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Extraction and separation of thorium(IV) and protactinium(V) by 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone
J. inorg,nucLChem., 1972,Vol.34, pp. 2627-2632. PergamonPress. Printedin Great Britain
EXTRACTION AND SEPARATION OF THORIUM(IV) AND PROTACTINIUM(V) BY 2-CARBETHOXY-5HYDROXY- 1-(4-TOLYL)-4-PYRIDONE M. J. H E R A K and M. J A N K O Laboratory of Analytical Chemistry, Faculty of Science, and Institute of Inorganic and Analytical Chemistry, University of Zagreb, Zagreb, Croatia, Yugoslavia (Received 19 October 1971)
Abstract--Extraction of thorium(IV) and protactinium(V) from hydrochloric acid solutions by 2-Carbethoxy-5-hydroxy-l-(4-tolyl)-4-pyridone (HA) has been investigated. The separation of protactinium from thorium is described. The mechanism of thorium extraction has been studied. Regardless of the initial thorium concentration in the aqueous phase thorium passes into the organic phase only as ThCIAz. HA. The composition of the extractable thorium complex was determined graphically from the dependence of the distribution ratios on the concentration of HA in the organic phase and on the hydrogen ion concentration in the aqueous phase, and was further confirmed by elemental analysis and by the i.r. spectra.
INTRODUCTION
THE EXTRACTIOr~ of thorium(IV) and protactinium(V) from hydrochloric acid solution by various extracting reagents, has been studied extensively. Day and Stoughton[1] have described the extraction of thorium(IV) by thenoyltrifluoroacetone (HTTA), and found that thorium forms two complexes, Th(TTA)4 and Th(TTA) ÷:t. With di-esters of orthophosphoric acid thorium forms ThR4(HR)2 and ThXR3(HR)~ complexes [2, 3], where X is chloride, nitrate or perchlorate ion and HR is the extractant. The extraction of thorium(IV) from hydrochloric acid solutions by dibutyl phosphate has been studied with chloroform and hexane as diluents [4], and the respective complexes were identified as ThR4(HR)2 and ThXR3(HR)2, where X is chloride ion. Several authors have reported the extraction of thorium(IV) by tri-n-butyl phosphate[5, 6] and tri-n-octyl phosphine oxide [7]. It has been found that protactinium (V) is readily extracted by various extrac1. 2. 3. 4. 5. 6. 7.
R.A. Day, Sr. and R. W. Stoughton, J. Am. chem. Soc. 72, 5662 (1950). D. F. Peppard andJ. R. Ferraro, J. inorg, nucl. Chem. 10, 275 (1959). D . F . Peppard, G. W. Mason and S. MeCarity, J. inorg, nucl. Chem. 13, 138 (1960). D. Dyrssen and D. H. Liem, Acta chem. scand. 18, 224 (1964). T. Sato, J. appL Chem. 16, 53 (1966). A. Alian and K. B. Zaborenko, Z. analyt. Chem. 238, 267 (1968). T. Sato and M. Iamatake, J. inorg, nucl. Chem. 31, 3633 (1969). 2627
2628
M . J . H E R A K and M. J A N K O
tants from hydrochloric acid solutions[8-12], but the separation of thorium and protactinium has been studied less extensively [ 14-17]. The extracting properties of 2-carbethoxy-5-hydroxy-l-(4-tolyl)-4-pyridone (HA), have been described previously[18], and in this paper the extraction of thorium(IV) and protactinium(V) from hydrochloric acid is described. An extraction mechanism for thorium is proposed and a procedure for the separation of protactinium from thorium is described. EXPERIMENTAL Chemicals 2-Carbethoxy-5-hydroxy-l-(4-tolyl)-4-pyridone (HA) was recrystallized twice from ethanol[18]. Thorium chloride solutions were prepared from the nitrate solution by precipitation with aqueous ammonia, the thorium hydroxide being washed thoroughly by decantation with ammonium nitrate solution and distilled water and then dissolved in hydrochloric acid of the required concentration. Thorium stock solutions were standardized gravimetrically. ~3aPa was obtained from the Institute "Boris Kidri~", Vin~a, Yugoslavia. Determination o f distribution ratios The extractions were carried out as described previously[18]. Thorium 1 was determined spectrophotometrically by thorin[19], using a Beckman spectrophotometer, Model DU-2. Thorium concentrations were measured in the aqueous phase and those in the organic phase were calculated by difference. The distribution of protactinium was followed by measuring the gamma-activity of the organic and aqueous phases using a scintillation counter (NaI/T1). Equilibrium between the two phases for both metals is achieved within 30 rain. Isolation o f thorium HA complex The extracted thorium species were obtained by shaking a 0.005 M chloroform solution of HA with an equal volume of 0.01 M thorium chloride in 0.01 M hydrochloric acid. The organic phase was separated and chloroform was evaporated under reduced pressure. The yellow residue was recrystallized three times from a chloroform-ligroin (1 : 2) mixture. Anal. Caled. for CooHsrN40~eCITh: C62"88; H 5"01; N 4"89. Found: C 62.49; H 5.82; N 4.23.
