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Xu-Fang Tan, I You-Shao Wang, l* Tai-Zhe Tan, 1 Ge-Fei Zhou, 1 Bo-Rong Bao 2. 1 Laiyang Agricultural College, Laiyang 265200, Shandong Province, P.R. ...
Journal of Radioanalytical and Nuclear Chemistry, Vol. 242, No. 1 (1999) 123-126

N,N,N',N'-tetrahexylsuccinylamide as a new extractant for the extraction of nitric acid, u r a n i u m ( V l ) and thorium(IV) ions Xu-Fang Tan, I You-Shao Wang, l* Tai-Zhe Tan, 1 Ge-Fei Zhou, 1 Bo-Rong Bao 2 1 Laiyang Agricultural College, Laiyang 265200, Shandong Province, P.R. China 2Institute of Nuclear Research, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800, P.R. China (Received March 23, 1999)

N,N,N',N'-tetrahexylsuccinylamide (THSA) was used for the extraction of U(VI) and Th(IV) ions from nitric acid media into n-dodecane. Extraction distribution ratios of U(VI) and Th(IV) as a function of nitric acid concentration, extractant concentration and temperature have been studied. It was found that THSA as a new extractant is superior in some aspects to TBP for extraction of U(VI) and Th(IV). The extraction of nitric acid was also investigated. At low acidity, the main adduct of THSA and HNO 3 is THSA'HNO 3. THSA(HNO3) 2 and THSA(HNO3) 3 also formed at high acidity. The composition of the species, equilibrium constants and enthalpies of the extraction reactions have also been calculated. The suggested formation of the 1:2:1 ratio of uranyl(VI) ion and the 1:4:2 ratio of thorium(IV) ion, nitrate ion and THSA as the extracted species was further confirmed by the 1R spectra of U(VI) and Th(IV) extracts.

Introduction

During the past twenty years, bidentate ligands as extractants have come to occupy an important field of solvent extraction. The special features of these extractants are their good selectivity and high extraction efficiency. 1 These characteristics are partly due to their ability to form chelate complexes. These extractants are successfully applied in different areas, such as the extraction of acitinides and lanthanides. There is a particular class of bifunctional ligands namely the multisubstituted alkylamides which have been investigated since SIDDALL III first suggested the substituted alkylamides as promising extractants for actinides in the early 1960's. 2-12 The diamides for tri-, tetra- and hexavalvent actinides, such as Am(III), Pu(IV) and U(VI), have excellent extractability from high acidic waste solutions, particularly high level radioactive wastes. 3,4 Some research work about the diamides for the extraction of HNO 3, U(VI) and Th(IV) has also been done. 5-12 In comparison with organophosphorus extractants, the main advantages of diamides and their radiolytic products are their easy and complete incinerability, and non-interference of their degradation products in the separation processes. These attractive features make them worthy candidates for further investigations in the nuclear waste management. In this paper, the extraction of nitric acid, uranium(VI) and thorium(IV) by N,N,N',N'-tetrahexylsuccinylamide(THSA) in n-dodecane as a new extractant has been systematically investigated and discussed. The extraction mechanisms and thermodynamic parameters are also presented.

Experimental

Synthesis of the extractant THSA was obtained by the reaction of di-nhexylanaine with succinyl chloride in methylene chloride medium: 13 (CH2COCI) 2 +2NH(C6H13)2

CHzClz >

(1)

(CH2CO - N(C6H 13)2 )2 THSA was purified by distillation under vacuum, and the final distilled THSA was checked by element analysis (found: N = 6.18%, C = 74.28% and H=12.47%; calculated for C28H56N202: N=6.23%, C=74.32% and H=12.70%) using IR and NMR spectrometry. The results showed that the purity of the product was higher than 98%.

Procedure and apparatus 1.0 ml of the aqueous phase containing a certain amount of U(VI) or Th(IV) and HNO 3 was shaken with 1 ml of the organic phase consisting of a given concentration of THSA in n-dodecane for 10 minutes. Samples of both phases were analyzed immediately after the phase separation. The concentration of U(VI) in the aqueous phase was determined by the Arsenazo-III spectrophotometric method. The concentration of Th(IV) in the aqueous phase was determined by the chlorophosphonazo-mA spectrophotometric method, and then the distribution ratios of U(VI) and Th(IV) were calculated.

