Recovery of cadmium and change in properties of a fibrous carbon electrode in electrolytic processing of ammonia washing solutions formed in cadmium plating

Article abstract of DOI:10.1134/S1070427207020140

The possibility of recovering cadmium deposited on fibrous carbon electrodes from ammonium washing solutions formed in cadmium plating via operation of a short-circuited electrochemical system or anodic dissolution was examined. A polarization study of electrode processes that occur on a renewable graphite microelectrode in ammonium solutions of varied composition was carried out. The change in the properties of fibrous carbon electrodes in their cyclic use in electrodeposition-recovery of cadmium and the possibility of their repeated use were analyzed.

Full text of DOI:10.1134/S1070427207020140

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 2, pp. 241 247.
Pleiades Publishing, Ltd., 2007.
Original Russian Text
V.I. Varentsova, V.K. Varentsov, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 2, pp. 242 248.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
Recovery of Cadmium and Change in Properties
of a Fibrous Carbon Electrode in Electrolytic Processing
of Ammonia Washing Solutions Formed in Cadmium Plating
V. I. Varentsova and V. K. Varentsov
Institute of Solid-State Chemistry and Mechanochemistry, Siberian Division,
Russian Academy of Sciences, Novosibirsk, Russia
Novosibirsk State Technical University, Novosibirsk, Russia
Received May 29, 2006
Abstract The possibility of recovering cadmium deposited on fibrous carbon electrodes from ammonium
washing solutions formed in cadmium plating via operation of a short-circuited electrochemical system or
anodic dissolution was examined. A polarization study of electrode processes that occur on a renewable
graphite microelectrode in ammonium solutions of varied composition was carried out. The change in
the properties of fibrous carbon electrodes in their cyclic use in electrodeposition recovery of cadmium
and the possibility of their repeated use were analyzed.
DOI: 10.1134/S1070427207020140
Owing to their specific properties, cadmium coat-
ings are used for protection of articles in aggressive
media (high humidity or tropic conditions) [1 3].
Cadmium(II) is to be removed from washing solutions
formed in cadmium plating for detoxication of these
solutions and recycling of cadmium into the electro-
plating process. Electrolysis is a way to simultaneous-
ly solve these two problems. With account of the low
concentration of cadmium(II) in washing solutions, it
is preferable to use electrolysis with 3D flow-through
electrodes and, in particular, with electrodes made of
fibrous carbon materials (FCM) [4].
properties. However, no unambiguous conclusion can
be made about whether these changes exert positive
or negative influence on the main process of metal
electrodeposition because of the scarcity of the avail-
able data.
This study was undertaken in order to examine
experimentally the possibility of recovery of cadmium
deposited on FCE, changes in the FCE properties
in an electrodeposition regeneration cycle, and in-
fluence exerted by these changes on the main process
for the example of electrolytic processing of washing
ammonium solutions formed in cadmium plating.
In the recent decades, electrolysis with fibrous car-
bon electrodes (FCE) has been successfully used to
recover noble and nonferrous metals in hydrometal-
lurgy and electroplating [4, 5]. The use of FCM for
electrolytic recovery of nonferrous metals from wash-
ing solutions formed in electroplating is due to the ne-
cessity for regeneration of carbon electrodes and re-
cycling of the recovered metal into main process.
An important issue is that of changes in the FCM
properties during their cyclic use in electrodeposition
recovery and of the influence exerted by these changes
on the parameters of both the processes. No system-
atic studies have been performed in this area. The re-
sults of previous studies [6 9] suggest that use of
FCM in cyclic processes will strongly affect their
EXPERIMENTAL
Industrial cadmium-plating ammonium electrolytes
of two compositions were chosen for study. Solution
1
no. 1 contained (g l ): CdSO4 50, (NH4)2SO4 150,
H3BO3 25 (pH 5); and solution no. 2: CdSO4 50,
(NH4)2SO4 250, urotropin 20, NF dispersant 75 ml l
1
(pH 6) [2, 3]. Supporting electrolytes contained all the
components listed above except cadmium. The elec-
trode polarization was carried out using a TES-14 dc
power supply in the galvanostatic mode, with the solu-
tion circulated by a pmp-304 peristaltic pump through
the FCE volume and an intermediate tank at a rate of
0.2 ml cm 2 s [9]. The solution was delivered to
1
241

242
VARENTSOVA, VARENTSOV
1
stant (26.8 A hmol ); I, current (A); U, cell voltage
(V); , experiment duration (h); and Mequiv , molar
mass of the metal equivalent. The cadmium(II) con-
centration in solution was determined by the atomic-
absorption method.
