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Reduction chromatoghraphy of cations
634
JOURNAL
01: CHROMATOGRAPHY
VOL.
2
(1959)
.:.., , !a’,
REDUCTION
CHROMATOGRAPHY
ANDRZE Eleclrolechzical
J G6RSKI
Labovatovy
OF CATIONS
EUG=NIUSZ
AND
of the Polish
Academy
ICEOCZKO
of Science,
Warsaw
(Potand)
. INTRODUCTION
When searching for phenomena that could give rise to chromatographic separations our attention was drawn to the possibility of separating metals on the basis of the differences in the values of their normal potentials. We anticipated that chromatographic separation could occur on passing a misture of cations through a chromatographic column packed with powdered metal, if the normal potential of this metal were lower than that of the cations passing through. The ions would be successively displaced from the solution in the order of decreasing normal potential. In the chromatographic method based upon this principle of displacement of metals from the solutions of their ions, the quality of the separation does not depend directly on the reduction potentials of the metals, but on the reduction equilibrium constants. These values can be, easily calculated. For esample for the equilibrium state of the reaction: Fe0 + the following
equation holds
~c~/~o+l-+
of the corresponding 0.440
$
Fe++
+
Pb”
=
AT rF
:
E,
Insertion
Pb++
-
+
B,
m++/m”
In Ii
values gives: 8.316 0.12G
Hence :
=
X
298.1
X
2.303
2 x 96494
log K
arc++
1-c = -
~I?lr++
=
4.17'Id"
The equilibrium constants of the displacement reactions of the ions Cd++, Co++, Ni++, Sn++, Cu’+ and Ag+ with iron, calculated as above, are the following: Fe++-
F&-f-
-
=
Fe++ Co+e
=
3.24’
105
F&f Ni”’
=
7.94’
100
ccl+*
19.15
Sri-e-l-
F&t-
cu*+
=
1.41 * Iof
=
3.IG.10”~
WC
2
REDUCTiON
(1959)
CHROMATOGRAPHY
These values show that chromatographic will be very extensive.
OF CATIONS
separations
EXPERIMENTAL
635
accomplished
with this method
PART
General A. Chromatopa$
Jaic columns
Chromatographic columns 600 mm long and at the bottom were used. B. Chvomatogrn$hic
IO
mm in diameter
fitted with stopcocks
beds
The columns were packed with powdered metals. In our investigations beds of powdered zinc, aluminium and iron were applied, Beds consisting of zinc and aluminium generally proved to be useless because of the evolution of hydrogen. This occurred not only when separating mixtures of cations from acid solution but also from basic or even weakly basic solutions. It was the main reason why we used beds of powdered iron in our investigations. We used two different types of powdered iron : I. Electrolytic iron powder (Swedish), containing o.og”/o C, o.orz% Si, 0.022% Mn, 0.00$3~~ S and O.OIS% P; the particles were of irregular shape, the size ranging from 0.2-0.4. mm. 2. Technical iron powder produced by “Toxa” (Polish), consisting of spherical grains with diameters ranging from 0.315-0.50 mm. The size of the grains chosen was such that good physical properties of the bed were obtained. Its hydraulic resistance must be sufficiently small and must not undergo any changes when metals are deposited on the bed. The columns were packed wet (in suspension) without suction being applied. Uniform packing of the beds was achieved by repeatedly tapping the columns with a wooden stick.
C. Initial
solution
Cations were separated from neutral, ammonia and cyanide solutions. The concentration of the cations was 0.01 moles per litre. The concentrations of ammonia and cyanide were as high as necessary for formation of the corresponding complexes. D. Flow rate The flow rate was chosen in accordance with the ..method of separation. It was quite low when the aim was to separate the cations in the form of separate layers, but higher when the frontal method was applied. In experiments where separate chromatographic layers were obtained in the column, the sequence of the deposited cations and the lengths of the layers were determined by visual observation. In the case of frontal chromatography alternate portions of effluent were analysed qualitatively in order to determine the sequence and the extent of separation of the ions. Polarography was applied to examine more closely the shape of .the front as regards the
A. G6RSK1, E. KEOCZKO
636
deposited ions; the changes in the amount mined calorimetrically.
