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Neutron activation analysis by standard addition and solvent extraction
Talmta, 1968, Vol. 15. pp. 257 to 261. Pa&t8mon Press. Printed in Northern Ireland
SHORT COMMUNICATIONS
Neutron A~~v~~~ Analysis by Standard Addition md Solvent Extr8etion. Determination of Impurities in Thorium and Iron (Received 12 April 1967. Accepted 20 Juty 1967) IN a previous paper’ a separation scheme was described for the simultaneous determiilatiOn of scamlmm, cobalt, iron, zinc, silver, mercury, chromium and rubidium in ahuninium by neutron and “O*Hgare fractionated by ~d~~~ne activation analysis. The induced Wo, 6sFe, %n, X1oAg (EDA) extraction. The induced %Sc is extracted with t~butylphosphate @‘BP), while Wr and -Rb are determined in the aqueous solution by gamma-ray spectrometry. rrsPa which is obtained in one of the fractions was shown in another paper* to be separated from Vo by extraction with thenoyhrifluoroacetone (PTA), thus allowing the determination of thorium in aluminhun. In the present communication studies have been performed in order to improve the separation procedure and to make it suitable for the determination of trace elements in thorium and iron.
Studies on the extractability of I1*Ag, GZn and *OrHgwith 0+3MTDA have shown that the degrees of extraction of the three radionuclides from 12&f hydrochloric acid are 1, 97 and 99% respectively. Accordingly llOAg can be stripped with 12.&fhydrochloric acid from the TDA extract before the elution of %n with 1M nitric acid; this makes possible the determination of silver and mercury in separate fractions. ~eterm~tion of ~~~~ in tiwium nitrate Elements present in trace amounts in thorium affect its physical metallurgy and the neutron economy in the “breeding” reaction: *mPa8-_ 27d
sYJ
(1)
Methods for the determination of trace elements in thorium have been developed.8 Emission spectroscopic methods have been widely used for the determination of many impurities in thoriumf while chemical methods, because of their greater accuracy, are sometimes of major importar~ce.~-~* The application of neutron-activation methods to the determination of impurities in thorium and its concentrates is dXicuIt, owing to the very high activity induced from thorium as a result of neutron irradiation. Thus, as can be seen from reaction (1) di&ulties will be met with in the determination of impurities giving rise to both short and long-lived radioisotopes. Methods of separation which would tzrvehigh decontamination factors from activated matrix comuonents should therefore 1) be applied, s&e no?ooling can be allowed. Samples of thorium nitrate (about 250 mg) are wrapped in thin ~~~ foils. For quantitative analvsis. the stim~Ies and standards are X &aced touether in an alumimum can and irradiated as de&bed previou&y.’ Each thorium sample is carefully removed from the ahrminium foil, transferred to a 1004 beaker and sub uently dissolved in 1.3M hydrochloric acid. The foil is washed with the minimium quantity 1o 1M nitric acid. The solution is then transferred to a 2%ml graduated flask, the inside walls of the beaker being washed with 1.3M hydrochloric acid, and then made up to the mark with 1*3Mhydrochloric acid. The extraction of rraPa with TTA*J’ is applied for its separation from other nuclides. By two successive extractions with O*%f TTA in xylene, Wpa (together with 5%) is ahnost completely removed from the irradiated thorium solution. The volm of organic and aqueous phase used are in 2:1 ratio. About 60% of DgFetogether with major proportions of the other radionuclides remain in the aqueous phase. Owing to the very high activity of the induced %, shaking should not be done by hand but on a suitably shielded mechanical shaker. The time required for reaching extraction equilibrium with TTA on the shaker is about 15 min. 257
258
Short communications
