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The extraction of vanadium(IV) from hydrochloric acid solutions by long-chain alkyl amine and alkyl ammonium compound
J. inorg nucl. Chem.. 1977. Vol 39, pp. 395 399. Pergamon Press. printed in Great Britain
THE EXTRACTION OF VANADIUM(IV) FROM HYDROCHLORIC ACID SOLUTIONS BY LONG-CHAIN ALKYL AMINE AND ALKYL AMMONIUM COMPOUND TAICHI SATO, SHUJI IKOMA and TAKATO NAKAMURA Department of Applied Chemistry, Faculty of Engineering,Shizuoka University, Hamamatsu, Japan (First received 16 September 1975; in revised form 7 May 1976) Abstract--The distribution of vanadium(IV) between hydrochloric acid solutions and organic solutions of
tri-n-octylamine or tricaprylmethylammonium chloride has been investigated under different conditions. Both phases have been examined by spectrophometry, and the IR spectral measurement and the measurements of the apparent molecular weight and magnetic moment have been carried out for the organic extracts. The mechanism of the extractions is discussed and structures proposed for the complexes formed. and a Model IR-F, a grating model for measurement between 700 and 200 cm 1, using a capillary filmbetween thallium halide plates. Measurement of apparent molecular weight and magnetic moment. For the complexes prepared from the organic solutions saturated with vanadium, the apparent molecular weights were determined in benzene on a Hitachi Model 115 isothermal molecular weight apparatus and the magnetic moments were measured by the Gouy method[9].
INTRODUCTION
High molecular weight amines have been used in the solvent extraction of vanadium(IV) from sulphuric acid solutions[l], but observations on the mechanism of extraction are few. Following earlier work on vanadium(IV) [2, 3] and the extraction of uranium(V1) and zirconium(IV) from hydrochloric acid solutions by long-chain alkylamine and alkyl ammonium chloride [4-7], we now report on the extraction of vanadium(IV) from hydrochloric acid solutions.
EXPERIMENTAL
Reagents. Tri-n-octylamine (Kao soap Co. Ltd., TOA, R3N), used without purification and tricaprylmethylammonium chloride (General Mills, Aliquat-336,R~R'NCI), purified by washing several times with aqueous sodium chloride solution and n-hexane[7], were diluted with benzene or cyclohexane and were not pre-equilibrated with hydrochloric acid solutions. Vanadium(IV) solutions were prepared by dissolution of vanadyl chloride in hydrochloric acid solutions of selected concentrations. Other chemicals were of analytical reagent grade. Extraction and analytical procedures. Equal volumes (15 ml) of the phases were shaken for 10min in 50 ml stoppered conical flasks in a thermostated water bath. (Preliminary experiments showed that equilibration is complete in 10 rain.) The mixture was centrifuged and separated and the phases were analysed to give the distribution coefficient. Vanadium was stripped from the organic phase with l M nitric acid for analysis and determined by back-titration as described elsewhere [3, 8]. Analyses of complexes. On the basis of the distribution results, the organic solutions saturated with vanadium were prepared as follows: 0.05 M TOA or 0.082 M Aliquat-336 in benzene was shaken for l0 min with 0.1 M aqueous solution of vanadyl chloride 0.06 M hydrochloric acid containing 9.8 M lithium chloride at 20°C. The organic phase, separated by centrifugation, was again equilibrated with a fresh aqueous solution; this procedure was repeated twelve times. The organic solutions were heated in vacuo at 60°C to remove benzene. The residues were examined by IR spectroscopy, dissolved in benzene and the solution washed with 1 M nitric acid. Vanadium in the acid layer was determined by the EDTA titration described above and chloride by Volhard's method with nitrobenzene. Spectrophotometry and IR spectral measurement. The absorption spectra were obtained on a Shimazu Model QV-50 spectrophotometer, using matched 1.00cm fused silica cells. The IR spectra of the samples prepared by evaporation of the organic diluent were determined on a Japan Spectroscopic Co. Ltd. Model IR-S, equipped with potassium chloride prisms (4000-550cm J) 395
RESULTS AND DISCUSSION Extraction isotherms The results for the extractions of vanadyl chloride (0.0072M) with benzene solutions of 0.1 M TOA and 0.082M Aliquat-336 from aqueous hydrochloric acid solutions at 20°C are illustrated in Figs. 1 and 2 and compared with those from a mixture of 0.1 M hydrochloric acid and lithium chloride at different concentrations. The distribution coefficients in the presence of hydrochloric acid pass through maxima at 5 and 6 M initial aqueous acidities with TOA and Aliquat-336, respectively, but in the mixture of hydrochloric acid and lithium chloride the distribution coefficient rises continuously with the total chloride concentration. This result indicates that the controlling factor is the total chloride ion concentration, but that hydrochloric acid competes for association with TOA and Aliquat-336. For the extraction of metal ions from aqueous halide media, however, high-molecular weight quaternary ammonium halides are generally more efficient than the corresponding secondary and tertiary amines. From Figs. 1 and 2 it is also seen that the extraction efficiency of the quaternary compound for vanadium is larger than that of TOA. This arises from ion association to produce neutral species by the chargeneutralization of anionic metal complexes, causing an increase in the extraction relative to long-chain alkyl amines, governed by a solvating reaction. In the extractions with TOA and Aliquat-336, log-log plots of D vs (CA-Cv), where D is the distribution coefficient, CA the total concentration of TOA or Aliquat-336 and Cv the vanadium concentration of the organic phase, at aqueous acidities (1-6 M), give straight lines with slopes of nearly unity, indicating that each vanadium ion is associated with one molecule of extractant. It is thus inferred that the extractions of vanadium(IV) with TOA and Aliquat-336, dominated by solvating and ion-exchange reactions respectively[4,5],
396
TAICHI SATO et al.