VOL.
of iron passing
2 (1959)
into solution were deter-
Ex~erinae&al. details A. Sefiaratiom
by memzs of classical clzromatographic
n&hods
These were carried out on beds of zinc, aluminium and iron. The results of the experiments proved unsatisfactory. Clearly distinct layers were obtained only for silver and copper cations in neutral and ammoniacal solutions. In all cases a distinct silvery grey layer of deposited silver was formed at the top of the bed immediately followed by a red layer of deposited copper. An interesting feature of the influ.ence of the presence of silver on the formation of the copper layer was observed. When silver ions are not present in the solution, the copper ions are deposited in the column as wide, poorly separated layers. The width of the layers depends on the concentration of the cupric ions and on the flow rate. When a mixture of silver and copper cations is passed through the column, the copper layer is much narrower and well shaped, the width being only slightly dependent on the flow rate. We suppose this is due to the creation of a copper-silver pile working on the column. Other cations give layers that are wider and more difficult to determine by means of visual observation. For esample lead cations are deposited after silver and copper in the form of a dark grey, wide, poorly shaped layer. B. Experimeds
in which frontal analysis
was z~sed
Very interesting results were obtained when the separation of cations in the effluent from the column was investigated. Frontal analysis was applied to separate the nitrates of silver, copper, lead, nickel and cadmium on a chromatographic bed of iron powder (“Toxa”). The esperimental conditions were the following: diameter of the column : 9.9 mm; height of the bed: 350 mm; empty space: 12 ml; concentration of cations in the influent: 0.01 M with respect to each cation; flow rate: approx. 0.2 ml/min. The content of the effluent was determined by qualitative analytical methods. The results of this experiment are given in Table I. TABLE
I
Prcscrrce of cations
in llte cfllrrcnt
(ml)
Cation 3
Fe-b’+
Cd++ Ni++ Pb++ cu++ &+
_
G
4 _
-
8
-
IO -
12
14
xl
x8
20
2a
24
2G
-
-
_
_
+
+
+
+
+
28
30
‘; + ‘r r = 1 1 r 1 1 3 f zz It: _ _ t _ not found in the effluent. Two clearly distinct layers at the top of the bed; 1 silver; lower layer: copper
As can be seen, the sequence of the ion?3 appearing the increasing normal potentials in neutral solution.
32
34
36
+
+
+
z : : _+ + + upper layer:
in the effluent is in the order of
VOL. 2 (1959)
REDUCTION
CHROMATOGRAPHY
637
OF CATIONS
An analogous experiment was carried out using a bed of powdered electrolytic iron under the following conditions: column diameter: 9.9 mm; height of the bed: 140 mm; empty space: 4.8 ml;’ concentration of the influent solution: 0.01 lkl with respect to each cation. Fractions of I ml were collected and analysed. The follov$ng sequence of cations in the effluent was established: cadmium-nickel, lead. Silver and copper were completely adsorbed on the column, where they formed two clearly distinct layers (copper below silver) ; their ions were not found in the effluent. In order to determine the shape of the front of the effluent in the method we have proposed, an esperiment was carried out in which lead and cadmium were separated from each other. The conditions were as follows : column diameter : 9.9 mm ; height of bed of powdered electrolytic iron: 202 mm; empty space: 6.S ml; initial
Fig.