The thorium solution is then made 6M in lithium chloride and 3M in hydrochloric acid; the extractability of isotopes from this medium with 0*3M TDA is similar to their extractability from 25M aluminium chloride-15M hydrochloric acid. In other words cobalt, niobium, iron, silver, zinc and mercury can be extracted with @3M TDA from 6M lithium chloride3M hydrochloric acid, while scandium, chromium, rare earths and rubidium remain in the aqueous phase.. Traces of protactinium (which may be left after extraction with ‘ITA) will also be extracted from this medium. Fractions containing cobalt, iron, silver and zinc are therefore contaminated with traces of =Pa. The possibility of eliminating rrsPa by another extraction with TTA has been considered. The extractability of rsrPa and the other isotopes with TTA from various media is shown in Table I. TAIU I.-EYJRAC~ION OF nssPa ANDormm ISOTOPESWITH 05M TTA Medium
Isotope
Extraction, %
1.7M HCI
99 0.1 0.1 79
3M HF-0.SM HCl
12M HCl lMHNOa
9? 0.1
It can be seen that the 1.7M hydrochloric acid, 12M hydrochloric acid and 1M nitric acid fractions can be partly freed from rssPa by one or two extractions with ‘ITA. Recovery values greater than 50 % for iron and 80 % for the other isotopes are obtainable, while satisfactory reproducibility of separation is achieved. When the modified separation scheme was applied to an irradiated sample solution of analytical reagent grade thorium nitrate none of the impurities listed above were detected, and only zirconium was identified (uiu 05Nb) in an “Indian Nuclear Pure” sample (Fig. lb). For testing the scheme, irradiated thorium nitrate was mixed with varying amounts of irradiated standard solutions. Typical TABLEII.-ANALYSIS OFIMPURITIES IN THORIUM NURA~E(50 mg)
Element
Nuclide identified”
Half-life
4”Sc(l.12)
85d
Amount added (as metal), PPm
Photopeak activity, CPm
At
Ant
2104 4217
1934 4008 5929
b.d$ 1.1 2.48
975
b.d.
2571 3353
2y.z
77 124 200
b.d. 124 220
90 183
92 208 277
b.d. 23.0 58.0
502 1026
426 923 1391
b.d. 2.38 5.80
Scandium
: -
Cobalt
*oco(l*33)
53y
Iron
LgFe(l.lO)
45d
Zinc
e5Zn(l.11)
245d
10 20
-
-
-
69 138
Mercury
‘O*Hg(O*28)
458d
1199 2286
;:
30 60 2 4
Amount found, PPm
* In brackets are given the energies of the photopeaks in (MeV) used for quantitative analysis. t See reference 1. $ b.d. = beyond detection.
Short communications 31MeV
(0
(b)
lO.OO(
100~
IO
.c
c*
I
I
Energy,
MeV
FIG. L-Gamma-ray spectra. a-Irradiated thorium solution. b-TBP extract. c-1.7M HCl strip solution. d-12M HCl strip solution. e-3M HF45M HCl strip solution. f-l M HNOa strip solution. g-Final TDA extract. h-1.7M HCl strip solution from Indian thorium.
259
260
Short communications TABLEIII.-EXTRACTION OFRADIOISOTOPES WITHISOPROPYL ETHER FROM9M HCI Extraction, %
Isotope &OFe rasPa 6”Co
99.9 (99.9)+
*O*H g
‘Yk Wr 1WS =Rb 141Ce(III)
+ These values in brackets have been reported in a previous paper.16 gamma-spectraof the artticially contaminated thorium solutionandof the isolated fractions are shown in Fig. 1. It is clear that rs*Pa contaminates %c, ‘Wo, 6eFe, “OAg and ssZn, while *O*Hgis very pure. The incomplete decontamination from *=Pa can be explained by the presence of a small amount of inextractable material .l* ‘Wo is also contaminated with B6Nb. Fortunately rsrPa and @jNb are less active, and their presence does not represent any diiJiculty in the analysis of these nuclides. 06Nb may be separated from cobalt by extraction with tribenzylamine from 11M hydrochloric acid’” or with a secondary amine, l4 thus allowing the determination of zirconium in thorium. In this case analysis should be carried out at least a month after irradiation, to allow for the growth of s8Nb. The results of quantitative analysis carried out as described1J6 on artificially contaminated thorium samples are presented in Table II. There was satisfactory agreement between the amount added and the amount found for all the elements. TABLEIV.-ANALYSIS OFIMPURITIES IN IRONOXIDE(50 mp)
Element *
Amount added (as metal), unm
Scandium
1 2 -
Amount found, $ uum b.d 1.06 2.12
5 10
b.d. 4.31 953
Thorium?
