- Email: [email protected]
Dithiodiglycolamide: novel ligand with highest selectivity and extractability for palladium
Tetrahedron Letters 52 (2011) 3929–3932
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Dithiodiglycolamide: novel ligand with highest selectivity and extractability for palladium R. Ruhela a,⇑, J. N. Sharma a, B. S. Tomar b, M. S. Murali b, R. C. Hubli a, A. K. Suri a a b
Hydrometallurgy Section, Bhabha Atomic Research Centre, Mumbai 400 085, India Radiochemistry Divison, Bhabha Atomic Research Centre, Mumbai 400 085, India
a r t i c l e
i n f o
Article history: Received 13 April 2011 Revised 16 May 2011 Accepted 22 May 2011 Available online 30 May 2011 Keywords: DTDGA Palladium HLW Distribution ratio Separation factor
a b s t r a c t A novel multidentate ligand N,N,N0 ,N0 -tetra(2-ethylhexyl) dithiodiglycolamide DTDGA has been synthesized and studied for its extraction behavior towards various elements present in high level liquid waste (HLW). The extractant showed remarkable extractability and selectivity for palladium vis a vis other metal ions present in HLW. The distribution ratio as well as the separation factor for palladium was found to be the highest reported so far thus making this extractant one of the most promising candidates for effective separation of palladium from HLW. Ó 2011 Elsevier Ltd. All rights reserved.
Separation and recovery of palladium from high level liquid waste (HLW) solutions originating from PUREX process of spent nuclear fuel is necessary from the viewpoint of various problems encountered during vitrification1 as well as the conceptualization of the process where HLW can be treated as a secondary source of these valuable metals.2 For this purpose various ligands namely, tertiary and quaternary amines (tri-n-octylamine, tri-n-octylmethylammonium chloride (TOMAC) and tri-n-octylmethylammonium nitrate (TOMAN)),3 a-benzoinoxime (ABO),4 dihexyl and dioctyl sulfides (DHS5 and DOS6), dihexyl disulfide (DHDS),5 dioctyl and bis-(2-ethylhexyl) sulfoxides (DOSO7 and BESO),6 triisobutylphosphinesulfide (TIPS)7 and benzoylmethylene triphenylphosphorane (BMTTP),8 have been developed during the last two decades. However, these ligands suffer from various limitations such as slow kinetics,5,7,8 poor decontamination factor,4,6 pH sensitivity,3 solubility3,4,7,8 and instability in acidic medium.5,6 To overcome these problems there is a need for development of newer ligands with improved extraction efficiency as well as selectivity. In a recent work, we have reported the synthesis of novel ‘S’ donor ligand namely N,N,N0 ,N0 -tetra (2-ethylhexyl) thiodiglycolamide (T(2EH)TDGA)9 and its remarkable selectivity for palladium extraction vis a vis other metal ions present in HLW. High selectivity and extractability of the ligand was attributed to the presence of thioetheric sulfur and amidic moiety appropriately placed in the ligand to chelate through more than one donor sites.9 However, there are
various aqueous streams where the concentration of palladium is in sub ppm levels for which an even more efficient extractant is required along with high selectivity. To seek an even more efficient ligand for the said purpose, another novel class of ligand namely, dithiodiglycolamide, has been explored by us. It was envisaged that judicial incorporation of one more sulfur atom would result in more chelation thereby increasing the overall extractability thus increasing the ligand economy while retaining the selectivity. We now report the synthesis of a novel ligand namely, N,N,N0 ,N0 tetra(2-ethylhexyl) dithiodiglycolamide (DTDGA) (Fig. 1) and demonstrate its superiority over previously reported ligands in palladium extraction from HLW. DTDGA was synthesized (Fig. 2) from commercially available and tailor-made materials.10 All other chemicals used in this study were of reagent grade. The extraction study of metal ions was carried out at 25 ± 1 °C.11 To establish the nature of extracted species, both the chemical (mole ratio method) as well as physical (ESI-MS) approaches were
⇑ Corresponding author. Tel.: +91 2225592959/621. E-mail address: [email protected] (R. Ruhela). 0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2011.05.099
Figure 1. N,N,N0 ,N0 -Tetra (2-ethylhexyl) dithiodiglycolamides (DTDGA).
