUSHI IKEDA 1*, TATSUYA SUZUKI ], MASAO AIDA 1, YASUHIKO FUJII 1 TOSHIAKI MITSUGASHIRA 2, MITSUO HARA 2 and MASAKI OZAWA 1"3 lResearch Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan 2Institute for Materials Research, Tohoku University, Oarai-machi, Higashiibaraki-gun, Ibaraki, 311-1313, Japan 3japan Nuclear Cycle Development Institute, Oarai-machi, Higashiibaraki-gun, Ibaraki, 311-1393, Japan (* Corresponding author, Tel&Fax: +81-3-5734-2958, E-mail: [email protected]) ABSTRACT A novel chromatographic separation technique using a tertiary pyridine type resin has been applied to the partitioning of the trivalent actinides (An) and lanthanides (Ln) and several successful results have been shown. In an alcoholic hydrochloric acid system, the trivalent An were clearly separated from the Ln, while no such group separation was achieved in an alcoholic nitric acid system. On the other hand, the nitric acid system was more effective for the intragroup (i.e. individual) separation of the trivalent An and the Ln than the hydrochloric acid system. On the basis of these results, a novel concept for the partitioning of the trivalent An and Ln using the present separation technique and its flowchart have been proposed with its advantages and disadvantages. © 2005 Elsevier Ltd. All rights reserved KEYWORDS Trivalent Actinides; Lanthanides; Pyridine Resin; Chromatography; Partitioning

454

455

Proceedings of INES-1, 2004

1. INTRODUCTION The treatment of radioactive wastes produced from the reprocessing process of spent fuels is a significant but still unsolved issue in the nuclear industry. Above all, the management of high-level radioactive wastes (HLW) is one of the most difficult problems due to their peculiar characters of high and long-lasting radioactivity. Many investigations have been carried out to develop effective techniques for the management of HLW. The partitioning and transmutation (PT) is one of the powerful strategies to reduce the HLW. In this strategy, specific radioactive nuclides that have high radioactivity are separated (partitioned) from the wastes and transmutated into other stable or low-level nuclides by using accelerators or fast-breeder reactors. At the moment, most of the target nuclides for the transmutation process are considered minor actinides (MA) (Chwaszczewski and S1owifiski, 2003). Therefore, the separation (i.e. partitioning) of MA from other fission products (FPs) is required prior to the transmutation process. It is not particularly difficult to separate MA from the majority of FPs by using general chemical separation methods. However, the separation from the lanthanides (Ln) is not so simple. It is well-known that the chemical properties of the Ln are similar to those of MA: these elements have similar ionic radii and, furthermore, the Ln and the MA over americium (95Am)show the same oxidation number of M(III) in solution. These similarities give rise to the difficulty on the separation of these elements. Although a large number of separation techniques, such as the solvent extraction or ion exchange method, have been developed for the partitioning of these elements, more effective techniques are still desired. Recently, we have developed a chromatographic separation technique using a tertiary pyridine resin for the partitioning of the trivalent actinides (An) from the Ln (Suzuki et al., 2003; Ikeda et al., 2004). Pyridine is classified as a soft-donor type extractant, which have soft-donor atoms of S or aromatic N in their structures. The soft-donor type extractant is considered one of the effective extractants for the An/Ln partitioning due to their selectivity between the trivalent An and Ln (Musikas et al., 1980; Choppin, 1995). In our separation system, the pyridine (N-donor) is resinified and utilized for a stationary phase. This makes multistage columnar operation possible, simplifying the separation process. Furthermore, the pyridine resin has high radiation-resistance and is easily reusable. These properties are favorable for practical uses. Up to the present, we have confirmed that the above separation technique is effective both for the partitioning of the trivalent An from the Ln and for the individual separation of these elements. The present paper gives several successful results of the separation of these elements. The application of the technique to the practical partitioning process is also proposed. 2. EXPERIMENTAL 2.1 Materials

The trivalent An used in the present study were 241Am, 242Cm, and and 242Cm was produced by the irradiation of shielded

252Cf. A mixed

241AMO2sample

sample of 241Am

in the Japan Materials Testing

Reactor (JMTR). A 252Cf sample was prepared from a spent 252Cf neutron source. Radioactive Ln