-2 4
1-74 3.85
Silver
-2
b.d. 2.6
Zinc
%l 120
Cobalt
Mercury
4
b.d. 71.0 105.0 3.69
* For the induced isotopes and energies of photopeaks used for quantitative analysis see Table II. t Determined by counting the 0.31 MeV peak activity of OsrPa. $ Average of two determinations, b.d. = beyond detection.
261
Short communications Determination of impurities in iron
The determination of impurities in iron by neutron activation analysis has been reported in a recent paper. l’ Nondestrucuve methods have been applied for some elements, while radiochemical separatron procedures using ion-exchange chromatography and solvent extraction techniques have been used for others. A preliminary removal of the mduced seFe has been performed by extraction with isopropyl ether. In this study the improved separation scheme has been applied for the determination of impurities in iron, after a preliminary separation of seFe with isopropyl ether.“ In Table III are presented our data on the extraction of iron and the other induced radioisotopes, from 9M hydrochloric acid; it is clear that only iron is quantitatively extracted, while the other isotopes remain in the aqueous layer. The aqueous solution is then made 6M in lithium chloride and 3Min hydrochloric acid and the induced radionuclides are subsequently fractionated as described hefore.lv* slCr which is obtained in the final aqueous phase to ther with the isotopes induced from alkali metals, alkaline earths and rare earths can be separa $ by extraction with tribenxylamlne.l~ Results obtained on arti6cially contaminated iron samples show that %z, ‘OCo, *=Pa, IlOAg, ‘5Zn and ‘“Hg are separated in a pure form, so that analysis can also be performed using simple counters without appreciable increase in the error. For quantitative analysis samples of ferrous materials are placed together with standards in an ahnninium can for pile irradiation.1 The results of quantitative analysis carried out as usual,1*16on art&ally contaminated iron samples, are shown in Table IV. Satisfactory agreement is obtained between the amount of element added and the amount found.
A. ALUN R. %lABANA
Nuclear Chemistry Department Analytical Division Atomic Energy Establishment Cairo, U.A.R.
Summary-The neutron activation analysis of trace impurities in thorium nitrate and in iron is facilitated by solvent extraction procedures prior to counting. Zusammenfassrmg-Die Neutronenaktivierungsanalyse von Spurenverunreinigungen in Thoriumnitrat und in Eisen wird durch Solventextraktionsschritte vor dem Z%hlen erleichtert. R&sum&-L’analyse par activation de neutrons de traces d’impuretes dam le nitrate de thorium et dam le fer est facilitee par des techniques #extraction par solvant avant comptage. REFERENCES A. Alian and A. Haggag, Taianta, 1967,14,1109. :: A. Alian and W. Sanad, AnaL Chim. Acta 1967, 38, 327. 3. C. V. Banks, Proceedbtgs of the Second International Conference on Peaceful Uses of Atomic Energy, Geneva (1958) vol. 28, P/918, 517. 4. V. A. Fassel and E. Dekalb, The Metal Thorium, American Society for Metals, Cleveland, Ohio (1958). 5. J. P. Burelbach and R. J. March, U.S. Atomic Energy Commission, ANL-5240 (1953). 6. F. L. Moore., Anal. Chem., 1956,28,997. 7. A. R. Eberle and M. W. Lermer, ibid., 1955, 27, 155. 8. J. H. Patterson and C. V. Banks, ibid., 1948, 20, 897. 9. L. Silverman and K. Trego, U.S. Atomic Energy Commission. NAA-SR-224 (1953). 10. R. P. Ericson and E. J. Fomefeld, U.S. Atomic Energy Commission, CC-2933 (1945). II. K. Hyde, Proc. First International Conference on Peaceful Uses of Atomic Energy, Geneva 1955, P/728. 12. C. J. Hardy, D. Seargill and J. M. Fletcher, J. Znorg. Nucl. Chem. 1958,7,257. 13. G. H. Morrison and H. Freiser, Solvent Extraction in Analytical Chemistry, Wiley, London, 1957. 14. T. Ishimori, E. Akatsu, K. Tsukuechi, T. Kobune, Y. Usuba, K. Kimura, G. Onawa and H. Uchyama, JAERZ-1106, 1966. 15. A. Alian and R. Parthasarathy, Anal. Chim. Acta, 1966,35, 69. 16. R. Malvano and P. Grosso, ibid., 1966, 34,253.