~d
concentration and the TOA or Aliquat-336 concentration at a fixed total concentration of 0.24M reveals a maximum at the molar ratio [V] initial aq/[TOA] or [Aliquat-336] = 1. However, the organic solutions saturated with vanadium gave vanadium/chiorine/TOA or Aliquat-336 molar ratios of 1:2:1. In addition, their IR spectra exhibit absorption due to the OH stretching and bending modes. Since Rossotti[10] has reported K = 1 0 -6° for the hydrolysis reaction VO 2++ H20 ~ VOOH ÷ + H ÷, it is thought that in the initial aqueous solution the vanadyl ion is not hydrolyzed under the experimental condition. We deduce that the species extracted according to eqns (1) and (2) are hydrolyzed to form the complexes of stoichiometry R3NHVO(OH)CI2 and R3R'NVO(OH)CI~.
~zx'
o
A"
fl
.r-
y
o.ol
/
I
IO
Iniliol oqueous totol chloride concn, M
Fig. 1. Extraction of vanadium(IV) from hydrochloric acid solutions with 0.1 M TOA in benzene (A in the presence of 0.1 M hydrochloric acid and lithium chloride, © in the presence of hydrochloricacid only).
5
01
g
a
ool
I
i I '''i
,
L
i
L , ,,,llo
Initial aqueous total chloride concn., M
Fig. 2. Extraction of vanadium(IV) from hydrochloric acid solutions with 0.082 M quaternary compoundin benzene (A in the presence of 0.1 M hydrochloricacid and lithiumchloride,O in the presence of hydrochloricacid only). are expressed by eqns (1) and (2), VOCI2(a) + R3NHCI(o) ~ R3NHVOC13(o)
(1)
and VOCl3-(a) + R3R'NCI(o) ~=~R3R'NVOC13(o)+ Cl-(a),
(2) in which (a) and (o) represent the aqueous and organic phases, respectively. These are also supported by the results of the continuous variation method: for the extraction from aqueous solutions containing 0.2M hydrochloric acid and 9.5 M lithium chloride, the variation of the vanadium concentration in the organic phase plotted as a function of initial aqueous vanadium
Temperature effect The extraction of vanadyl chloride (0.0072 M) from 3 and 6 M hydrochloric acid or 0.1 M hydrochloric acid in the presence of 9 M lithium chloride with 0.1 M TOA or 0.082 M Aliquat-336 in benzene at temperatures between 10 and 50°C gave the results shown in Table 1. The heats of reaction (chances in enthalpy, kcal/mol) for eqns (1) and (2) were estimated to be respectively, -0.78, -0.84 and -1.5 in 3M HC1, 6M HC1 and 0.1M HCI+9M LiCI with TOA, and 2.7, 0.59 and 1.2, respectively, in 3 M HC1, 6 M HC1 and 0.1 M HCI+9 M LiCI with Aliquat-336. These values are close to that for the energy of hydrogen bond[11]. Electronic acid IR spectra For the spectra of the aqueous solution of vanadyl chloride (0.0072 M) in hydrochloric acid only (Fig. 3), the following results were observed: at low acidities, the characteristic absorption due to aquo ion [VO(H20)5]~+ [12, 13] appears as a band center ca. 770 m/z which accompanies a shoulder at 625 m/z; with increasing acidity the latter disappears and the absorption at 770m/z; shifts toward shorter wavelength on formation of the species such as VOCI÷, VOC12 and VOC13-; the band at 1080m/z appears above 8M hydrochloric acid and in 10 M acid the spectrum shows the absorption due to the formation of the species VOCL2-[14]; a band at 400 m/z, probably results from the formation of trivalent vanadium. At higher acidities the absorption ascribed to the presence of a brown intermediate species which has an oxo bridge, VOV'+[15], appears at 445 m/z. This also corresponds to the result for the UV spectra: the characteristic charge transfer band due to tetravalent vanadium ion which appears as a shoulder at 240 m/z shifts toward shorter wavelength with increasing concentration of hydrochloric acid. Similar results are observed in the aqueous vanadyl chloride solutions containing hydrochloric acid and lithium chloride. The spectra of the organic phases extracted with TOA and Aliquat-336 from vanadyl chloride solutions containing 0.064).1M hydrochloric acid and 9.8M lithium chloride show absorptions due to the 5-coordinated species of tetravalent vanadium. As a representative spectrum, the result for the extraction with Aliquat-336 is given in Fig. 4. In contrast, the organic phases extracted from aqueous vanadyl chloride solutions (0.0072 M) in 7 M hydrochloric acid at below 7 M exhibit absorptions due to charge-transfer at about 280 m/z and 370--380m/z, although the absorption bands corresponding to the aquo ion [VO(H:O)5]2÷ are not observed at 625 and 770 m/z. In
The extraction of vanadium(IV) from hydrochloric acid solutions
397
Table 1. Temperature dependence of distribution coefficientonthe extraction of vanadium(IV) from hydrochloric acid solutions with 0.1 M TOA and 0.082 M quaternary compound in benzene
Temperature,
Distribution coefficient
E: troctani 3M HCl
*C
R~N
I
6M HCl
O.IM HCI+9M LiCI
I0
00346
00516
0.166
20
0.0335
OO485
0.150
30
00310
00461
0.139
40
0.128
50
0 120
I0
0 0662
0.133
0 439
20
0 0829
0 139
0.462
;~3R'NCI
30
0.0988
0142
0487
40
0 II I
0 144
0531
50
0.128
0148
0577
~
02
•i-
co
~o~
05 04
03
£
02 °
)
©
500 400
500
GO0 700 800 900 Wavelength, m,u.