Figure 1 demonstrates the results of experiments on
modeling of the electrolytic recovery of cadmium(II)
from a catching bath for an automated cadmium-plat-
ing line. A portion of the cadmium-plating electrolyte
was introduced at regular intervals of time (15 min)
into a solution circulated between the electrolyzer
and the intermediate tank, which models a catching
bath. The Cd(II) concentration in the solution model-
ing a single washing of articles changed by 27 to
1
81 mg l . The electrolytic recovery of cadmium(II)
2
was carried out at a current density of 750 A m .
Fig. 1. Kinetic curves of electrolytic recovery of cadmi-
The kinetic curves presented in Fig. 1 reflect the
change in the cadmium(II) concentration in a solution
before introduction of a portion of the cadmium-plat-
ing electrolyte. It can be seen that the time in which
a constant cadmium(II) concentration in solution is
attained and the level of this constant concentration
increase with the amount of the electrolyte introduced
in a single washing. The fact that a constant cadmi-
um(II) concentration in solution is reached shows that,
under the chosen electrolysis conditions, the whole
amount of cadmium(II) introduced in article washing
is recovered by electrolysis between two successive
washings. Depending on the introduced amount of
electrolyte modeling washing of articles with different
um(II) from electrolyte no. 1 in modeling of the electro-
lytic recovery of cadmium(II) from a catching bath. Initial
1
cadmium(II) concentration 330 mg l , dilution factor n =
20, interval between washings 15 min. (c) Cd(II) concen-
tration, and ( ), time. Rise in the cadmium(II) concentration
1
upon a single washing (mg l ): (1) 27, (2) 54, and (3) 81.
an electrode with a back current lead from the back
side with respect to the counter electrode. The FCE
was made of NT-1 carbonized carbon graphite mate-
rial, its geometric area was 2 cm2. A perforated tita-
nium or platinum plate served as a current lead, and
a platinum wire, as a counter electrode. To measure
changes in the mass and electrical conductivity of
the FCE electrode, it was washed with distilled water
and dried at 80 100 C. The steady-state electrode
potential of a cadmium plate and FCE in the elec-
trolytes were measured relative to a saturated silver
chloride reference electrode and recalculated to
the hydrogen scale, without drying of the FCE.
1
surface areas, this concentration is 10 35 mg l be-
fore deposition of a certain amount of cadmium onto
FCE. After that the efficiency of cadmium electrode-
position decreases, which is characterized by an in-
crease in its concentration in solution. Evidently,
the main reason for the decrease in the process ef-
ficiency is that the reaction surface area and the rate
of electrolyte circulation decrease because of the plug-
ging of the pore space in FCE by the deposited metal.
The electrical conductivity of FCE was measured
with a VM-509 ac bridge and the steady-state elec-
trode potential, with an OR-265/1 pH-meter, using
the procedure and setup described in [4]. Polarization
curves were measured in the potentiodynamic mode
with an RA-2 polarograph on a graphite microelec-
trode 2 mm in diameter with a surface freshened in
the electrolyte solution [10], with a potential sweep
The amount of cadmium deposited per 1 g of FCE
varies with the electrolyte composition and is deter-
mined by the deposit structure and by the localization
of cadmium within the FCE volume, which are gov-
erned by specific features of cadmium electrodeposi-
tion from the electrolytes under consideration. In
the case of metal electrodeposition onto FCM cath-
odes, the overvoltages of hydrogen evolution on FCM
and on a metal being deposited are important for
the metal distribution throughout the electrode volume
[4]. The overvoltage of hydrogen evolution on cadmi-
um is 1.1 V, and that on graphite, 0.8 V [1, 11]. There-
fore, the overgrowth of the electrode with cadmium
predominantly occurs on the metal deposited during
1
rate of 50 mV s .
