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Concentration and separation of indium, gallium, thallium, antimony and bismuth by extraction with alkylphosphoric acids
Tahnta.
1967. Vol. 14. pp. 801 to 808.
Pergamon Press Ltd.
Printed in Northern Ireland
CONCENTRATION AND SEPARATION OF INDIUM, GALLIUM, THALLIUM, ANTIMONY AND BISMUTH BY EXTRACTION WITH ALKYLPHOSPHORIC ACIDS I. S. LEVIN, A. A. SHATALOVA, T. G. AZARENKO, I. A. VOFWNA, N. A. BURTOVAYA-BALAKIREVAand T. F. RODINA Institute of Mineral Treatment, Derzhavina 18, Novosibirsk, U.S.S.R. (Received 7 July 1966. Accepted 9 February 1967)
Summa~-The use of alkylphosphoric acids for solvent extraction separations is described, and the use of antisynergic agents for stripping is discussed. ALKYLPHOSPHORICacids (APA) have found a practical application in the production
technology of uranium, thorium, vanadium, scandium and indium, where they are used for the extraction, separation, and concentration of actinides and lanthanides. This class of extracting agents appears to be of much promise in the production ofhighpurity metals and their compounds, as well as for purely analytical use, because of the following factors : they give high distribution coefficients in extractions from solutions of different oxy-acids over a wide range of concentrations ; the distribution coefficients do not decrease with a decrease in the concentration of the metal being extracted; it is possible to strip the extracts selectively with salts, acids, and mixtures of acids with antisynergic agents; they have low solubility in mineral acids. We have studied the extraction mechanisms for gallium, indium, thallium(III), antimony(II1) and (V), bismuth, and tin(I1) and (IV), and the role of diluents and antisynergic agents. We have also examined the analytical possibilities of APA, using chiefly 1 N solutions of mono-2-ethylhexylphosphoric acid (MEHPA) and di-2-ethylhexylphosphoric acid (DEHPA) in heptane, and also a 1N mixture of pyro-2-ethylhexylphosphoric acids (PEHPA) in heptane. Certain problems can be solved by changing the extractant used, since in many cases the three acids behave differently. Extraction from solutions of oxy-acids
As can be seen from Fig. 1, the extraction of gallium, indium, thallium(III), antimony(III), bismuth and tin(IV) by APA from sulphuric acid solutions is practically quantitative over a wide range of acid concentration, and (which is also of importance) over a wide range of metal concentration. This behaviour can be made use of both for the extraction separation of micro-quantities of the metal to be determined, and for removal of the matrix element. The equilibrium in the extraction of indium, gallium, thallium(III), antimony(III), bismuth and tin(I1) is established in 20-30 set, and in 60-70 min for the extraction of antimony(V) and tin(IV). Figure 2 shows that the nature of the APA is of decisive importance for the extraction of gallium, thallium and bismuth. All the metals mentioned above can be separated by extraction from almost any quantity of the following elements, which are characterized by their low extractability into APA from acid media: alkali and alkaline earth metals, copper, zinc, iron( 8
801
I. S. LEVINet al.
802
cobalt, nickel, manganese(I1) or (VII), mercury, arsenic(II1) or (V), selenium, tellurium,germanium, chromium(II1) or (VI), silver, gold, platinum metals,1-3 and also lead if the latter is extracted from perchloric or nitric acid solution. This holds, with minor variations, for nitric and perchloric acid media as well as for sulphuric acid. 100
80
s
60
-
.-E ‘; 0
f w
40
20
0
I
I
I
I
2
4
a
12
HZS04,
I
2
4
a HzSO4,
FIG.
16
N
FIG. I.-Effect of sulphuric acid concentration O-Sb(II1); A-Ga; O-Tl(III);
0
16
12
on extraction with PEH~A. Cl-In; n-Bi.
