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Solvent extraction of Fe(III) by di-(2-ethylhexyl)phosphoric acid from phosphoric acid solutions
Polyhedron
Vol. 3, No.
5, pp. 615617,
027FS387/84 $3.00 + .OO 0 1984 Pergamon Press Ltd.
1984
Printed in Great Britain.
NOTE SOLVENT EXTRACTION OF Fe@) BY DI-(2-ETHYLHEXYL)PHOSPHORIC ACID FROM PHOSPHORIC ACID SOLUTIONS S. MELES and M. V. PROSTENIK’ INA, Research and Development Division, 41000 Zagreb, Yugoslavia (Received 23 August 1983; accepted 10 October 1983) Abstract-The extraction of iron(II1) from aqueous phosphoric acid was studied using di-(2-ethylhexyl)phosphoric acid and trioctylphosphine oxide in nonaromatic hydrocarbon diluent. Distribution ratios have been investigated as a function of concentration of iron(III), phosphoric acid concentration, extractant concentration and extraction temperature. The apparent enthalpy change for the extraction reaction has been calculated from the temperature dependence data. It was found that the extractant dependency for iron(II1) is first power indicating hydrolysis of iron(II1) in the aqueous phase. Di(2-ethylhexyl)phosphoric acid (abbreviated as HDEHP or simply HA) is widely used in hydrometallurgical processes for the separation and purification of a number of metals such as uranium, rare earth, copper, cobalt and nickel.‘” Iron is a very common impurity in raw industrial acid metal solutions in either the divalent or trivalent states and, therefore, it is of importance to know its properties in a given extraction system. The extraction of Fe(II1) with HDEHP from sulphuric, hydrochloric, perchloric and nitric acid solutions has been studied in detai1.7-‘3 On the contrary, the extraction of Fe(II1) from phosphoric acid solutions has received little attention, although iron is associated with uranium in the wet process phosphoric acid and is coextracted during the uranium recovery by HDEHP-TOP0’4*‘5 (TOP0 = trioctylphosphine oxide). Kletenik16 has reported extraction of iron(II1) from phosphoric acid with a crude reaction with P205 2-ethyl- 1-hexanol mixture of (comprising the undetermined ratio of mono- and di-(2-ethylhexyl)phosphoric acid and di-(2ethylhexyl)pyrophosphoric acid). The extraction is characterised by unusually high distribution coefficients. Bunus et aLL7studied the influence of iron, particularly Fe(I1) in uranium(IV) extraction from phosphoric acid and with HDEHP and HDEHP-TOP0 mixtures but no details on Fe(II1) extraction were given. Therefore, the purpose of the present investigation was to define in some detail the Fe(II1)
*Author to whom correspondence should he addressed.
extraction by HDEHP and HDEHP-TOP0 phosphoric acid solutions.
from
EXPERIMENTAL Reagents. Analytical grade phosphoric acid and FeC13.6H20 (“Kemika”-Zagreb) were used. HDEHP and TOP0 were used as purchased from Mobil Co. Procedure. Aqueous solutions were prepared by dissolving Fe(II1) chloride in phosphoric acid of selected concentrations. Organic solutions were prepared from HDEHP and TOP0 and nonaromatic hydrocarbon diluent Mobil 190/210. Distribution ratio measurements were performed at 20°C in the thermostated bath with the exception of temperature studies. Equal ,volumes of aqueous and organic solutions were mixed mechanically for 20 min to ensure thermal and’ chemical equilibrium. Preliminary experiments had shown that the equilibrium is reached after 10 min. Phases were disengaged by centrifugation and the aqueous phase was analysed for iron content by atomicabsorption spectrophotometry or spectrophotometrically with 2,2’-bipyridine. RESULTS AND DISCUSSION Typical isotherms for the extraction of Fe(II1) by 0.3 M and 0.5 M HDEHP in kerosene from 1.5 M and 5.1 M H3P04 as well as with the mixture of 0.3 M HDEHP 0.075 M TOP0 are presented in Fig. 1. The values of distribution coefficient obtained for Fe(II1) as a function of H,PO, concentration are presented in Fig. 2. The distribution coefficient decreases rapidly with increasing concentration of phosphoric acid.