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R. Ruhela et al. / Tetrahedron Letters 52 (2011) 3929–3932
0.0010
100
0.0008
80
0.0006
60
%E (Pd)
[Pd]org. (M)
Figure 2. Reaction scheme.
0.0004
40 20
0.0002
0
0.0000 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25
0
[DTDGA]org. /[Pd]aq.
4
6
8
10
12
followed. Figure 3 shows the variation of [Pd]org. vs [DTDGA]/[Pd]aq. It can be inferred from the figure that the stoichiometry of the species (Pd to DTDGA) is 1:1. Figure 4 shows the ESI-MS of the extracted species. The peak at m/z 888 corresponds to Pd(N03)2 DTDGA, thus confirming the stoichiometry determined by mole ratio method. The multiple peaks between m/z 759–765 correspond
16
Figure 5. Kinetics of extraction of Pd(II) from aqueous solution (103 M Pd in 3.0 M HNO3) to organic phase (0.001 M DTDGA/n-dodecane).
to PdDTDGA with a number of stable isotopes of palladium having comparable abundance. Figure 5 shows the percentage extraction of Pd as a function of contact time. It is evident that almost complete extraction was achieved within 2–5 min. Moreover under the given experimental
(C8H17)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C8H17)2.Pd (NO3)2 , (m/z, 888), (C8H17)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C8H17)2.Pd , (m/z, 760), (C6H12)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C6H12)2.PdO2N2 , (m/z, 708), (C6H12)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C6H12)2.PdO2 , (m/z, 680) (C6H11)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C6H11)( C5H9), (m/z, 522)
761.4 2.358e+7
760.4 1.508e+7 763.4 1.284e+7 764.4 8.154e+6
%
680.4 2.521e+6 523.5 1.249e+6
200 Figure 4. ESI-MS (% abundance vs m/z) of 10
14
Time (min)
Figure 3. Mole ratio plot, org.: DTDGA/n-dodecane, aq: 0.98 103 M Pd in 3.0 M HNO3.
1
2
500 4
759.4 5.764e+6 709.8 3.672e+6 759.8 3.639e+6
600
800 4
M DTDGA/n-hexane after contacting with 10
888.1 1.524e+6
900
M Pd in 3.0 M nitric acid medium.
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R. Ruhela et al. / Tetrahedron Letters 52 (2011) 3929–3932
BMTPP TOMAC
2.5 x 10-4M Pd in 1.0M HNO3, 0.05M TOMAN
DTDGA DHDS DHS
2.5 x 10-4M Pd in 1.0M HNO3, 0.001M
DOSO T(2EH)TDGA DTDGA
Tracer Pd in 3.0M HNO3, 0.0025M
Tracer Pd in 3.0M HNO3, 0.0005M
DOS ABO TIPS
Tracer Pd in 3.0M HNO3, 0.0001M 0.1
DTDGA
DTDGA
DTDGA
1
10
100
1000
10000
DPd Figure 6. Comparison of distribution coefficients (DPd) of Pd with various extractants under the given experimental conditions.
400
109
0.0025M DTDGA/n-dodecane after contacting with HLW stock solution
Pd
Counts
300 200 100 0 0 400
100 109
20 0 99
Pd
300
40 0
500
Mo
Counts
106
200 241
100
Eu
181
Hf & 144Ce
181
Ru &
89
Sr
Hf 181
Am 125
Hf
137 106
Sb
0 0
100
700
HLW stock solution
300 154
60 0
20 0
300
40 0
500
Ru
Cs
60 0
700
Enengy (keV) Figure 7. c-Spectra of HLW stock solution and organic phase after contacting with HLW stock solution.