16
20
N
2.-Effect of sulphuric acid concentration O-Sb(II1); U-In; W--Tl(II1);
on extraction with DEHPA. A-Ga; W-Bi.
however, to strip some of the metals extracted, and hydrofluoric required as stripping agent. Such metals reduce the capacity of the extractant and are considered as “poisons” in technological processes. In analysis, It is difficult,
acid is usually
Extraction with alkylphosphoric
acids
803
on the other hand, this creates additional possibilities for their separation. In certain cases, gallium, indium, thallium, antimony(II1) and bismuth can be separated at the stripping stage from titanium, zirconium, hafnium, selenium, thorium, tin(IV) and iron(II1). Oxalate does not interfere with the extraction of indium and tin(I1) or (IV),4 but prevents the extraction of antimony and bismuth;5 it can therefore be used as stripping agent in the separation of these metals. Extraction from hydrohaiic acid media With halide ions, the metals gallium, indium, thallium(III), antimony(III), bismuth and tin form anionic complexes which are weakly extractable into APA, and in several instances hydrohalic acids can be used as efficient stripping agents, permitting manifold concentration of these metals. The degree of concentration that can be achieved is limited by the minimum volume of stripping agent permissible analytically. Antimony(III), indium, gallium and tin(I1) or (IV) are extracted quantitatively from dilute hydrochloric acid ; even hydroxide and basic salt precipitates do not affect the extraction. Intensive shaking leads to a rapid shift of the equilibrium and the disappearance of the precipitate. With increase in the concentration of hydrochloric or hydrobromic acid, the extractability falls sharply. The distribution coefficients (D) sometimes decrease with change in the acid in the order HCI-HBr-HI-HF, and sometimes in the reverse order. Thus for extraction from isomolar solutions of the hydrohalic acids, the order of the D values is: In-HI
> HF > HBr > HCl > HBr > HI > HF Sn(II)-HF > HBr > HCl Sn(IV jNBr > HCI > HF Bi-HCI > HBr > HI.
Sb(III)-HCl
The behaviour of bismuth and thallium(II1) in extractions from hydrohalic acid or halide solutions is peculiar; they are not extracted into APA even from solutions containing comparatively minor concentrations of chloride, bromide or iodide, and appear to form halide complexes of the type MeHalLm-@+ where m is the charge on the metal ion. Antimony(V) also shows unusual behaviour, being easily extracted with MEHPA or DEHPA from high or low concentrations of hydrohalic acid, but not from medium concentrations (Fig. 3). If only the right-hand branch of the extraction curve was observed, it could be interpreted as indicating the presence of strongly hydrolysed ionic or molecular species in the aqueous phase, but the existence of the left-hand branch, showing that extraction occurs even if hydroxide or basic salt precipitates are present, can only be explained by a change in the mechanism of extraction, from chelate formation to production of molecular species, as happens with tribufylphosphate. The behaviour of gallium and thallium also seems anomalous but for gallium this is only so if the extractant is DEHPA (Fig. 4). The behaviour of thallium(II1) is the same for all three extractants. We have shown that in extraction of gallium and antimony(V) from weakly acidic solutions an exchange reaction is involved and that the amount of halide found in the organic phase is insignificant, whereas from strongly acidic media the organic phase extracts molecular species such as HGaCI,*nDEHPA and HSbCI,*nAPA. Further
bxl , .ft F’m;. b-Effect
of hydrohalic acid concentration on extraction of antimony(V) PEHPA-I, HCI; IV, HBr MEBPA-II, HCI; V, HFlr DEHPA-III, HCI; VI, HBr
work is being undertaken on the ~ompositjo~ of these species. The change in the mechanism of extraction is also shown by the fact that in APA extractions halides can act as salting-out agents. Thus the ~stribution coefficient for gaflium in extration from 1M hydrochloric acid with DEHPA can be increased from 0.07 to more than 100 by saturating the solution with calcium chloride. A further
. 60 s ._ 5L '; 40 w
FIG. 4.-l3%ct of hydrohalic acid concentration on extraction of @i&urn and thallium with DEHPA. I and III-HC1; IX and IV-HBr O-TKIIIl; A-Ga.