The efficiency of electrolytic recovery of cad-
mium was evaluated by the degree of recovery,
= (c0
CE = [(c0 c )VF ]/I Meqiv ; and electric power con-
sumption W = IU /(c0 c )V. Here c0 and c are
c )/c0; current efficiency by cadmium,
the initial and final cadmium concentrations in solu-
1
tion (g l ); V, solution volume (l); F, Faraday con-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

RECOVERY OF CADMIUM AND CHANGE IN PROPERTIES OF A FIBROUS CARBON ELECTRODE 243
the initial stage of electrolysis. No less important is
the solution pH, which is responsible for the stabil-
ity of ammine complexes of cadmium; at pH > 5,
Cd(NH3)22+ complexes predominate in the solution
5
(Kn = 1.8 10 ) [2, 12]. In addition, electrolyte no. 2
contains cadmium(II) complexes with urotropin and
a surfactant additive, and, therefore, the electrodeposi-
tion of cadmium from this electrolyte should be char-
acterized by a higher polarizability [2, 3]. Thus,
the varied content of components of the supporting
electrolyte, inherent to washing solutions, should af-
fect the polarization characteristics of the cathodic
process in cadmium-plating electrolytes.
The polarization curves characterizing cadmium(II)
discharge on a graphite microelectrode at different
dilutions of the supporting electrolyte and a constant
1
cadmium(II) concentration in the solution (300 mg l )
are shown in Fig. 2. The polarization curves have four
characteristic portions. The first of these (portion II)
ranges from the steady-state potential to a sharp rise in
current, which is associated with cadmium(II) reduc-
tion. This portion apparently corresponds to oxygen
reduction, and the fourth portion, to intense hydrogen
evolution. For both the electrolytes, the reduction of
cadmium(II) is determined by a clearly pronounced
plateau of the limiting current (third portion), whose
length is about 500 mV for electrolyte no. 1 and 300
to 500 mV for electrolyte no. 2 and increases with
the dilution of the solution. For both the electrolytes,
the height of the plateau of the limiting current is
proportional to the cadmium(II) concentration in a so-
lution.
For electrolyte no. 1, the run of the polarization
curve is little affected by dilution of the supporting
electrolyte, with the potential of the onset of cadmium
deposition only somewhat shifted in the positive di-
rection. For electrolyte no. 2, a strong effect is ob-
served. In this case, the potential of the onset of cad-
mium deposition is shifted in the positive direction,
the length of the plateau characterizing cadmium de-
position at the limiting current becomes longer, and
the limiting current itself also increases. In addition,
electrolyte no. 2 possesses a higher electrical conduc-
tivity (0.21 Cm cm ), which is approximately 1.5 1.7
times that of electrolyte no. 1. Therefore, electrode-
position of cadmium from electrolyte no. 2 is char-
acterized by a higher polarizability, which is clearly
seen in curve 1 in Fig. 2b.
Fig. 2. Polarization curves characterizing the electrode pro-
cesses on graphite microelectrode in electrolyte nos. (a) 1
and (b) 2. (i) Current density, (E) potential; the same for
1
1
Fig. 6. Cadmium(II) concentration (mg l ): (1, 2) 300,
(3) 150, and (4) 50. Supporting electrolyte dilution factor
(times): (a) (1) 0, (2) 50, (3, 4) 20; (b) (1) 0, (2) 50, and
(3, 4) 5. (I, II, III, IV) For explanation see text.
It was shown experimentally that, in the case of
electrolytic recovery of cadmium(II) from electrolyte
no. 1, cadmium is deposited on FCE on the front
(closer to the counter electrode, anode) side of the elec-
trode, whereas in the case of recovery from elec-
trolyte no. 2, it is localized on the back (closer to
the current lead) side of the electrode. The electro-
lytic deposits of cadmium also differ in structure. In
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

244
VARENTSOVA, VARENTSOV
Table 1. Degree of anodic dissolution, , of cadmium
deposited onto FCE in a supporting ammonium solution;
current efficiency by cadmium, CE; dissolution rate v;
and energy expenditure W for dissolution of 1 g of cad-
mium at varied anode current density i (dissolution time
0.5 h, solution volume 100 ml, geometric surface area
of the anode 2 cm2)
and falls-off into the solution. In the case of cadmi-
um(II) electrodeposition from electrolyte no. 2, cad-
mium is deposited on the back side of the electrode
and then grows into the electrode, with the amount of
deposited cadmium equal to 6.0 6.5 g per 1 g of FCE.
Cadmium deposited on FCE should be regenerated
and recycled into the electroplating process. A prom-
ising way to achieve this objective is anodic dissolu-
tion.