SHORT COMMUNICATIONS
Neutron A~~v~~~ Analysis by Standard Addition md Solvent Extr8etion. Determination of Impurities in Thorium and Iron (Received 12 April 1967. Accepted 20 Juty 1967) IN a previous paper’ a separation scheme was described for the simultaneous determiilatiOn of scamlmm, cobalt, iron, zinc, silver, mercury, chromium and rubidium in ahuninium by neutron and “O*Hgare fractionated by ~d~~~ne activation analysis. The induced Wo, 6sFe, %n, X1oAg (EDA) extraction. The induced %Sc is extracted with t~butylphosphate @‘BP), while Wr and -Rb are determined in the aqueous solution by gamma-ray spectrometry. rrsPa which is obtained in one of the fractions was shown in another paper* to be separated from Vo by extraction with thenoyhrifluoroacetone (PTA), thus allowing the determination of thorium in aluminhun. In the present communication studies have been performed in order to improve the separation procedure and to make it suitable for the determination of trace elements in thorium and iron.
Studies on the extractability of I1*Ag, GZn and *OrHgwith 0+3MTDA have shown that the degrees of extraction of the three radionuclides from 12&f hydrochloric acid are 1, 97 and 99% respectively. Accordingly llOAg can be stripped with 12.&fhydrochloric acid from the TDA extract before the elution of %n with 1M nitric acid; this makes possible the determination of silver and mercury in separate fractions. ~eterm~tion of ~~~~ in tiwium nitrate Elements present in trace amounts in thorium affect its physical metallurgy and the neutron economy in the “breeding” reaction: *mPa8-_ 27d
sYJ
(1)
Methods for the determination of trace elements in thorium have been developed.8 Emission spectroscopic methods have been widely used for the determination of many impurities in thoriumf while chemical methods, because of their greater accuracy, are sometimes of major importar~ce.~-~* The application of neutron-activation methods to the determination of impurities in thorium and its concentrates is dXicuIt, owing to the very high activity induced from thorium as a result of neutron irradiation. Thus, as can be seen from reaction (1) di&ulties will be met with in the determination of impurities giving rise to both short and long-lived radioisotopes. Methods of separation which would tzrvehigh decontamination factors from activated matrix comuonents should therefore 1) be applied, s&e no?ooling can be allowed. Samples of thorium nitrate (about 250 mg) are wrapped in thin ~~~ foils. For quantitative analvsis. the stim~Ies and standards are X &aced touether in an alumimum can and irradiated as de&bed previou&y.’ Each thorium sample is carefully removed from the ahrminium foil, transferred to a 1004 beaker and sub uently dissolved in 1.3M hydrochloric acid. The foil is washed with the minimium quantity 1o 1M nitric acid. The solution is then transferred to a 2%ml graduated flask, the inside walls of the beaker being washed with 1.3M hydrochloric acid, and then made up to the mark with 1*3Mhydrochloric acid. The extraction of rraPa with TTA*J’ is applied for its separation from other nuclides. By two successive extractions with O*%f TTA in xylene, Wpa (together with 5%) is ahnost completely removed from the irradiated thorium solution. The volm of organic and aqueous phase used are in 2:1 ratio. About 60% of DgFetogether with major proportions of the other radionuclides remain in the aqueous phase. Owing to the very high activity of the induced %, shaking should not be done by hand but on a suitably shielded mechanical shaker. The time required for reaching extraction equilibrium with TTA on the shaker is about 15 min. 257
258
Short communications