indication of the change in mechanism is provided by the infrared absorption spectra. When gallium is extracted with DEHPA at pH - 2, the spectrum of the extract shows a considerable decrease in the intensity in the range of hydroxyl stretching modes
805
Extraction with alkylphosphoricacids
(2550-2700 cm-l), caused by replacement of the hydrogen by metal.6-8 When the extraction is made from concentrated hydrochloric acid solutions, the intensity of the 2550-2700 cm-l band does not change but there is a sharp drop in the intensity of the band which has a maximum at 1240 cm-l, corresponding to the P=O vibration. Similar changes are observed for the extraction of antimony(V) from concentrated hydrochloric acid solutions (Fig. 5). It should be noted that for extraction of gallium and antimony(V) with tributylphosphate from hydrochloric acid there is only a 70-80 cm-l shift of the P=O band (Fig. 6) whereas the spectra of the DEHPA extracts show a considerable decrease in intensity as well as a shift that may be as small as 10-20 cm-l. r
-I-
7
0’
/-
/’ /I
I I
25 cm-’
cm-’
FIG. L-Infrared spectra of extracts I-DEHPA; 2-Ga-DEHPA (from HCI, pH 2); 3--Ga-DEHPA (from cont. HCI); 4-Sb(V)-DEHPA (from cont. HCl).
FIG. 6.-Infrared spectra of extracts I-‘IBP; 2-HCI; 3-Ga; 4--Sb(V).
Antisynergic stripping Antisynergism is manifested in APA systems by the reduction in the extracting ability of these reagents by addition of other solvents, especially alcohols, ketones and trialkylphosphates,9-21 and is apparently caused by interaction between the components of the mixed extractant, according to the equation XS + y(APA), -+ ky(APA);xS where S represents the second solvent and m = n/k. The degree of association (n)
806
I. S. LEvm et al.
of the APA depends on such factors as the nature of the diluent and the presence of moisture. The utilization of antisynergism not only facilitates stripping, but also extends the range of stripping agents available, so that the most convenient one for a particular purpose can be selected. A typical example is shown in Fig. 7. Strictly speaking, all diluents can be regarded as potential antisynergic agents, but there is no universal comprehensive explanation so far of their influence on extraction with APA. To explain it entirely in terms of dielectric constants, dipole moments, polarizability, etc., is to oversimplify the problem. This is clearly shown by the data summarized in Table I.
FIG. ‘I.-Antisynergic effect in the system MEHPA-TBP-H,SO,-Bi. I-Bi-MEHPA; [Bi] 1 g/l.; [MEHPA] 0.25N II-Bi-MEHPA-TBP; [MEHPA] 0.25N, [TBP] 1.25N III-Bi-TBP; [TBP] 3.76N.
It seems to us that the decisive factor is hydrogen bonding between the APA and the diluent. It leads to depolymerization of the extracting agent, resulting in a greater accessibility of hydrogen ions to the cations being extracted. The influence of the nature of these cations is being studied. SEPARATION
METHODS
Indium Indium can be extracted from l-2N sulphuric, nitric or perchloric acid solution with a 1N solution of mono-, di- or pyro-2-ethylhexylphosphoric acid (or a similar APA) in a saturated hydrocarbon. Feebly extracted impurities such as copper, zinc and cadmium remain in the aqueous phase after scrubbing. Gallium, thallium, antimony, bismuth, tin, titanium, zirconium, hafnium, scandium, uranium, thorium, and molybdenum are extracted along with the indium. Gallium, however, is not extracted if DEHPA is used. Iron(II1) must be reduced before the extraction. Antimony and bismuth are stripped with an oxalic acid solution, but if bismuth is present
Extraction with alkylphosphoric
acids
807
in large amounts it can be stripped with potassium iodide solution. The indium is then stripped with hydrochloric or hydrobromic acid or by addition of an antisynergic agent and extraction with an oxygen acid (sulphuric is best). The other elements are either not stripped or do not interfere if the indium is then determined with Rhodamine 6 G. TABLE I.-INFLUENCE OF DILUENTSON THE EXTRACXIONOF INDIUM WITH MEHPA AND DEHPA
DEHPA
MEHPA D
Diluent
&
p
Iso-octane Bromoform Benzene Carbon tetrachloride Dichloroethane Nitrobenzene Dibutyl ether Isobutanol
1.94 10.36 2.284
2.06 0
0.63
2.238 5.4 34.82 3.06 17.7
0 1.23 2.99 1.22 1.79
051 0.4 0.4 0.34 0.02
.+-dielectric sulphuric acid.
