Extraction Behavior of Actinides and Metal Ions by the

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Extraction Behavior of Actinides and Metal Ions by the Promising Extractant, N,N,N#,N#-Tetraoctyl-3,6dioxaoctanediamide (DOODA) a

a

a

Yuji Sasaki , Yasuji Morita , Yoshihiro Kitatsuji & Takaumi Kimura a

a

Japan Atomic Energy Agency, Tokai, Ibaraki, Japan

Available online: 23 Apr 2010

To cite this article: Yuji Sasaki, Yasuji Morita, Yoshihiro Kitatsuji & Takaumi Kimura (2010): Extraction Behavior of Actinides and Metal Ions by the Promising Extractant, N,N,N#,N#-Tetraoctyl-3,6-dioxaoctanediamide (DOODA), Solvent Extraction and Ion Exchange, 28:3, 335-349 To link to this article: http://dx.doi.org/10.1080/07366291003680723

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Solvent Extraction and Ion Exchange, 28: 335–349, 2010 Copyright © Taylor & Francis Group, LLC ISSN 0736-6299 print / 1532-2262 online DOI: 10.1080/07366291003680723


Extraction Behavior of Actinides and Metal Ions by the Promising Extractant, N,N,N0 ,N0 -Tetraoctyl-3,6dioxaoctanediamide (DOODA) Yuji Sasaki, Yasuji Morita, Yoshihiro Kitatsuji, and Takaumi Kimura Japan Atomic Energy Agency, Tokai, Ibaraki, Japan

Abstract: The extraction of actinides, fission products, some non-nuclear elements,

and nitric acid by N,N,N0 ,N0 -tetraoctyl-3,6-dioxaoctanediamide (DOODA-C8) in dodecane was extensively studied. Also studied was the extraction of HNO3 and Nd(III) by the tetradodecyl analog of DOODA-C8 in dodecane. Both extractants contain two ether oxygen atoms in the backbone chain carrying the two amide groups and can thus act as tetradentate ligands. The extractability of actinides decreases in the order Pu(IV) > U(VI), Am(III) > Np(V) in the extraction from nitric acid and Pu(IV) > Am(III) >> U(VI) in the extraction from perchloric acid. Ions of di-, tri-, tetra-, hexa-, and heptavalent metals strongly differ in the extractability by DOODA-C8 but, except for lanthanides(III), there is no visible correlation of their distribution ratios with ionic radii. Due to the efficient extraction of actinides, weak extraction of fission products, and sufficient extraction capacity, DOODA-C8 is a promising extractant for the recovery of minor actinides from high-level radioactive wastes. Keywords: Solvent extraction, DOODA, novel extractant, Am, Pu, Tc, diamide

INTRODUCTION Novel extractants have been widely developed for use in the reprocessing of spent nuclear fuel and the partitioning of metals from high-level radioactive waste. Tributylphosphate (TBP) and N,N-dialkylamides, which function as unidentate ligands, can extract U(VI) and Pu(IV). Malonamides and octylphenyl-N, N-diisobutyl-carbamoylmethylphosphine oxide (CMPO), capable of bidentate chelation, show high D values for Am(III) and Cm(III). These extractants have Address correspondence to Yuji Sasaki, Nuclear Science and Engineering Directorate, Research Group for Actinide Seperation Chemistry, Tokai, Ibaraki 319-1195, Japan. E-mail: [email protected]


336

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been widely studied in process development for the recovery of actinides.[1–7] Amide extractants were limited to mono- and bidentate ligands until the last decade. Recently, tridentate ligands were developed and examined; not only hard oxygen, but also soft nitrogen or sulfur donor atoms are introduced into the center of their structures.[8–12] Both high extractability and high selectivity of these extractants are expected. For instance, thiodiglycolamide (TDGA), which has a sulfur atom in the ether position between two amides, has selectivity for platinum, lanthanides, and actinides; 2,2’-(methylimino)bis(N,N-dioctylacetamide) (MIDOA) and its analogous compound N-n-hexyl-bis-(N-methyl-N-n-octylethylamide)amine (HBMOEAA), having a nitrogen atom in the same position as the sulfur atom in TDGA, shows good extractability for palladium, rhodium, and some oxo-anions. However, Am and Cm, classified as hard acids, are not extracted as much by TDGA and MIDOA. On the other hand, N,N,N0 ,N0 -tetraoctyl-diglycolamide (TODGA), having three hard oxygen donors in the central frame is a very strong extractant. Am and Cm extraction by diglycolamide (DGA) is accompanied by several fission products, for example, Sr(II), Zr(IV), Tc(VII), and Pd(II).[13–14] Therefore, the extraction process using DGAs requires the use of masking agents to suppress the FP extraction and third-phase formation. A novel extractant showing sufficiently high recovery of Am and Cm with few metals coextracted is desirable. The new tetradentate extractant, DOODA (N,N,N0 ,N0 -tetraalkyl-3,6-dioxaoctanediamide) was synthesized and tested for metal ion extraction.[9] DOODA has two ether oxygen atoms introduced into the carbon chain

