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Extraction of nitric acid by TBP solutions in organic solvents
Notes
239
complex exhibited a band at 377 cm -1 which we have assigned to the Pu-O asymmetric stretching vibration of the Pu-O-As group. A similar assignment has been made to bands at 370, 384 and 382 cm -1 for the complexes MCI2(PhaAsO)~, where M = Mn, Fe and Co, respectively[15]. Additional bands are observed at 224 and 226 cm -1, respectively, for the phosphine oxide and atsine oxide complexes. This type of absorption band has been tentatively assigned to the Pu-O stretching vibration of the Pu-O2-NO group. Ferraro and Walker[16] have attributed an absorption in the region of 250 cm -* for uranyl nitrate as the U-O stretch of the U-O2-NO group.
Acknowledgement-The author wishes to thank R. L. Deaton for his assistance in the performance of these experiments. D O N A L D L. P L Y M A L E
Monsanto Research Corporation Mound Laboratory* Miamisburg, Ohio
*Mound Laboratory is operated by Monsanto Research Corporation for the U.S. Atomic Energy Commission under Contract No. AT-33-I-GEN-53. 15. G . A . Rodley, D. M. L. Goodgame and F. A. Cotton,J. chem. Soc. 1499 (1965). 16. J. R. Ferraro and A. Walker, J. chem. Phys. 45,550 (1966).
J. inorg,nucl.Chem.,1969,Vol.31, pp. 239 to 241. PergamonPress. Printedin Great Britain
Extraction of nitric acid by TBP solutions in organic solvents* (Received lMay1968) FoR THE understanding of the behaviour of organic tributylphosphate (TBP) solutions in extractions from aqueous nitric acid, it is important to know which part of this compound is bound to nitric acid and which part is in the free state. This question has been considered for kerosene solutions by Alcock, Grimely, Healy, Kennedy and McKay[1]. In connection with studies of the extraction of plutonium and of hafnium, we have performed similar experiments with solutions of TBP in benzene, carbon tetrachloride and chloroform. It is well known that at high nitric acid activities one TBP molecule may bind more than one nitric acid molecule, and for the solvents used by us we actually found this to be the case when the aqueous phase was 7 molar HNO3. At lower acid concentrations we may, however, assume as a first approximation that all of the nitric acid in the organic phase 3' is present as TBP-HNOa. On this basis the molarity of free TBP in the organic phase is equal to the total TBP molarity minus the molarity of nitric acid in the organic phase, i.e. [TBP'HNOa]o = [HNO3]o
and
[TBP]tre~ = [TBPltot.-[HNO3]o.
1. K. Alcock, S. S. Grimely, T. V. Healy, J. Kennedy and H. A. C. McKay, Trans. Faraday Soc. 52, 39 (1956).
240
Notes
If we assume the activity coefficients of TBP and of T B P . H N O s in the organic phase to be independent of the T B P and HNO3 c o n c e n t r a t i o n s - n o t so much because this assumption is likely to be very accurate, but rather because we do not have any satisfactory information concerning these q u a n t i t i e s - w e may write the equilibrium constant for the reaction: T B P o + H+q. + NO~'aq.~ T B P ' H N O a o as
Kaso.
[HNOs]o ([TBP]tot. - [HNOa]o " a . s o . "
Here aHNOsindicates the activity of the nitric acid. Distribution coefficients of nitric acid were determined by mechanically shaking equal volumes (10 or 20 ml) of aqueous nitric acid and of organic TBP solution for 15 rain. After 20 min standing the two phases were separated by centrifuging. The nitric acid in the organic phase was back-extracted into water by shaking with three batches of the latter. The acid content of both fractions was determined by semi-microtitration with N a O H solutions. The total acid balance was accurate to within 3 per cent. Results are given in Table 1. From the KHso~ values actual acid distribution coefficients are easily calculated.