The thorium solution is then made 6M in lithium chloride and 3M in hydrochloric acid; the extractability of isotopes from this medium with 0*3M TDA is similar to their extractability from 25M aluminium chloride-15M hydrochloric acid. In other words cobalt, niobium, iron, silver, zinc and mercury can be extracted with @3M TDA from 6M lithium chloride3M hydrochloric acid, while scandium, chromium, rare earths and rubidium remain in the aqueous phase.. Traces of protactinium (which may be left after extraction with ‘ITA) will also be extracted from this medium. Fractions containing cobalt, iron, silver and zinc are therefore contaminated with traces of =Pa. The possibility of eliminating rrsPa by another extraction with TTA has been considered. The extractability of rsrPa and the other isotopes with TTA from various media is shown in Table I. TAIU I.-EYJRAC~ION OF nssPa ANDormm ISOTOPESWITH 05M TTA Medium
Isotope
Extraction, %
1.7M HCI
99 0.1 0.1 79
3M HF-0.SM HCl
12M HCl lMHNOa
9? 0.1
It can be seen that the 1.7M hydrochloric acid, 12M hydrochloric acid and 1M nitric acid fractions can be partly freed from rssPa by one or two extractions with ‘ITA. Recovery values greater than 50 % for iron and 80 % for the other isotopes are obtainable, while satisfactory reproducibility of separation is achieved. When the modified separation scheme was applied to an irradiated sample solution of analytical reagent grade thorium nitrate none of the impurities listed above were detected, and only zirconium was identified (uiu 05Nb) in an “Indian Nuclear Pure” sample (Fig. lb). For testing the scheme, irradiated thorium nitrate was mixed with varying amounts of irradiated standard solutions. Typical TABLEII.-ANALYSIS OFIMPURITIES IN THORIUM NURA~E(50 mg)
Element
Nuclide identified”
Half-life
4”Sc(l.12)
85d
Amount added (as metal), PPm
Photopeak activity, CPm
At
Ant
2104 4217
1934 4008 5929
b.d$ 1.1 2.48
975
b.d.
2571 3353
2y.z
77 124 200
b.d. 124 220
90 183
92 208 277
b.d. 23.0 58.0
502 1026
426 923 1391
b.d. 2.38 5.80
Scandium
: -
Cobalt
*oco(l*33)
53y
Iron
LgFe(l.lO)
45d
Zinc
e5Zn(l.11)
245d
10 20
-
-
-
69 138
Mercury
‘O*Hg(O*28)
458d
1199 2286
;:
30 60 2 4
Amount found, PPm
* In brackets are given the energies of the photopeaks in (MeV) used for quantitative analysis. t See reference 1. $ b.d. = beyond detection.
Short communications 31MeV
(0
(b)
lO.OO(
100~
IO
.c
c*
I
I
Energy,
MeV
FIG. L-Gamma-ray spectra. a-Irradiated thorium solution. b-TBP extract. c-1.7M HCl strip solution. d-12M HCl strip solution. e-3M HF45M HCl strip solution. f-l M HNOa strip solution. g-Final TDA extract. h-1.7M HCl strip solution from Indian thorium.
259
260
Short communications TABLEIII.-EXTRACTION OFRADIOISOTOPES WITHISOPROPYL ETHER FROM9M HCI Extraction, %
Isotope &OFe rasPa 6”Co
99.9 (99.9)+
*O*H g
‘Yk Wr 1WS =Rb 141Ce(III)
+ These values in brackets have been reported in a previous paper.16 gamma-spectraof the artticially contaminated thorium solutionandof the isolated fractions are shown in Fig. 1. It is clear that rs*Pa contaminates %c, ‘Wo, 6eFe, “OAg and ssZn, while *O*Hgis very pure. The incomplete decontamination from *=Pa can be explained by the presence of a small amount of inextractable material .l* ‘Wo is also contaminated with B6Nb. Fortunately rsrPa and @jNb are less active, and their presence does not represent any diiJiculty in the analysis of these nuclides. 06Nb may be separated from cobalt by extraction with tribenzylamine from 11M hydrochloric acid’” or with a secondary amine, l4 thus allowing the determination of zirconium in thorium. In this case analysis should be carried out at least a month after irradiation, to allow for the growth of s8Nb. The results of quantitative analysis carried out as described1J6 on artificially contaminated thorium samples are presented in Table II. There was satisfactory agreement between the amount added and the amount found for all the elements. TABLEIV.-ANALYSIS OFIMPURITIES IN IRONOXIDE(50 mp)
Element *
Amount added (as metal), unm
Scandium
1 2 -
Amount found, $ uum b.d 1.06 2.12
5 10
b.d. 4.31 953
Thorium?