T. Changes
of the
ion
concentrations nncl clisylaced tographic column.
iron
in the
cl:llucnt
from
the chroxns-
concentration of solution : 0.01 M with respect to each cation ; flow rate: approx. 0.07 ml/min. The concentration of cations in the eIYluent was determined polarographically. At the same time the shape of the front of the displaced iron was investigated calorimetrically with ammonium rhodanide, using Hilger’s “Spekker” photo-calorimeter. The results are shown in Fig. I, where the concentrations of the cations investigated are plotted against the volume of the effluent. In this figure it can be seen that the fronts of cadmium and leacl have a very regular shape, whereas that of iron is irregular. It is, interesting that the concentrations of cadmium and lead in the effluent reach a:constant value below that of their initial value, which is shown in the figure by a horizontal dashed line. The separation of different cations in the front of the effluent, using an ammoniacal solution was also investigated. The conditions were as follows : column diameter: iron; height of the bed: 137 mm; empty space: 9.9 mm: bed of powdered “Toxa” 7.0 ml; the concentration of the cations Ag(NHJ2+, Cu(NH,),++, Ni(NH,),++ an-d was 0.01 M with respect to each complex cation. The concentration of. Cd(NH&++
638
A.
:
GdRSKI,
E.
KEOCZI
VOL.
2
(1959)
the ammonia was as high as was necessary to obtain the required complexes. The flow rate was approx. 0.1 ml/min. The presence of the examined cations was established by qualitative analytical methods. The results of this experiment are given in Table II. TABLE
o/ cations iretRc e~Z’lr4o1rt(ml)
Presence
Cation
4
a
6
8
IO
ra
x4
II
x6
x8
zo
_
aa
a4
aG
28
30
32
34
F+l-
_
_
_
-
-
-
-
-
_
_
-
_
_
_
_
_
ccl++
-
-
-
-
-
-
+
+
+
-t-
+
+
+
+
+
+
+
Ni++
_
_
-
_
-
-
Ag+
-
-
-
_
-
_
_
_
-
-
_
_
-
-
_-
-
-i
3G _
-I_i_
Nickel is not separated from cadmium, which can be attributed to the fact that the bed was not high enough. As regards copper, this appeared in the effluent sooner than in the experiments with neutral solutions. The sequence of the cations in the effluent is therefore the same as that of the normal potentials of the metals concerned in ammoniacal solution. It must be pointed out that the effluent did not contain any ferrous ions. A similar experiment was carried to separate the cyanide complexes of silver, copper, nickel and cadmium, in which the conditions were as follows: column diameter: 9.9 mm; height of bed: 123 mm; empty space: 4.5 ml; initial concentration of the solution: 0.01 M with respect to each complex cation. Potassium cyanide was added in an amount sufficient to obtain the required compleses. The flow rate was about 0.1 ml/min. Table III shows the results of this experiment. II I
TABLE
Prcse~lccof cnliom irt tlic efllrcc~rt ftnl)
Cation 2
4
G
8
IO
F&-lcd++
_ _
_ -
_ -
_
-
Ni++ cu+-lAg”
_
_
+ _
+ + _
-t_ + -
ra -
I4 _ -
+
+
t
t
IG _
f-
r8 -
t
30
--
24
-02
-
21 -
-08 -
30 _
32 -
34 _
31
-
-
-I-
+
+
+
+
+
+
+
_
+
-
-
-
-
-
-
-
_
_
--* The first traces
of hg+
appeared
in the
54th
ml of effluent.
The data obtained show that copper appears in the effluent before other cations, in spite of the fact that its normal potential in cyanide solution is’ only - 0.43, whereas for cadmium the tialue of the normal potential is - 1.03. The main cause of this phenomenon seems to be the very small value of the instability constant of the copper complex (I’ = 5 IO-28) compared with that of other cations. This experl
VOL. 2
(1959)
REDUCTIdN
CHROMATOGRAPHY
OF CATIONS
639
iment was prolonged until all the separated cations appeared in the effluent. The first traces of silver ions appeared in the 54th ml of effluent. No ferrous ions are observed in the effluent. SUMMARY
A new method of separating cations -reduction chromatography-is proposed, 2. It was shown that chromatographic separation can be based on the differences of the normal potentials of metals, since these differences give rise to mutual displacement. 3. Frontal analysis of several cations in neutral, ammoniacal and cyanide solutions on a bed of powdered iron has been carried out. I.