Table 1. Values of KHNO3 for different solutions of TBP, with averages for each solvent. Solvent Approx. aqueous acid molarity
CoHs 0.9
2.9
CC14 0.9
2.9
CHCia 0.9
2.9
Total TBP molarity in organic phase 0.10 0.30 0.50 0.70 1.00 Average value
0.22 0.28 0.23 0.24 0.26 0.17 0.30 0.18 0.30 0.17 0-24
0.12 0-09 0-16 0.11 0.17 0.11 0.21 0.12 0.25 0-12 0-15
0.110 0.051 0-045 0-025 0.035 0.032 0.040 0.039 0.042 0.035 0.046
Considering the assumption involved in the equation used for calculating Kaso,, the values found for this quantity are remarkably constant. In this connection it is also of interest that Fomin and Mairova[2] have reported a value KHNO,= 0"22 for the extraction of nitric acid into 1 molar TBP in benzene and that from partition measurements of Voden, Nikitina and Pushlenkov[3] for nitric acid between water and 0-18 molar TBP in carbon tetrachloride we calculate KHNO,= 0"16. In both cases the agreement is surprisingly good. Acid activities were calculated from the equation: aHNO3= [H+],q. " [NOs-],,. • c~~" T_+2 = (CHNo,~q. " C~2" T_+2. 2. V . V . Fomin and E. P. Mairova, Z h . neorg. C h e m . 3, 2113 (1958). 3. V . G . Voden, G. P. Nikitina and M. F. Pushlenkov, R u s s . J. R a d i o c h e m . 1,121 (1959).
Notes
241
Here CHNO8is the total molar acid concentration in water, a the degree of dissociation of nitric acid and y± the average activity coefficient of the H ÷ and the NOz- ions. Values were taken from the table by Davis and De Bruin[4].
Acknowledgements-The first named author is indebted to the Government of the United Arab Republic and grateful for financial support to the Ministry of Higher Education (Cairo), Department of Mission. He also wishes to thank the authorities of the Atomic Energy Establishment (Cairo) for giving him the opportunity to carry out his research. This work is part of the research program of the Institute for Nuclear Physics Research (IKO), made possible by financial support from the Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organization for Pure Scientific Research (ZWO).
lnstituut voor Kernphysisch Onderzoek Ooster Ringd(ik 18 Amsterdam-O Netherlands
M. K. K. SHEHATAT A. H. W. ATEN, Jr.
*This work has been described in greater detail in: M.K.K. Shehata, "Solvent extraction study of traces of plutonium and hafnium in the tetravalent state from nitric acid solution". Thesis, University of Amsterdam 1968. t Present address: Atomic Energy Establishment, Chemistry Department, Anshas, Egypt. 4. W. Davis Jr. and H. J. De Bruin, J. inorg, nucl. Chem. 26, 1069 (1964).
J. inorg,nucl.Chem..1969.Vol. 3I, pp. 241 to 245. PergamonPress. Printedin Great Britain
Melting point of Cm~03 (Received 10 May 1968) CURIUM-244 oxide is being considered as a fuel material for thermionic isotopic power sources operating at temperatures near 1750°C. A high-melting oxide is required to prevent melting on temperature excursions and to allow a greater margin for safety in the operation of the power source. McHenry has reported the melting point of a curium oxide, believe to be Cm~O3, as 1950°C[1]. This melting temperature appears low for several reasons. (l) Plots of log P vs. 1/ T from measurements of vaporization rates of CmzO3 show no effect of the heat of fusion up to 2335°C [2]. (2) Cm203 exhibits structures and bond energies quite similar to those of the lighter rare-earth sesquioxides[2, 3], which generally melt between 2200-24000C; the heat and entropy of fusion of CmzOz should be about the same, and would fix the melting temperature in the same range as for rareearth sesquioxides. (3) Since the molecular weight of ~Cm203 is so large (536 g/mole), aggregate light cation impurity levels of the order of 1 wt per cent would amount to 10 mole per cent, which could lower the melting temperature of the oxide by 200-300°C.
1. R. E. McHenry, Trans.Am. nucl. Soc. 8, 75 (1965). 2. P. K. Smith and D. E. Peterson, High Temperature Evaporation and Thermodynamic Properties of Cm203. Abstracts of Papers, 155th Am. Chem. Soc. Meet. San Francisco, April 1-5. No. 0-031 (1968). 3. W. C. Mosley, B-Type ~Cm203: A Candidate Isotopic Power Fuel. Abstracts of Papers, 155th Am. Chem. Soc. Meet. San Francisco, April 1-5, No. 0-173 (1968).
