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Liquid-liquid extraction of Np(V) using 1-nitroso 2-naphthol and its radiochemical separation from fission products
3886
Notes
J. inorg,nucl.Chem.. 1969.Vol.31. pp. 3886to 3888. PergamonPress. Printedin Great Britain
Liquid-liquid extraction of Np(V) using 1-nitroso 2-naphthol and its radiochemical separation from fission products (Received 5 June 1969) INTRODUCTION on the separation of neptunium by solvent extraction of the tetra- and hexavalent oxidation states are available, but relatively few methods have been reported which involve the neptunium(V). The complexing of NpO~ + by TTA, 8-hydroxyquinoline, l-nitroso 2-naphthol and a few other reagents has been reported [4, 5] and reviewed [6]. The possibility of separating neptunium from plutonium and uranium by extraction of Np(V) with l-nitroso 2-naphthol has also been described[7]. We now report further studies on the extraction behaviour of Np(V) using this reagent. Some parameters not studied previously [7] have now been investigated in detail. The extraction behaviour of other elements under the optimum conditions for the extraction of Np(V) has also been studied and a procedure for the separation of neptunium from fission products is suggested.
EXTENSIVEreports[l-3]
EXPERIMENTAL Radioactive tracers. 2~gNp was prepared by irradiating uranyl nitrate in the Pakistan Research Reactor (PARR) at Islamabad and separated by extraction as Np(IV) into 0.2 M TTA in xylene [8, 9]. The purity was checked by 3~-spectrometry[10] using a 3 x 3 in. Nal(TI) crystal ~/-spectrometer in conjunction with a 512 channel Nuclear Data pulse height analyser. Radioactive tracers for other elements were obtained from the Radiochemical Centre, Amersham, and were mostly carrier free. Extraction procedure. A 239Np(VI) solution in 1.0 M HCI was made 1.0 M with respect to NH2 O H . HC1. After a 3 min shaking, during which time the neptunium was reduced [ l l] to Np(V), the pH of the solution was adjusted by the addition of NH4OH and buffered with 0.01 M borax solution at 9-17. An equal volume of the l-nitroso 2-naphthol reagent solution in isoamyl alcohol was then added and the mixture shaken for 5 rain. The aqueous and organic layers were separated and counted in a well-type Nal(TI) crystal ~/-scintillation counter and the distribution constant (Ka) and percentage extraction determined. Test for the existence of Np(V). (i) Zirconium phenylarsonate, which coprecipitates[7] Np(VI), was precipitated from the solution. The presence of negligible neptunium activity in the precipitate established the absence of Np(VI). (ii) An extraction with T T A in xylene, which extracts Np(IV) quantitatively[8], was performed. No activity was found in the organic phase showing that Np(IV) was absent. 1. J. J. Katz and G. T. Seaborg In The Chemistry of the Actinide Elements, p. 209. Methuen, London (1957). 2. C. F. Metz and G. R. Waterbury In Treatise on Analytical Chemistry (Edited by 1. M. Kolthoff and P. J. Elwing), Part I 1, Vol. 9, p. 259. Wiley, New York (1962). 3. A. J. Moses In Analytical Chemistry of the Actinide Elements, p. 27. Pergamon Press, Oxford (1963). 4. 1. P. Alimarin and Yu. A. Zolotov, Talanta 9, 891 (1962). 5. Yu. A. Zolotov and I. P. Alimarin, J. inorg, nucl. Chem. 25, 691 (1963). 6. A. D. Gel'man, A. 1. Moskvin, L. M. Zaitsev and M. P. Mefod'eva In Complex compounds of transuranium elements, p. 8. Consultants Bureau Translation, New York (1962). 7. I. P. Alimarin, Yu. A. Zolotov and E. S. Pal'shin, Dokl. Akad. Nauk SSSR 124, 328 (1959); Radiokhimiya 2, 637 (1960). 8. F. L. Moore,Analyt. Chem. 29,941 (1957). 9. S. M. Qaim, Nucl. Phys. 84, 411 (1966); 88, 285 (1966). 10. C. M. Lederer, G. M. Hollander and 1. Perlman, The Table of Isotopes. Wiley, New York (1967). 11. J. C. Hindman, L. B. Magnusson and T. J. LaChapelle, paper 15.2 In The Transuranium elements. National Nuclear Energy Series. Div. IV., 14B McGraw-Hill, New York (1949).