Received
February
6th, 1959
JOURNAL
01: CHROMATOGRAPHY
VOL.
2
(1959)
.:.., , !a’,
REDUCTION
CHROMATOGRAPHY
ANDRZE Eleclrolechzical
J G6RSKI
Labovatovy
OF CATIONS
EUG=NIUSZ
AND
of the Polish
Academy
ICEOCZKO
of Science,
Warsaw
(Potand)
. INTRODUCTION
When searching for phenomena that could give rise to chromatographic separations our attention was drawn to the possibility of separating metals on the basis of the differences in the values of their normal potentials. We anticipated that chromatographic separation could occur on passing a misture of cations through a chromatographic column packed with powdered metal, if the normal potential of this metal were lower than that of the cations passing through. The ions would be successively displaced from the solution in the order of decreasing normal potential. In the chromatographic method based upon this principle of displacement of metals from the solutions of their ions, the quality of the separation does not depend directly on the reduction potentials of the metals, but on the reduction equilibrium constants. These values can be, easily calculated. For esample for the equilibrium state of the reaction: Fe0 + the following
equation holds
~c~/~o+l-+
of the corresponding 0.440
$
Fe++
+
Pb”
=
AT rF
:
E,
Insertion
Pb++
-
+
B,
m++/m”
In Ii
values gives: 8.316 0.12G
Hence :
=
X
298.1
X
2.303
2 x 96494
log K
arc++
1-c = -
~I?lr++
=
4.17'Id"
The equilibrium constants of the displacement reactions of the ions Cd++, Co++, Ni++, Sn++, Cu’+ and Ag+ with iron, calculated as above, are the following: Fe++-
F&-f-
-
=
Fe++ Co+e
=
3.24’
105
F&f Ni”’
=
7.94’
100
ccl+*
19.15
Sri-e-l-
F&t-
cu*+
=
1.41 * Iof
=
3.IG.10”~
WC
2
REDUCTiON
(1959)
CHROMATOGRAPHY
These values show that chromatographic will be very extensive.
OF CATIONS
separations
EXPERIMENTAL
635
accomplished
with this method
PART
General A. Chromatopa$
Jaic columns
Chromatographic columns 600 mm long and at the bottom were used. B. Chvomatogrn$hic
IO
mm in diameter
fitted with stopcocks
beds
The columns were packed with powdered metals. In our investigations beds of powdered zinc, aluminium and iron were applied, Beds consisting of zinc and aluminium generally proved to be useless because of the evolution of hydrogen. This occurred not only when separating mixtures of cations from acid solution but also from basic or even weakly basic solutions. It was the main reason why we used beds of powdered iron in our investigations. We used two different types of powdered iron : I. Electrolytic iron powder (Swedish), containing o.og”/o C, o.orz% Si, 0.022% Mn, 0.00$3~~ S and O.OIS% P; the particles were of irregular shape, the size ranging from 0.2-0.4. mm. 2. Technical iron powder produced by “Toxa” (Polish), consisting of spherical grains with diameters ranging from 0.315-0.50 mm. The size of the grains chosen was such that good physical properties of the bed were obtained. Its hydraulic resistance must be sufficiently small and must not undergo any changes when metals are deposited on the bed. The columns were packed wet (in suspension) without suction being applied. Uniform packing of the beds was achieved by repeatedly tapping the columns with a wooden stick.
C. Initial
solution
Cations were separated from neutral, ammonia and cyanide solutions. The concentration of the cations was 0.01 moles per litre. The concentrations of ammonia and cyanide were as high as necessary for formation of the corresponding complexes. D. Flow rate The flow rate was chosen in accordance with the ..method of separation. It was quite low when the aim was to separate the cations in the form of separate layers, but higher when the frontal method was applied. In experiments where separate chromatographic layers were obtained in the column, the sequence of the deposited cations and the lengths of the layers were determined by visual observation. In the case of frontal chromatography alternate portions of effluent were analysed qualitatively in order to determine the sequence and the extent of separation of the ions. Polarography was applied to examine more closely the shape of .the front as regards the
A. G6RSK1, E. KEOCZKO
636
deposited ions; the changes in the amount mined calorimetrically.