239
complex exhibited a band at 377 cm -1 which we have assigned to the Pu-O asymmetric stretching vibration of the Pu-O-As group. A similar assignment has been made to bands at 370, 384 and 382 cm -1 for the complexes MCI2(PhaAsO)~, where M = Mn, Fe and Co, respectively[15]. Additional bands are observed at 224 and 226 cm -1, respectively, for the phosphine oxide and atsine oxide complexes. This type of absorption band has been tentatively assigned to the Pu-O stretching vibration of the Pu-O2-NO group. Ferraro and Walker[16] have attributed an absorption in the region of 250 cm -* for uranyl nitrate as the U-O stretch of the U-O2-NO group.
Acknowledgement-The author wishes to thank R. L. Deaton for his assistance in the performance of these experiments. D O N A L D L. P L Y M A L E
Monsanto Research Corporation Mound Laboratory* Miamisburg, Ohio
*Mound Laboratory is operated by Monsanto Research Corporation for the U.S. Atomic Energy Commission under Contract No. AT-33-I-GEN-53. 15. G . A . Rodley, D. M. L. Goodgame and F. A. Cotton,J. chem. Soc. 1499 (1965). 16. J. R. Ferraro and A. Walker, J. chem. Phys. 45,550 (1966).
J. inorg,nucl.Chem.,1969,Vol.31, pp. 239 to 241. PergamonPress. Printedin Great Britain
Extraction of nitric acid by TBP solutions in organic solvents* (Received lMay1968) FoR THE understanding of the behaviour of organic tributylphosphate (TBP) solutions in extractions from aqueous nitric acid, it is important to know which part of this compound is bound to nitric acid and which part is in the free state. This question has been considered for kerosene solutions by Alcock, Grimely, Healy, Kennedy and McKay[1]. In connection with studies of the extraction of plutonium and of hafnium, we have performed similar experiments with solutions of TBP in benzene, carbon tetrachloride and chloroform. It is well known that at high nitric acid activities one TBP molecule may bind more than one nitric acid molecule, and for the solvents used by us we actually found this to be the case when the aqueous phase was 7 molar HNO3. At lower acid concentrations we may, however, assume as a first approximation that all of the nitric acid in the organic phase 3' is present as TBP-HNOa. On this basis the molarity of free TBP in the organic phase is equal to the total TBP molarity minus the molarity of nitric acid in the organic phase, i.e. [TBP'HNOa]o = [HNO3]o
and
[TBP]tre~ = [TBPltot.-[HNO3]o.
1. K. Alcock, S. S. Grimely, T. V. Healy, J. Kennedy and H. A. C. McKay, Trans. Faraday Soc. 52, 39 (1956).
240
Notes
If we assume the activity coefficients of TBP and of T B P . H N O s in the organic phase to be independent of the T B P and HNO3 c o n c e n t r a t i o n s - n o t so much because this assumption is likely to be very accurate, but rather because we do not have any satisfactory information concerning these q u a n t i t i e s - w e may write the equilibrium constant for the reaction: T B P o + H+q. + NO~'aq.~ T B P ' H N O a o as
Kaso.
[HNOs]o ([TBP]tot. - [HNOa]o " a . s o . "
Here aHNOsindicates the activity of the nitric acid. Distribution coefficients of nitric acid were determined by mechanically shaking equal volumes (10 or 20 ml) of aqueous nitric acid and of organic TBP solution for 15 rain. After 20 min standing the two phases were separated by centrifuging. The nitric acid in the organic phase was back-extracted into water by shaking with three batches of the latter. The acid content of both fractions was determined by semi-microtitration with N a O H solutions. The total acid balance was accurate to within 3 per cent. Results are given in Table 1. From the KHso~ values actual acid distribution coefficients are easily calculated.