CH2

H2C H2C C8H17

O

O

O

C N

H2C

CH2 C

C8H17 H2C

N C8H17

O

C12H25

C8H17

O

CH2 O O

C N

CH2 C

O

C12H25

DOODA-C8

DOODA-C12 H2 C H2C H3 C

O

O O

C N

CH2 CH2 C

CH3 N

O

DOODA used by Narita et al. in reference 15

Figure 1. Structure of three DOODA derivatives.

C12H25 N C12H25


Extraction Behavior of Actinides and Metal Ions

337

connected with two amide groups (see Fig. 1), and these four oxygen atoms may bond with a metal ion as electron donors. Narita et al. reported the lanthanide (Ln) extraction by DOODA having methyl and phenyl groups and showed that the extractability trend of Ln is diglycolamide >> DOODA > malonamide.[15] In this paper, DOODA-C8 (N,N,N0 ,N0 -tetraoctyl-3,6-dioxaoctane-diamide) and DOODA-C12 (N,N,N0 ,N0 -tetradodecyl-3,6-dioxaoctane-diamide), which are well-soluble in hydrocarbons, were employed, and the extraction properties of DOODA for actinide and some metal ions from nitric or perchloric acid into n-dodecane have been investigated.

EXPERIMENTAL SECTION Reagents DOODA compounds were purchased from Wako-Pure Chemical Ind. Ltd. The method to produce DOODA by Wako-Pure Chemical Ind. Ltd. was as follows: The initial reagents for the organic synthesis of DOODA-C8 were 3,6-dioxaoctanedioic acid and N,N-dioctylamine. The 3,6-dioxaoctanedioic chloride can be synthesized from the reaction between 3,6-dioxaoctanedioic acid and thionyl chloride; the chloride was then reacted with the secondary amine in an ice bath. After synthesis, this compound was purified by silica gel column chromatography twice, and its purity was confirmed to be over 98% by gas-chromatography or liquid-chromatography analysis.[16] DOODA-C8 is a slightly yellow liquid, and DOODA-C12 is a white solid sample. The signals of DOODA-C8 by 1H NMR are the complexed peaks at 0.8-1.5 ppm for -C7H15, triplet at 3.1–3.3 ppm for N-CH2-, singlet at 3.7 ppm for O-C2H4-O, and singlet at 4.2 ppm for O-CH2-CO. Other chemical reagents, for example, n-dodecane, HNO3, and HClO4, were of the analytical grade.

Solvent Extraction The solvent extraction was performed by using DOODA as an extractant and two kinds of acids, HNO3 and HClO4. Two cm3 of the organic phase were taken and mixed with the same volume of the aqueous phase, in which the radioactive isotopes (Tc-99, U-233, Np-237, Pu-238, and Am-241) or the nonradioactive elements were included. Concentrations of the actinide ions used at the extraction experiments to obtain D values, in ppm, were 5 10-2 for Th, 0.1 for U, 1 for Np, and 3 10-4 for Am, and those of the nonradioactive metal are 100. The organic phase was pre-equilibrated once with the same concentration of HNO3 or HClO4 as the extraction experiment and with the same volume ratio. The aqueous and the organic phases were shaken mechanically for 30 min. at 25 0.1 C. After centrifugation, 0.50 cm3

Y. Sasaki et al.

aliquots taken from both aqueous and organic phases were counted on a liquid scintillation counter (Tri-Carb 1600 TR, Packard Instrument Company) for the beta and alpha activities in 5 cm3 of the scintillation cocktail. Prior to the extraction experiments, Pa-233 coexisting with Np-237 was removed.[17] The amounts of the nonradioactive metal ions in the sample solutions prepared from the aqueous phase were measured by an ICP-AES (SPS 3100, Seiko Instruments Inc) or an ICP-MS (SPQ 9000, Seiko-EG&G). The metal concentration in the organic phase was obtained from subtraction of that in the aqueous phase from initial concentration. Acid concentrations in both phases after extraction were measured by the potentiometric method, namely the aliquot of the sample solution put in the water were titrated with NaOH. The unit of the concentration, mol/dm3, is expressed as M in this paper, and the D values are defined as the ratio of metal concentration in the organic phase against that in the aqueous phase ([metal]org/[metal]aq).