RESULTS AND DISCUSSION
Dependence of thorium extraction on hydrochloric acid concentration The variation of the thorium distribution ratio, Da-h, with the hydrogen ion concentration is shown in Fig. 1. The ionic strength in the aqueous phase was 8. 9. 10. 1 I. 12. 13. 14. 15. 16. 17. 18. 19.
J. Golden and A. G. Maddock, J. inorg, nucl. Chem. 2, 46 (1956). V.A. Mikhailov, V. B. Schevchenko and V. A. Kolganov, Zh. neorg. Khim. 3, 1959 (1958). J. Shankar, K. S. Venkateswarhi and G. Gopinathan, J. inorg, nucl. Chem. 25, 57 (1963). A . T . Casey and A. G. Maddock, J. inorg, nucl. Chem, 10, 298 (1959). G. Bouissirres andJ. Vernois, Compt. rend. 244, 2508 (1957). R. Guillaumont, Bull. soc. chim. Fr. 132 (1965). F. L. Moore, Analyt. Chem. 29, 1660 (1957). A. Gable, J. Golden and A. C. Maddock, Can. J. Chem. 34, 284 (1956). D. F. Peppard, G. W. Masson and M. V. Gergel, J. inorg, nucl. Chem. 3, 370 (1957). N, P. Rudenko, A. G. Seed and A. V. Lapitskii, Radiokhim. 7, 32 (1965). M.J. Herak, M. Janko and K. Bla~evi~, Croat. chem. A cta 41, 85 (I 969). G. Chariot, Les Methodes de la ChimieAnalitique. Masson et Cie, Paris (1961).
Extraction and separation of thorium(IV)
2629
:Slope 3
I -2
tog concn.
I -I
i o
HCI [M]
Fig. 1. Dependence of DTh on hydrogen ion concentration from (l::]) 0.2; (©) 0.3; (A) 0"5 M (NaC1 + HC1). HA concentration in CHCIs: ([:]) 0.005; (©) 0.007 and (A) 0-01 M. Initial ThC4 concentration 3 × 10-4 M.
constant at 0.2, 0.3 or 0.5 M (HCI+NaC1), and the concentration of H A in chloroform was 0-005, 0.007 or 0.01 M. In all cases straight lines with slope - 3 were obtained, indicating that only 3 hydrogen ions are released per atom of thorium during the extraction. Dependence o f thorium extraction on H A concentration Figure 2 shows the variation of Drh with HA concentration at constant HCI concentrations of 0.01, 0-05 and 0.3 M. Straight lines with slope 4 were obtained. Taking into account the results obtained and the fact that H A is a monomer in chloroform solution [21 ], we propose the following extraction mechanism:
Th4+q+ Cl~q+ 4HAo ~ ThCIA3.HA0 + 3H*. Since Peppard et al. [3], and Dyrssen et ai. [4] have reported that at high thorium concentrations the extraction mechanism differs from that at low thorium concentrations, we have determined the thorium: H A ratio at thorium concentrations from 1 × 10-5 to 1.2 × 10-1 M (Fig. 3). The concentration of hydrochloric acid was 0.1 M and that of H A 5 × 10-a M. By plotting the molar ratio of H A and 20. E. L. Zebroski, H. W. Alter and F. K. Heumann, J . A m . chem. Soc. 73, 5646 (1951). 21. M. Janko and M. J. Herak, Croat. chem. Acta 3, 179 (1971).