constant ; p-dipole
Diluent
E
Carbon tetrachloride Benzene Heptane Bromobenzene Nitrobenzene Dibutyl ether Isoamyl acetate Isobutanol TBP
2.238 2.284 1.924 10.36 3482 3.06 4.63 17.7
moment ; D-distribution
coefficient;
D
Y 0
0 1.73 3.99 1.22 1.8 1.79
9.3 8.5 7.7 5,7 1.1 0.63 0.09 0.03 0001
O.OlM indium,
1.5N
Antimony Antimony(II1) can be extracted from 1-4N sulphuric, nitric or perchloric acid with a 1N solution of mono-, di- or pyroalkylphosphoric acid in a saturated hydrocarbon. Feebly extracted species such as copper and zinc remain in the aqueous phase after scrubbing with l-2N sulphuric acid. Thallium and bismuth are stripped with a halide solution and then antimony(II1) is stripped with hydrochloric, hydrobromic or oxalic acid, or by adding an antisynergic agent and an oxy-acid. The choice of stripping agent is determined by the other elements present in the extract. The expediency of extracting antimony(V) from concentrated hydrochloric or hydrobromic acid is being examined. Bismuth Bismuth can be extracted from l-6N sulphuric acid with a freshly diluted or stabilized22 IN solution of pyroalkylphosphoric acid in a saturated hydrocarbon. The organic phase is scrubbed with I-2N sulphuric acid to free it from feebly extracted species such as zinc and cadmium etc. Bismuth is stripped with a hydrohalic acid, oxalic acid, halide, or ammonium oxalate solution, the best choice being potassium iodide solution, as the bismuth can then be determined calorimetrically in the aqueous phase. Zumumnenf&ssnng-Die Venvendung von Alkylphosphorsluren extraktiven Tremnmgen wird beschrieben und der Gebrauch synergischer Agentien zur Rilckextraktion diskutiert.
zu anti-
RCsnm&Gn d&r-it l’emploi d’acides alkylphosphoriques pour les separations par extraction par solvant et disc&e de l’emploi d’agents antisynergiques pour les r&extractions.