VOL.
of iron passing
2 (1959)
into solution were deter-
Ex~erinae&al. details A. Sefiaratiom
by memzs of classical clzromatographic
n&hods
These were carried out on beds of zinc, aluminium and iron. The results of the experiments proved unsatisfactory. Clearly distinct layers were obtained only for silver and copper cations in neutral and ammoniacal solutions. In all cases a distinct silvery grey layer of deposited silver was formed at the top of the bed immediately followed by a red layer of deposited copper. An interesting feature of the influ.ence of the presence of silver on the formation of the copper layer was observed. When silver ions are not present in the solution, the copper ions are deposited in the column as wide, poorly separated layers. The width of the layers depends on the concentration of the cupric ions and on the flow rate. When a mixture of silver and copper cations is passed through the column, the copper layer is much narrower and well shaped, the width being only slightly dependent on the flow rate. We suppose this is due to the creation of a copper-silver pile working on the column. Other cations give layers that are wider and more difficult to determine by means of visual observation. For esample lead cations are deposited after silver and copper in the form of a dark grey, wide, poorly shaped layer. B. Experimeds
in which frontal analysis
was z~sed
Very interesting results were obtained when the separation of cations in the effluent from the column was investigated. Frontal analysis was applied to separate the nitrates of silver, copper, lead, nickel and cadmium on a chromatographic bed of iron powder (“Toxa”). The esperimental conditions were the following: diameter of the column : 9.9 mm; height of the bed: 350 mm; empty space: 12 ml; concentration of cations in the influent: 0.01 M with respect to each cation; flow rate: approx. 0.2 ml/min. The content of the effluent was determined by qualitative analytical methods. The results of this experiment are given in Table I. TABLE
I
Prcscrrce of cations
in llte cfllrrcnt
(ml)
Cation 3
Fe-b’+
Cd++ Ni++ Pb++ cu++ &+
_
G
4 _
-
8
-
IO -
12
14
xl
x8
20
2a
24
2G
-
-
_
_
+
+
+
+
+
28
30
‘; + ‘r r = 1 1 r 1 1 3 f zz It: _ _ t _ not found in the effluent. Two clearly distinct layers at the top of the bed; 1 silver; lower layer: copper
As can be seen, the sequence of the ion?3 appearing the increasing normal potentials in neutral solution.
32
34
36
+
+
+
z : : _+ + + upper layer:
in the effluent is in the order of
VOL. 2 (1959)
REDUCTION
CHROMATOGRAPHY
637
OF CATIONS
An analogous experiment was carried out using a bed of powdered electrolytic iron under the following conditions: column diameter: 9.9 mm; height of the bed: 140 mm; empty space: 4.8 ml;’ concentration of the influent solution: 0.01 lkl with respect to each cation. Fractions of I ml were collected and analysed. The follov$ng sequence of cations in the effluent was established: cadmium-nickel, lead. Silver and copper were completely adsorbed on the column, where they formed two clearly distinct layers (copper below silver) ; their ions were not found in the effluent. In order to determine the shape of the front of the effluent in the method we have proposed, an esperiment was carried out in which lead and cadmium were separated from each other. The conditions were as follows : column diameter : 9.9 mm ; height of bed of powdered electrolytic iron: 202 mm; empty space: 6.S ml; initial
Fig.