Notes
3887
RESULTS Selection o f optimum conditions for the extraction o f neptunium The effect of pH on the extraction of Np(V) was investigated using a 0.075 M solution of the reagent in isoamyl alcohol. Extraction was negligible at pH < 6 but increased sharply between 7 and 8. Maximum extraction (about 94.5 per cent) occurred at pH ~ 9 when a Ka value of 17.2 was obtained. These results agree with the published data[7]. Above pH 9.5 the separation of the phases became increasingly difficult. Increasing the volume of the organic phase did not affect the extraction, nor did increased contact time. The extraction of Np(V) at pH 9.17 was studied over the reagent concentration range of 0-0-0.2 M. Typical results are given in Fig. 1. In the absence of the reagent only about 2 per cent of neptunium(V) is extracted in isoamyl alcohol. The extraction increases with increasing reagent concentration up to about 0-045 M when it becomes almost independent of the reagent concentration. With more than 0.125 molar concentration the separation of phases becomes difficult and occasionally part of the reagent precipitates at the interface. Alimarin et al. [7] have previously reported that the extraction
1
~ 1
0
0
0
~
~
1
0
0
.
-
0
1
0'06 0'12 0"18 1 ,- Reagent concentration [moteslitre- ]
Fig. 1. The effect of 1-nitroso 2-naphthol concentration on the extraction of Np(V) at pH 9.17. is independent of reagent concentration. Their investigations, however, were limited to the concentration range 0.015-0.060 M, for which the variation in the percentage extraction is rather small. Extraction by a 0.075 M solution of the reagent in the solvents amyl alcohol, isoamyl alcohol, n-butyl alcohol, benzene, xylene, chloroform and diethyl ether was studied. Appreciable extraction occurred only with alcohols. With n-butyl alcohol about 50 per cent neptunium(V) was extracted and with isoamyl alcohol about 93 per cent. Use of the latter solvent is therefore recommended. Since it appeared possible that alcohols might reduce Np(V) to Np(IV), this was checked by successive extraction and back extraction. The organic extract containing Np(V) was shaken with an equal volume of dilute HCI at pH < 2 when almost all the neptunium passed into the aqueous phase. On readjusting the pH to 9 and re-extracting neptunium with the reagent solution, more than 90 per cent of the activity passed into the organic phase showing that Np(V) is stable in the presence of alcohols. Ions such as fluoride, phosphate, oxalate and carbonate interfered in the extraction of neptunium (V). Small amounts of borax, used in the buffer, however, had no effect and chloride and nitrate ions did not influence the extraction over the concentration range 1-5 moles/1. Neptunium(V) is back extracted into an aqueous medium o f p H ~< 2. Alimarin et al. [7] recommend back extraction with HCI or HNO.~. We have observed that with these acids a small part of the reagent also enters the aqueous phase. Perchloric acid was found to be better, an equal volume of 2 M HCIO4 back extracting about 90 per cent neptunium(V) in less than 2 min.