Table 1 Extraction of HLW elements, org.: 0.0025 M DTDGA/n-dodecane, aq: 3.0 M HNO3 solutions spiked with genuine HLW and other ‘c’ tracers Element
241
Distribution ratio (DM)
0.0011
Am
152+154
Eu
0.0006
144
Ce
0.0008
conditions, the extraction of palladium was quantitative irrespective of the nature of diluents. Figure 6 shows the comparison of extraction efficiency of DTDGA with ligands namely, DOS, ABO, DOSO, TIPS, DHS, DHDS, TOMAN, TOMAC, BMTPP and T(2EH)TDGA. Since most of the ligands work under different conditions, their comparison with DTDGA has been made under the best conditions, reported in the literature. A very high distribution ratio of palladium was obtained with DTDGA as compared to other previously known extractants thus making it one of the highly efficient extractants for the same purpose. From Figure 7, it can be inferred that except palladium any other element is hardly extracted thus giving very high selectivity.
99
Mo
125
181
0.0007
0.0001
Sb
0.0003
Hf
106
Ru
0.0002
137
Cs
0.00014
109
Pd
325.3
Table 1 shows the distribution ratio of various elements present in HLW. The separation factor (DPd/DM) of the order of P105 for palladium vis a vis other HLW elements makes this extractant very promising for further studies. References and notes 1. (a) Ache, H. J.; Baetsle, L.; Bush, H. R. P.; Nechaev, A. F.; Popik, U. P.; Ying, Yu. IAEA Tech. Rep. Ser. 1989, 308; (b) Sundaram, S. K.; Perez Jr., J. M. PNNL-13347, Pacific Northwest National Laboratory: Richland, WA; 2000, 2. 2. (a) Acres, G. J. K. Platinum Met. Rev. 1984, 28, 150; (b) Kolarik, Z.; Renard, E. V. Platinum Met. Rev. 2003, 47, 74; (c) Kolarik, Z.; Renard, E. V. Platinum Met. Rev. 2003, 47, 123.
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R. Ruhela et al. / Tetrahedron Letters 52 (2011) 3929–3932
3. (a) Mezhov, E. A.; Kuchmunov, V. A.; Druzhenkov, V. V. Radiochemistry 2002, 44, 135; (b) Mezhov, E. A.; Kuchmunov, V. A.; Druzhenkov, V. V. Radiochemistry 2002, 44, 146; (c) Giridhar, P.; Venkatesan, K. A.; Srinivasan, T. G.; Vasudeva Rao, P. R. Hydrometallurgy 2006, 81, 30. 4. Dakshinamoorthy, A.; Dhami, P. S.; Naik, P. W.; Dudwadkar, S. K.; Munshi, S. K.; Dey, P. K.; Venugopal, V. Desalination 2008, 232, 26. 5. (a) Al-Bazi, S. J.; Freiser, H. Solvent Extr. Ion Exch. 1987, 5, 265; (b) Guyon, V.; Guy, A.; Foos, J.; Chomel, R.; Moutarde, T.; Lebuzyte, G.; Lemaire, M. J. Radioanal. Nucl. Chem. Lett. 1994, 187, 19. 6. Shukla, J. P.; Singh, R. K.; Sawant, S. R.; Varadarajan, N. Anal. Chim. Acta 1993, 276, 181. 7. Rizvi, G. H.; Mathur, J. N.; Murali, M. S.; Iyer, R. H. Sep. Sci. Technol. 1996, 31, 1805. 8. MohanRaj, M.; Dharmaraja, A.; Panchanatheswaran, K.; Venkatesan, K. A.; Srinivasan, T. G.; Rao, V. Hydrometallurgy 2006, 84, 118. 9. (a) Ruhela, R.; Sharma, J. N.; Tomar, B. S.; Panja, S.; Tripathi, S. C.; Hubli, R. C.; Suri, A. K. Radiochim. Acta 2010, 98, 209; (b) Ruhela, R.; Sharma, J. N.; Tomar, B. S.; Adya, V. C.; Sheshgiri, T. K.; Hubli, R. C.; Suri, A. K. Sep. Sci. Technol. 2011, 46, 965. 10. Synthesis of DTDGA: Potassium hydroxide (KOH) (2.8 g, 0.05 mol) was added to 50 ml of methanol (MeOH) in three necked round bottom flask fitted with air condenser. 1,2-Ethane-dithiol (2.35 g, 0.025 mol) dissolved in 50 ml MeOH was added to this mixture in one lot and stirred for 30 min. To the stirred solution was added in a dropwise fashion 15.85 g (0.05 mol) of N,N-2-ethylhexyl-2chloroacetamide dissolved in 100 ml MeOH. The reaction mixture was stirred