CE
i,
A m
v,
W,
W h g
2
1
1
g m 2 h
%
The anodic polarization curves reflecting cadmium
dissolution show that cadmium dissolves without any
difficulties in both the electrolytes and the potentials
corresponding to a steep rise in the anodic current
are close (Fig. 2). The results obtained in studying
the anodic dissolution of the cadmium deposit on FCE
in the supporting solutions of electrolyte nos. 1 and 2
at different anode current densities are listed in Ta-
ble 1. It can be seen that cadmium well dissolves in
both the solutions and the degree of dissolution in-
creases with the current density.
Electrolyte no. 1
50
79.2
96.0
89.6
99.5
385
230
140
120
400 (105)*
480 (210)
445 (315)
500 (410)
0.28 (1.00)
0.50 (1.43)
1.27 (1.80)
1.60 (1.95)
100
150
200
Electrolyte no. 2
50
100
150
200
87.7
90.8
92.8
99.9
450
215
145
120
465 (105)
450 (210)
460 (315)
500 (410)
0.2 (0.86)
0.60 (1.38)
1.21 (1.80)
1.60 (1.95)
*
Values of the parameters at CE = 100%.
If anodic polarization of an FCE by a metal is
performed without separation of the electrode spaces,
dissolved cadmium is deposited on the cathode to give
an electrolytic powder of cadmium.
the case of electrodeposition from electrolyte no. 1,
the deposit is porous, its adhesion to the surface of
carbon fibers is weak, and deposit scales off. The cad-
mium deposit formed from electrolyte no. 2 is less
porous and covers each fiber of the FCE. The amount
of cadmium deposited on FCE from electrolyte no. 1
does not exceed 4.5 g per 1 g of FCE, the deposit
grows on fibers in the direction of the electrolyte bulk
If the electrode spaces are separated with an ion-
exchange membrane and the anodic dissolution is per-
formed in the supporting solution of the correspond-
ing electrolyte, a solution of the cadmium-plating
electrolyte can be obtained. Such a procedure for re-
cycling of cadmium deposited on the FCE can be
performed in the same electrolyzer that is used for
electrolytic recovery of cadmium. It follows from
the data of Table 1 that, depending on the anode cur-
rent density, the current efficiency by cadmium ex-
ceeds 100% by a factor of 1.2 4.5 for both the elec-
trolytes. The rate of anodic dissolution depends on
the current density only slightly. If, however, the rate
of the anodic dissolution of cadmium is calculated
for a 100% current efficiency the rate is 4 4.5 times
lower at low current densities and increases as the cur-
rent density becomes higher. The electric energy ex-
penditure for dissolution of 1 g of cadmium is low; its
values differ by a factor of 5 8 for current densities
Fig. 3. Steady-state electrode potential (V) of (1 4) cad-
2
of 50 and 200 A m . If the energy expenditure for
mium electrode (E ) and (5, 6) FCM electrode (E
) vs.
Cd
FCM
dissolution of 1 g of cadmium is calculated for a cur-
rent efficiency of 100%, the difference tends to zero.
The aforesaid shows that there occurs a concurrent
reaction accompanied by dissolution of cadmium.
Such a reaction may be cadmium dissolution through
operation of a short-circuited electrochemical system
(SES) constituted by FCE, cadmium, and electrolyte
solution.
the dilution factor n of the electrolyte for the supporting
solution and cadmium(II). Composition of supporting
1
solutions (g l ): electrolyte no. 1 (NH ) SO 150 and
4 2
4
H BO 25; electrolyte no. 2 (NH ) SO 250, urotropin 20,
3
3
4 2
4
1
and NF dispersant 75 ml l . Electrolyte dilution (I) by
supporting solution, cadmium(II) concentration 100 mg l
1
,
and (II) by cadmium(II). Electrolyte: (2, 3, 5) no. 1 and
(1, 4, 6) no. 2.
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RECOVERY OF CADMIUM AND CHANGE IN PROPERTIES OF A FIBROUS CARBON ELECTRODE 245
Measurements of the steady-state electrode poten-
tials of cadmium (ECd) and FCE (EFCE) in solutions
of electrolyte nos. 1 and 2 demonstrated (Fig. 3) that
EFCE is independent of the electrolyte dilution, whereas
ECd depends on the electrolyte dilution for cadmium
and components of a supporting solution. For elec-
trolyte no. 2, this dependence is more pronounced
(curves 1, 4). The difference between the steady-state
potentials of cadmium and FCE for both the elec-
trolytes remains considerable (850 950 mV). There-
fore, cadmium deposited on FCE must dissolve in
the supporting ammonium electrolyte via SES opera-
tion.