3888
Notes
Extraction of other elements. The extraction behaviour of tracer amounts of the following elements (representing some of the typical groups of fission products) was investigated under the optimum conditions for the extraction of Np(V) (0.075 M solution of the reagent in isoamyl alcohol at pH 9"17). 45Ca, 51Cr, 54Mn, eSZn, 9°Sr, asZr-95Nb, l°eRu, x141n, 137Cs, 147pr, l~'SHf, lS2Ta, 1921r, 2°7Bi, 21°Pb and 2~Pa. In most cases the extraction was less than 10 per cent. With, for example, Zr and Sr, however, large amounts of the activity were extracted. The extraction of Np(V) with this reagent is, therefore, not very selective and cannot be applied alone to the separation of Np(V) from fission products. However, by combining other steps with the solvent extraction of Np(V) it was possible to obtain neptunium free from all fission products. The procedure is described below. Suggested procedure for the separation of neptunium from fission products Dissolve the irradiated uranium oxide in HNO3 and heat to almost dryness. Add appropriate quantities of HCI, NH2OH • HC1 and KI solutions to make their concentrations l M, 1 M and 2 M respectively. Warm the mixture at 60° for 5 min to reduce [8] neptunium to the tetravalent state (reduction can also be achieved by passing SO2 into a hot solution). Add sodium acetate solution taking care that the pH does not exceed 3. Shake the mixture for 5 rain and centrifuge off the sodium uranylacetate precipitate. Repeat this precipitation after adding 20 mg of uranium carrier. Neptunium (IV) remains in solution. To the supernate add l0 mg of La carrier and 10 mg each of Zr and Sr hold-back carriers. Add H F dropwise. Collect the LaF3 precipitate which carries Np(IV) and discard the supernate. Dissolve the precipitate in a few drops of concentrated HNO3 containing H3BO3 and KBrO3. Neptunium is oxidised to the (VI) state. Add 3 drops of H F and centrifuge off the LaF3 precipitate. Np(VI) remains in solution. Heat the mixture till fuming occurs. Then add HCI and NH2OH • HCI and adjust their concentrations to 1M. This reduces neptunium to the pentavalent state. Add 10 mg of Zr carder and precipitate as zirconium phenylarsonate. Discard the precipitate. Np(V) stays in solution. Adjust the pH of the solution by adding NH4OH and buffer it with 0.01 M borax solution at 9.17. Extract neptunium(V) by shaking for 5 min with an equal volume of 0.075 M 1-nitroso 2-naphthol solution in isoamyl alcohol. Discard the aqueous phase. Scrub the organic phase twice with a l M solution of NH2OH • HCl in ammonia and then strip the neptunium(V) by shaking the organic layer with an equal volume of 2 M HCIO4. Mount and count. Neptunium separated by this method was counted for ~- and T-rays when a half-life value of 2.3 days, characteristic of 239Np, was obtained. This was further confirmed by T-spectrometric analysis. Separation of neptunium by the above method from a 60 day old fission product solution gave a decontamination factor of 10s. The separation can be completed in about l hr. The overall yield is approximately 60 per cent.
Acknowledgements - We thank the Reactor Operation and Maintenance Staffat Islamabad for carrying out the irradiations and our colleagues at Lahore for helpful comments and discussions.
Atomic Energy Centre Lahore Pakistan
S.M. QAIM J. HAN1F
Notes
J. inorg,nucl.Chem.. 1969.Vol.31. pp. 3886to 3888. PergamonPress. Printedin Great Britain
Liquid-liquid extraction of Np(V) using 1-nitroso 2-naphthol and its radiochemical separation from fission products (Received 5 June 1969) INTRODUCTION on the separation of neptunium by solvent extraction of the tetra- and hexavalent oxidation states are available, but relatively few methods have been reported which involve the neptunium(V). The complexing of NpO~ + by TTA, 8-hydroxyquinoline, l-nitroso 2-naphthol and a few other reagents has been reported [4, 5] and reviewed [6]. The possibility of separating neptunium from plutonium and uranium by extraction of Np(V) with l-nitroso 2-naphthol has also been described[7]. We now report further studies on the extraction behaviour of Np(V) using this reagent. Some parameters not studied previously [7] have now been investigated in detail. The extraction behaviour of other elements under the optimum conditions for the extraction of Np(V) has also been studied and a procedure for the separation of neptunium from fission products is suggested.