I000 I100 1200
Fig. 3. Absorption spectra of aqueous vanadyl chloride solutions in 0.0072 M containing hydrochloric acid at different concentrations (numerals on curves are initial aqueous hydrochloric acid concentrations, M; absorbance on the left represents the solutions in below 6 M acid and on the right in above 6 M acid; thickness of cell, 1.00 cm).
O6
05 !ii
IO
u~04-, 0:3
\'~
02 0
~ '\ ~
300
O~(sa~uratecl)
400
h
500
,, ,
, ,
,
,.
600 700 800 900 Wavelength, rnff
1000 I I O0 t 200
Fig. 4. Absorption spectra of the organic solutions from the extraction of vanadyl chloride solutions containing 0.1 M hydrochloric acid and 9.8 M lithium chloride with 0.082 M quaternary compound in benzene or cyclohexane (numerals on curves are initial aqueous vanadyl chloride concentrations, M; continuous (or broken) and chain lines denote the extractions with quaternary compound in benzene and cyclohexane, respectively; absorbance on the left represents the organic solutions from the extraction with quaternary compound in benzene or cyclohexane and on the right the organic solution saturated with vanadium; dilution x 1 and x 2 in continuous (or chain) and broken lines, respectively; thickness of cell, 1.00cm). JINC I,'()L ~9 NO 3--B
398
TAICHI SATO et aL
these extractions, the colours of the organic phases ranged from yellow to pale yellowish-green, with a change to reddish--orange or red-brown as the aqueous acidity increased. The spectra of the organic phases from extraction from aqueoous solutions > 8 M acid show an absorption band at about 480 m/z. It is thus presumed that the intermediate species, VOW ÷, is also formed in the organic phases on extraction at high aqueous acidities. In order to clarify these spectral results, the complexes prepared from the organic solutions saturated with vanadium were examined spectrophotometrically in benzene or cyclohexane. The results are shown in Table 2. If we assume that the extracted species is in a point group C4~ symmetry, the absorption bands at 810 and 940 m/z (12300 and 10600cm -~) for the complex with TOA or at 820 and 965 m/z (12200 and 10400 cm-~) for the complex with Aliquat-336, which appear in addition to the charge-transfer bands, are assigned to the transitions
2B2~2B~ and 2B2--*2E(I), respectively[12]. Since the values of 10 Dq, indicating the transition from the ground state 2Bz to the state 2B~, for the complexes are similar, it appears that the strength of the ligand field is almost the same in the both complexes. The IR spectra of the organic extractions from the aqueous solutions at different vanadyl chloride concentrations containing hydrochloric acid and lithium chloride with 0.1 M TOA or 0.082 M Aliquat-336 in benzene at 20°C were compared with those from the extraction of hydrochloric acid solution alone. The spectra of the complexes prepared by drying the organic phases saturated with vanadium were examined and their frequencies and probably band assignments are given in Table 3. From these it is seen that the spectra of the benzene-free complexes resemble those in the benzene solution with minor differences in the band frequencies and intensities. Since the splitting in the V=O stretching
Table 2. Electronicspectra of vanadylcomplexeswith TOA and quaternarycompound
Xmox, mH.
~, cm -t
Probable
R3R'NVO(OH)C12
R~NH VO(OH)Cl2 E
~mox, m ~ :
~, cm "1
285
35100:
assignment I000
~B2 "-"2E(II)
280
35700
375
26700
I00
378
26500
I O0
2B2 --, 2A,
810
12300
46
820
12200
22
ZB2 -.> 2Bl
965
10600
53
962
10400
28
2Bz 4 2 E ( I )
1000
molar extinction coefficient Table 3. IR spectral data for the complexesformed in the extraction of vanadyl chloride solutionswith TOA and quaternary compoundin benzene
Frequency, cm-' R3NHCI.H20 5360(wb)
(R3NH)VO(OH)CI2 3400(wb)
R3R'NCI'SH20 5400(msb)
(R3R'N)VO(OH)CI2 5400(wb)
2940(s)
2940(s)
2920(s)
2920(s)
2880(ms)
2880(ms)
2860 (ms)
2860(ms)
1755(vw)
NH* stretching OH bending OH bending
1625(vw)
t625(vw)
1620(w)
t 6 2 0 (vw)
1465(m)
1465(m)
1465(m)
1465(m)
I 380(w)
1375(w)
1380(w)
4:30(s)
CH3 degenerate bending CH2 scissoring CH3 sym bending
996(wsh)
1005(m)
7 I 5(w)
CH stretching (sym e asym.)
