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Synergic effect in ion exchange in mixed solvent media
J. inorg,nucl.Chem., 1969,Vol. 3I, pp. 199to 204. PergamonPress. Printedin Great Britain
SYNERGIC
EFFECT IN ION EXCHANGE MIXED SOLVENT MEDIA
IN
J. S U B R A H M A N Y A M and M. N. SASTRI Chemical Laboratories, Andhra University, Waltair, South India
(Received 16 March 1968) A b s t r a e t - A synergic effect is observed in the ion exchange adsorption of cobalt(lI) from acetonealcohol-HCl media. Solvent extraction, spectrophotometric and ultrasonic studies were carried out to explain the mechanism of this effect.
FRITZ and Pietrzyk[1] using binary mixtures of alcohols in the adsorption studies of some transitional elements on the anion exchanger Dowex- 1, observed a linear increase in adsorption with the concentration of one of the component solvents. Korkisch e t a/.[2], reported similar results with acetone-methanol mixtures in nitric acid media in their anion exchange studies with uranium, thorium and rare earths. However, in a few cases where binary alcohol mixtures were used, adsorption maxima were noted. The use of acetone-hydrochloric acid mixtures for the ion exchange separation of cobalt and nickel has already been reported by us [3]. It is now observed that in ketone-alcohol-hydrochloric acid media, the ion exchange uptake of cobalt(II) is significantly higher than in the individual solvent media of corresponding composition i.e. a synergic effect is observed. Although the phenomenon of synergism is well known in solvent extraction processes, its occurrence in ion exchange processes has not been reported. The results are described in this paper. EXPERIMENTAL
Materials Amberlite IRA-400 ( - 7 0 + 100 mesh)(Analytical grade) anion exchange resin supplied by Rohm and Haas Co. was used. AnalaR hydrochloric acid was diluted to the required concentration and standardised. Cobalt(II) chloride AnalaR solutions were prepared and standardised by a complexometric method using standard 0.01 M Na~EDTA (Merck proanalyse) solutions.
Solvents Acetone, methanol, ethanol, methyl isobutyl ketone, methyl isobutyl carbinol and isoamyl alcohol were purified according to prescribed procedures. The binary solvent mixtures were prepared by taking the appropriate volume of each solvent and/or hydrochloric acid and the volume changes, if any, on mixing were ignored. The compositions are expressed as mole fractions by weight of acetone.
Distribution coefficient ( Ka) determinations Approximately 1 g of the air dried resin was weighed accurately into a 100 ml stoppered flask. About 1 m-equiv, of cobalt(II) along with the desired organic solvent-water-hydrochloric acid mixture 1. J. S. Fritz and D. J. Pietrzyk, Talanta 8, 143 ( 1961). 2. I. Hazan, S. S. Ahluwali and J. Korkisch, Z. analyt. Chem. 206,324 (1964). 3. J. Subrahmanyam and M. N. Sastri, Z. analyt. Chem. 189, 172 (1962). 199
200
J. SUBRAHMANYAM and M. N. SASTRI
was introduced into the flask. The flask was stoppered and shaken in a mechanical shaker for 24 hr at the laboratory temperature. An aliquot of the supernatant liquid was taken and the metal content estimated after evaporating the organic solvent. The estimations were carded out using standard solutions of EDTA. The distribution coefficients Kd were calculated from the formula Kd =
m-equiv, metal in the resirdg of air dried resin m-equiv, metal in solution/ml of the solution"
Solvent extraction studies 20 ml of the aqueous phase containing 15 mg of cobalt chloride and the requisite amount of hydrochloric acid were extracted in a separating funnel with 20 ml of the organic solvent mixture preequilibrated with an aqueous solution of the same composition but containingno cobalt. After shaking for 5 min the cobalt content in both the phases were estimated by complexometric titration using standard Na~EDTA solution. The percentage extraction (E) was calculated from the equation E=