2630
M . J . H E R A K and M. J A N K O
/
Q
~ ! /
Slope 4
-21 logconcn,reagent[M] Fig. 2. Dependence of D,rh on the H A concentration in the presence of (O) 0.01; (A) 0.05 and t~) 0-3 M hydrochloric acid in the aqueous phase. Initial ThCts concentration 3 x 10 -4 M.
T0
~000
(~01
0
0
0
i 005
Q
u
I 0.1
l'Th4+~q Fig. 3. Determination of Th: H A ratio as a function of the initial thorium concentration in the aqueous phase.
Extractionand separationof thorium(IV)
263 t
thorium in the organic phase against the initial thorium concentration in the aqueous phase, it was found that 4 molecules of ligand are bound to one thorium atom. This result confirms that the extraction mechanism is the same at all thorium concentrations studied. Since the composition of the extractable thorium complex does not depend on the initial thorium concentration, it was possible to saturate the organic phase with thorium as described in the experimental section. The analytical data for the complex isolated are consistent with the equation given above. The presence of chloride in the extracted species was confirmed qualitatively, and in the absence of thorium no chloride was extracted into the organic phase. The complex was back-extracted from the organic phase with 5 M nitric acid and the chloride was precipitated with AgNO3.
Extraction of protactinium as a function of hydrochloric acid concentration The extraction of protactinium(V) at tracer levels by H A from hydrochloric acid solution is shown in Table 1. It was found that protactinium is extracted completely from 0.1 to 9 M HCI solutions. Table 1. Dependence ofprotactinium extractionon hydrochloric acid concentration HCl Pa extracted (M) (%) 0'1 0.5 1'0 2"0 3.0 5-0 7'0 9-0
97.5 99.3 97.4 99.0 99"4 97'0 96.1 95.4
T o prevent adsorption of protactinium the extractions were carded out in polyethylene bottles. Back-extraction of protactinium from the organic phase can be achieved with 0-1 M H F or 0.4 M oxalic acid solution (Table 2). The extraction of protactinium was also studied in the presence of various concentrations of thorium (Table 3). It is seen that the extraction is not affected by th e presence of thorium as low concentrations.
Separation of protactinium and thorium The difference in extraction properties of thorium and protactinium was utilized for their separation, as in the following simple experiment. A thorium nitrate sample (100 mg) was irradiated with thermal neutrons in a reactor and then dissolved in 5 ml 3 M HCI. This solution was shaken for 15 min with an equal
2632
M . J . H E R A K and M. J A N K O Table 2. Back-extraction of protactinium from the organic phase with H F and/or oxalic acid solutions
HF (M)
Dpa
0.001 0.005 0.01 0.03 0"05 0.10
595 0.29 0-20 0.02 0.002 0.001
Oxalic acid (M)
Dpa
0.01 0.04 0.10 0.20 0-30 0.40
905 68.0 4-0 1.1 0-42 0.09
Table 3. Dependence of protactinium extraction on the thorium concentration in the aqueous solution. H A conch. 0.005 M in the organic phase, and HCI 0.5M in the aqueous phase ThCh concn, (M) 5x 5x 5x 1x 5x
10-5 10-4 lO-a I0 -: 10-~
Pa extracted (%) 99.9 99.8 99.8 99.7 98.5
volume of HA dissolved in chloroform. The phases were separated and the activities of equal volumes of the organic and aqueous phases were measured. After a single extraction the distribution ratio for protactinium was 1000. Thorium was not present in the organic phase. The high purity of the separated protactinium was checked on a multichannel gamma-analyzer and by measuring its half-life, after back-extraction with either 0.1 M H F or 5% oxalic acid solution. The separation of protactinium from thorium by HA is fast and simple, and can be successfully applied for the preparative separation of these metals. By using the method described, protactinium of very high purity can be obtained.