17 t O(vw)
2350 (w)
970(ms) 954 (ms) 9:35 (ms) 715(w)
OH stretching NH÷ stretching
3000(rob)
1:380(w)
Probable assignment
968 (ms) 955(ms) 725(w)
725(w) 430(s)
s=strong, ms.medium strong, m.medium, w=weak, vw.very weok sh - shoulder, b. brood
'V-O stretching
CH2 rocking V-CI stretching
The extraction of vanadium(IV) from hydrochloric acid solutions band for the complex with TOA in more than that for the complex with Aliquat-336 (Table 3), it is thought that in the former the symmetry is lower than the latter. Structure o f complexes When the data for the apparent molecular weights of the vanadyl complexes with TOA and Aliquat-336 are compared with the theoretical values of the molecular weights for monomeric species, it is considered that the complexes exist as dimers, in agreement with the fact that the observed values of the magnetic moments for the complexes, 0.64 and 0.58 B.M. respectively, are smaller than the spin-only value for vanadium(IV), t/Left= 1.73 B.M.[22]. Hence the following structures, [I] and [II], are proposed for the species extracted with TOA and quaternary compound, respectively: O
c~--II-- o
//
V
R~NHC1
H
CIHNR~
/ v j
OH
',', CI O
IIt
r lUl These are also supported by electron spin resonance spectral results [23]. Acknowledgements--We thank Mr. O. Terao for assistance with part of the experimental work and also thank the Kao Soap Co. Ltd. for a sample of TOA. REFERENCES
1. e.g., C. F. Colman, K. B. Brown, J. G. Moore and K. A. Allen, Proceedings of the Second international Conference on the
399
Peaceful Uses of Atomic Energy, Geneva, 1958. Vol. 28, p. 278. United Nations (1958). 2. T. Sato and Y. TAkeda, J. Inorg. Nucl. Chem. 32, 3387 (t970). 3. T. Sato, S. Kotani and O. Terao, Proceedings o/International Solvene Extraction Conference, Lyon, 1974, Vol. 3, p. 2249. Soc. Chem. Ind. (1974). 4. T. Sato, J. Appl. Chem. 16, 143 (1966). 5. T. Sato, J. 1norg. Nucl. Chem. 34, 3835 (1972). 6. T. Sato and H. Watanabe, Anal. Chim. Acta 54, 439 (1971). 7. T. Sato and H. Watanabe. Anal. Chim. Acta 49, 463 (1970). 8. J. Kinnumen and B. Wennerstrand, Chemist-Anal~'st 46, 92 (1957). 9. T. F. Gray, Chemistry of the Solid State, (Edited by W. E. Garner), p. 147. Butterworths, London (1955). 10. F. J. C. Rossotti and H. S. Rossotti, Acta Chim. Scand. 9, 117'7 (1955). 11. e.g., G. C. Pimental and A. L. McClellan, The Hydrogen Bond, pp. 350-363. Freeman, San Francisco (1960). 12. C.J. Ballhausen and H. B. Gray, lnorg. Chem. l, 111 (1962). 13. I. Bernal and D. H. Rieger, lnorg. Chem. 2, 256 (1963); J. C. Evans, ibid. 2,372 (1963); C. J. J~rgensen, Absorption Spectra and Chemical Bonding in Complexes, p. 271. Pergamon Press, Oxford (1962). 14. P. A. Kiltz and D. Nicholls, J. Chem. Soc. (A), 1175 (19661. 15. T. W. Newton and F. B. Baker, lnorg. Chem. 3,569 (1%4); J. H. Espenson, ibid. 4, 1533 (1965). 16. e.g., R. C. Lord and R. E. Merrifield, J. Chem. Phys. 21, 166 (1953); J. R. O. Barcelo and J. Bellanato, Spectrochim. Acta 8, 27 (1956); E. A V. Ebsworth and N. Sheppard, ibid. 13. 261 (1959); J. Bellanato, ibid. 16, 1344 (I%0L 17. L. J. Bellamy, Infra-red Spectra of Complex Molecules, 2nd Edn, p. 260. Wiley, New York (1958). 18. T. Sato, Z Appl. Chem. 15, 10 (1965). 19. J. Belbin, L. H. Holmes, Jr. and S. P. McGlynn, Z lnorg. Nucl. Chem. 25, 1359 (1963); D. N. Sathyanarayana and C, (L Patel, ibid. 30, 207 (1968). 20. J. B. White and J. Selbin, ,L lnorg. Nucl. Chem. 32, 2434 ( 1970/. 21. K. Nakamoto, Infrared Spectra o.f lnorganic and Coordination Compounds, 2nd Edn, p. 214. Wiley, New York (1970). 22. e.g., R. J. H. Clark, J. Chem. Soc. 1377 (1963); F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 2nd Edn, p. 637. Interscience, New York (1966); B. N. Figgs, Introduction to Ligand Fields, p. 258. lnterscience, New York (1%6). 23. T. Sato, T. Nakamura and O. Terao, J. lnorg. Nucl. Chem. 39, 401 (1977).