RESULTS AND DISCUSSION Extraction Behavior of Actinides The extraction behavior of An by DOODA-C8 from nitric acid into n-dodecane was investigated, and the results are shown in Fig. 2. Figure 2(a) shows the relationship between D(An) and HNO3, and Fig. 2(b) depicts that for D(An) and the DOODA concentration.

103

102

102 Aqueous phase: HNO3 Organic phase: 0.1M DOODA-C8/ n-dodecane

U(VI) Np(V) Pu(IV) Am(III)

101

101

10

D(An)

U(VI) Pu(IV) Am(III)

D(An)


338

0

100

(b) 10–1

10–1 (a) 10–2 10–1

100 HNO3 concentration/M

101

10–2 10–2

Aqueous phase: 3M HNO3 Organic phase: DOODA-C8/ /n-dodecane

10–1 DOODA concentration/M

100

Figure 2. Dependence of D(An) on HNO3 and DOODA-C8 concentration at 25 C. (a) HNO3 dependence at 0.1 M DOODA; (b) DOODA dependence at 3 M HNO3.



339

As shown in Fig. 2(a), D(An) increases with HNO3 concentration, whose behavior is similar to that of TODGA.[18] This behavior is considered as an acid-driven aggregation reaction among metal, extractant, and NO3-.[19] The D values with 0.1 M DOODA/n-dodecane at 3 M HNO3 were 5.7 for U(VI), 27 for Pu(IV), and 7.8 for Am(III), and these values increase with HNO3 and DOODA concentration, which is applicable to extract An(III), An(IV), and An(VI) from HLW. The extraction trend for the different oxidation states is An(IV) > An(III) An(VI) > An(V) at the same acidity. This trend for actinide extraction is similar to that for TODGA. Actinyl ions such An(V) and An(VI) show the same or lower D values than that of An(III).[20] Assuming that DOODA is monomeric, the slopes of the extractant dependences are taken to indicate the number of DOODA molecules associated with the metal in the extraction reactions. As shown in Fig. 2(b), the dependencies of log D vs. log[DOODA-C8] for extractant concentrations up to 0.2 M are near a slope of 2 at low concentrations and then decrease, possibly indicating the aggregation at higher concentrations. The slope values for D(An) obtained at 0.1 M DOODA (1.7 for U(VI), 1.5 for Np(V), 1.8 for Pu(IV) and 2.3 for Am(III)) in Fig. 2(b) are summarized in Table 1 and are interpreted to indicate that mainly two molecules of DOODA contribute to the extraction reaction of An. DOODA has lower D(An) than TODGA but has a sufficient high D(An) to extract quantitatively by multistage extraction. It is noteworthy that the small D(An) can be taken at low HNO3 concentration to strip easily from the organic phase by diluted HNO3, and also the low D(FP) determined at 3 M HNO3 indicates the redundancy of a masking agent in the aqueous phase. Therefore, employment of DOODA is favorable for the reversible extraction of Am and Cm and for an efficient recycle of DOODA. Table 1. Slope values in log-log plots for DOODA-C8 (HNO3) at 25 C* Metal Ca(II) Mn(VII) Y(III) Tc(VII) Ba(II) Nd(III) W(VI) Hg(II) Bi(III) Np(V) Am(III)

Slope

Metal

Slope

1.94 0.02 1.75 0.02 (2.36) 1.29 0.07 1.69 0.03 2.2 0.1 1.59 0.05 1.12 0.02 2.7 0.2 1.5 0.2 2.3 0.1

Sc(III) Sr(II) Mo(VI) Cd(II) La(III) Eu(III) Au(III) Pb(II) U(VI) Pu(IV)

(1.97) 1.54 0.02 0.73 0.07 1.88 0.3 2.02 0.07 2.08 0.09 0.98 0.1 1.65 0.01 1.7 0.1 1.8 0.08

*Data in Fig. 2(b), 5(b), 6(b), and 7(b) were used.