EXTRACTION AND SEPARATION OF THORIUM(IV) AND PROTACTINIUM(V) BY 2-CARBETHOXY-5HYDROXY- 1-(4-TOLYL)-4-PYRIDONE M. J. H E R A K and M. J A N K O Laboratory of Analytical Chemistry, Faculty of Science, and Institute of Inorganic and Analytical Chemistry, University of Zagreb, Zagreb, Croatia, Yugoslavia (Received 19 October 1971)
Abstract--Extraction of thorium(IV) and protactinium(V) from hydrochloric acid solutions by 2-Carbethoxy-5-hydroxy-l-(4-tolyl)-4-pyridone (HA) has been investigated. The separation of protactinium from thorium is described. The mechanism of thorium extraction has been studied. Regardless of the initial thorium concentration in the aqueous phase thorium passes into the organic phase only as ThCIAz. HA. The composition of the extractable thorium complex was determined graphically from the dependence of the distribution ratios on the concentration of HA in the organic phase and on the hydrogen ion concentration in the aqueous phase, and was further confirmed by elemental analysis and by the i.r. spectra.
INTRODUCTION
THE EXTRACTIOr~ of thorium(IV) and protactinium(V) from hydrochloric acid solution by various extracting reagents, has been studied extensively. Day and Stoughton[1] have described the extraction of thorium(IV) by thenoyltrifluoroacetone (HTTA), and found that thorium forms two complexes, Th(TTA)4 and Th(TTA) ÷:t. With di-esters of orthophosphoric acid thorium forms ThR4(HR)2 and ThXR3(HR)~ complexes [2, 3], where X is chloride, nitrate or perchlorate ion and HR is the extractant. The extraction of thorium(IV) from hydrochloric acid solutions by dibutyl phosphate has been studied with chloroform and hexane as diluents [4], and the respective complexes were identified as ThR4(HR)2 and ThXR3(HR)2, where X is chloride ion. Several authors have reported the extraction of thorium(IV) by tri-n-butyl phosphate[5, 6] and tri-n-octyl phosphine oxide [7]. It has been found that protactinium (V) is readily extracted by various extrac1. 2. 3. 4. 5. 6. 7.
R.A. Day, Sr. and R. W. Stoughton, J. Am. chem. Soc. 72, 5662 (1950). D. F. Peppard andJ. R. Ferraro, J. inorg, nucl. Chem. 10, 275 (1959). D . F . Peppard, G. W. Mason and S. MeCarity, J. inorg, nucl. Chem. 13, 138 (1960). D. Dyrssen and D. H. Liem, Acta chem. scand. 18, 224 (1964). T. Sato, J. appL Chem. 16, 53 (1966). A. Alian and K. B. Zaborenko, Z. analyt. Chem. 238, 267 (1968). T. Sato and M. Iamatake, J. inorg, nucl. Chem. 31, 3633 (1969). 2627
2628
M . J . H E R A K and M. J A N K O
tants from hydrochloric acid solutions[8-12], but the separation of thorium and protactinium has been studied less extensively [ 14-17]. The extracting properties of 2-carbethoxy-5-hydroxy-l-(4-tolyl)-4-pyridone (HA), have been described previously[18], and in this paper the extraction of thorium(IV) and protactinium(V) from hydrochloric acid is described. An extraction mechanism for thorium is proposed and a procedure for the separation of protactinium from thorium is described. EXPERIMENTAL Chemicals 2-Carbethoxy-5-hydroxy-l-(4-tolyl)-4-pyridone (HA) was recrystallized twice from ethanol[18]. Thorium chloride solutions were prepared from the nitrate solution by precipitation with aqueous ammonia, the thorium hydroxide being washed thoroughly by decantation with ammonium nitrate solution and distilled water and then dissolved in hydrochloric acid of the required concentration. Thorium stock solutions were standardized gravimetrically. ~3aPa was obtained from the Institute "Boris Kidri~", Vin~a, Yugoslavia. Determination o f distribution ratios The extractions were carried out as described previously[18]. Thorium 1 was determined spectrophotometrically by thorin[19], using a Beckman spectrophotometer, Model DU-2. Thorium concentrations were measured in the aqueous phase and those in the organic phase were calculated by difference. The distribution of protactinium was followed by measuring the gamma-activity of the organic and aqueous phases using a scintillation counter (NaI/T1). Equilibrium between the two phases for both metals is achieved within 30 rain. Isolation o f thorium HA complex The extracted thorium species were obtained by shaking a 0.005 M chloroform solution of HA with an equal volume of 0.01 M thorium chloride in 0.01 M hydrochloric acid. The organic phase was separated and chloroform was evaporated under reduced pressure. The yellow residue was recrystallized three times from a chloroform-ligroin (1 : 2) mixture. Anal. Caled. for CooHsrN40~eCITh: C62"88; H 5"01; N 4"89. Found: C 62.49; H 5.82; N 4.23.