THE EXTRACTION OF VANADIUM(IV) FROM HYDROCHLORIC ACID SOLUTIONS BY LONG-CHAIN ALKYL AMINE AND ALKYL AMMONIUM COMPOUND TAICHI SATO, SHUJI IKOMA and TAKATO NAKAMURA Department of Applied Chemistry, Faculty of Engineering,Shizuoka University, Hamamatsu, Japan (First received 16 September 1975; in revised form 7 May 1976) Abstract--The distribution of vanadium(IV) between hydrochloric acid solutions and organic solutions of
tri-n-octylamine or tricaprylmethylammonium chloride has been investigated under different conditions. Both phases have been examined by spectrophometry, and the IR spectral measurement and the measurements of the apparent molecular weight and magnetic moment have been carried out for the organic extracts. The mechanism of the extractions is discussed and structures proposed for the complexes formed. and a Model IR-F, a grating model for measurement between 700 and 200 cm 1, using a capillary filmbetween thallium halide plates. Measurement of apparent molecular weight and magnetic moment. For the complexes prepared from the organic solutions saturated with vanadium, the apparent molecular weights were determined in benzene on a Hitachi Model 115 isothermal molecular weight apparatus and the magnetic moments were measured by the Gouy method[9].
INTRODUCTION
High molecular weight amines have been used in the solvent extraction of vanadium(IV) from sulphuric acid solutions[l], but observations on the mechanism of extraction are few. Following earlier work on vanadium(IV) [2, 3] and the extraction of uranium(V1) and zirconium(IV) from hydrochloric acid solutions by long-chain alkylamine and alkyl ammonium chloride [4-7], we now report on the extraction of vanadium(IV) from hydrochloric acid solutions.
EXPERIMENTAL
Reagents. Tri-n-octylamine (Kao soap Co. Ltd., TOA, R3N), used without purification and tricaprylmethylammonium chloride (General Mills, Aliquat-336,R~R'NCI), purified by washing several times with aqueous sodium chloride solution and n-hexane[7], were diluted with benzene or cyclohexane and were not pre-equilibrated with hydrochloric acid solutions. Vanadium(IV) solutions were prepared by dissolution of vanadyl chloride in hydrochloric acid solutions of selected concentrations. Other chemicals were of analytical reagent grade. Extraction and analytical procedures. Equal volumes (15 ml) of the phases were shaken for 10min in 50 ml stoppered conical flasks in a thermostated water bath. (Preliminary experiments showed that equilibration is complete in 10 rain.) The mixture was centrifuged and separated and the phases were analysed to give the distribution coefficient. Vanadium was stripped from the organic phase with l M nitric acid for analysis and determined by back-titration as described elsewhere [3, 8]. Analyses of complexes. On the basis of the distribution results, the organic solutions saturated with vanadium were prepared as follows: 0.05 M TOA or 0.082 M Aliquat-336 in benzene was shaken for l0 min with 0.1 M aqueous solution of vanadyl chloride 0.06 M hydrochloric acid containing 9.8 M lithium chloride at 20°C. The organic phase, separated by centrifugation, was again equilibrated with a fresh aqueous solution; this procedure was repeated twelve times. The organic solutions were heated in vacuo at 60°C to remove benzene. The residues were examined by IR spectroscopy, dissolved in benzene and the solution washed with 1 M nitric acid. Vanadium in the acid layer was determined by the EDTA titration described above and chloride by Volhard's method with nitrobenzene. Spectrophotometry and IR spectral measurement. The absorption spectra were obtained on a Shimazu Model QV-50 spectrophotometer, using matched 1.00cm fused silica cells. The IR spectra of the samples prepared by evaporation of the organic diluent were determined on a Japan Spectroscopic Co. Ltd. Model IR-S, equipped with potassium chloride prisms (4000-550cm J) 395
RESULTS AND DISCUSSION Extraction isotherms The results for the extractions of vanadyl chloride (0.0072M) with benzene solutions of 0.1 M TOA and 0.082M Aliquat-336 from aqueous hydrochloric acid solutions at 20°C are illustrated in Figs. 1 and 2 and compared with those from a mixture of 0.1 M hydrochloric acid and lithium chloride at different concentrations. The distribution coefficients in the presence of hydrochloric acid pass through maxima at 5 and 6 M initial aqueous acidities with TOA and Aliquat-336, respectively, but in the mixture of hydrochloric acid and lithium chloride the distribution coefficient rises continuously with the total chloride concentration. This result indicates that the controlling factor is the total chloride ion concentration, but that hydrochloric acid competes for association with TOA and Aliquat-336. For the extraction of metal ions from aqueous halide media, however, high-molecular weight quaternary ammonium halides are generally more efficient than the corresponding secondary and tertiary amines. From Figs. 1 and 2 it is also seen that the extraction efficiency of the quaternary compound for vanadium is larger than that of TOA. This arises from ion association to produce neutral species by the chargeneutralization of anionic metal complexes, causing an increase in the extraction relative to long-chain alkyl amines, governed by a solvating reaction. In the extractions with TOA and Aliquat-336, log-log plots of D vs (CA-Cv), where D is the distribution coefficient, CA the total concentration of TOA or Aliquat-336 and Cv the vanadium concentration of the organic phase, at aqueous acidities (1-6 M), give straight lines with slopes of nearly unity, indicating that each vanadium ion is associated with one molecule of extractant. It is thus inferred that the extractions of vanadium(IV) with TOA and Aliquat-336, dominated by solvating and ion-exchange reactions respectively[4,5],
396
TAICHI SATO et al.