for 12 h at room temperature followed by stirring for 8 h at 40 °C. The resulting solution was filtered and evacuated to remove the solvent. Hexane was added to the residue and resulting organic solution was successively washed with 0.5 M HCl, 2.5 wt % Na2CO3 solution and water, and then dried over anhydrous Na2SO4. This was then concentrated in vacuum (0.01 mmHg) at 60 °C to give DTDGA with 99.2% purity and 95% yield. Elemental Anal. Calcd for C38H76S2O2N2: C, 69.45; H, 11.65; S, 9.76; O, 4.87; N, 4.26. Found: C, 69.48; H, 11.69; S, 9.77; O, 5.17; N, 3.89. 1H NMR (CDCl3): 0.92–0.95 (m, 24H), 1.2–1.3 (m, 32H), 1.34–1.44 (m, 4H), 2.95 (s, 4H), 3.18 (d, 4H), 3.35 (m, 4H), 3.37 (s, 4H). GC–MS: 23.11 min, 0.89%, m/z 375 calculated for HS–CH2–CH2–S–CH2– C(O)–N(C8H17)2 and 49.58 min, 99.11%, m/z 656 calculated for DTDGA (C8H17)2N–C(O)–CH2–S–CH2–CH2–S–CH2–C(O)–N(C8H17)2. 11. Solvent extraction experiments: Metal ion distribution ratios were determined by mixing equal volume of the organic and aqueous phases, which were equilibrated for 10 min and centrifuged. 109Pd was added as a tracer for palladium in the HLW along with some other radioisotopes, viz., 99Mo, 89Sr and 181 Hf, which were not originally present in the HLW. The phases were separated and dispensed into glass vials from which 20 ll of each phase was taken for radiometric assay using High Purity Germanium (HPGe) detector based gamma spectrometry system. The results are reported as distribution ratio and are calculated as the radioactivity in the organic phase divided by that in aqueous phase. Each experiment was done in duplicate and the results agree to within 5%. For inactive experiments palladium estimation was done using Atomic Absorption Spectrometry and distribution ratio was calculated by dividing palladium concentration in organic phase to that in aqueous phase.
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Dithiodiglycolamide: novel ligand with highest selectivity and extractability for palladium R. Ruhela a,⇑, J. N. Sharma a, B. S. Tomar b, M. S. Murali b, R. C. Hubli a, A. K. Suri a a b
Hydrometallurgy Section, Bhabha Atomic Research Centre, Mumbai 400 085, India Radiochemistry Divison, Bhabha Atomic Research Centre, Mumbai 400 085, India
a r t i c l e
i n f o
Article history: Received 13 April 2011 Revised 16 May 2011 Accepted 22 May 2011 Available online 30 May 2011 Keywords: DTDGA Palladium HLW Distribution ratio Separation factor
a b s t r a c t A novel multidentate ligand N,N,N0 ,N0 -tetra(2-ethylhexyl) dithiodiglycolamide DTDGA has been synthesized and studied for its extraction behavior towards various elements present in high level liquid waste (HLW). The extractant showed remarkable extractability and selectivity for palladium vis a vis other metal ions present in HLW. The distribution ratio as well as the separation factor for palladium was found to be the highest reported so far thus making this extractant one of the most promising candidates for effective separation of palladium from HLW. Ó 2011 Elsevier Ltd. All rights reserved.