808
I. S. LEvIN et al. REFERENCES
1. I. S. Levin and T. G. Azarenko, Kompleksnaya pererabotka polymetallichskogo cirya, p. 411. Izdat Metallurgia, Moscow, 1965. 2. Idem, Zh. Analit. Khim., 1963,18,1335. 3. K. Kimura, &all. Chem, Sot. Japan, 1961, 34,63. 4. I. S. Levin, Zh. Priklad. Khim., 1962, 35,2368. 5. 1. S. L&n and A. A. Shatalova, Dokl. Akad. Nuuk. S.S.S.R., 1965, 161,1158. 6. D. E. Peppard and J. R. Ferraro, J. Ittorg. Nuci. Chem., 1959, 10,275. 7. J. R. Ferraro, ibid., 1962,24,47.X 8. T. Sato, ibid., 1962,24, 699; 1965, 27, 1853. 9. J. R. Ferraro and T. V. Healy, ibid., 1962, 24, 1463. 10. T. V. Healy, D. F. Peppard and G. W. Mason, ibid., 1962, 24, 1429. 11. T. V. Healy and J. R. Ferraro, ibid., 1962, 24, 1449. 12. C. Deptula and S. Mint, Nucleonica, 1961, 6, 197. 13. M. Taube, Polish Acad. Sci., Inst. Nucl. Res. Reps., 1961, No. 270, 1. 14. Idem, Radiokhimia, 1963,4,260. 15. D. Dyrssen and S. Ekberg, Acta Chem. Scat& 1959,13,1909. 16. D. F. Peppard, G. W. Mason and R. J. Sironen, J. Inorg. Nucl. Chem., 1959,10,117. 17. G. W. Mason, S. McCarty and IX F. Peppard, ibid., 1962,24,967. 18. K. Anil, J. Sci, I&. Res. India, 1965, 24,82. 19. W. Milkowski, Proc. Sot. AnaL Chem., 1965,2,74. 20. F. A. Se&on, Ckem. fig., 1964,71,112. 21. L. Bakos and E. Szabo, Magy. Tud. Akad. Kern. Tud. Oszf. Kozlemen, 1964,22, 399. 22. Yu. B. Kletenik, Zh. Analit. Khim., 1963, 18, 66.
1967. Vol. 14. pp. 801 to 808.
Pergamon Press Ltd.
Printed in Northern Ireland
CONCENTRATION AND SEPARATION OF INDIUM, GALLIUM, THALLIUM, ANTIMONY AND BISMUTH BY EXTRACTION WITH ALKYLPHOSPHORIC ACIDS I. S. LEVIN, A. A. SHATALOVA, T. G. AZARENKO, I. A. VOFWNA, N. A. BURTOVAYA-BALAKIREVAand T. F. RODINA Institute of Mineral Treatment, Derzhavina 18, Novosibirsk, U.S.S.R. (Received 7 July 1966. Accepted 9 February 1967)
Summa~-The use of alkylphosphoric acids for solvent extraction separations is described, and the use of antisynergic agents for stripping is discussed. ALKYLPHOSPHORICacids (APA) have found a practical application in the production
technology of uranium, thorium, vanadium, scandium and indium, where they are used for the extraction, separation, and concentration of actinides and lanthanides. This class of extracting agents appears to be of much promise in the production ofhighpurity metals and their compounds, as well as for purely analytical use, because of the following factors : they give high distribution coefficients in extractions from solutions of different oxy-acids over a wide range of concentrations ; the distribution coefficients do not decrease with a decrease in the concentration of the metal being extracted; it is possible to strip the extracts selectively with salts, acids, and mixtures of acids with antisynergic agents; they have low solubility in mineral acids. We have studied the extraction mechanisms for gallium, indium, thallium(III), antimony(II1) and (V), bismuth, and tin(I1) and (IV), and the role of diluents and antisynergic agents. We have also examined the analytical possibilities of APA, using chiefly 1 N solutions of mono-2-ethylhexylphosphoric acid (MEHPA) and di-2-ethylhexylphosphoric acid (DEHPA) in heptane, and also a 1N mixture of pyro-2-ethylhexylphosphoric acids (PEHPA) in heptane. Certain problems can be solved by changing the extractant used, since in many cases the three acids behave differently. Extraction from solutions of oxy-acids
As can be seen from Fig. 1, the extraction of gallium, indium, thallium(III), antimony(III), bismuth and tin(IV) by APA from sulphuric acid solutions is practically quantitative over a wide range of acid concentration, and (which is also of importance) over a wide range of metal concentration. This behaviour can be made use of both for the extraction separation of micro-quantities of the metal to be determined, and for removal of the matrix element. The equilibrium in the extraction of indium, gallium, thallium(III), antimony(III), bismuth and tin(I1) is established in 20-30 set, and in 60-70 min for the extraction of antimony(V) and tin(IV). Figure 2 shows that the nature of the APA is of decisive importance for the extraction of gallium, thallium and bismuth. All the metals mentioned above can be separated by extraction from almost any quantity of the following elements, which are characterized by their low extractability into APA from acid media: alkali and alkaline earth metals, copper, zinc, iron( 8