~d
concentration and the TOA or Aliquat-336 concentration at a fixed total concentration of 0.24M reveals a maximum at the molar ratio [V] initial aq/[TOA] or [Aliquat-336] = 1. However, the organic solutions saturated with vanadium gave vanadium/chiorine/TOA or Aliquat-336 molar ratios of 1:2:1. In addition, their IR spectra exhibit absorption due to the OH stretching and bending modes. Since Rossotti[10] has reported K = 1 0 -6° for the hydrolysis reaction VO 2++ H20 ~ VOOH ÷ + H ÷, it is thought that in the initial aqueous solution the vanadyl ion is not hydrolyzed under the experimental condition. We deduce that the species extracted according to eqns (1) and (2) are hydrolyzed to form the complexes of stoichiometry R3NHVO(OH)CI2 and R3R'NVO(OH)CI~.
~zx'
o
A"
fl
.r-
y
o.ol
/
I
IO
Iniliol oqueous totol chloride concn, M
Fig. 1. Extraction of vanadium(IV) from hydrochloric acid solutions with 0.1 M TOA in benzene (A in the presence of 0.1 M hydrochloric acid and lithium chloride, © in the presence of hydrochloricacid only).
5
01
g
a
ool
I
i I '''i
,
L
i
L , ,,,llo
Initial aqueous total chloride concn., M
Fig. 2. Extraction of vanadium(IV) from hydrochloric acid solutions with 0.082 M quaternary compoundin benzene (A in the presence of 0.1 M hydrochloricacid and lithiumchloride,O in the presence of hydrochloricacid only). are expressed by eqns (1) and (2), VOCI2(a) + R3NHCI(o) ~ R3NHVOC13(o)
(1)
and VOCl3-(a) + R3R'NCI(o) ~=~R3R'NVOC13(o)+ Cl-(a),
(2) in which (a) and (o) represent the aqueous and organic phases, respectively. These are also supported by the results of the continuous variation method: for the extraction from aqueous solutions containing 0.2M hydrochloric acid and 9.5 M lithium chloride, the variation of the vanadium concentration in the organic phase plotted as a function of initial aqueous vanadium
Temperature effect The extraction of vanadyl chloride (0.0072 M) from 3 and 6 M hydrochloric acid or 0.1 M hydrochloric acid in the presence of 9 M lithium chloride with 0.1 M TOA or 0.082 M Aliquat-336 in benzene at temperatures between 10 and 50°C gave the results shown in Table 1. The heats of reaction (chances in enthalpy, kcal/mol) for eqns (1) and (2) were estimated to be respectively, -0.78, -0.84 and -1.5 in 3M HC1, 6M HC1 and 0.1M HCI+9M LiCI with TOA, and 2.7, 0.59 and 1.2, respectively, in 3 M HC1, 6 M HC1 and 0.1 M HCI+9 M LiCI with Aliquat-336. These values are close to that for the energy of hydrogen bond[11]. Electronic acid IR spectra For the spectra of the aqueous solution of vanadyl chloride (0.0072 M) in hydrochloric acid only (Fig. 3), the following results were observed: at low acidities, the characteristic absorption due to aquo ion [VO(H20)5]~+ [12, 13] appears as a band center ca. 770 m/z which accompanies a shoulder at 625 m/z; with increasing acidity the latter disappears and the absorption at 770m/z; shifts toward shorter wavelength on formation of the species such as VOCI÷, VOC12 and VOC13-; the band at 1080m/z appears above 8M hydrochloric acid and in 10 M acid the spectrum shows the absorption due to the formation of the species VOCL2-[14]; a band at 400 m/z, probably results from the formation of trivalent vanadium. At higher acidities the absorption ascribed to the presence of a brown intermediate species which has an oxo bridge, VOV'+[15], appears at 445 m/z. This also corresponds to the result for the UV spectra: the characteristic charge transfer band due to tetravalent vanadium ion which appears as a shoulder at 240 m/z shifts toward shorter wavelength with increasing concentration of hydrochloric acid. Similar results are observed in the aqueous vanadyl chloride solutions containing hydrochloric acid and lithium chloride. The spectra of the organic phases extracted with TOA and Aliquat-336 from vanadyl chloride solutions containing 0.064).1M hydrochloric acid and 9.8M lithium chloride show absorptions due to the 5-coordinated species of tetravalent vanadium. As a representative spectrum, the result for the extraction with Aliquat-336 is given in Fig. 4. In contrast, the organic phases extracted from aqueous vanadyl chloride solutions (0.0072 M) in 7 M hydrochloric acid at below 7 M exhibit absorptions due to charge-transfer at about 280 m/z and 370--380m/z, although the absorption bands corresponding to the aquo ion [VO(H:O)5]2÷ are not observed at 625 and 770 m/z. In
The extraction of vanadium(IV) from hydrochloric acid solutions
397
Table 1. Temperature dependence of distribution coefficientonthe extraction of vanadium(IV) from hydrochloric acid solutions with 0.1 M TOA and 0.082 M quaternary compound in benzene
Temperature,
Distribution coefficient
E: troctani 3M HCl
*C
R~N
I
6M HCl
O.IM HCI+9M LiCI
I0
00346
00516
0.166
20
0.0335
OO485
0.150
30
00310
00461
0.139
40
0.128
50
0 120
I0
0 0662
0.133
0 439
20
0 0829
0 139
0.462
;~3R'NCI
30
0.0988
0142
0487
40
0 II I
0 144
0531
50
0.128
0148
0577
~
02
•i-
co
~o~
05 04
03
£
02 °
)
©
500 400
500
GO0 700 800 900 Wavelength, m,u.