* Author for correspondence. Present address: Department of Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100094, P.R. China.

0236-5 731/99/USD 17. O0 9 1999 AkadOmiai Kiad6, Budapest All rights reserved

Elsevier Science B. K, Amsterdam Akad~miai Kiad6, Budapest

XU-FANG TAN et al.: N , N , N ' , N ' -TETRAHEXYLSUCCINYLAMIDE AS A NEW EXTRACTANT

0.1-1.0 mol/1 THSA was equilibrated with 1.0 mol/1 and 3.0 mol/1 HNO 3 for 10 minutes. After the phase separation, the aqueous phase was titrated with 0.05 mol/l NaOH solution to determine the nitric acid concentration. IR spectra were recorded with a 5DXC Nicolet Fourier transformation spectrometer, using KBr window cells. Signals of 96 scans at a resolution of 4 cm-1 were averaged before the Fourier transformation.

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=O

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-1.6 -1.8

R e s u l t s and discussion

Extraction of nitric acid

I

I

0o

log [THSA]

THSA was found to extract nitric acid into the organic phase. The nature of the extracted species and the equilibrium constant (KH+) are presented for the following reaction: 4 Ha+ + NO~a + nTHSA o ---) HNO3"nTHSAo

-;.0 -0'8 -06-o,

-1.2

Fig. 1. Extraction f u n c t i o n s o f H N O 3 as a function o f T H S A concentration at 25 ~

[HNO3] = 1.0 mol/l

(2) i

The equilibrium constant (KH+) of Eq. (2) can be written as follows: KH ~ [HNO3" nTHSA]~ (3) [ H+ ]a [NO3 ]a [THSA] n

where Eq. (4) is based on the assumption that the HNO 3 extracted forms completely the adduct HNO3.nTHSA and [H+]o = [H+]a initial - [H+]a

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The concentrations of the diamide and HNO 3 were restricted to not more than 1.0mol/l, molar concentrations instead of activities were employed in all the calculations. Rewriting the above equation in logarithmic form:

-

-0.4 -

-1'.o -0'8 -0'.6

g2

o'.o

log [THSA] initial

Fig. 2. Distribution ratios o f H N O 3 as a function o f initial T H S A concentration at 25 ~

[HNO3] = 3.0 mol/1

[THSA]o = [THSA]o initial - n([H+]a initial - [H+]a) By plotting the left side of Eq. (4) against log [THSA](o), a straight line with a slope equalling to n and intercept equalling to log KH+ were obtained. The result of n = 1.0 indicates that only one HNO 3 molecule is attached to each THSA molecule (Fig. 1). The value of KH+ calculated from the intercept was 0.25 mol-2.12. Figure 2 shows the effect of the initial THSA concentration on the extraction of HNO 3 (the slope is 1.0). The result is similar to the study on N,N'-dimethylN,N'-dioctylmalonamide 14 and N,N,N',N'-tetrabutylglutaramide 15 reported by MUSIKAS et al. In any case, the plots of log D vs. log [diamide] give a straight line with the slope of about 1.1 in 3-~4 mol/1 nitric acid medium. As a result of detailed IR spectra studies, the formation of THSA-HNO 3 adducts, for example, (THSA)2.HNO 3 (1637 cm-1), THSA'HNO 3 (1578cm -1) and THSA'(HNO3) 2 (1543cm-1), are responsible for such phenomenon. 124

Extraction of uranium(VI) and thorium(IV) Distribution ratios of U(VI) and Th(IV) as a function of aqueous HNO 3 concentration, extractant concentration and temperature: Figure 3 demonstrates the effect of the HNO 3 concentration on the distribution ratios of U(VI) and Th(IV). The distribution ratios of U(VI) increase with the increasing concentration of HNO 3 until a maximum is reached which is due to the competition of U(VI) and HNO 3 for the coordination sites of THSA. The maximum is observed at around 5 mol/l for U(VI), and at around 7 mol/1 in the case of Th(IV). The results in Fig. 3 indicate that U and Th could be achieved more efficently if the extraction is carried out at medium acidity (for instance, less than 1.5 mol/l HNO3), and could be coextracted when the nitric acid concentration surpasses 3 mol/I.