100 CoV0 CV + CoVo
where Co is the concentration of cobalt in the organic phase, V0 is the volume of the organic phase after equilibration, C is the concentration of the metal in the aqueous phase and V is the volume of the aqueous phase after equilibration. Spectrophotometric studies The absorption spectra were taken on a Hilger UVISPEK spectrophotometer using 1 cm glass cells. Solutions for the spectra were prepared by mixing aliquot quantities of Co(C104)2, HCI, and organic solvents (85% v/v) in 25 ml volumetric flasks. A reference cell containing the solution of the same composition except for cobalt(II) was used as the blank. Ultrasonic studies A fixed path double crystal interferometer was employed in these studies. The liquid mixtures were prepared by mixing the freshly distilled liquids in the requisite proportions by volume. The density (D) at each composition was determined by the hydrostatic method. The ultrasonic velocity V was calculated [4] from the relation V=21Afmlsec where I is the length of the cell and Afis the frequency interval between any two consecutive maximum deflections. From the values of V and D the adiabatic compressibility,/3 was calculated from the relation 13= ~ -1~ atm-.1 RESULTS AND DISCUSSION F i g u r e 1 s h o w s the v a r i a t i o n o f the Kd v a l u e s for c o b a l t ( I I ) o n the a n i o n e x c h a n g e r as a f u n c t i o n o f the p r o p o r t i o n s o f a c e t o n e a n d alcohol. T h e total o r g a n i c s o l v e n t c o n t e n t w a s 85 per cent. T h e m a x i m u m in Kd s h o w s a shift tow a r d s the left w i t h i n c r e a s e in h y d r o c h l o r i c acid c o n c e n t r a t i o n . S t u d i e s with l i t h i u m c h l o r i d e i n s t e a d o f h y d r o c h l o r i c acid s h o w e d a s i m i l a r trend. I n o r d e r to u n d e r s t a n d the n a t u r e o f the s p e c i e s a d s o r b e d o n the ion e x c h a n g e r , s o l v e n t e x t r a c t i o n s t u d i e s of c o b a l t i n t o m i x t u r e s o f m e t h y l i s o b u t y l k e t o n e methyl isobutyl carbinol and methyl isobutyl ketone-isoamyl alcohol from 4. Ram Parshad, lndianJ. Phys. 15, 323 (1941).
Synergic effect in ion exchange in mixed solvent media
201
I.S S
•
Ss ~
J
I0; v
I01 -O ACETONE-llIk'THANOL MIXTURES -& ACETONEoLr'I'HANOL MIXTURES Sl O
I
I,=
I
I
I
0.2 0.4 0:6 0.8 1.0 MOLE FRACTION OF ACETONE
Fig. 1. The uptake of Co(I I) on the anion exchanger from mixtures of alcohol-acetonehydrochloric acid media.
aqueous solutions containing 6, 7 and 8 M HCI were carried out. Figure 2 gives the variation of the percentage extraction of cobalt(lI) with the mole fraction of methyl isobutyl ketone in the organic mixtures. Extraction into methyl isobutyl ketone-isoamyl alcohol mixture at 8 M HCI could not be carried out owing to the miscibility of the two phases. In all these extractions a synergic effect analogous to that reported by Goble and Maddock [5] in the extraction of Pa(V) was observed. These workers also noticed a similar effect in the extraction of some other elements by these solvent mixtures, but no results appear to have been published. In the present studies, a very interesting trend emerges from the solvent extraction and ion exchange results in ketone-alcohol mixtures. From Fig. 1 it is seen 5. A. G. Goble and A. G. Maddock, Trans. Faraday Soc. 55, 591 (1962).
202
J. S U B R A H M A N Y A M
2_
lOT-
¢
and M. N. S A S T R I
~ MIBK--CARBINOL,
&---~ MIBK--ISOAMYL
ALCOHOL
Z O
C-U < n. ix
i0 d
6 M. Hcl
....& .......
\ 1
A....
\
0 U w a.
i O
i
i
I
0.2 0.4 0.6 O.8 MOLE FRACTION OF MIBK.