615
Notes
1
0
5
0
-1
-2 -1
Fig. 1. Equilibrium loading isotherms for Fe(II1) extraction at 20°C; 0 0.3 M HDEHP, 5.1 M H3P04; 0 0.3 M HDEHP+ 0.075 M TOPO, 5.1 M H,PO,; 0 0.5 M HDEHP, 5.1 M H,PO.,; x 0.5 M HDEHP, 1.5 M H,PO,.
-0.5
0 Log IHOEHPI
Fig. 3. Dependence of the extraction of Fe(II1) on HDEHP concentrations; 0 in 5.1 M H,PO, at 20°C; IJ in 1.5 M H,POI at 20°C; l in 1.5 M HJPOdat 20°C with TOP0 (HDEHP/TOPO molar ratio 4). neutral organophosphorus compounds such as tributylphosphine oxide (TBPO) in combination with HDEHP had a negative influence on the extraction of Fe(II1) from nitric acid solutions. The variations of the distribution coefficients as a function of extractant concentration are shown in Fig. 3. The extractant dependency was performed at low and high acidity. It has been shown by Baker and Baes” that HDEHP is a dimer (H2A2) in n-octane and this is probably the same in a hydrocarbon diluent such as Mobil 190/210. The results show slopes of about 1.4 at 1.5 M and 5.1 M H,PO, respectively, with and without the presence of TOPO. This may be considered as a first power dependence on the extractant concentration. For the extraction of Fe(III), the third power dependence is expected with following equilibrium reaction
04
3
2
1
12
acidity
3 4 5 in molarity H3P04
Fig. 2. Distribution ratios as a function of acidity in aqueous phase: l with 0.3 M HDEHP at 20°C; q with 0.3 M HDEHP + 0.075 M TOP0 at 20°C; 0 with 0.3 M HDEHP + 0.075 M TOP0 at 0°C.
TOP0 alone (examined in the concentration range from 0.075 M to 0.75 M) shows no detectable extraction of iron(II1) from 1.5 and 5.1 M H3P04. In the mixtures with HDEHP, TOP0 had only a slightly negative effect on Fe(II1) extraction similar to the effect observed earlier by Blake et ~1.‘~that
Fe+3 + 3H,A, +
Fe(HA,), + 3H + .
Islam et aLzo have shown that Fe(II1) hydrolyzes in aqueous phase Fe+3 + H,O -_
Fe(OH)+’ + Hi
and that the extraction of Fe(II1) with HDEHP in benzene from sulphate solutions is first power dependent on extractant concentration. That could be accepted also for extraction of Fe(II1) with HDEHP from phosphoric acid Fe(OH)+* + H 2A Z_
Fe(OH)A, + 2H + .
617
Notes
- 24.43 f 1.95 for 0.3 M TOP0 and 5.1 M H,PO,,
HDEHP + 0.075 M
in the temperature range 2060°C. The above study indicates that there is a difference in enthalpy between HDEHP and HDEHP-TOP0 extraction of about 10 kJmol_’ from which may be concluded that Fe(II1) forms a stronger complex with HDEHP than with HDEHP-TOP0 mixture. REFERENCES
12
33
3.&
3.6
15
3
l/TAO3
Fig. 4. Dependence of the extraction of Fe(II1) with HDEHP on temperature; 0 0.3 M HDEHP + 0.075 M TOPG from 5.1 M H,PGd; n 0.3 M HDEHP + 0.075 M TOP0 from 1.5 M H,PG.,; l 0.3 M HDEHP from 1.5 M H,P04; 0 0.5 M HDEHP from 1.5 M H,PQ.