I000 I100 1200
Fig. 3. Absorption spectra of aqueous vanadyl chloride solutions in 0.0072 M containing hydrochloric acid at different concentrations (numerals on curves are initial aqueous hydrochloric acid concentrations, M; absorbance on the left represents the solutions in below 6 M acid and on the right in above 6 M acid; thickness of cell, 1.00 cm).
O6
05 !ii
IO
u~04-, 0:3
\'~
02 0
~ '\ ~
300
O~(sa~uratecl)
400
h
500
,, ,
, ,
,
,.
600 700 800 900 Wavelength, rnff
1000 I I O0 t 200
Fig. 4. Absorption spectra of the organic solutions from the extraction of vanadyl chloride solutions containing 0.1 M hydrochloric acid and 9.8 M lithium chloride with 0.082 M quaternary compound in benzene or cyclohexane (numerals on curves are initial aqueous vanadyl chloride concentrations, M; continuous (or broken) and chain lines denote the extractions with quaternary compound in benzene and cyclohexane, respectively; absorbance on the left represents the organic solutions from the extraction with quaternary compound in benzene or cyclohexane and on the right the organic solution saturated with vanadium; dilution x 1 and x 2 in continuous (or chain) and broken lines, respectively; thickness of cell, 1.00cm). JINC I,'()L ~9 NO 3--B
398
TAICHI SATO et aL
these extractions, the colours of the organic phases ranged from yellow to pale yellowish-green, with a change to reddish--orange or red-brown as the aqueous acidity increased. The spectra of the organic phases from extraction from aqueoous solutions > 8 M acid show an absorption band at about 480 m/z. It is thus presumed that the intermediate species, VOW ÷, is also formed in the organic phases on extraction at high aqueous acidities. In order to clarify these spectral results, the complexes prepared from the organic solutions saturated with vanadium were examined spectrophotometrically in benzene or cyclohexane. The results are shown in Table 2. If we assume that the extracted species is in a point group C4~ symmetry, the absorption bands at 810 and 940 m/z (12300 and 10600cm -~) for the complex with TOA or at 820 and 965 m/z (12200 and 10400 cm-~) for the complex with Aliquat-336, which appear in addition to the charge-transfer bands, are assigned to the transitions
2B2~2B~ and 2B2--*2E(I), respectively[12]. Since the values of 10 Dq, indicating the transition from the ground state 2Bz to the state 2B~, for the complexes are similar, it appears that the strength of the ligand field is almost the same in the both complexes. The IR spectra of the organic extractions from the aqueous solutions at different vanadyl chloride concentrations containing hydrochloric acid and lithium chloride with 0.1 M TOA or 0.082 M Aliquat-336 in benzene at 20°C were compared with those from the extraction of hydrochloric acid solution alone. The spectra of the complexes prepared by drying the organic phases saturated with vanadium were examined and their frequencies and probably band assignments are given in Table 3. From these it is seen that the spectra of the benzene-free complexes resemble those in the benzene solution with minor differences in the band frequencies and intensities. Since the splitting in the V=O stretching
Table 2. Electronicspectra of vanadylcomplexeswith TOA and quaternarycompound
Xmox, mH.
~, cm -t
Probable
R3R'NVO(OH)C12
R~NH VO(OH)Cl2 E
~mox, m ~ :
~, cm "1
285
35100:
assignment I000
~B2 "-"2E(II)
280
35700
375
26700
I00
378
26500
I O0
2B2 --, 2A,
810
12300
46
820
12200
22
ZB2 -.> 2Bl
965
10600
53
962
10400
28
2Bz 4 2 E ( I )
1000
molar extinction coefficient Table 3. IR spectral data for the complexesformed in the extraction of vanadyl chloride solutionswith TOA and quaternary compoundin benzene
Frequency, cm-' R3NHCI.H20 5360(wb)
(R3NH)VO(OH)CI2 3400(wb)
R3R'NCI'SH20 5400(msb)
(R3R'N)VO(OH)CI2 5400(wb)
2940(s)
2940(s)
2920(s)
2920(s)
2880(ms)
2880(ms)
2860 (ms)
2860(ms)
1755(vw)
NH* stretching OH bending OH bending
1625(vw)
t625(vw)
1620(w)
t 6 2 0 (vw)
1465(m)
1465(m)
1465(m)
1465(m)
I 380(w)
1375(w)
1380(w)
4:30(s)
CH3 degenerate bending CH2 scissoring CH3 sym bending
996(wsh)
1005(m)
7 I 5(w)
CH stretching (sym e asym.)