I I.O
Fig. 2. Solvent extraction of Co(II) into mixtures of methyl isobutyl carbinol/isoamyl alcohol-MIBK.
that the maximum in Kd shows a shift towards the lower concentration of acetone with increase in hydrochloric acid concentration. On the other hand in solvent extraction, the extraction maxima show a shift towards increasing concentration of ketone with increasing concentration of hydrochloric acid. In fact, the two curves approximate to mirrorimages. The spectra of cobalt(tI) in acetone-alcohol mixtures as well as in individual solvents are given in Fig. 3. The absorption maxima at 610 mix (sh), 625 mix, 665 mix and 695 mix characteristic of the chlorocomplex correspond to those reported by Fine[6] and Katzin and Gebert[7]. The spectra in acetone-alcohol mixtures bring out the shoulder at 610 mix and the peaks 625 mix, 665 mix and 695 mix, and these have been assigned to COC14= species by Rutner[8] from the reflectance spectra of chlorocobaltous complex ions on the Dowex-1 anion exchange resin. 6, D. A. Fine, J.Am. chem. Soc. 84, 1139 (1962). 7. L. I. Katzin and E. Gebert, J. Am. chem. Soc. 72, 5464 (1950). 8. E. Rutner, J. phys. Chem. 65, 1027 (1961).
Synergiceffectin ion exchangein mixedsolventmedia
203
800
700 IZ lad
c -* c -" •
= & o = •
ACETONE-METHANOL ACETONE--ETHANOL ACETONE ETHANOL METHANOL
MIXTURE MIXTURE
600
u.
u0
SO0
z
0
I-" U 400 Z I.x W 30( < J
200 J
0I[ I00
. . . .,
SOO
540
--'"
,
,
580 620 660 700 WAVE LENGTH~ I11/,/
,
740
7BO
Fig. 3. Absorption spectra of Co(II) in 0.44 molefractionof acetone in alcohol-acetone mixtures at 1.5 M HCI. While the spectrophotometric data prove the existence of adsorbable anionic species under these conditions, the differences in the various media described above might be considered to arise from shifts in the equilibrium between the two anionic species COC13- and COC14=, which are reported to give nearly overlapping absorption maxima [6]. The important feature of the spectrum in the mixed solvent system is the marked hyperchromic effect indicating increased formation of the adsorbable anionic species, possibly CoC4 =. This effect is relatively much greater in acetone-methanol mixtures in which the synergic effect also is greater. Krishnamurty [9] has calculated the adiabatic compressibilities (/3) of mixtures of acetone and methyl alcohol by determining the ultrasonic velocities at different compositions and observed a minimum compressibility at about 0.40 mole fraction of acetone. Similar studies have now been carried out with acetone-alcohol mixtures (Fig. 4), in which the compressibility is found to give a minimum value at about 0.44 mole fraction of acetone. It is significant that this concentration corresponds to that at which the ion exchange distribution coefficient shows a maximum value. The increase in the ultrasonic velocity (i.e. the decrease in the adiabatic compressibility) is considered to indicate a decrease in the aggregation 9. B h . K r i s h n a m u r t y , J .
scient. Ind. Res. 17B, 3 9 7 ( 1 9 5 8 ) .
204
J. SUBRAHMANYAM and M. N. SASTR1 0.----4 ACETONE-ETHANOL MIXTURES ACETONE-METHANOL MIXTURES IO9 1220
IOS
1210
1(3(
12OO
--q 97
ttgo
93,'
1180
x
i
g
85
I
O
-r~
-
i ~-'-'-
I
0.2 0"4 0.6 0.8 MOLE FRACTION OF ACETONE
1160
I.O
Fig. 4. Ultrasonic velocities in alcohol-acetone mixtures.
of the component molecules in the system. The similarity in trend between the ion exchange distribution and the compressibility curves is quite striking and points to a solvent-solvent interaction playing a major role in the observed effect. Studies with copper(II) have yielded similar though less striking results. Nickel(II) was not extracted. Acknowledgement-The authors express their grateful thanks to Professor Bh. Krishnamurty of the Physics department for providing facilities for carrying out the ultrasonic studies.