RESULTS AND DISCUSSION
Dependence of thorium extraction on hydrochloric acid concentration The variation of the thorium distribution ratio, Da-h, with the hydrogen ion concentration is shown in Fig. 1. The ionic strength in the aqueous phase was 8. 9. 10. 1 I. 12. 13. 14. 15. 16. 17. 18. 19.
J. Golden and A. G. Maddock, J. inorg, nucl. Chem. 2, 46 (1956). V.A. Mikhailov, V. B. Schevchenko and V. A. Kolganov, Zh. neorg. Khim. 3, 1959 (1958). J. Shankar, K. S. Venkateswarhi and G. Gopinathan, J. inorg, nucl. Chem. 25, 57 (1963). A . T . Casey and A. G. Maddock, J. inorg, nucl. Chem, 10, 298 (1959). G. Bouissirres andJ. Vernois, Compt. rend. 244, 2508 (1957). R. Guillaumont, Bull. soc. chim. Fr. 132 (1965). F. L. Moore, Analyt. Chem. 29, 1660 (1957). A. Gable, J. Golden and A. C. Maddock, Can. J. Chem. 34, 284 (1956). D. F. Peppard, G. W. Masson and M. V. Gergel, J. inorg, nucl. Chem. 3, 370 (1957). N, P. Rudenko, A. G. Seed and A. V. Lapitskii, Radiokhim. 7, 32 (1965). M.J. Herak, M. Janko and K. Bla~evi~, Croat. chem. A cta 41, 85 (I 969). G. Chariot, Les Methodes de la ChimieAnalitique. Masson et Cie, Paris (1961).
Extraction and separation of thorium(IV)
2629
:Slope 3
I -2
tog concn.
I -I
i o
HCI [M]
Fig. 1. Dependence of DTh on hydrogen ion concentration from (l::]) 0.2; (©) 0.3; (A) 0"5 M (NaC1 + HC1). HA concentration in CHCIs: ([:]) 0.005; (©) 0.007 and (A) 0-01 M. Initial ThC4 concentration 3 × 10-4 M.
constant at 0.2, 0.3 or 0.5 M (HCI+NaC1), and the concentration of H A in chloroform was 0-005, 0.007 or 0.01 M. In all cases straight lines with slope - 3 were obtained, indicating that only 3 hydrogen ions are released per atom of thorium during the extraction. Dependence o f thorium extraction on H A concentration Figure 2 shows the variation of Drh with HA concentration at constant HCI concentrations of 0.01, 0-05 and 0.3 M. Straight lines with slope 4 were obtained. Taking into account the results obtained and the fact that H A is a monomer in chloroform solution [21 ], we propose the following extraction mechanism:
Th4+q+ Cl~q+ 4HAo ~ ThCIA3.HA0 + 3H*. Since Peppard et al. [3], and Dyrssen et ai. [4] have reported that at high thorium concentrations the extraction mechanism differs from that at low thorium concentrations, we have determined the thorium: H A ratio at thorium concentrations from 1 × 10-5 to 1.2 × 10-1 M (Fig. 3). The concentration of hydrochloric acid was 0.1 M and that of H A 5 × 10-a M. By plotting the molar ratio of H A and 20. E. L. Zebroski, H. W. Alter and F. K. Heumann, J . A m . chem. Soc. 73, 5646 (1951). 21. M. Janko and M. J. Herak, Croat. chem. Acta 3, 179 (1971).