17 t O(vw)
2350 (w)
970(ms) 954 (ms) 9:35 (ms) 715(w)
OH stretching NH÷ stretching
3000(rob)
1:380(w)
Probable assignment
968 (ms) 955(ms) 725(w)
725(w) 430(s)
s=strong, ms.medium strong, m.medium, w=weak, vw.very weok sh - shoulder, b. brood
'V-O stretching
CH2 rocking V-CI stretching
The extraction of vanadium(IV) from hydrochloric acid solutions band for the complex with TOA in more than that for the complex with Aliquat-336 (Table 3), it is thought that in the former the symmetry is lower than the latter. Structure o f complexes When the data for the apparent molecular weights of the vanadyl complexes with TOA and Aliquat-336 are compared with the theoretical values of the molecular weights for monomeric species, it is considered that the complexes exist as dimers, in agreement with the fact that the observed values of the magnetic moments for the complexes, 0.64 and 0.58 B.M. respectively, are smaller than the spin-only value for vanadium(IV), t/Left= 1.73 B.M.[22]. Hence the following structures, [I] and [II], are proposed for the species extracted with TOA and quaternary compound, respectively: O
c~--II-- o
//
V
R~NHC1
H
CIHNR~
/ v j
OH
',', CI O
IIt
r lUl These are also supported by electron spin resonance spectral results [23]. Acknowledgements--We thank Mr. O. Terao for assistance with part of the experimental work and also thank the Kao Soap Co. Ltd. for a sample of TOA. REFERENCES
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399
Peaceful Uses of Atomic Energy, Geneva, 1958. Vol. 28, p. 278. United Nations (1958). 2. T. Sato and Y. TAkeda, J. Inorg. Nucl. Chem. 32, 3387 (t970). 3. T. Sato, S. Kotani and O. Terao, Proceedings o/International Solvene Extraction Conference, Lyon, 1974, Vol. 3, p. 2249. Soc. Chem. Ind. (1974). 4. T. Sato, J. Appl. Chem. 16, 143 (1966). 5. T. Sato, J. 1norg. Nucl. Chem. 34, 3835 (1972). 6. T. Sato and H. Watanabe, Anal. Chim. Acta 54, 439 (1971). 7. T. Sato and H. Watanabe. Anal. Chim. Acta 49, 463 (1970). 8. J. Kinnumen and B. Wennerstrand, Chemist-Anal~'st 46, 92 (1957). 9. T. F. Gray, Chemistry of the Solid State, (Edited by W. E. Garner), p. 147. Butterworths, London (1955). 10. F. J. C. Rossotti and H. S. Rossotti, Acta Chim. Scand. 9, 117'7 (1955). 11. e.g., G. C. Pimental and A. L. McClellan, The Hydrogen Bond, pp. 350-363. Freeman, San Francisco (1960). 12. C.J. Ballhausen and H. B. Gray, lnorg. Chem. l, 111 (1962). 13. I. Bernal and D. H. Rieger, lnorg. Chem. 2, 256 (1963); J. C. Evans, ibid. 2,372 (1963); C. J. J~rgensen, Absorption Spectra and Chemical Bonding in Complexes, p. 271. Pergamon Press, Oxford (1962). 14. P. A. Kiltz and D. Nicholls, J. Chem. Soc. (A), 1175 (19661. 15. T. W. Newton and F. B. Baker, lnorg. Chem. 3,569 (1%4); J. H. Espenson, ibid. 4, 1533 (1965). 16. e.g., R. C. Lord and R. E. Merrifield, J. Chem. Phys. 21, 166 (1953); J. R. O. Barcelo and J. Bellanato, Spectrochim. Acta 8, 27 (1956); E. A V. Ebsworth and N. Sheppard, ibid. 13. 261 (1959); J. Bellanato, ibid. 16, 1344 (I%0L 17. L. J. Bellamy, Infra-red Spectra of Complex Molecules, 2nd Edn, p. 260. Wiley, New York (1958). 18. T. Sato, Z Appl. Chem. 15, 10 (1965). 19. J. Belbin, L. H. Holmes, Jr. and S. P. McGlynn, Z lnorg. Nucl. Chem. 25, 1359 (1963); D. N. Sathyanarayana and C, (L Patel, ibid. 30, 207 (1968). 20. J. B. White and J. Selbin, ,L lnorg. Nucl. Chem. 32, 2434 ( 1970/. 21. K. Nakamoto, Infrared Spectra o.f lnorganic and Coordination Compounds, 2nd Edn, p. 214. Wiley, New York (1970). 22. e.g., R. J. H. Clark, J. Chem. Soc. 1377 (1963); F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 2nd Edn, p. 637. Interscience, New York (1966); B. N. Figgs, Introduction to Ligand Fields, p. 258. lnterscience, New York (1%6). 23. T. Sato, T. Nakamura and O. Terao, J. lnorg. Nucl. Chem. 39, 401 (1977).