The process of cadmium dissolution via SES op-
eration can be independently used for cadmium regen-
eration, because it is a simpler cadmium regeneration
technique, which has been effectively used previous-
ly for regeneration of zinc and palladium deposited
on FCE [13]. The studies performed demonstrated
Fig. 4. Kinetic curves of dissolution of cadmium depos-
ited onto FCE through SES operation in the supporting so-
lutions of electrolyte nos. (1) 2 and (2) 1. Solution volume
that cadmium deposited on FCE dissolves in the sup-
100 ml. m
Mass of soluble Cd,
time.
Cd
porting solution of the corresponding electrolyte at
a considerable rate (Fig. 4). Solutions containing 35
1
40 g l CdSO4 were obtained as a result of the cad-
the anodic cycle and also to the possible interaction
of the electrolyte components with the FCM fibers
[6, 7]. The less pronounced changes in the elec-
trical conductivity and FCM mass in electrolyte no. 2
may be due to adsorption of the electrolyte com-
ponents (urotropin and NF dispersant) on the FCE
surface.
mium dissolution through SES operation. These solu-
tions can be used for preparation of cadmium-plating
electrolytes.
In the course of cadmium regeneration, FCE un-
dergoes cyclic cathodic and anodic polarizations. It
has been shown previously [6 9] that the FCE prop-
erties can be considerably changed in the process.
Therefore, it was necessary to study how the prop-
erties of fibrous carbon electrodes change after sev-
eral cycles of cadmium electrodeposition regenera-
tion. The results obtained in measuring the mass and
the electrical conductivity of FCE after several cy-
cles of cadmium electrodeposition dissolution are
listed in Table 2.
The change in the FCE properties can affect the pro-
cess of cadmium electrodeposition. Figure 5 shows
the results obtained in studying the cadmium electro-
deposition on FCE samples on performing five cycles
of cadmium electrodeposition dissolution. It can be
seen that the parameters of the electrolytic recovery
of cadmium on fibrous carbon electrodes on their
cycling in electrolyte no. 1 are not deteriorated sig-
nificantly, with only a 10 15% decrease in
served during cadmium recovery via anodic dissolu-
ob-
Cd
It follows from the data of Table 2 that, when
cadmium is dissolved in a cycle through operation
of a short-circuited electrochemical system, the mass
of FCE and its electrical conductivity decrease. This
is due to electrode processes occurring in the cathodic
and anodic periods of the polarization. The decrease
in the FCE mass may also be due to mechanical dis-
integration of carbon fibers. The electrical conductiv-
ity decreases by a factor of 1.7 2. More significant
changes in the FCE properties are observed after cad-
mium is regenerated via anodic dissolution. The FCE
mass increases, whereas the electrical conductivity
decreases by a factor of 6 12, depending on the elec-
trolyte composition. This is due to the formation of
oxide groups on the surface of carbon fibers during
Table 2. Change in mass, m, and electrical conductivity
of FCE after five cycles of cadmium electrodeposition
dissolution
Electrolyte
no.
m,
%
,
Cycle
1
Cm cm
Initial FCE
0.024
0.012
0.014
0.002
0.004
Electrodeposition dissolu-
tion via SES operation
1
2
6.2
3.0
Electrodeposition anodic
dissolution
1
2
+8.2
+7.0
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 2 2007

246
VARENTSOVA, VARENTSOV
tion (Fig. 5a). The mass of cadmium deposited per
unit FCE mass changed only slightly, compared with
that of the starting material.
As for the results obtained in electrolyte no. 2,
the parameters of cadmium electrodeposition on the
electrodes used in five cadmium electrodeposition
dissolution cycles are improved (Fig. 5b). The adhe-
sion of deposited cadmium to the surface of carbon
fibers becomes considerably better, the deposit is
more uniformly distributed across the electrode thick-
ness, and the amount of cadmium deposited per 1 g
of FCE increases to 7 7.5 g.
It is known that the efficiency of the electrochem-
ical process in 3D flow-through electrodes is charac-
terized by a distribution of the potential, polarization,
and local current densities across the electrode thick-
ness. The change in the distribution of the electro-
chemical process across the thickness of the FCM elec-
trode, which is responsible for the change in the effi-
ciency of cadmium electrodeposition in the cyclic
deposition dissolution, may be due to presence of
such components as urotropin and NF dispersant in
electrolyte no. 2. Presumably, the positive effect of
urotropin and NF dispersant on the electrolytic re-
covery of cadmium from ammonium electrolytes is
accounted for by the interaction of these components
with the surface of carbon fibers of the electrode
during its cyclic polarization. To verify this sugges-
tion, special polarization studies were carried out.