2630
M . J . H E R A K and M. J A N K O
/
Q
~ ! /
Slope 4
-21 logconcn,reagent[M] Fig. 2. Dependence of D,rh on the H A concentration in the presence of (O) 0.01; (A) 0.05 and t~) 0-3 M hydrochloric acid in the aqueous phase. Initial ThCts concentration 3 x 10 -4 M.
T0
~000
(~01
0
0
0
i 005
Q
u
I 0.1
l'Th4+~q Fig. 3. Determination of Th: H A ratio as a function of the initial thorium concentration in the aqueous phase.
Extractionand separationof thorium(IV)
263 t
thorium in the organic phase against the initial thorium concentration in the aqueous phase, it was found that 4 molecules of ligand are bound to one thorium atom. This result confirms that the extraction mechanism is the same at all thorium concentrations studied. Since the composition of the extractable thorium complex does not depend on the initial thorium concentration, it was possible to saturate the organic phase with thorium as described in the experimental section. The analytical data for the complex isolated are consistent with the equation given above. The presence of chloride in the extracted species was confirmed qualitatively, and in the absence of thorium no chloride was extracted into the organic phase. The complex was back-extracted from the organic phase with 5 M nitric acid and the chloride was precipitated with AgNO3.
Extraction of protactinium as a function of hydrochloric acid concentration The extraction of protactinium(V) at tracer levels by H A from hydrochloric acid solution is shown in Table 1. It was found that protactinium is extracted completely from 0.1 to 9 M HCI solutions. Table 1. Dependence ofprotactinium extractionon hydrochloric acid concentration HCl Pa extracted (M) (%) 0'1 0.5 1'0 2"0 3.0 5-0 7'0 9-0
97.5 99.3 97.4 99.0 99"4 97'0 96.1 95.4
T o prevent adsorption of protactinium the extractions were carded out in polyethylene bottles. Back-extraction of protactinium from the organic phase can be achieved with 0-1 M H F or 0.4 M oxalic acid solution (Table 2). The extraction of protactinium was also studied in the presence of various concentrations of thorium (Table 3). It is seen that the extraction is not affected by th e presence of thorium as low concentrations.
Separation of protactinium and thorium The difference in extraction properties of thorium and protactinium was utilized for their separation, as in the following simple experiment. A thorium nitrate sample (100 mg) was irradiated with thermal neutrons in a reactor and then dissolved in 5 ml 3 M HCI. This solution was shaken for 15 min with an equal
2632
M . J . H E R A K and M. J A N K O Table 2. Back-extraction of protactinium from the organic phase with H F and/or oxalic acid solutions
HF (M)
Dpa
0.001 0.005 0.01 0.03 0"05 0.10
595 0.29 0-20 0.02 0.002 0.001
Oxalic acid (M)
Dpa
0.01 0.04 0.10 0.20 0-30 0.40
905 68.0 4-0 1.1 0-42 0.09
Table 3. Dependence of protactinium extraction on the thorium concentration in the aqueous solution. H A conch. 0.005 M in the organic phase, and HCI 0.5M in the aqueous phase ThCh concn, (M) 5x 5x 5x 1x 5x
10-5 10-4 lO-a I0 -: 10-~
Pa extracted (%) 99.9 99.8 99.8 99.7 98.5
volume of HA dissolved in chloroform. The phases were separated and the activities of equal volumes of the organic and aqueous phases were measured. After a single extraction the distribution ratio for protactinium was 1000. Thorium was not present in the organic phase. The high purity of the separated protactinium was checked on a multichannel gamma-analyzer and by measuring its half-life, after back-extraction with either 0.1 M H F or 5% oxalic acid solution. The separation of protactinium from thorium by HA is fast and simple, and can be successfully applied for the preparative separation of these metals. By using the method described, protactinium of very high purity can be obtained.