801
I. S. LEVINet al.
802
cobalt, nickel, manganese(I1) or (VII), mercury, arsenic(II1) or (V), selenium, tellurium,germanium, chromium(II1) or (VI), silver, gold, platinum metals,1-3 and also lead if the latter is extracted from perchloric or nitric acid solution. This holds, with minor variations, for nitric and perchloric acid media as well as for sulphuric acid. 100
80
s
60
-
.-E ‘; 0
f w
40
20
0
I
I
I
I
2
4
a
12
HZS04,
I
2
4
a HzSO4,
FIG.
16
N
FIG. I.-Effect of sulphuric acid concentration O-Sb(II1); A-Ga; O-Tl(III);
0
16
12
on extraction with PEH~A. Cl-In; n-Bi.
16
20
N
2.-Effect of sulphuric acid concentration O-Sb(II1); U-In; W--Tl(II1);
on extraction with DEHPA. A-Ga; W-Bi.
however, to strip some of the metals extracted, and hydrofluoric required as stripping agent. Such metals reduce the capacity of the extractant and are considered as “poisons” in technological processes. In analysis, It is difficult,
acid is usually
Extraction with alkylphosphoric
acids
803
on the other hand, this creates additional possibilities for their separation. In certain cases, gallium, indium, thallium, antimony(II1) and bismuth can be separated at the stripping stage from titanium, zirconium, hafnium, selenium, thorium, tin(IV) and iron(II1). Oxalate does not interfere with the extraction of indium and tin(I1) or (IV),4 but prevents the extraction of antimony and bismuth;5 it can therefore be used as stripping agent in the separation of these metals. Extraction from hydrohaiic acid media With halide ions, the metals gallium, indium, thallium(III), antimony(III), bismuth and tin form anionic complexes which are weakly extractable into APA, and in several instances hydrohalic acids can be used as efficient stripping agents, permitting manifold concentration of these metals. The degree of concentration that can be achieved is limited by the minimum volume of stripping agent permissible analytically. Antimony(III), indium, gallium and tin(I1) or (IV) are extracted quantitatively from dilute hydrochloric acid ; even hydroxide and basic salt precipitates do not affect the extraction. Intensive shaking leads to a rapid shift of the equilibrium and the disappearance of the precipitate. With increase in the concentration of hydrochloric or hydrobromic acid, the extractability falls sharply. The distribution coefficients (D) sometimes decrease with change in the acid in the order HCI-HBr-HI-HF, and sometimes in the reverse order. Thus for extraction from isomolar solutions of the hydrohalic acids, the order of the D values is: In-HI
> HF > HBr > HCl > HBr > HI > HF Sn(II)-HF > HBr > HCl Sn(IV jNBr > HCI > HF Bi-HCI > HBr > HI.