EXTENSIVEreports[l-3]
EXPERIMENTAL Radioactive tracers. 2~gNp was prepared by irradiating uranyl nitrate in the Pakistan Research Reactor (PARR) at Islamabad and separated by extraction as Np(IV) into 0.2 M TTA in xylene [8, 9]. The purity was checked by 3~-spectrometry[10] using a 3 x 3 in. Nal(TI) crystal ~/-spectrometer in conjunction with a 512 channel Nuclear Data pulse height analyser. Radioactive tracers for other elements were obtained from the Radiochemical Centre, Amersham, and were mostly carrier free. Extraction procedure. A 239Np(VI) solution in 1.0 M HCI was made 1.0 M with respect to NH2 O H . HC1. After a 3 min shaking, during which time the neptunium was reduced [ l l] to Np(V), the pH of the solution was adjusted by the addition of NH4OH and buffered with 0.01 M borax solution at 9-17. An equal volume of the l-nitroso 2-naphthol reagent solution in isoamyl alcohol was then added and the mixture shaken for 5 rain. The aqueous and organic layers were separated and counted in a well-type Nal(TI) crystal ~/-scintillation counter and the distribution constant (Ka) and percentage extraction determined. Test for the existence of Np(V). (i) Zirconium phenylarsonate, which coprecipitates[7] Np(VI), was precipitated from the solution. The presence of negligible neptunium activity in the precipitate established the absence of Np(VI). (ii) An extraction with T T A in xylene, which extracts Np(IV) quantitatively[8], was performed. No activity was found in the organic phase showing that Np(IV) was absent. 1. J. J. Katz and G. T. Seaborg In The Chemistry of the Actinide Elements, p. 209. Methuen, London (1957). 2. C. F. Metz and G. R. Waterbury In Treatise on Analytical Chemistry (Edited by 1. M. Kolthoff and P. J. Elwing), Part I 1, Vol. 9, p. 259. Wiley, New York (1962). 3. A. J. Moses In Analytical Chemistry of the Actinide Elements, p. 27. Pergamon Press, Oxford (1963). 4. 1. P. Alimarin and Yu. A. Zolotov, Talanta 9, 891 (1962). 5. Yu. A. Zolotov and I. P. Alimarin, J. inorg, nucl. Chem. 25, 691 (1963). 6. A. D. Gel'man, A. 1. Moskvin, L. M. Zaitsev and M. P. Mefod'eva In Complex compounds of transuranium elements, p. 8. Consultants Bureau Translation, New York (1962). 7. I. P. Alimarin, Yu. A. Zolotov and E. S. Pal'shin, Dokl. Akad. Nauk SSSR 124, 328 (1959); Radiokhimiya 2, 637 (1960). 8. F. L. Moore,Analyt. Chem. 29,941 (1957). 9. S. M. Qaim, Nucl. Phys. 84, 411 (1966); 88, 285 (1966). 10. C. M. Lederer, G. M. Hollander and 1. Perlman, The Table of Isotopes. Wiley, New York (1967). 11. J. C. Hindman, L. B. Magnusson and T. J. LaChapelle, paper 15.2 In The Transuranium elements. National Nuclear Energy Series. Div. IV., 14B McGraw-Hill, New York (1949).
Notes
3887
RESULTS Selection o f optimum conditions for the extraction o f neptunium The effect of pH on the extraction of Np(V) was investigated using a 0.075 M solution of the reagent in isoamyl alcohol. Extraction was negligible at pH < 6 but increased sharply between 7 and 8. Maximum extraction (about 94.5 per cent) occurred at pH ~ 9 when a Ka value of 17.2 was obtained. These results agree with the published data[7]. Above pH 9.5 the separation of the phases became increasingly difficult. Increasing the volume of the organic phase did not affect the extraction, nor did increased contact time. The extraction of Np(V) at pH 9.17 was studied over the reagent concentration range of 0-0-0.2 M. Typical results are given in Fig. 1. In the absence of the reagent only about 2 per cent of neptunium(V) is extracted in isoamyl alcohol. The extraction increases with increasing reagent concentration up to about 0-045 M when it becomes almost independent of the reagent concentration. With more than 0.125 molar concentration the separation of phases becomes difficult and occasionally part of the reagent precipitates at the interface. Alimarin et al. [7] have previously reported that the extraction
1
~ 1
0
0
0
~
~
1
0
0
.
-
0
1
0'06 0'12 0"18 1 ,- Reagent concentration [moteslitre- ]
Fig. 1. The effect of 1-nitroso 2-naphthol concentration on the extraction of Np(V) at pH 9.17. is independent of reagent concentration. Their investigations, however, were limited to the concentration range 0.015-0.060 M, for which the variation in the percentage extraction is rather small. Extraction by a 0.075 M solution of the reagent in the solvents amyl alcohol, isoamyl alcohol, n-butyl alcohol, benzene, xylene, chloroform and diethyl ether was studied. Appreciable extraction occurred only with alcohols. With n-butyl alcohol about 50 per cent neptunium(V) was extracted and with isoamyl alcohol about 93 per cent. Use of the latter solvent is therefore recommended. Since it appeared possible that alcohols might reduce Np(V) to Np(IV), this was checked by successive extraction and back extraction. The organic extract containing Np(V) was shaken with an equal volume of dilute HCI at pH < 2 when almost all the neptunium passed into the aqueous phase. On readjusting the pH to 9 and re-extracting neptunium with the reagent solution, more than 90 per cent of the activity passed into the organic phase showing that Np(V) is stable in the presence of alcohols. Ions such as fluoride, phosphate, oxalate and carbonate interfered in the extraction of neptunium (V). Small amounts of borax, used in the buffer, however, had no effect and chloride and nitrate ions did not influence the extraction over the concentration range 1-5 moles/1. Neptunium(V) is back extracted into an aqueous medium o f p H ~< 2. Alimarin et al. [7] recommend back extraction with HCI or HNO.~. We have observed that with these acids a small part of the reagent also enters the aqueous phase. Perchloric acid was found to be better, an equal volume of 2 M HCIO4 back extracting about 90 per cent neptunium(V) in less than 2 min.