SYNERGIC
EFFECT IN ION EXCHANGE MIXED SOLVENT MEDIA
IN
J. S U B R A H M A N Y A M and M. N. SASTRI Chemical Laboratories, Andhra University, Waltair, South India
(Received 16 March 1968) A b s t r a e t - A synergic effect is observed in the ion exchange adsorption of cobalt(lI) from acetonealcohol-HCl media. Solvent extraction, spectrophotometric and ultrasonic studies were carried out to explain the mechanism of this effect.
FRITZ and Pietrzyk[1] using binary mixtures of alcohols in the adsorption studies of some transitional elements on the anion exchanger Dowex- 1, observed a linear increase in adsorption with the concentration of one of the component solvents. Korkisch e t a/.[2], reported similar results with acetone-methanol mixtures in nitric acid media in their anion exchange studies with uranium, thorium and rare earths. However, in a few cases where binary alcohol mixtures were used, adsorption maxima were noted. The use of acetone-hydrochloric acid mixtures for the ion exchange separation of cobalt and nickel has already been reported by us [3]. It is now observed that in ketone-alcohol-hydrochloric acid media, the ion exchange uptake of cobalt(II) is significantly higher than in the individual solvent media of corresponding composition i.e. a synergic effect is observed. Although the phenomenon of synergism is well known in solvent extraction processes, its occurrence in ion exchange processes has not been reported. The results are described in this paper. EXPERIMENTAL
Materials Amberlite IRA-400 ( - 7 0 + 100 mesh)(Analytical grade) anion exchange resin supplied by Rohm and Haas Co. was used. AnalaR hydrochloric acid was diluted to the required concentration and standardised. Cobalt(II) chloride AnalaR solutions were prepared and standardised by a complexometric method using standard 0.01 M Na~EDTA (Merck proanalyse) solutions.
Solvents Acetone, methanol, ethanol, methyl isobutyl ketone, methyl isobutyl carbinol and isoamyl alcohol were purified according to prescribed procedures. The binary solvent mixtures were prepared by taking the appropriate volume of each solvent and/or hydrochloric acid and the volume changes, if any, on mixing were ignored. The compositions are expressed as mole fractions by weight of acetone.
Distribution coefficient ( Ka) determinations Approximately 1 g of the air dried resin was weighed accurately into a 100 ml stoppered flask. About 1 m-equiv, of cobalt(II) along with the desired organic solvent-water-hydrochloric acid mixture 1. J. S. Fritz and D. J. Pietrzyk, Talanta 8, 143 ( 1961). 2. I. Hazan, S. S. Ahluwali and J. Korkisch, Z. analyt. Chem. 206,324 (1964). 3. J. Subrahmanyam and M. N. Sastri, Z. analyt. Chem. 189, 172 (1962). 199
200
J. SUBRAHMANYAM and M. N. SASTRI
was introduced into the flask. The flask was stoppered and shaken in a mechanical shaker for 24 hr at the laboratory temperature. An aliquot of the supernatant liquid was taken and the metal content estimated after evaporating the organic solvent. The estimations were carded out using standard solutions of EDTA. The distribution coefficients Kd were calculated from the formula Kd =
m-equiv, metal in the resirdg of air dried resin m-equiv, metal in solution/ml of the solution"
Solvent extraction studies 20 ml of the aqueous phase containing 15 mg of cobalt chloride and the requisite amount of hydrochloric acid were extracted in a separating funnel with 20 ml of the organic solvent mixture preequilibrated with an aqueous solution of the same composition but containingno cobalt. After shaking for 5 min the cobalt content in both the phases were estimated by complexometric titration using standard Na~EDTA solution. The percentage extraction (E) was calculated from the equation E=