Sb(III)-HCl
The behaviour of bismuth and thallium(II1) in extractions from hydrohalic acid or halide solutions is peculiar; they are not extracted into APA even from solutions containing comparatively minor concentrations of chloride, bromide or iodide, and appear to form halide complexes of the type MeHalLm-@+ where m is the charge on the metal ion. Antimony(V) also shows unusual behaviour, being easily extracted with MEHPA or DEHPA from high or low concentrations of hydrohalic acid, but not from medium concentrations (Fig. 3). If only the right-hand branch of the extraction curve was observed, it could be interpreted as indicating the presence of strongly hydrolysed ionic or molecular species in the aqueous phase, but the existence of the left-hand branch, showing that extraction occurs even if hydroxide or basic salt precipitates are present, can only be explained by a change in the mechanism of extraction, from chelate formation to production of molecular species, as happens with tribufylphosphate. The behaviour of gallium and thallium also seems anomalous but for gallium this is only so if the extractant is DEHPA (Fig. 4). The behaviour of thallium(II1) is the same for all three extractants. We have shown that in extraction of gallium and antimony(V) from weakly acidic solutions an exchange reaction is involved and that the amount of halide found in the organic phase is insignificant, whereas from strongly acidic media the organic phase extracts molecular species such as HGaCI,*nDEHPA and HSbCI,*nAPA. Further
bxl , .ft F’m;. b-Effect
of hydrohalic acid concentration on extraction of antimony(V) PEHPA-I, HCI; IV, HBr MEBPA-II, HCI; V, HFlr DEHPA-III, HCI; VI, HBr
work is being undertaken on the ~ompositjo~ of these species. The change in the mechanism of extraction is also shown by the fact that in APA extractions halides can act as salting-out agents. Thus the ~stribution coefficient for gaflium in extration from 1M hydrochloric acid with DEHPA can be increased from 0.07 to more than 100 by saturating the solution with calcium chloride. A further
. 60 s ._ 5L '; 40 w
FIG. 4.-l3%ct of hydrohalic acid concentration on extraction of @i&urn and thallium with DEHPA. I and III-HC1; IX and IV-HBr O-TKIIIl; A-Ga.
indication of the change in mechanism is provided by the infrared absorption spectra. When gallium is extracted with DEHPA at pH - 2, the spectrum of the extract shows a considerable decrease in the intensity in the range of hydroxyl stretching modes
805
Extraction with alkylphosphoricacids
(2550-2700 cm-l), caused by replacement of the hydrogen by metal.6-8 When the extraction is made from concentrated hydrochloric acid solutions, the intensity of the 2550-2700 cm-l band does not change but there is a sharp drop in the intensity of the band which has a maximum at 1240 cm-l, corresponding to the P=O vibration. Similar changes are observed for the extraction of antimony(V) from concentrated hydrochloric acid solutions (Fig. 5). It should be noted that for extraction of gallium and antimony(V) with tributylphosphate from hydrochloric acid there is only a 70-80 cm-l shift of the P=O band (Fig. 6) whereas the spectra of the DEHPA extracts show a considerable decrease in intensity as well as a shift that may be as small as 10-20 cm-l. r
-I-
7
0’
/-
/’ /I
I I
25 cm-’
cm-’
FIG. L-Infrared spectra of extracts I-DEHPA; 2-Ga-DEHPA (from HCI, pH 2); 3--Ga-DEHPA (from cont. HCI); 4-Sb(V)-DEHPA (from cont. HCl).
FIG. 6.-Infrared spectra of extracts I-‘IBP; 2-HCI; 3-Ga; 4--Sb(V).
Antisynergic stripping Antisynergism is manifested in APA systems by the reduction in the extracting ability of these reagents by addition of other solvents, especially alcohols, ketones and trialkylphosphates,9-21 and is apparently caused by interaction between the components of the mixed extractant, according to the equation XS + y(APA), -+ ky(APA);xS where S represents the second solvent and m = n/k. The degree of association (n)
806
I. S. LEvm et al.
of the APA depends on such factors as the nature of the diluent and the presence of moisture. The utilization of antisynergism not only facilitates stripping, but also extends the range of stripping agents available, so that the most convenient one for a particular purpose can be selected. A typical example is shown in Fig. 7. Strictly speaking, all diluents can be regarded as potential antisynergic agents, but there is no universal comprehensive explanation so far of their influence on extraction with APA. To explain it entirely in terms of dielectric constants, dipole moments, polarizability, etc., is to oversimplify the problem. This is clearly shown by the data summarized in Table I.
FIG. ‘I.-Antisynergic effect in the system MEHPA-TBP-H,SO,-Bi. I-Bi-MEHPA; [Bi] 1 g/l.; [MEHPA] 0.25N II-Bi-MEHPA-TBP; [MEHPA] 0.25N, [TBP] 1.25N III-Bi-TBP; [TBP] 3.76N.