T. Changes
of the
ion
concentrations nncl clisylaced tographic column.
iron
in the
cl:llucnt
from
the chroxns-
concentration of solution : 0.01 M with respect to each cation ; flow rate: approx. 0.07 ml/min. The concentration of cations in the eIYluent was determined polarographically. At the same time the shape of the front of the displaced iron was investigated calorimetrically with ammonium rhodanide, using Hilger’s “Spekker” photo-calorimeter. The results are shown in Fig. I, where the concentrations of the cations investigated are plotted against the volume of the effluent. In this figure it can be seen that the fronts of cadmium and leacl have a very regular shape, whereas that of iron is irregular. It is, interesting that the concentrations of cadmium and lead in the effluent reach a:constant value below that of their initial value, which is shown in the figure by a horizontal dashed line. The separation of different cations in the front of the effluent, using an ammoniacal solution was also investigated. The conditions were as follows : column diameter: iron; height of the bed: 137 mm; empty space: 9.9 mm: bed of powdered “Toxa” 7.0 ml; the concentration of the cations Ag(NHJ2+, Cu(NH,),++, Ni(NH,),++ an-d was 0.01 M with respect to each complex cation. The concentration of. Cd(NH&++
638
A.
:
GdRSKI,
E.
KEOCZI
VOL.
2
(1959)
the ammonia was as high as was necessary to obtain the required complexes. The flow rate was approx. 0.1 ml/min. The presence of the examined cations was established by qualitative analytical methods. The results of this experiment are given in Table II. TABLE
o/ cations iretRc e~Z’lr4o1rt(ml)
Presence
Cation
4
a
6
8
IO
ra
x4
II
x6
x8
zo
_
aa
a4
aG
28
30
32
34
F+l-
_
_
_
-
-
-
-
-
_
_
-
_
_
_
_
_
ccl++
-
-
-
-
-
-
+
+
+
-t-
+
+
+
+
+
+
+
Ni++
_
_
-
_
-
-
Ag+
-
-
-
_
-
_
_
_
-
-
_
_
-
-
_-
-
-i
3G _
-I_i_
Nickel is not separated from cadmium, which can be attributed to the fact that the bed was not high enough. As regards copper, this appeared in the effluent sooner than in the experiments with neutral solutions. The sequence of the cations in the effluent is therefore the same as that of the normal potentials of the metals concerned in ammoniacal solution. It must be pointed out that the effluent did not contain any ferrous ions. A similar experiment was carried to separate the cyanide complexes of silver, copper, nickel and cadmium, in which the conditions were as follows: column diameter: 9.9 mm; height of bed: 123 mm; empty space: 4.5 ml; initial concentration of the solution: 0.01 M with respect to each complex cation. Potassium cyanide was added in an amount sufficient to obtain the required compleses. The flow rate was about 0.1 ml/min. Table III shows the results of this experiment. II I
TABLE
Prcse~lccof cnliom irt tlic efllrcc~rt ftnl)
Cation 2
4
G
8
IO
F&-lcd++
_ _
_ -
_ -
_
-
Ni++ cu+-lAg”
_
_
+ _
+ + _
-t_ + -
ra -
I4 _ -
+
+
t
t
IG _
f-
r8 -
t
30
--
24
-02
-
21 -
-08 -
30 _
32 -
34 _
31
-
-
-I-
+
+
+
+
+
+
+
_
+
-
-
-
-
-
-
-
_
_
--* The first traces
of hg+
appeared
in the
54th
ml of effluent.
The data obtained show that copper appears in the effluent before other cations, in spite of the fact that its normal potential in cyanide solution is’ only - 0.43, whereas for cadmium the tialue of the normal potential is - 1.03. The main cause of this phenomenon seems to be the very small value of the instability constant of the copper complex (I’ = 5 IO-28) compared with that of other cations. This experl
VOL. 2
(1959)
REDUCTIdN
CHROMATOGRAPHY
OF CATIONS
639
iment was prolonged until all the separated cations appeared in the effluent. The first traces of silver ions appeared in the 54th ml of effluent. No ferrous ions are observed in the effluent. SUMMARY
A new method of separating cations -reduction chromatography-is proposed, 2. It was shown that chromatographic separation can be based on the differences of the normal potentials of metals, since these differences give rise to mutual displacement. 3. Frontal analysis of several cations in neutral, ammoniacal and cyanide solutions on a bed of powdered iron has been carried out. I.
Received
February
6th, 1959