Y. Sasaki et al. 100

100 Aqueous phase: HNO3 Organic phase: DOODA, TODGA /n-dodecane Temperature: 25 °C

10–1

Aqueous phase: 3M HNO3 Organic phase: DOODA, TODGA /n-dodecane Temperature: 25 °C

D(HNO3)

HNO3 concentration in the organic phase/M


340

10–2

10–1

(a)

(b)

0.1M DOODA-C8 0.1M DOODA-C12 0.1M TODGA

10–3 10–1

100

DOODA-C8 DOODA-C12 TODGA

101

equilibrated HNO3 concentration/M

10–2 10–2

10–1

100

DOODA concentration/M

Figure 3. Extraction behavior of HNO3 by DOODA-C8, DOODA-C12, and TODGA at 25 C. (a) HNO3 dependence at 0.1 M extractant concentration; (b) dependence of extractant concentration at 3 M HNO3.

Extraction of Nitric Acid Extraction of nitric acid was investigated. The HNO3 concentration in the organic phase by DOODA-C8 and DOODA-C12 is plotted against equilibrium HNO3 concentration in Fig. 3(a), and the relationship between D(HNO3) and DOODA concentration is shown in Fig. 3(b). Here, these figures include the results on HNO3 extraction by TODGA as a reference. As shown in Fig. 3(a), the HNO3 concentration in the organic phase increases with equilibrium HNO3 in the aqueous phase. It is clear that this behavior and the D(HNO3) values by DOODA with the different lengths of alkyl chain (n-octyl and n-dodecyl groups) attached to the N atoms are very similar to those for TODGA.

Extraction Capacity of DOODA The extraction capacity of DOODA-C8 and DOODA-C12 was measured. Figure 4 shows the relationship between Nd concentration in the aqueous phase before extraction and that in the organic phase after extraction, and the maximum Nd concentration in the organic phase corresponds to the extraction capacity.[21] The experimental condition used was 0.1 M DOODA/n-dodecane for the organic phase and 3 M HNO3 with maximal 100 mM Nd for the aqueous phase. Therefore, the extraction capacity here is a conditional value. As shown in Fig. 4, the extraction capacity of DOODA-C8/n-dodecane (19 mM) is lower


341

Nd concentration in organic phase after extraction/mM


30 DOODA(C8) DOODA(C12)

25

20

limiting organic phase concentration

15

10

5

0

Third phase system for DOODA(C8)

0

20

40

Aqueous phase: 3M HNO3 Organic phase: 0.1M DOODA/ n-dodecane Temperature: 25 °C

60

80

100

Nd concentration in initial aqueous phase/mM

Figure 4. Relationship between Nd concentration in the aqueous phase before extraction and that in the organic phase after extraction at 25 C. Loading capacity of DOODA-C8, 19 mM; that of DOODA-C12, 25 mM Nd at 3 M HNO3, 0.1 M DOODA, and 100 mM Nd in the initial solution.

than that of 0.1 M DOODA-C12/n-dodecane (25 mM), and Fig. 4 suggests the presence of a third phase using DOODA-C8. These results can be compared with those for DGA compounds having the same length of alkyl chains.[21] TODGA, which has the same four n-octyl groups in the amide groups as DOODA-C8, has a capacity of 6.4 mM, 1/3 that of DOODA. DOODA, whose central frame is composed of a long chain (NCO-CH2-O-C2H4-O-CH2-CON), resists the formation of a third phase, and also has a high loading capacity. N,N,N0 ,N0 Tetradodecyl diglycolamide (TDdDGA), which has four n-dodecyl groups like DOODA-C12, has a capacity of 32.5 mM, higher than that of DOODA. Both extractants do not form a third phase. As mentioned above, D(An) with DOODA is relatively low, and a high concentration of DOODA can be employed in order to increase the D values and also the loading capacity.