Separation and recovery of palladium from high level liquid waste (HLW) solutions originating from PUREX process of spent nuclear fuel is necessary from the viewpoint of various problems encountered during vitrification1 as well as the conceptualization of the process where HLW can be treated as a secondary source of these valuable metals.2 For this purpose various ligands namely, tertiary and quaternary amines (tri-n-octylamine, tri-n-octylmethylammonium chloride (TOMAC) and tri-n-octylmethylammonium nitrate (TOMAN)),3 a-benzoinoxime (ABO),4 dihexyl and dioctyl sulfides (DHS5 and DOS6), dihexyl disulfide (DHDS),5 dioctyl and bis-(2-ethylhexyl) sulfoxides (DOSO7 and BESO),6 triisobutylphosphinesulfide (TIPS)7 and benzoylmethylene triphenylphosphorane (BMTTP),8 have been developed during the last two decades. However, these ligands suffer from various limitations such as slow kinetics,5,7,8 poor decontamination factor,4,6 pH sensitivity,3 solubility3,4,7,8 and instability in acidic medium.5,6 To overcome these problems there is a need for development of newer ligands with improved extraction efficiency as well as selectivity. In a recent work, we have reported the synthesis of novel ‘S’ donor ligand namely N,N,N0 ,N0 -tetra (2-ethylhexyl) thiodiglycolamide (T(2EH)TDGA)9 and its remarkable selectivity for palladium extraction vis a vis other metal ions present in HLW. High selectivity and extractability of the ligand was attributed to the presence of thioetheric sulfur and amidic moiety appropriately placed in the ligand to chelate through more than one donor sites.9 However, there are
various aqueous streams where the concentration of palladium is in sub ppm levels for which an even more efficient extractant is required along with high selectivity. To seek an even more efficient ligand for the said purpose, another novel class of ligand namely, dithiodiglycolamide, has been explored by us. It was envisaged that judicial incorporation of one more sulfur atom would result in more chelation thereby increasing the overall extractability thus increasing the ligand economy while retaining the selectivity. We now report the synthesis of a novel ligand namely, N,N,N0 ,N0 tetra(2-ethylhexyl) dithiodiglycolamide (DTDGA) (Fig. 1) and demonstrate its superiority over previously reported ligands in palladium extraction from HLW. DTDGA was synthesized (Fig. 2) from commercially available and tailor-made materials.10 All other chemicals used in this study were of reagent grade. The extraction study of metal ions was carried out at 25 ± 1 °C.11 To establish the nature of extracted species, both the chemical (mole ratio method) as well as physical (ESI-MS) approaches were
⇑ Corresponding author. Tel.: +91 2225592959/621. E-mail address: [email protected] (R. Ruhela). 0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2011.05.099
Figure 1. N,N,N0 ,N0 -Tetra (2-ethylhexyl) dithiodiglycolamides (DTDGA).
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0.0010
100
0.0008
80
0.0006
60
%E (Pd)
[Pd]org. (M)
Figure 2. Reaction scheme.
0.0004
40 20
0.0002
0
0.0000 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25
0
[DTDGA]org. /[Pd]aq.
4
6
8
10
12
followed. Figure 3 shows the variation of [Pd]org. vs [DTDGA]/[Pd]aq. It can be inferred from the figure that the stoichiometry of the species (Pd to DTDGA) is 1:1. Figure 4 shows the ESI-MS of the extracted species. The peak at m/z 888 corresponds to Pd(N03)2 DTDGA, thus confirming the stoichiometry determined by mole ratio method. The multiple peaks between m/z 759–765 correspond
16
Figure 5. Kinetics of extraction of Pd(II) from aqueous solution (103 M Pd in 3.0 M HNO3) to organic phase (0.001 M DTDGA/n-dodecane).
to PdDTDGA with a number of stable isotopes of palladium having comparable abundance. Figure 5 shows the percentage extraction of Pd as a function of contact time. It is evident that almost complete extraction was achieved within 2–5 min. Moreover under the given experimental
(C8H17)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C8H17)2.Pd (NO3)2 , (m/z, 888), (C8H17)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C8H17)2.Pd , (m/z, 760), (C6H12)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C6H12)2.PdO2N2 , (m/z, 708), (C6H12)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C6H12)2.PdO2 , (m/z, 680) (C6H11)2N-C(O)-CH2-S-CH2-CH2-S-CH2-C(O)-N(C6H11)( C5H9), (m/z, 522)
761.4 2.358e+7
760.4 1.508e+7 763.4 1.284e+7 764.4 8.154e+6
%
680.4 2.521e+6 523.5 1.249e+6
200 Figure 4. ESI-MS (% abundance vs m/z) of 10
14
Time (min)
Figure 3. Mole ratio plot, org.: DTDGA/n-dodecane, aq: 0.98 103 M Pd in 3.0 M HNO3.