-2 4
1-74 3.85
Silver
-2
b.d. 2.6
Zinc
%l 120
Cobalt
Mercury
4
b.d. 71.0 105.0 3.69
* For the induced isotopes and energies of photopeaks used for quantitative analysis see Table II. t Determined by counting the 0.31 MeV peak activity of OsrPa. $ Average of two determinations, b.d. = beyond detection.
261
Short communications Determination of impurities in iron
The determination of impurities in iron by neutron activation analysis has been reported in a recent paper. l’ Nondestrucuve methods have been applied for some elements, while radiochemical separatron procedures using ion-exchange chromatography and solvent extraction techniques have been used for others. A preliminary removal of the mduced seFe has been performed by extraction with isopropyl ether. In this study the improved separation scheme has been applied for the determination of impurities in iron, after a preliminary separation of seFe with isopropyl ether.“ In Table III are presented our data on the extraction of iron and the other induced radioisotopes, from 9M hydrochloric acid; it is clear that only iron is quantitatively extracted, while the other isotopes remain in the aqueous layer. The aqueous solution is then made 6M in lithium chloride and 3Min hydrochloric acid and the induced radionuclides are subsequently fractionated as described hefore.lv* slCr which is obtained in the final aqueous phase to ther with the isotopes induced from alkali metals, alkaline earths and rare earths can be separa $ by extraction with tribenxylamlne.l~ Results obtained on arti6cially contaminated iron samples show that %z, ‘OCo, *=Pa, IlOAg, ‘5Zn and ‘“Hg are separated in a pure form, so that analysis can also be performed using simple counters without appreciable increase in the error. For quantitative analysis samples of ferrous materials are placed together with standards in an ahnninium can for pile irradiation.1 The results of quantitative analysis carried out as usual,1*16on art&ally contaminated iron samples, are shown in Table IV. Satisfactory agreement is obtained between the amount of element added and the amount found.
A. ALUN R. %lABANA
Nuclear Chemistry Department Analytical Division Atomic Energy Establishment Cairo, U.A.R.
Summary-The neutron activation analysis of trace impurities in thorium nitrate and in iron is facilitated by solvent extraction procedures prior to counting. Zusammenfassrmg-Die Neutronenaktivierungsanalyse von Spurenverunreinigungen in Thoriumnitrat und in Eisen wird durch Solventextraktionsschritte vor dem Z%hlen erleichtert. R&sum&-L’analyse par activation de neutrons de traces d’impuretes dam le nitrate de thorium et dam le fer est facilitee par des techniques #extraction par solvant avant comptage. REFERENCES A. Alian and A. Haggag, Taianta, 1967,14,1109. :: A. Alian and W. Sanad, AnaL Chim. Acta 1967, 38, 327. 3. C. V. Banks, Proceedbtgs of the Second International Conference on Peaceful Uses of Atomic Energy, Geneva (1958) vol. 28, P/918, 517. 4. V. A. Fassel and E. Dekalb, The Metal Thorium, American Society for Metals, Cleveland, Ohio (1958). 5. J. P. Burelbach and R. J. March, U.S. Atomic Energy Commission, ANL-5240 (1953). 6. F. L. Moore., Anal. Chem., 1956,28,997. 7. A. R. Eberle and M. W. Lermer, ibid., 1955, 27, 155. 8. J. H. Patterson and C. V. Banks, ibid., 1948, 20, 897. 9. L. Silverman and K. Trego, U.S. Atomic Energy Commission. NAA-SR-224 (1953). 10. R. P. Ericson and E. J. Fomefeld, U.S. Atomic Energy Commission, CC-2933 (1945). II. K. Hyde, Proc. First International Conference on Peaceful Uses of Atomic Energy, Geneva 1955, P/728. 12. C. J. Hardy, D. Seargill and J. M. Fletcher, J. Znorg. Nucl. Chem. 1958,7,257. 13. G. H. Morrison and H. Freiser, Solvent Extraction in Analytical Chemistry, Wiley, London, 1957. 14. T. Ishimori, E. Akatsu, K. Tsukuechi, T. Kobune, Y. Usuba, K. Kimura, G. Onawa and H. Uchyama, JAERZ-1106, 1966. 15. A. Alian and R. Parthasarathy, Anal. Chim. Acta, 1966,35, 69. 16. R. Malvano and P. Grosso, ibid., 1966, 34,253.