Extraction Behavior of Non-Actinide Metal Ions The D values for 54 elements from nitric acid to n-dodecane were measured. Here, DOODA-C8 was employed in these related experiments. The HNO3 and DOODA dependence of D(M) for extractable metals was investigated, and the results are shown in Fig. 5-7. It is clear that the D values of Ca(II), Sc(III),

342


10

1

104 Aqueous phase: HNO3 Organic phase: 0.1M DOODA-C8/ n-dodecane Temperature: 25 °C

103

Aqueous phase: 3M HNO3 Organic phase: DOODA-C8/ n-dodecane Temperature: 25 °C

D(M)

100

101 100

10–1

(a) 10

–2

10–1


Sc Y La Nd Eu Bi

10–1

(b) 10–2 10–2

101

Sc Y La Nd Eu Bi

10–1

100

DOODA concentration/M

Figure 5. Dependence of D(M) on HNO3 and DOODA-C8 concentration at 25 C (1). M: Sc, Y, La, Nd, Eu, Bi (a) HNO3 dependence at 0.1 M DOODA; (b) DOODA-C8 dependence at 3 M HNO3. 103

102

Mo W Pd Tc Re Au

102

Aqueous phase: HNO3 Organic phase: 0.1M DOODA-C8/ n-dodecane Temperature: 25 °C

1 1

101

D(M)

101 D(M)


D(M)

102

10

100

0

10–1

10–1

10–2 10–1

(a) 100 HNO3 concentration/M

101

10–2 10–2

(b) Mo W Pd Tc Re Au

Aqueous phase: 3M HNO3 Organic phase: DOODA-C8/n-dodecane Temperature: 25 °C


100

Figure 6. Dependence of D(M’) on HNO3 and DOODA-C8 concentration at 25 C (2). M’: Mo, W, Pd, Tc, Re, Au (a) HNO3 dependence at 0.1 M DOODA, (b) DOODA-C8 dependence at 3 M HNO3.

Sr(II), Y(III), Tc(VII), Pd(II), Cd(II), Ba(II), Ln(III), W(VI), Re(VII), Au(III), Hg(II), Pb(II), and Bi(III) can be >1 if respective concentrations of HNO3 and DOODA are employed. The HNO3 dependence shows three patterns:

Extraction Behavior of Actinides and Metal Ions 102


100

102

Ca Sr Ba Mn Cd Hg Pb Zr

10–1

10–2 10–1

101

Aqueous phase: HNO3 Organic phase: 0.1M DOODA-C8/ n-dodecane Temperature: 25oC

D(M)

D(M)

101

343


101

Aqueous phase: Aqueous phase: 3M3M HNO 3 HNO 3 Organic phase: Organic phase: DOODA-C 8/ DOODA-C8/ n-dodecane n-dodecane Temperature: 25oC

100

10–1

(b) 10–2 10–2


Ca Sr Ba Mn Cd Hg Pb

100

Figure 7. Dependence of D(M) on HNO3 and DOODA-C8 concentration at 25 C (3). M”: Ca, Sr, Ba, Mn, Cd, Hg, Pb, Zr (a) HNO3 dependence at 0.1 M DOODA, (b) DOODA-C8 dependence at 3 M HNO3

1. gradual increase of D with HNO3 (Sc(III), Y(III), La(III), Nd(III), Eu(III), Bi(III), Ca(II), Cd(II), Mn(VII), Au(III), Sr(II), and Zr(IV)), which is the same behavior of the actinides; 2. no specific dependence or gradual decrease (W(VI), Pd(II), Tc(VII), Re(VII), Mo(VI), and Hg(II)). The extractable oxo-anions belong mostly to the pattern (2); the D values for these ions show weak dependence on the acid concentration in the aqueous phase. Pattern (3); gradual increasing and decreasing D after maximum at 3M HNO3 (Ba(II) and Pb(II)), this behavior can be seen in divalent metal ions with larger ionic radii. The slope values of log D vs. log[extractant] for 21 metal ions are summarized in Table 1. The trivalent scandium, gold, and bismuth have relatively high D values. Thus, M(III) including lanthanide and actinides are well-extracted by DOODA. The metals are classified into three groups following their slope values in Table 1. Mo and Tc, the oxo-anions, show slopes of 1; Ca, Sr, Ba, La, Nd, Eu, Pb, Pu, and Am, which belong to alkaline earth metals and 3A group and their related metals, show slopes of 2; and Bi shows a slope of 3. While most of the metals form 1:1 or 1:2 complexes, the oxo-anions show 1:1 ratio (metal:ligand). The metal-complex having a molar ratio of one:three (¼metal:ligand) is rarely formed, due to its large central frame. The extraction behavior of 25 metals from HClO4 was also investigated (see Fig. 8 and Table 2). The dependences of D(M) on DOODA concentration