Enthalpy changes associated with the extraction reaction at constant phosphoric acid and extractant concentration were calculated according to Van’t Hoffs equation AH
log D -= (l/T)
-2.303R
The plots of log D vs l/T for HDEHP and HDEHP-TOP0 shown in Fig. 4 are linear with slopes of - AH/2.303R, the values of which, along with their precision were computed by linear regression using a UNIVAC 1100 computer. The extraction of Fe(II1) was found to be exothermic and AH values for the extraction reaction have been found to be in kJmol-‘: - 35.05 + 1.3
for
0.3M
HDEHP
and
1.5 M
H,PO,; -40.32 f 11.6 for 0.5 M HDEHP and 1.5 M H3PQ - 27.66 & 1.23 for 0.3 M HDEHP + 0.075 M TOP0 and 1.5 M H,P04;
G. M. Ritcey, A. W. Ashbrook and B. H. Lucas, CIM Bulletin, 111 (Jan. 1975) U.S. Pat. 3,399,055 (1968). C. J. Bouboulis, CIM Special Volwne 1979, 21, 32. J. A. Golding, S. Fouda and V. Saleh, Ibid. 1979,21, 227. A. K. De, S. M. Khopkar and R. A. Chalmers, Solvent Extraction of Metals, Chap. 9. Van Nostrand, Reinhold, New York (1970). 5. R. J. Leimala and B. G. Nyman, CIM Special Volume, 1979, 21, 475. 6. A. S. Kertes, Recent Advances in Liquid-Liquid Extraction (Edited by C. Hanson), Chap. 2. Pergamon Press, Oxford (1971). ?I. C. F. Baes and H. T. Baker, J. Phys. Chem. 1960, 64, 89. g S. N. Karapacheva and L. V. Ilozheva, Radio’ khimiya, 1969, 11, 37. 9. J. W. Roddy and C. F. Coleman and Sumio Arai, J. Inorg. Nucl. Chem. 197 1, 33, 1099. 10. J. E. Barnes, J. H. Setchfield and G. 0. R. Williams, J. Znorg. Nucl. Chem. 1976, 38, 1065. 11. F. Islam, H. Rahman, N. Ah, J. Znorg. Nucl. Chem. 1979, 41, 217. 12. V. L. Bykhovtsov, Radiokhimiya 1970, 12, 792. 13. T. Sato and T. Nakaumura, Proc. Int. Solvent. Ext. Conf. 1971, 1, 238. 14. F. J. Hurst and D. J. Crouse, Znd. Eng. Chem. Proc. Des. Develop. 1974, 13, 3; 286. 15. W. W. Berry and A. V. Henrickson, US. Pat. 4,302, 427 (1981). 16. Yu. B. Kletenik, Zzv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk. 1964, 8, 109. 17. F. T. Bunus, V. C. Domocos and P. Dimitresen, J. Inorg. Nucl. Chem. 1978, 40, 117. 18. C. A. Blake, D. E. Homer and J. M. Schmitt, Rep. ORNL 2259 (1959). 19. H. T. Baker and C. F. Baes, J. Inorg, Nucl. Chem. 1962, 24, 1277. 20. F. Islam, H. Rahman and M. Ah, J. Inorg. Nucl. Chem. 1979, 41, 217.
Vol. 3, No.
5, pp. 615617,
027FS387/84 $3.00 + .OO 0 1984 Pergamon Press Ltd.
1984
Printed in Great Britain.
NOTE SOLVENT EXTRACTION OF Fe@) BY DI-(2-ETHYLHEXYL)PHOSPHORIC ACID FROM PHOSPHORIC ACID SOLUTIONS S. MELES and M. V. PROSTENIK’ INA, Research and Development Division, 41000 Zagreb, Yugoslavia (Received 23 August 1983; accepted 10 October 1983) Abstract-The extraction of iron(II1) from aqueous phosphoric acid was studied using di-(2-ethylhexyl)phosphoric acid and trioctylphosphine oxide in nonaromatic hydrocarbon diluent. Distribution ratios have been investigated as a function of concentration of iron(III), phosphoric acid concentration, extractant concentration and extraction temperature. The apparent enthalpy change for the extraction reaction has been calculated from the temperature dependence data. It was found that the extractant dependency for iron(II1) is first power indicating hydrolysis of iron(II1) in the aqueous phase. Di(2-ethylhexyl)phosphoric acid (abbreviated as HDEHP or simply HA) is widely used in hydrometallurgical processes for the separation and purification of a number of metals such as uranium, rare earth, copper, cobalt and nickel.‘” Iron is a very common impurity in raw industrial acid metal solutions in either the divalent or trivalent states and, therefore, it is of importance to know its properties in a given extraction system. The extraction of Fe(II1) with HDEHP from sulphuric, hydrochloric, perchloric and nitric acid solutions has been studied in detai1.7-‘3 On the contrary, the extraction of Fe(II1) from phosphoric acid solutions has received little attention, although iron is associated with uranium in the wet process phosphoric acid and is coextracted during the uranium recovery by HDEHP-TOP0’4*‘5 (TOP0 = trioctylphosphine oxide). Kletenik16 has reported extraction of iron(II1) from phosphoric acid with a crude reaction with P205 2-ethyl- 1-hexanol mixture of (comprising the undetermined ratio of mono- and di-(2-ethylhexyl)phosphoric acid and di-(2ethylhexyl)pyrophosphoric acid). The extraction is characterised by unusually high distribution coefficients. Bunus et aLL7studied the influence of iron, particularly Fe(I1) in uranium(IV) extraction from phosphoric acid and with HDEHP and HDEHP-TOP0 mixtures but no details on Fe(II1) extraction were given. Therefore, the purpose of the present investigation was to define in some detail the Fe(II1)
*Author to whom correspondence should he addressed.