XU-FANGTANet al.: N,N,N',N'-TETRAHEXYLSUCCINYLAMIDE ASANEWEXTRACTANT

2,0

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The extraction data indicate that THSA is clearly superior to TBP for the extraction of U(VI) and Th(IV) in Table 1. The results of investigating THSA concentration effect are shown in Fig. 4. The plots of log D M vs. log [THSA] are straight lines with slopes of 1.2 and 1.98 for U(VI) and Th(IV), respectively. Thus, the suggested complexes are UO2(NO3)2"THSA and Th(NO3)4.2THSA as described previously.9 The extraction reactions o f the present system can be expressed by

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UO 2+ + 2NO~a + THSA o = UO2(NO3)2"THSAo

(5)

Tha4+ + 4NO~a + 2THSA o = Th(NO3)4-2THSAo

(6)

Then, the extraction constant Kex can be defined as

Fig. 3. Distributionratios of U(VI) and Th(IV) as a functionof

[M(NO3)rn" nTHSA]o

aqueous HNO3 concentrationat 25 ~ [U(VI)] = [Tb(IV)]= 5.010 -3 tool/l, [THSA]= [TBP]= 0.5 mol/l

Kex

[Mm+]a[NO3]m[THSA]~ (7)

DM --

m

n

[NO3 ]a [THSA]o 1000

,

-

,

9

,

-

i

9

,

-

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where M refers to UO 2+ and Th 4+, by taking the logarithm and arranging,

100

log D M = log Kex + m log [NOg] a + n log [THSA]o

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1 0.1 9 THSA-U " TBP-Th " TBP-U

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2

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5

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6

7

[HNO3] , mol/I

Fig. 4. Distributionratios of U(VI) and Th(IV) as a functionof THSA

(8)

This relation is supported by the slope analysis obtained from Fig. 4, and the values of the extraction constants (Kex) (3.0 mol/1 HNO 3, 2.82 mol/l NOg) 16 are calculated to be 7.21 mol-3.13 and 0.141 mol-6'l 6 for U(VI) and Th(IV), respectively. The values are higher than those obtained in 50% OK (kerosene)-50% TMB (1,2,4-trimethylbenzene) system owing to the diluent effect. 9 Results of investigating the temperature effect show (Fig. 5) that D M decreases with increasing temperature for the extraction reactions of U(VI) and Th(IV).

concentrationat 25 ~ [U(VI)]= [Th(IV)]= 5.0' 10-3 mol/l, [HNO3]= 3.0 mol/l

Table 1. U-Th separationfactors ~ = Du/D,rh in n-dodecaneat differentacidities [HNO3], mol/1 THSA Dw DTh c~ TBP Dv DTh

1

2

3

4

5

6

7

107.7 23.6 4.56

109.9 74.4 1.48

152.0 93.9 1.62

126.8 167.4 0.757

5.88 0.132 44.5

14.3 0.737 19.4

22.5 2.10 12.1

1.24 0.092 13.4

4.00 0.340 11.8

7.26 0.596 12.2

8.06 0.729 11.1

10.7 0.830 12.9

10.9 0.830 13.1

7.26 0.810 8.96

125

XU-FANGTANet al.: N,N,N',N'-TErRAHEXYLSUCCTNYIAMIDEASANEWEXTRACTANT

Conclusions 2.0

The extraction of U(VI) and Th(IV) from nitric acid medium by THSA in n-dodecane is more efficient than with TBP. At low acidity (less than 1.5 mol/1 HNO3), an efficient U-Th separation can be reached. Coextraction of U(VI) and Th(IV) can be obtained when the HNO 3 concentration exceeds 3 mol/1. The main adduct of THSA and HNO 3 is THSA-HNO 3 at low acidity, but also THSA.(HNO3) 2 and THSA.(HNO3) 3 appear, in addition to THSA.HNO 3 at higher acidity. The extraction reactions for U(VI) and Th(IV) are exothermic, and the suggested composition of extracted species are UO2(NO3)2-THSA and Th(NO3)4-2THSA. THSA is considered to be a promising exractant.