344


102

U Pu Am

102

101

100

D(M)

Aqueous phase: 3M HClO4 Organic phase: DOODA/n-dodecane Organic phase: Aqueous phase: DOODA-C 8/n-dodecane oC 3M HClO25 Temperature: 4

(b)

100 10–1

(a) 10–2 10–4

–3

–2

10–2 10–4

10–1

10 10 DOODA concentration/M

102

101

Ca Sr Ba Pb Sc Y Bi

10–1

10–3 10–2 DOODA concentration/M

10–1

103 Aqueous Aquoeusphase: phase: 0.10.1M M HNO HClO 3 4 Organic phase: Organic phase: DOODA-C8/n-dodecane DOODA/n-dodecane Temperature: 25 oC

102 101

10

10

(c)

–1


(d)

100

Cd Hg Cu Zr Hf

10–1

Mo W Mn Tc Re Pd Au

–2

10–3 10–3

D(M)

100 D(M)


D(An)

101

Aqueous phase: Organic 3M HClOphase: 4 DOODA/n-dodecane Organic phase: Aqueous phase: DOODA-C / 3M HClO 8 4 n-dodecane Temperature: 25 oC

10–2

100

10–3 10–3

Aqueous phase: Aqueous phase: 3M HClO4 HClO4 Organic3M phase: DOODA-C 8/n-dodecane Organic phase: Temperature: 25 OC DOODA/n-dodecane


100

Figure 8. Extraction of D(M) and dependence on DOODA-C8 concentration from HClO4 at 25 C. (a) Behavior of M ¼ U, Pu, Am at 3 M HClO4; (b) M ¼ Ca, Sr, Ba, Pb, Sc, Y, Bi at 3 M HClO4; (c) M ¼ Mo, W, Mn, Tc, Re, Pd, Au at 0.1 M HClO4; (d) M ¼ Cd, Hg, Cu, Zr, Hf at 3 M HClO4.

are shown in Figs. 8(a)-(d). The values of D(Pu) and D(Am) are obviously higher than D(U), which indicates that DOODA has weak interaction with actinyl ions. Metals in class 2 (Ca, Sr, Ba), 3 (Sc, Y, Ln), and 4 (Zr and Hf) have high D values. Due to the weak affinity of ClO4- with metal ions, higher D values can be seen in comparison with those for HNO3. For instance, D for Pu(IV) and Am(III) from 3 M HNO3 into 1 mM DOODA/n-dodecane are respectively 0.0063 and


345

Table 2. Slope values in log-log plots for DOODA-C8 (HClO4) at 25 C*


Metal Ca(II) Mn(VII) Sr(II) Zr(IV) Tc(VII) Cd(II) La(III) Eu(III) W(VI) Au(III) Pb(II) U(VI) Am(III)

Slope

Metal

Slope

1.70 0.03 2.12 0.09 2.18 0.1 3.03 0.08 2.13 0.07 0.55 0.05 2.52 0.06 2.23 0.3 0.57 0.04 0.52 0.03 1.54 0.1 0.93 0.02 2.5 0.2

Sc(III) Cu(II) Y(III) Mo(VI) Pd(II) Ba(II) Nd(III) Hf(IV) Re(VII) Hg(II) Bi(III) Pu(IV)

2.8 0.3 1.29 0.02 2.3 0.1 1.03 0.02 0.84 0.05 1.7 0.1 2.41 0.08 4.2 0.6 1.5 0.2 1.41 0.06 2.8 0.7 2.18 0.05

*: Data in Figs. 8(a)-(d) were used.