456

A. Ikeda et aL

samples (141Ce, 147Nd, 16°Tb, 168Tm, and 169yb) were produced by the irradiation of their stable isotopes using an electron linac at the Laboratory of Nuclear Science, Tohoku University. Other chemicals including stable Ln compounds and solvents were reagent grade and supplied by Wako Pure Chemical Ind., Ltd. and Kanto Kagaku. The resin employed for separation experiments was a tertiary pyridine type resin embedded in silica beads. The chemical structure of tertiary pyridine resin is given in Fig. 1. The resin was synthesized in our laboratory. The detailed properties of the resin have been described in previous papers (Suzuki et al., 2003; Nogami, Fujii and Sugo, 1996; Nogami et al., 1996). H2

/cH Fig. 1. Chemical structure of tertiary pyridine resin 2.2 Chromatography experiments Feed samples for chromatography experiments were prepared by dissolving dried mixtures of trivalent An and Ln samples into alcoholic hydrochloric acid solutions or alcoholic nitric acid solutions. Each feed sample was injected into a resin column, in which the pyridine resin was packed as a stationary phase, with a constant flow rate. Subsequently, an eluent was introduced into the resin column. The eluent was identical with the solvent of each feed sample. The effluent from the column was collected in fractions. Then, the trivalent An and radioactive Ln in the fractions were detected by a- and 7-ray spectroscopy. In the experiments using stable Ln, the Ln in the fractions were detected by ICP-atomic emission spectroscopy. The volume of the resin column was 1 cm-~ × 10 cm or 1 cm-¢I)× 50 c m All the experiments were carried out in ambient temperature. 3. RESULTS AND DISCUSSION 3.1 Separation oftrivalent actinides from lanthanides Figure 2 shows a typical chromatogram of the trivalent An and the Ln in a methanolic hydrochloric acid solution and Fig. 3 shows that in a methanolic nitric acid solution. Each feed sample contained approximately 0.5 mg of the An. In the hydrochloric acid system, the trivalent An were adsorbed in the pyridine resin more strongly than the Ln. Consequently, the trivalent An were eluted more slowly than the Ln and they were clearly separated. On the other hand, the trivalent An and the Ln were eluted in the reverse order of their ionic radii (Shannon, 1976) and no group separation was observed between the trivalent An and the Ln in the nitric acid system. The elution order of these elements was not affected by the alcohol content and the type of alcohols in solvent, although their adsorbability and separability

Proceedings of lNES-1, 2004 .

lO

r

'

i

,

i

,i

I

,

!

.

i

\

,

•

w

'

457 i

10

,

i

.

i

•

i

,

141Am

o

.'~- 08

•

O8

141Ce

\ j

i°

i °,

~ i

?

\

o'"Cm ° "-"

i ° ~

i o

02

00

,

20

40

60

t

,

80

Volume

of

I

,

100 effluent

120 /em

140

160

180

20

40 Volume

~

Fig. 2. Elution chromatogram oftrivalent An and Ln in alcoholic hydrochloric acid system. (Solvent: 70 vol%-conc. HCI*/30 vol%-methanol, Flow rate: 100 cm3/h, Resin Bed: 1 cm-O × 10 cm) * conc. HCI: 11.7 mol/dm3-HC1 solution

of

60

80

effluent

/ cm

100

120

3

Fig. 3. Elution chromatogram of trivalent An and Ln in alcoholic nitric acid system. (Solvent: 60 vol%-conc. HNO3*/40 vol%methanol, Flow rate: 100 cm3/h, Resin Bed: 1 cm-O × 10 cm) * conc. HNO3:13.5 mol/dm3-HNO3 solution

gradually increased with an increase of alcohol content in solvent. Therefore, the separation o f the trivalent An from Ln can be achieved only in the hydrochloric acid system. 3.2 Individual separation oftrivalent actinides and lanthanides The individual separation of the trivalent An and Ln is one o f the most challenging problems in separation science due to their similar chemical properties. In the PT strategy, several actinides including

•

10

i

r

,

i

,

,

i

,

i

,

i

,

,

,

,

i

08

,

10

-i--y

-<3--

La

i--

Ce

i Heavier

;r Ln

08

--~--Pr

O-- Nd <--Sm

,~ 06

--~--Eu

04

I

~

-o-~d

--o--Dy --+--Ho Er Tm ,--e--Yb :

i

-x---~--

02

00

04 Lighter

ca

Ln

i 02

--~--Lu

35

06

i

40

45

50 Volume

55

60 of effluent

65

70

75

80

85

/ cm ~

Fig. 4. Elution chromatogram of yttrium and Ln in alcoholic hydrochloric acid system. (Solvent: 50 vol%-conc. HCI*/50 vol%-methanol, Flow rate: 50 cmVh, Resin Bed: 1 cm-O × 50 cm) * conc. HCI: 11.7 mol/dm3-HC1 solution