100 CoV0 CV + CoVo
where Co is the concentration of cobalt in the organic phase, V0 is the volume of the organic phase after equilibration, C is the concentration of the metal in the aqueous phase and V is the volume of the aqueous phase after equilibration. Spectrophotometric studies The absorption spectra were taken on a Hilger UVISPEK spectrophotometer using 1 cm glass cells. Solutions for the spectra were prepared by mixing aliquot quantities of Co(C104)2, HCI, and organic solvents (85% v/v) in 25 ml volumetric flasks. A reference cell containing the solution of the same composition except for cobalt(II) was used as the blank. Ultrasonic studies A fixed path double crystal interferometer was employed in these studies. The liquid mixtures were prepared by mixing the freshly distilled liquids in the requisite proportions by volume. The density (D) at each composition was determined by the hydrostatic method. The ultrasonic velocity V was calculated [4] from the relation V=21Afmlsec where I is the length of the cell and Afis the frequency interval between any two consecutive maximum deflections. From the values of V and D the adiabatic compressibility,/3 was calculated from the relation 13= ~ -1~ atm-.1 RESULTS AND DISCUSSION F i g u r e 1 s h o w s the v a r i a t i o n o f the Kd v a l u e s for c o b a l t ( I I ) o n the a n i o n e x c h a n g e r as a f u n c t i o n o f the p r o p o r t i o n s o f a c e t o n e a n d alcohol. T h e total o r g a n i c s o l v e n t c o n t e n t w a s 85 per cent. T h e m a x i m u m in Kd s h o w s a shift tow a r d s the left w i t h i n c r e a s e in h y d r o c h l o r i c acid c o n c e n t r a t i o n . S t u d i e s with l i t h i u m c h l o r i d e i n s t e a d o f h y d r o c h l o r i c acid s h o w e d a s i m i l a r trend. I n o r d e r to u n d e r s t a n d the n a t u r e o f the s p e c i e s a d s o r b e d o n the ion e x c h a n g e r , s o l v e n t e x t r a c t i o n s t u d i e s of c o b a l t i n t o m i x t u r e s o f m e t h y l i s o b u t y l k e t o n e methyl isobutyl carbinol and methyl isobutyl ketone-isoamyl alcohol from 4. Ram Parshad, lndianJ. Phys. 15, 323 (1941).
Synergic effect in ion exchange in mixed solvent media
201
I.S S
•
Ss ~
J
I0; v
I01 -O ACETONE-llIk'THANOL MIXTURES -& ACETONEoLr'I'HANOL MIXTURES Sl O
I
I,=
I
I
I
0.2 0.4 0:6 0.8 1.0 MOLE FRACTION OF ACETONE
Fig. 1. The uptake of Co(I I) on the anion exchanger from mixtures of alcohol-acetonehydrochloric acid media.
aqueous solutions containing 6, 7 and 8 M HCI were carried out. Figure 2 gives the variation of the percentage extraction of cobalt(lI) with the mole fraction of methyl isobutyl ketone in the organic mixtures. Extraction into methyl isobutyl ketone-isoamyl alcohol mixture at 8 M HCI could not be carried out owing to the miscibility of the two phases. In all these extractions a synergic effect analogous to that reported by Goble and Maddock [5] in the extraction of Pa(V) was observed. These workers also noticed a similar effect in the extraction of some other elements by these solvent mixtures, but no results appear to have been published. In the present studies, a very interesting trend emerges from the solvent extraction and ion exchange results in ketone-alcohol mixtures. From Fig. 1 it is seen 5. A. G. Goble and A. G. Maddock, Trans. Faraday Soc. 55, 591 (1962).
202
J. S U B R A H M A N Y A M
2_
lOT-
¢
and M. N. S A S T R I
~ MIBK--CARBINOL,
&---~ MIBK--ISOAMYL
ALCOHOL
Z O
C-U < n. ix
i0 d
6 M. Hcl
....& .......
\ 1
A....
\
0 U w a.
i O
i
i
I
0.2 0.4 0.6 O.8 MOLE FRACTION OF MIBK.