4.67 10-4 from calculation by extrapolation, and those for 3 M HClO4 and D by the same DOODA concentration from 3M HClO4 are, respectively, 37.5 and 19.42. Such the same trend as actinide extraction can be seen in Ca(II), Sc(III), Sr (II), Y(III), Zr(IV), Cd(II), Ba(II), Ln(III), Hf(IV), Pb(II), and Bi(III). On the other hand, D values for oxo-anions (e.g., Mo, Tc, W, and Re) have a small difference between these two acids, working as the counteranion. From Table 2, metals showing a slope of 1 in log D vs. log[extractant] plots are Cu, Mo, Pd, Cd, W, Au, Hg, and U; those giving slopes near 2 are Ca, Mn, Sr, Y, Tc, Ba, Nd, Eu, Re, Pb, and Pu; those giving slopes 3 or higher are Sc, Zr, La, Hf, Bi, and Am. Di-, tri-, and tetravalent metal ions have a higher order of DOODA associated with the extraction reaction, and these metal ions have high D values due to the stability of the metal complex in the organic phase. The oxo-anions examined here have extraction reactions with a lower order of DOODA than 3. The trend for trivalent metal ions extraction is Am > Y > Sc,Bi; their ionic radii (pm) are 100 (Am), 90.0 (Y), 74.5 (Sc), and 102 (Bi) (coordination number of 6).[22] The relationship between the D values and the ionic radii of these metals is shown in Fig. 9. Figure 9(a) shows the results using HNO3 and Fig. 9(b) show that for HClO4 medium. As shown in these figures, the poor correlation of D values for metals in alkaline-earth and 3A groups with ionic radii can be seen in contrast to that for TODGA.23 The D values for lanthanides were measured and plotted against their atomic numbers (Fig. 10). The D values decrease gradually with the atomic number, which indicates that Ln ions having a lower charge density are readily extracted. The maximum separation factor (SF ¼ DLn/DLn) can be seen for the Ce/Lu pair (DCe/DLu ¼ 24). These results are in good agreement with other research work on DOODA15 but with the reverse extraction trend by tridentate extractant (DGA).[12,24]

346


103 Bi(III)

HClO4

Sc(III)

102

101 Pb(II) Ln(III)

In(III) Y(III) Zr(IV) Sc(III) Hf(IV)

Pb(II) Ca(II)

Ba(II)

Cd(II) Ba(II)

100 Sr(II)

Sr(II) Cu(II)

(a)

Y(III)

80

Bi(III)

102 101

Ca(II) Cd(II)

10–1 70

3M HClO4 0.01M DOODA-C8/ n-dodecane

Pu(IV)

Am(III)

100

Am(III)

103 D(M)

D(M)

90 100 110 120 130 140 Ionic radii/pm

10–1 70

80

Hg(II)

(b)

90 100 110 120 130 140 Ionic radii/pm

Figure 9. Relationship between ionic radii of metals and their D values at 25 C. Ionic radii were used when their coordination number is six, as taken from ref. 24. D values were calculated from the relation of log D vs. log[extractant], under the conditions: 3 M HNO3-0.1 M DOODA-C8/n-dodecane or 3 M HClO4-0.01 M DOODA-C8/ndodecane.

101

HClO4 HNO3

100 D(Ln)


104

3M HNO3 0.1M DOODA-C8 /n-dodecane

Pu(IV)

Ln(III)

HNO3

10–1 Organicphase: phase: Organic DOODA/n-dodecane(HClO ) 0.20.2mM mM DOODA-C 4 4) 8/n-dodecane (HClO 5050mM mM DOODA-C 8/n-dodecane (HNO DOODA/n-dodecane(HNO ) 3) 3

Aqueousphase: phase: Aqueous , HNO3 HClO 3M3M HClO , 4HNO

10–2 56

4

58

3

60 62 64 66 68 Atomic number of Ln

70

72

Figure 10. Dependence of D(Ln) on their atomic numbers at 25 C. The D values were obtained from 0.2 mM DOODA and 3 M HClO4, and 50 mM DOODA and 3 M HNO3.


347


CONCLUSION The new tetradentate diamide, DOODA, having four donor oxygen atoms in the central frame is examined for metal extractions. In addition to Pu and Am, scandium, gold, and bismuth are extracted by DOODA from nitric acid. Metals in the alkaline earth metal group and the class 3 and 4, including lanthanides and actinides show higher D values in HClO4 than those in HNO3. The low D(FP) values determined at 3 M HNO3 indicate the redundancy of a masking agent in the aqueous phase. The loading capacities of DOODA-C8 are low (19 mM) and limited by third-phase formation. On the other hand, 0.1 M DOODA-C12 can extract 25 mM Nd into n-dodecane with no third-phase formation. It is clear that DOODA-C12 is a promising extractant for the recovery of MA in high-level radioactive liquid waste, having some advantages of reversible actinide extraction, the redundancy of a masking agent, and the possibility of increasing the extractant concentration and the loading capacity. In future work, additional experiments for chemical stability and radiolysis of DOODA will be carried out.

ACKNOWLEDGMENT The authors would like to express their deep thanks to the staff of Wako-Pure Chemical Industries for the organic synthesis of DOODA.

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