1
2
500 4
759.4 5.764e+6 709.8 3.672e+6 759.8 3.639e+6
600
800 4
M DTDGA/n-hexane after contacting with 10
888.1 1.524e+6
900
M Pd in 3.0 M nitric acid medium.
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BMTPP TOMAC
2.5 x 10-4M Pd in 1.0M HNO3, 0.05M TOMAN
DTDGA DHDS DHS
2.5 x 10-4M Pd in 1.0M HNO3, 0.001M
DOSO T(2EH)TDGA DTDGA
Tracer Pd in 3.0M HNO3, 0.0025M
Tracer Pd in 3.0M HNO3, 0.0005M
DOS ABO TIPS
Tracer Pd in 3.0M HNO3, 0.0001M 0.1
DTDGA
DTDGA
DTDGA
1
10
100
1000
10000
DPd Figure 6. Comparison of distribution coefficients (DPd) of Pd with various extractants under the given experimental conditions.
400
109
0.0025M DTDGA/n-dodecane after contacting with HLW stock solution
Pd
Counts
300 200 100 0 0 400
100 109
20 0 99
Pd
300
40 0
500
Mo
Counts
106
200 241
100
Eu
181
Hf & 144Ce
181
Ru &
89
Sr
Hf 181
Am 125
Hf
137 106
Sb
0 0
100
700
HLW stock solution
300 154
60 0
20 0
300
40 0
500
Ru
Cs
60 0
700
Enengy (keV) Figure 7. c-Spectra of HLW stock solution and organic phase after contacting with HLW stock solution.
Table 1 Extraction of HLW elements, org.: 0.0025 M DTDGA/n-dodecane, aq: 3.0 M HNO3 solutions spiked with genuine HLW and other ‘c’ tracers Element
241
Distribution ratio (DM)
0.0011
Am
152+154
Eu
0.0006
144
Ce
0.0008
conditions, the extraction of palladium was quantitative irrespective of the nature of diluents. Figure 6 shows the comparison of extraction efficiency of DTDGA with ligands namely, DOS, ABO, DOSO, TIPS, DHS, DHDS, TOMAN, TOMAC, BMTPP and T(2EH)TDGA. Since most of the ligands work under different conditions, their comparison with DTDGA has been made under the best conditions, reported in the literature. A very high distribution ratio of palladium was obtained with DTDGA as compared to other previously known extractants thus making it one of the highly efficient extractants for the same purpose. From Figure 7, it can be inferred that except palladium any other element is hardly extracted thus giving very high selectivity.
99
Mo
125
181
0.0007
0.0001
Sb
0.0003
Hf
106
Ru
0.0002
137
Cs
0.00014
109
Pd
325.3
Table 1 shows the distribution ratio of various elements present in HLW. The separation factor (DPd/DM) of the order of P105 for palladium vis a vis other HLW elements makes this extractant very promising for further studies. References and notes 1. (a) Ache, H. J.; Baetsle, L.; Bush, H. R. P.; Nechaev, A. F.; Popik, U. P.; Ying, Yu. IAEA Tech. Rep. Ser. 1989, 308; (b) Sundaram, S. K.; Perez Jr., J. M. PNNL-13347, Pacific Northwest National Laboratory: Richland, WA; 2000, 2. 2. (a) Acres, G. J. K. Platinum Met. Rev. 1984, 28, 150; (b) Kolarik, Z.; Renard, E. V. Platinum Met. Rev. 2003, 47, 74; (c) Kolarik, Z.; Renard, E. V. Platinum Met. Rev. 2003, 47, 123.