Table 1. Values of KHNO3 for different solutions of TBP, with averages for each solvent. Solvent Approx. aqueous acid molarity
CoHs 0.9
2.9
CC14 0.9
2.9
CHCia 0.9
2.9
Total TBP molarity in organic phase 0.10 0.30 0.50 0.70 1.00 Average value
0.22 0.28 0.23 0.24 0.26 0.17 0.30 0.18 0.30 0.17 0-24
0.12 0-09 0-16 0.11 0.17 0.11 0.21 0.12 0.25 0-12 0-15
0.110 0.051 0-045 0-025 0.035 0.032 0.040 0.039 0.042 0.035 0.046
Considering the assumption involved in the equation used for calculating Kaso,, the values found for this quantity are remarkably constant. In this connection it is also of interest that Fomin and Mairova[2] have reported a value KHNO,= 0"22 for the extraction of nitric acid into 1 molar TBP in benzene and that from partition measurements of Voden, Nikitina and Pushlenkov[3] for nitric acid between water and 0-18 molar TBP in carbon tetrachloride we calculate KHNO,= 0"16. In both cases the agreement is surprisingly good. Acid activities were calculated from the equation: aHNO3= [H+],q. " [NOs-],,. • c~~" T_+2 = (CHNo,~q. " C~2" T_+2. 2. V . V . Fomin and E. P. Mairova, Z h . neorg. C h e m . 3, 2113 (1958). 3. V . G . Voden, G. P. Nikitina and M. F. Pushlenkov, R u s s . J. R a d i o c h e m . 1,121 (1959).
Notes
241
Here CHNO8is the total molar acid concentration in water, a the degree of dissociation of nitric acid and y± the average activity coefficient of the H ÷ and the NOz- ions. Values were taken from the table by Davis and De Bruin[4].
Acknowledgements-The first named author is indebted to the Government of the United Arab Republic and grateful for financial support to the Ministry of Higher Education (Cairo), Department of Mission. He also wishes to thank the authorities of the Atomic Energy Establishment (Cairo) for giving him the opportunity to carry out his research. This work is part of the research program of the Institute for Nuclear Physics Research (IKO), made possible by financial support from the Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organization for Pure Scientific Research (ZWO).
lnstituut voor Kernphysisch Onderzoek Ooster Ringd(ik 18 Amsterdam-O Netherlands
M. K. K. SHEHATAT A. H. W. ATEN, Jr.
*This work has been described in greater detail in: M.K.K. Shehata, "Solvent extraction study of traces of plutonium and hafnium in the tetravalent state from nitric acid solution". Thesis, University of Amsterdam 1968. t Present address: Atomic Energy Establishment, Chemistry Department, Anshas, Egypt. 4. W. Davis Jr. and H. J. De Bruin, J. inorg, nucl. Chem. 26, 1069 (1964).
J. inorg,nucl.Chem..1969.Vol. 3I, pp. 241 to 245. PergamonPress. Printedin Great Britain
Melting point of Cm~03 (Received 10 May 1968) CURIUM-244 oxide is being considered as a fuel material for thermionic isotopic power sources operating at temperatures near 1750°C. A high-melting oxide is required to prevent melting on temperature excursions and to allow a greater margin for safety in the operation of the power source. McHenry has reported the melting point of a curium oxide, believe to be Cm~O3, as 1950°C[1]. This melting temperature appears low for several reasons. (l) Plots of log P vs. 1/ T from measurements of vaporization rates of CmzO3 show no effect of the heat of fusion up to 2335°C [2]. (2) Cm203 exhibits structures and bond energies quite similar to those of the lighter rare-earth sesquioxides[2, 3], which generally melt between 2200-24000C; the heat and entropy of fusion of CmzOz should be about the same, and would fix the melting temperature in the same range as for rareearth sesquioxides. (3) Since the molecular weight of ~Cm203 is so large (536 g/mole), aggregate light cation impurity levels of the order of 1 wt per cent would amount to 10 mole per cent, which could lower the melting temperature of the oxide by 200-300°C.
1. R. E. McHenry, Trans.Am. nucl. Soc. 8, 75 (1965). 2. P. K. Smith and D. E. Peterson, High Temperature Evaporation and Thermodynamic Properties of Cm203. Abstracts of Papers, 155th Am. Chem. Soc. Meet. San Francisco, April 1-5. No. 0-031 (1968). 3. W. C. Mosley, B-Type ~Cm203: A Candidate Isotopic Power Fuel. Abstracts of Papers, 155th Am. Chem. Soc. Meet. San Francisco, April 1-5, No. 0-173 (1968).