3888
Notes
Extraction of other elements. The extraction behaviour of tracer amounts of the following elements (representing some of the typical groups of fission products) was investigated under the optimum conditions for the extraction of Np(V) (0.075 M solution of the reagent in isoamyl alcohol at pH 9"17). 45Ca, 51Cr, 54Mn, eSZn, 9°Sr, asZr-95Nb, l°eRu, x141n, 137Cs, 147pr, l~'SHf, lS2Ta, 1921r, 2°7Bi, 21°Pb and 2~Pa. In most cases the extraction was less than 10 per cent. With, for example, Zr and Sr, however, large amounts of the activity were extracted. The extraction of Np(V) with this reagent is, therefore, not very selective and cannot be applied alone to the separation of Np(V) from fission products. However, by combining other steps with the solvent extraction of Np(V) it was possible to obtain neptunium free from all fission products. The procedure is described below. Suggested procedure for the separation of neptunium from fission products Dissolve the irradiated uranium oxide in HNO3 and heat to almost dryness. Add appropriate quantities of HCI, NH2OH • HC1 and KI solutions to make their concentrations l M, 1 M and 2 M respectively. Warm the mixture at 60° for 5 min to reduce [8] neptunium to the tetravalent state (reduction can also be achieved by passing SO2 into a hot solution). Add sodium acetate solution taking care that the pH does not exceed 3. Shake the mixture for 5 rain and centrifuge off the sodium uranylacetate precipitate. Repeat this precipitation after adding 20 mg of uranium carrier. Neptunium (IV) remains in solution. To the supernate add l0 mg of La carrier and 10 mg each of Zr and Sr hold-back carriers. Add H F dropwise. Collect the LaF3 precipitate which carries Np(IV) and discard the supernate. Dissolve the precipitate in a few drops of concentrated HNO3 containing H3BO3 and KBrO3. Neptunium is oxidised to the (VI) state. Add 3 drops of H F and centrifuge off the LaF3 precipitate. Np(VI) remains in solution. Heat the mixture till fuming occurs. Then add HCI and NH2OH • HCI and adjust their concentrations to 1M. This reduces neptunium to the pentavalent state. Add 10 mg of Zr carder and precipitate as zirconium phenylarsonate. Discard the precipitate. Np(V) stays in solution. Adjust the pH of the solution by adding NH4OH and buffer it with 0.01 M borax solution at 9.17. Extract neptunium(V) by shaking for 5 min with an equal volume of 0.075 M 1-nitroso 2-naphthol solution in isoamyl alcohol. Discard the aqueous phase. Scrub the organic phase twice with a l M solution of NH2OH • HCl in ammonia and then strip the neptunium(V) by shaking the organic layer with an equal volume of 2 M HCIO4. Mount and count. Neptunium separated by this method was counted for ~- and T-rays when a half-life value of 2.3 days, characteristic of 239Np, was obtained. This was further confirmed by T-spectrometric analysis. Separation of neptunium by the above method from a 60 day old fission product solution gave a decontamination factor of 10s. The separation can be completed in about l hr. The overall yield is approximately 60 per cent.
Acknowledgements - We thank the Reactor Operation and Maintenance Staffat Islamabad for carrying out the irradiations and our colleagues at Lahore for helpful comments and discussions.
Atomic Energy Centre Lahore Pakistan
S.M. QAIM J. HAN1F