extraction by HDEHP and HDEHP-TOP0 phosphoric acid solutions.
from
EXPERIMENTAL Reagents. Analytical grade phosphoric acid and FeC13.6H20 (“Kemika”-Zagreb) were used. HDEHP and TOP0 were used as purchased from Mobil Co. Procedure. Aqueous solutions were prepared by dissolving Fe(II1) chloride in phosphoric acid of selected concentrations. Organic solutions were prepared from HDEHP and TOP0 and nonaromatic hydrocarbon diluent Mobil 190/210. Distribution ratio measurements were performed at 20°C in the thermostated bath with the exception of temperature studies. Equal ,volumes of aqueous and organic solutions were mixed mechanically for 20 min to ensure thermal and’ chemical equilibrium. Preliminary experiments had shown that the equilibrium is reached after 10 min. Phases were disengaged by centrifugation and the aqueous phase was analysed for iron content by atomicabsorption spectrophotometry or spectrophotometrically with 2,2’-bipyridine. RESULTS AND DISCUSSION Typical isotherms for the extraction of Fe(II1) by 0.3 M and 0.5 M HDEHP in kerosene from 1.5 M and 5.1 M H3P04 as well as with the mixture of 0.3 M HDEHP 0.075 M TOP0 are presented in Fig. 1. The values of distribution coefficient obtained for Fe(II1) as a function of H,PO, concentration are presented in Fig. 2. The distribution coefficient decreases rapidly with increasing concentration of phosphoric acid.
615
Notes
1
0
5
0
-1
-2 -1
Fig. 1. Equilibrium loading isotherms for Fe(II1) extraction at 20°C; 0 0.3 M HDEHP, 5.1 M H3P04; 0 0.3 M HDEHP+ 0.075 M TOPO, 5.1 M H,PO,; 0 0.5 M HDEHP, 5.1 M H,PO.,; x 0.5 M HDEHP, 1.5 M H,PO,.
-0.5
0 Log IHOEHPI
Fig. 3. Dependence of the extraction of Fe(II1) on HDEHP concentrations; 0 in 5.1 M H,PO, at 20°C; IJ in 1.5 M H,POI at 20°C; l in 1.5 M HJPOdat 20°C with TOP0 (HDEHP/TOPO molar ratio 4). neutral organophosphorus compounds such as tributylphosphine oxide (TBPO) in combination with HDEHP had a negative influence on the extraction of Fe(II1) from nitric acid solutions. The variations of the distribution coefficients as a function of extractant concentration are shown in Fig. 3. The extractant dependency was performed at low and high acidity. It has been shown by Baker and Baes” that HDEHP is a dimer (H2A2) in n-octane and this is probably the same in a hydrocarbon diluent such as Mobil 190/210. The results show slopes of about 1.4 at 1.5 M and 5.1 M H,PO, respectively, with and without the presence of TOPO. This may be considered as a first power dependence on the extractant concentration. For the extraction of Fe(III), the third power dependence is expected with following equilibrium reaction
04
3
2
1
12
acidity
3 4 5 in molarity H3P04
Fig. 2. Distribution ratios as a function of acidity in aqueous phase: l with 0.3 M HDEHP at 20°C; q with 0.3 M HDEHP + 0.075 M TOP0 at 20°C; 0 with 0.3 M HDEHP + 0.075 M TOP0 at 0°C.
TOP0 alone (examined in the concentration range from 0.075 M to 0.75 M) shows no detectable extraction of iron(II1) from 1.5 and 5.1 M H3P04. In the mixtures with HDEHP, TOP0 had only a slightly negative effect on Fe(II1) extraction similar to the effect observed earlier by Blake et ~1.‘~that
Fe+3 + 3H,A, +
Fe(HA,), + 3H + .