I I.O
Fig. 2. Solvent extraction of Co(II) into mixtures of methyl isobutyl carbinol/isoamyl alcohol-MIBK.
that the maximum in Kd shows a shift towards the lower concentration of acetone with increase in hydrochloric acid concentration. On the other hand in solvent extraction, the extraction maxima show a shift towards increasing concentration of ketone with increasing concentration of hydrochloric acid. In fact, the two curves approximate to mirrorimages. The spectra of cobalt(tI) in acetone-alcohol mixtures as well as in individual solvents are given in Fig. 3. The absorption maxima at 610 mix (sh), 625 mix, 665 mix and 695 mix characteristic of the chlorocomplex correspond to those reported by Fine[6] and Katzin and Gebert[7]. The spectra in acetone-alcohol mixtures bring out the shoulder at 610 mix and the peaks 625 mix, 665 mix and 695 mix, and these have been assigned to COC14= species by Rutner[8] from the reflectance spectra of chlorocobaltous complex ions on the Dowex-1 anion exchange resin. 6, D. A. Fine, J.Am. chem. Soc. 84, 1139 (1962). 7. L. I. Katzin and E. Gebert, J. Am. chem. Soc. 72, 5464 (1950). 8. E. Rutner, J. phys. Chem. 65, 1027 (1961).
Synergiceffectin ion exchangein mixedsolventmedia
203
800
700 IZ lad
c -* c -" •
= & o = •
ACETONE-METHANOL ACETONE--ETHANOL ACETONE ETHANOL METHANOL
MIXTURE MIXTURE
600
u.
u0
SO0
z
0
I-" U 400 Z I.x W 30( < J
200 J
0I[ I00
. . . .,
SOO
540
--'"
,
,
580 620 660 700 WAVE LENGTH~ I11/,/
,
740
7BO
Fig. 3. Absorption spectra of Co(II) in 0.44 molefractionof acetone in alcohol-acetone mixtures at 1.5 M HCI. While the spectrophotometric data prove the existence of adsorbable anionic species under these conditions, the differences in the various media described above might be considered to arise from shifts in the equilibrium between the two anionic species COC13- and COC14=, which are reported to give nearly overlapping absorption maxima [6]. The important feature of the spectrum in the mixed solvent system is the marked hyperchromic effect indicating increased formation of the adsorbable anionic species, possibly CoC4 =. This effect is relatively much greater in acetone-methanol mixtures in which the synergic effect also is greater. Krishnamurty [9] has calculated the adiabatic compressibilities (/3) of mixtures of acetone and methyl alcohol by determining the ultrasonic velocities at different compositions and observed a minimum compressibility at about 0.40 mole fraction of acetone. Similar studies have now been carried out with acetone-alcohol mixtures (Fig. 4), in which the compressibility is found to give a minimum value at about 0.44 mole fraction of acetone. It is significant that this concentration corresponds to that at which the ion exchange distribution coefficient shows a maximum value. The increase in the ultrasonic velocity (i.e. the decrease in the adiabatic compressibility) is considered to indicate a decrease in the aggregation 9. B h . K r i s h n a m u r t y , J .
scient. Ind. Res. 17B, 3 9 7 ( 1 9 5 8 ) .
204
J. SUBRAHMANYAM and M. N. SASTR1 0.----4 ACETONE-ETHANOL MIXTURES ACETONE-METHANOL MIXTURES IO9 1220
IOS
1210
1(3(
12OO
--q 97
ttgo
93,'
1180
x
i
g
85
I
O
-r~
-
i ~-'-'-
I
0.2 0"4 0.6 0.8 MOLE FRACTION OF ACETONE
1160
I.O
Fig. 4. Ultrasonic velocities in alcohol-acetone mixtures.
of the component molecules in the system. The similarity in trend between the ion exchange distribution and the compressibility curves is quite striking and points to a solvent-solvent interaction playing a major role in the observed effect. Studies with copper(II) have yielded similar though less striking results. Nickel(II) was not extracted. Acknowledgement-The authors express their grateful thanks to Professor Bh. Krishnamurty of the Physics department for providing facilities for carrying out the ultrasonic studies.