3932
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3. (a) Mezhov, E. A.; Kuchmunov, V. A.; Druzhenkov, V. V. Radiochemistry 2002, 44, 135; (b) Mezhov, E. A.; Kuchmunov, V. A.; Druzhenkov, V. V. Radiochemistry 2002, 44, 146; (c) Giridhar, P.; Venkatesan, K. A.; Srinivasan, T. G.; Vasudeva Rao, P. R. Hydrometallurgy 2006, 81, 30. 4. Dakshinamoorthy, A.; Dhami, P. S.; Naik, P. W.; Dudwadkar, S. K.; Munshi, S. K.; Dey, P. K.; Venugopal, V. Desalination 2008, 232, 26. 5. (a) Al-Bazi, S. J.; Freiser, H. Solvent Extr. Ion Exch. 1987, 5, 265; (b) Guyon, V.; Guy, A.; Foos, J.; Chomel, R.; Moutarde, T.; Lebuzyte, G.; Lemaire, M. J. Radioanal. Nucl. Chem. Lett. 1994, 187, 19. 6. Shukla, J. P.; Singh, R. K.; Sawant, S. R.; Varadarajan, N. Anal. Chim. Acta 1993, 276, 181. 7. Rizvi, G. H.; Mathur, J. N.; Murali, M. S.; Iyer, R. H. Sep. Sci. Technol. 1996, 31, 1805. 8. MohanRaj, M.; Dharmaraja, A.; Panchanatheswaran, K.; Venkatesan, K. A.; Srinivasan, T. G.; Rao, V. Hydrometallurgy 2006, 84, 118. 9. (a) Ruhela, R.; Sharma, J. N.; Tomar, B. S.; Panja, S.; Tripathi, S. C.; Hubli, R. C.; Suri, A. K. Radiochim. Acta 2010, 98, 209; (b) Ruhela, R.; Sharma, J. N.; Tomar, B. S.; Adya, V. C.; Sheshgiri, T. K.; Hubli, R. C.; Suri, A. K. Sep. Sci. Technol. 2011, 46, 965. 10. Synthesis of DTDGA: Potassium hydroxide (KOH) (2.8 g, 0.05 mol) was added to 50 ml of methanol (MeOH) in three necked round bottom flask fitted with air condenser. 1,2-Ethane-dithiol (2.35 g, 0.025 mol) dissolved in 50 ml MeOH was added to this mixture in one lot and stirred for 30 min. To the stirred solution was added in a dropwise fashion 15.85 g (0.05 mol) of N,N-2-ethylhexyl-2chloroacetamide dissolved in 100 ml MeOH. The reaction mixture was stirred
for 12 h at room temperature followed by stirring for 8 h at 40 °C. The resulting solution was filtered and evacuated to remove the solvent. Hexane was added to the residue and resulting organic solution was successively washed with 0.5 M HCl, 2.5 wt % Na2CO3 solution and water, and then dried over anhydrous Na2SO4. This was then concentrated in vacuum (0.01 mmHg) at 60 °C to give DTDGA with 99.2% purity and 95% yield. Elemental Anal. Calcd for C38H76S2O2N2: C, 69.45; H, 11.65; S, 9.76; O, 4.87; N, 4.26. Found: C, 69.48; H, 11.69; S, 9.77; O, 5.17; N, 3.89. 1H NMR (CDCl3): 0.92–0.95 (m, 24H), 1.2–1.3 (m, 32H), 1.34–1.44 (m, 4H), 2.95 (s, 4H), 3.18 (d, 4H), 3.35 (m, 4H), 3.37 (s, 4H). GC–MS: 23.11 min, 0.89%, m/z 375 calculated for HS–CH2–CH2–S–CH2– C(O)–N(C8H17)2 and 49.58 min, 99.11%, m/z 656 calculated for DTDGA (C8H17)2N–C(O)–CH2–S–CH2–CH2–S–CH2–C(O)–N(C8H17)2. 11. Solvent extraction experiments: Metal ion distribution ratios were determined by mixing equal volume of the organic and aqueous phases, which were equilibrated for 10 min and centrifuged. 109Pd was added as a tracer for palladium in the HLW along with some other radioisotopes, viz., 99Mo, 89Sr and 181 Hf, which were not originally present in the HLW. The phases were separated and dispensed into glass vials from which 20 ll of each phase was taken for radiometric assay using High Purity Germanium (HPGe) detector based gamma spectrometry system. The results are reported as distribution ratio and are calculated as the radioactivity in the organic phase divided by that in aqueous phase. Each experiment was done in duplicate and the results agree to within 5%. For inactive experiments palladium estimation was done using Atomic Absorption Spectrometry and distribution ratio was calculated by dividing palladium concentration in organic phase to that in aqueous phase.