Islam et aLzo have shown that Fe(II1) hydrolyzes in aqueous phase Fe+3 + H,O -_
Fe(OH)+’ + Hi
and that the extraction of Fe(II1) with HDEHP in benzene from sulphate solutions is first power dependent on extractant concentration. That could be accepted also for extraction of Fe(II1) with HDEHP from phosphoric acid Fe(OH)+* + H 2A Z_
Fe(OH)A, + 2H + .
617
Notes
- 24.43 f 1.95 for 0.3 M TOP0 and 5.1 M H,PO,,
HDEHP + 0.075 M
in the temperature range 2060°C. The above study indicates that there is a difference in enthalpy between HDEHP and HDEHP-TOP0 extraction of about 10 kJmol_’ from which may be concluded that Fe(II1) forms a stronger complex with HDEHP than with HDEHP-TOP0 mixture. REFERENCES
12
33
3.&
3.6
15
3
l/TAO3
Fig. 4. Dependence of the extraction of Fe(II1) with HDEHP on temperature; 0 0.3 M HDEHP + 0.075 M TOPG from 5.1 M H,PGd; n 0.3 M HDEHP + 0.075 M TOP0 from 1.5 M H,PG.,; l 0.3 M HDEHP from 1.5 M H,P04; 0 0.5 M HDEHP from 1.5 M H,PQ.
Enthalpy changes associated with the extraction reaction at constant phosphoric acid and extractant concentration were calculated according to Van’t Hoffs equation AH
log D -= (l/T)
-2.303R
The plots of log D vs l/T for HDEHP and HDEHP-TOP0 shown in Fig. 4 are linear with slopes of - AH/2.303R, the values of which, along with their precision were computed by linear regression using a UNIVAC 1100 computer. The extraction of Fe(II1) was found to be exothermic and AH values for the extraction reaction have been found to be in kJmol-‘: - 35.05 + 1.3
for
0.3M
HDEHP
and
1.5 M
H,PO,; -40.32 f 11.6 for 0.5 M HDEHP and 1.5 M H3PQ - 27.66 & 1.23 for 0.3 M HDEHP + 0.075 M TOP0 and 1.5 M H,P04;
G. M. Ritcey, A. W. Ashbrook and B. H. Lucas, CIM Bulletin, 111 (Jan. 1975) U.S. Pat. 3,399,055 (1968). C. J. Bouboulis, CIM Special Volwne 1979, 21, 32. J. A. Golding, S. Fouda and V. Saleh, Ibid. 1979,21, 227. A. K. De, S. M. Khopkar and R. A. Chalmers, Solvent Extraction of Metals, Chap. 9. Van Nostrand, Reinhold, New York (1970). 5. R. J. Leimala and B. G. Nyman, CIM Special Volume, 1979, 21, 475. 6. A. S. Kertes, Recent Advances in Liquid-Liquid Extraction (Edited by C. Hanson), Chap. 2. Pergamon Press, Oxford (1971). ?I. C. F. Baes and H. T. Baker, J. Phys. Chem. 1960, 64, 89. g S. N. Karapacheva and L. V. Ilozheva, Radio’ khimiya, 1969, 11, 37. 9. J. W. Roddy and C. F. Coleman and Sumio Arai, J. Inorg. Nucl. Chem. 197 1, 33, 1099. 10. J. E. Barnes, J. H. Setchfield and G. 0. R. Williams, J. Znorg. Nucl. Chem. 1976, 38, 1065. 11. F. Islam, H. Rahman, N. Ah, J. Znorg. Nucl. Chem. 1979, 41, 217. 12. V. L. Bykhovtsov, Radiokhimiya 1970, 12, 792. 13. T. Sato and T. Nakaumura, Proc. Int. Solvent. Ext. Conf. 1971, 1, 238. 14. F. J. Hurst and D. J. Crouse, Znd. Eng. Chem. Proc. Des. Develop. 1974, 13, 3; 286. 15. W. W. Berry and A. V. Henrickson, US. Pat. 4,302, 427 (1981). 16. Yu. B. Kletenik, Zzv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk. 1964, 8, 109. 17. F. T. Bunus, V. C. Domocos and P. Dimitresen, J. Inorg. Nucl. Chem. 1978, 40, 117. 18. C. A. Blake, D. E. Homer and J. M. Schmitt, Rep. ORNL 2259 (1959). 19. H. T. Baker and C. F. Baes, J. Inorg, Nucl. Chem. 1962, 24, 1277. 20. F. Islam, H. Rahman and M. Ah, J. Inorg. Nucl. Chem. 1979, 41, 217.