00

50

100 Volume

150 of

200 effluent

/ em

250

300

3

Fig. 5. Elution chromatogram of yttrium and Ln in alcoholic nitric acid system. (Solvent: 70 vol%-conc. HNO3*/30 vol%methanol, Flow rate: 50 cm3/h, Resin Bed: 1 cm-O × 50 cm) * conc. HNO3:13.5 mol/dm3-HNO3 solution

458

A. I k e d a e t al.

Am and Cm should be isolated from other An and FPs for the transmutation process. We applied the present separation technique using the pyridine resin to the individual separation of the trivalent An and Ln. Figs. 4 and 5 show the elution chromatograms of stable Ln (57La - 71Lu, except 61Pm) and yttrium (39Y) both in a methanolic hydrochloric acid solution and in a methanolic nitric acid solution.

In the hydrochloric acid system (Fig. 4), the Ln except La were eluted in the reverse order of their ionic radii. Although each elution curve was slightly separated from the neighboring ones, a clear individual separation was not observed. The variation of alcohol content in the solvent had almost no effect on the improvement of the separability of these elements. On the other hand, the elution chromatogram in the nitric acid system was slightly different from that in the hydrochloric acid system. The elution curves o f these elements were divided into two parts, that is, heavier Ln group (62Sm - 71Lu) and lighter one (57La - 60Nd), as shown in Fig. 5. This result implies that the nitric acid system could be effective for the individual separation of these elements if experimental conditions are optimized. Fig. 6 shows a successful example of the individual separation: a rough intragroup separation of the Ln was achieved by changing the composition of nitric acid and methanol in eluent. Furthermore, the trivalent An were also separated individually by using the nitric acid system, as shown in Fig. 7 (Ikeda et aL, 2004). The separability of these elements could be improved further by optimizing other experimental conditions, such as the size of resin column or operating temperature. Volume

ratio of soh'ent

conc. H N O : H O : M e O H = 1 : 0 : 9

4:0:6

3:5:2

--1--y o--

La

lO

,,#1 ,

08

, I )

--A-- Ce

--7 Pr --~--Nd <--Sm --, Eu --O--Gd

•~

o6

,.:

200

300 Volume

400

500

of effluent/em

600

i

oz O0

.e

o

Cm 2s2 Cf

•

~.. 1oo

200

300

400

Volume of effluent / cm5

3

Fig. 6. Elution chromatography of yttrium and Ln in methanolic nitric acid system. (Flow rate: 50 cm3/h, Resin Bed: 1 cm-O × 50 cm)

....

.

, ',

,

\

"

i',

I:" r"

/

141A m .........

-

:t

04

100

:

~ ' ~ : : :.

1

--*-- Tb + Ho --X-- Er --~--Tm --~--Yb --~-- Lu 700

/ ,'",\ i ,: :

Fig. 7. Elution chromatography of trivalent An in alcoholic nitric acid system.

(Solvent: 40 vol%-conc. HNO3*/60 vol%methanol, Flow rate: 50 cm3/h, Resin Bed: 1 cm-O × 10 cm) • conc. HNO~: 13.5 mol/dm3-HNO~ solution

3.3 Concept of the partitioning process using tertiary_ pyridine resin On the basis of the results obtained above, we propose a novel concept of the partitioning process using the tertiary pyridine resin as shown in Fig. 8. The process is composed of three steps: Step 1. separation of the trivalent An and the Ln from other fissile An and FPs, Step 2. separation of the trivalent An from the Ln, and Step 3. individual separation of the trivalent An and the Ln. Step 1 and Step 2 are

Proceedings of lNES-1, 2004

Step 1

459

Step 2

Step 3

• .....•

~_~ An(III), Ln(IIl) [ _ ~ Spent Fuel FPs2 [i I An(Ill), Ln(IlI)

• ........... •

I Transmutation O1"