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Fig. 5. Distributionratios of U(VI) and Th(IV) as a functionof temperature; [THSA]= 0.5 mol/l, [U(VI)]= [Th(IV)]= 5.010 -3 mol/I, [HNO3]= 3.0 mol/1 This means that the extraction reactions of U(VI) and Th(IV) are exothermic, similarly to TBP. 17 The relationship of log D M vs. 1/T is a straight line. According to the thermodynamic formula:

[

0 lo___ggD M ] 0(1 / T) Jp

AH

(9)

2.303R

the enthalpies o f the extraction reactions can be calculated to be -15.68 kJ.mo1-1 and -18.75 kJ-mo1-1 for U(VI) and Th(IV), respectively. IR spectra of the extracts of U(VI) and Th(IV): In order to gain a new insight into the structures of THSA with U(VI) and Th(IV) complexes, the IR the spectra of U(VI) and Th(IV) extracts were investigated. The main features observed are: the free stretching vibration of C=O at 1645 cm -1 is shifted to a lower frequency with the appearance of new bands at 1602 cm -1, 1574 cm-1 for U(VI) and at 1616 cm - l , 1588 cm-1 for Th(IV), respectively. The results demonstrate that the coordination states of two C=O groups of THSA are different, one is somewhat closer than the other from UO 2+ or Th 4+. THSA chelates UO22+ or Th 4+ to form irregular seven-mumbered rings, 18 the results being similar to N,N,N',N'-tetrahexylmalonamide (THMA) extraction of U(VI) in toluene (at 1622 and 1582 cm-1). 19 These features confirm that THSA acts as a bidentate ligand in the extracted complexes.

126

References 1. Q. Z. TIAN, M. A. HUGHES, Proc. of ISEC'93, Vol. 1, SCI ElsevierApplied Science, London,New York, 1993, p. 404. 2. T. H. SIDDALL,III, J. Inorg.Nucl. Chem., 26 (1963) 883. 3. C. MUSNAS,Sep. Sci. Technol.,23 (t988)No. 12-13, 1121. 4. G. M. NA1R,D. R. PRABHU,G. R. MAHAJAN,J. P SHUK1A,Solv. Extr. Ion Exch., I (1993) 813. 5. Y. S. WANG,C. H. SHI~, J. K. ZHU, B. R. BAO, J. Radioanal. Nuel. Chem., 212. (1996) 101. 6. Y. S. WANG,C. H. SHEN, Y. H. YANG,J. K. ZHU, B. R. BAO, J. Radioanal.Nucl. Chem., 213 (1996) 199. 7. Y. S. WANG,G. X. SUN, D. F. XIE, B. R. BAO, W. G. CAO, J. Radioanal.Nucl. Chem., 214 (1996) 67. 8. Y. S. WAbr3,S. X. SUN, Y. Z. YANG,B. R. BAO,J. Radioanal. Nucl. Chem., 218 (1997) 123. 9. Y. S. WANG,G. X. SUN, B. R. BAO, S. X. SUN, J. Radioanal. Nucl. Chem., 219 (1997) 119. 10. Y. S. WANG,B. R. BAO,W. G. CAO,J. Radioanal.Nucl. Chem., 222 (1997) 279. 11. Y. S. WANG,G. X. SUN,B. R. BAO,J. Radioanal. Nucl. Chem., 224 (1997) 151. 12. Y. S. WANG,Q. F. CAI, X. F. TAN, C. C. WANG,B. R. BAO, J. Radioanal.Nucl. Chem., 237 (1998) 187. 13. R. S. STANLEY, K. WOLF, Organic Functional Group Preparations, Vol. 1, AcademicPress, New York, 1968, p. 277. 14. C. MUSIKAS,H. HUBERT,Solv. Extr. Ion Exch., 5 (1987) 151. 15. M. C. CHARBONNEL,C. MUSIKAS,Solv. Extr. Ion Exch., 6 (1988) 46l. 16. Y. J. YIN, Handbookof College Chemistry, ShandongScience& TechnologyPress, Jinan, 1985, p. 302 (in Chinese). 17. B. R. BAO, Y. Z. BAO, C. H. SHEN, Y. S. WANG,Z. B. CAO, J. Radioanal.Nucl. Chem., 162 (1992) 391. 18. C. H. SHEN, B. R. BAO, J. K. ZHU, G. D. WANG, J. QIAN, Z. B. CAO,J. Radioanal.Nucl. Chem., 212 (1996) 187. 19. G. X. SUN, J. T. HAN, Y. L. LI, B. R. BAO, Chinese J. Appl. Chem., 15 (1998)No. 4, 29.