It seems to us that the decisive factor is hydrogen bonding between the APA and the diluent. It leads to depolymerization of the extracting agent, resulting in a greater accessibility of hydrogen ions to the cations being extracted. The influence of the nature of these cations is being studied. SEPARATION
METHODS
Indium Indium can be extracted from l-2N sulphuric, nitric or perchloric acid solution with a 1N solution of mono-, di- or pyro-2-ethylhexylphosphoric acid (or a similar APA) in a saturated hydrocarbon. Feebly extracted impurities such as copper, zinc and cadmium remain in the aqueous phase after scrubbing. Gallium, thallium, antimony, bismuth, tin, titanium, zirconium, hafnium, scandium, uranium, thorium, and molybdenum are extracted along with the indium. Gallium, however, is not extracted if DEHPA is used. Iron(II1) must be reduced before the extraction. Antimony and bismuth are stripped with an oxalic acid solution, but if bismuth is present
Extraction with alkylphosphoric
acids
807
in large amounts it can be stripped with potassium iodide solution. The indium is then stripped with hydrochloric or hydrobromic acid or by addition of an antisynergic agent and extraction with an oxygen acid (sulphuric is best). The other elements are either not stripped or do not interfere if the indium is then determined with Rhodamine 6 G. TABLE I.-INFLUENCE OF DILUENTSON THE EXTRACXIONOF INDIUM WITH MEHPA AND DEHPA
DEHPA
MEHPA D
Diluent
&
p
Iso-octane Bromoform Benzene Carbon tetrachloride Dichloroethane Nitrobenzene Dibutyl ether Isobutanol
1.94 10.36 2.284
2.06 0
0.63
2.238 5.4 34.82 3.06 17.7
0 1.23 2.99 1.22 1.79
051 0.4 0.4 0.34 0.02
.+-dielectric sulphuric acid.
constant ; p-dipole
Diluent
E
Carbon tetrachloride Benzene Heptane Bromobenzene Nitrobenzene Dibutyl ether Isoamyl acetate Isobutanol TBP
2.238 2.284 1.924 10.36 3482 3.06 4.63 17.7
moment ; D-distribution
coefficient;
D
Y 0
0 1.73 3.99 1.22 1.8 1.79
9.3 8.5 7.7 5,7 1.1 0.63 0.09 0.03 0001
O.OlM indium,
1.5N
Antimony Antimony(II1) can be extracted from 1-4N sulphuric, nitric or perchloric acid with a 1N solution of mono-, di- or pyroalkylphosphoric acid in a saturated hydrocarbon. Feebly extracted species such as copper and zinc remain in the aqueous phase after scrubbing with l-2N sulphuric acid. Thallium and bismuth are stripped with a halide solution and then antimony(II1) is stripped with hydrochloric, hydrobromic or oxalic acid, or by adding an antisynergic agent and an oxy-acid. The choice of stripping agent is determined by the other elements present in the extract. The expediency of extracting antimony(V) from concentrated hydrochloric or hydrobromic acid is being examined. Bismuth Bismuth can be extracted from l-6N sulphuric acid with a freshly diluted or stabilized22 IN solution of pyroalkylphosphoric acid in a saturated hydrocarbon. The organic phase is scrubbed with I-2N sulphuric acid to free it from feebly extracted species such as zinc and cadmium etc. Bismuth is stripped with a hydrohalic acid, oxalic acid, halide, or ammonium oxalate solution, the best choice being potassium iodide solution, as the bismuth can then be determined calorimetrically in the aqueous phase. Zumumnenf&ssnng-Die Venvendung von Alkylphosphorsluren extraktiven Tremnmgen wird beschrieben und der Gebrauch synergischer Agentien zur Rilckextraktion diskutiert.
zu anti-
RCsnm&Gn d&r-it l’emploi d’acides alkylphosphoriques pour les separations par extraction par solvant et disc&e de l’emploi d’agents antisynergiques pour les r&extractions.
808
I. S. LEvIN et al. REFERENCES
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