A graphite electrode was preliminarily subjected to
up to five cycles of cathodic anodic polarization in
Fig. 5. Kinetic curves of electrolytic recovery of cadmi-
um(II) during electrolysis on initial and regenerated FCE
from electrolyte nos. (a) 1 and (b) 2. (a) Initial cadmium
1
electrolyte nos. 1 and 2 containing 300 mg l of
cadmium(II).
1
2
concentration 300 mgl , n = 20, current density 500 Am
;
1
(b) Initial cadmium concentration 250 mg l , n = 5, cur-
It follows from Fig. 6 that cyclic treatment of FCE
in a solution containing no urotropin and NF disper-
sant (electrolyte no. 1) has virtually no effect on
the run of the polarization curve (Fig. 6, curve 1). In
a solution containing urotropin, the polarization curve
is shifted toward electronegative potentials already
after the first cycle, the slope of the second portion
of the polarization curve markedly increases (Fig. 6,
curve 3), and, consequently, the polarizability is en-
hanced, too. Renewal of the electrode surface by cut-
ting in a solution returns the polarization curve to
the initial state, i.e., makes the run of the polarization
curve similar to that measured in the initial solution
without any cyclic treatment (curve 2). The most sig-
nificant changes in the cathodic portion of the curve
are observed during the first three cycles of polariza-
tion (curves 3, 4), which is probably due to adsorp-
tion of urotropin and NF dispersant on the surface of
carbon fibers. Further increase in the number of po-
2
rent density 750 A m . ( ) Degree of Cd(II) recovery,
( ) time. (1) Initial FCM; FCM after five cycles of
cadmium electrodeposition dissolution (2) through SES
operation, and (3) via anodic dissolution.
Fig. 6. Polarization curves of cadmium(II) recovery in cy-
clic cathodic anodic polarization of a graphite microelec-
trode in electrolyte nos. (1) 1, cycles 1 5; and 2: (2) 1st
cycle, (3) 2nd cycle, and (4) 3rd 5th cycles.
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RECOVERY OF CADMIUM AND CHANGE IN PROPERTIES OF A FIBROUS CARBON ELECTRODE 247
larization cycles has no effect on the cathodic polari-
zation curve.
are not deteriorated upon their cycling. The degree
of electrolytic recovery of cadmium from solutions
containing organic components is 20 30% higher,
the structure of the deposit and its distribution across
the electrode thickness of the electrode are better,
with up to 7.5 g of cadmium deposited per 1 g of
electrode.
CONCLUSIONS
(1) It was demonstrated that cadmium(II) can be
electrolytically recovered from ammonium solutions
formed in catching baths on a fibrous carbon elec-
trode. The structure of the electrolytic deposit of cad-
mium and its distribution across the electrode thick-
ness depend on the solution composition. The amount
of cadmium deposited per 1 g of the fibrous carbon
material is 4.5 6.5 g.
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1
taining 35 40 g l CdSO4 were obtained. In the case
of cadmium regeneration via anodic dissolution,
an electrolytic powder of cadmium can also be ob-
tained.
(4) A change in the mass and electrical conductiv-
ity of fibrous carbon electrodes in their cycling in
electrodeposition dissolution of cadmium was found.
The most pronounced changes were observed in cad-
mium recovery via anodic dissolution: the mass of
the electrode subjected to five cycles increased by
7 8%, whereas its electrical conductivity decreased
by a factor of 6 12, depending on the solution com-
position.
11. Varypaev, V.N. and Krasikov, V.L., Zh. Prikl. Khim.,
1980, vol. 53, no. 3, pp. 586 590.
12. Yatsimirskii, K.B. and Vasil’ev, V.P., Konstanty
nestoikosti kompleksnykh soedinenii (Instability Con-
stants of Complex Compounds), Moscow: Akad.
Nauk SSSR, 1959.
(5) It was found that the characteristics of cad-
mium(II) electroreduction on fibrous carbon electrodes
13. Varentsova, V.I. and Varentsov, V.K., Zh. Prikl.
Khim., 2003, vol. 76, no. 11, pp. 1788 1793.
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