Recycling

~'"'• C f

V U, Np, Pu I

FPsl

Recycling



or

Disposal



Fig. 8. Flowchart of novel partitioning process using tertiary pyridme resin

performed in the hydrochloric acid system and Step 3 is done in the nitric acid system. Recently, we have confirmed that the trivalent An and Ln are easily separated from other An (U, Np, and Pu) by using the pyridine resin with a hydrochloric acid solution, that is, U, Np, and Pu are strongly adsorbed in the resin and hardly eluted from the column, while the trivalent An and the Ln are eluted. Therefore, Step 1 can be achieved by using the pyridine resin in the hydrochloric acid system. Step 2 and Step 3 can be performed in the hydrochloric acid and nitric acid systems, respectively, as mentioned in the above sections. The advantage of this partitioning method is its simplicity. A single separating agent is required for all the separations in the process. The separating agent of tertiary pyridine resin has high resistance both to radiation and to acid, enabling its long-term use and recycling. Furthermore, the equipment, procedures, and reagents employed in the process are also simple. The resin column is structurally simple and easy to construct compared with other separating apparatuses, such as the mixer-settler used in the solvent extraction method. All the separation steps are achieved by just passing samples through the resin column with a single eluent and no back extraction is required. The resin column can be reused after just washing by water and preconditioning. The solvents employed in the whole process are hydrochloric acid, nitric acid, alcohols, and water and no complicated organic solvent is required. However, the present partitioning method also has several disadvantages. All the separation steps should be performed in considerably high concentration of acidic solutions and, therefore, the acid erosion of equipment are expected. Furthermore, the solvent system should be changed from the hydrochloric acid system to the nitric acid one between Step 2 and Step 3. In addition to these

460

A. Ikeda et aL

disadvantages, the behavior of FPs in the process is still unclear. Several improvements are still required for the present partitioning process using the pyridine resin. 4. CONCLUSION The present study has demonstrated that a novel chromatographic separation technique using a tertiary pyridine resin is a powerful tool for the partitioning of the trivalent An and the Ln. The technique can be applied both to the separation of the trivalent An from the Ln and the individual separation of the trivalent An and the Ln. That is, the group separation of the trivalent An from the Ln is achieved in an alcoholic hydrochloric acid solution and, furthermore, the individual separation of these elements is done in an alcoholic nitric acid solution by using the pyridine resin. By combining these two solution systems, a practical partitioning process using the present separation technique has been proposed, although several improvements are still required.

ACKNOWLEDGMENT The authors thank Mr. Keisuke Itoh and Mr. Kouhei Otake for their experimental support.

REFERENCES Choppin, GR. (1995), Comparative solution chemistry of the 4fand 5f elements, J. Alloys. Compd., 223, 174. Chwaszczewski S., Stowiflski B. (2003), Transmutation of radioactive watste, Appl. Energy, 75,87. Ikeda A., Suzuki T., Aida M., Ohtake K., Fujii Y., Itoh K., Hara M., Mitsugashira T. (2004), Effect of f-electron configurations on the adsorption of trivalent f-elements on tertiary pyridine resin in hydrochloric acid/alcohol mixed solvents, J. Alloys Compd, 374, 245. Ikeda A., Suzuki Y., Aida M., Fujii Y., Itoh K., Mitsugashira T., Hara M., Ozawa M. (2004), Effect of alcohols on elution chromatography of trivalent actinides and lanthanides using tertiary pyridine resin with hydrochloric acid-alcohol mixed solvents, J. Chromatog. A, 1041, 195. Ikeda A., Suzuki T., Aida M., Otake K., Fujii Y., Itoh K., Mitsugashira T., Hara M., Ozawa M. (2004), Chromatographic separation of trivalent actinides by using tertiary pyridine resin with methanolic nitric acid solutions, J. Nucl. Sci. Technol., 41, 915. Musikas, C., LeMarois, G, Fitoussi, R., Cuillerdier, C. (1980), Properties and uses of nitrogen and sulfur donor iigands in actinide separations, Actinide Separations (ACS Symposium Series Vol. 117, Navratil, J.D. and Schulz, W.W. eds.), American Chemical Society, Washington, D. C., p. 131. Nogami, M., Fujii, Y., Sugo, T. (1996), Radiation resistance of pyridine type anion exchange resins for spent fuel treatment, J. Radioanal. Nucl. Chem., Art., 203, 109.

Proceedings of INES-1, 2004

461

Nogami, M., Aida, M., Fujii, Y., Maekawa, A., Ohe, S., Kawai, H., Yoneda, M. (1996), Ion-exchange selectivity of tertiary pyridine-type anion-exchange resin for treatment of spent nuclear fuels, Nucl. Technol., 115, 293. Shannon, R.D. (1976), Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Cryst., A32, 751. Suzuki T., Aida M., Ban Y., Fujii Y., Hara M., Mitsugashira T. (2003), Group separation of trivalent actinides and lanthanides by tertiary pyridine-type anion-exchange resin embedded in silica beads, J. Radioanal. Nucl. Chem., 255, 581.