Kinetics of Thallium Dissolution in Aqueous Solutions of Hydrochloric Acid

Article abstract of DOI:10.1134/S0036024419090231

Abstract: Potentiometry is used to study the kinetics of electrochemical oxidation and reduction of thallium in aqueous solutions of hydrochloric acid. Kinetic parameters are calculated to characterize the mechanism of the electro-oxidation of thallium: c

Full text of DOI:10.1134/S0036024419090231

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2019, Vol. 93, No. 9, pp. 1817–1821. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Fizicheskoi Khimii, 2019, Vol. 93, No. 9, pp. 1410–1414.
COLLOID CHEMISTRY
AND ELECTROCHEMISTRY
Kinetics of Thallium Dissolution in Aqueous Solutions
of Hydrochloric Acid
G. T. Sarbaevaa,*, E. Zh. Tuleshovaa,**, G. N. Zhylysbaevaa, and M. T. Sarbaevaa
a Akhmet Yassawi University, Turkestan, 161200 Kazakhstan
* е-mail: gulnar.sarbayeva@ayu.edu.kz
** е-mail: elmira.tuleshova@ayu.edu.kz
Received May 18, 2018; revised November 26, 2018; accepted January 15, 2019
Abstract—Potentiometry is used to study the kinetics of electrochemical oxidation and reduction of thallium
in aqueous solutions of hydrochloric acid. Kinetic parameters are calculated to characterize the mechanism
of the electro-oxidation of thallium: coefficient of diffusion D, heterogeneous rate constant ks of the electrode
process, and effective activation energy Eeff. The effect the modes of electrolysis (current density, electrolyte
concentration, and temperature) have on the dimensional characteristics of the obtained thallium(I) chloride
is studied. The optimum parameters of electrolysis for preparing dispersed powders of thallium(I) chloride
are revealed.
Keywords: potentiodynamic polarization curves, electrochemical behavior, thallium, hydrochloric acid, cur-
rent density
DOI: 10.1134/S0036024419090231
INTRODUCTION
alternating current would therefore seem to be relevant
and timely.
One of the main priorities of innovative industrial-
ization is the development of metallurgy and the pro-
duction of finished metal products and their com-
pounds. It is therefore important to use new ways of
producing metals and their compounds, or to extract
them from solutions. One promising technique now in
use is polarization with an alternating current of
industrial frequency, which is of interest to researchers
in regard to the oxidation with destruction of passivat-
ing films. A feature of the processes that occur under
the action of alternating current of industrial frequency
is that by changing the direction of the current, it is pos-
sible to remove oxide films and create conditions for the
subsequent dissolution of the metal [1–6].
Of special interest are electrochemical processes
with the participation of metals—thallium in particu-
lar, due to the increasing need for it in different
branches of medicine, technology, and industry. Sys-
tematic studies that allow us to establish patterns of the
electro-oxidation of thallium with the subsequent syn-
thesis of its compounds, could result in both intensifi-
cation of its production and the solving of resource-
saving problems.
The aim of this work was to study the patterns of the
electrochemical behavior of thallium upon its polar-
ization with a sinusoidal alternating current and a
preparation of thallium(I) chloride.
EXPERIMENTAL
To clarify the mechanism of oxidation reactions
that proceed on metallic thallium surface, we studied
its electrochemical behavior using an Autolab poten-
tiostat. Data were recorded with ІPC 2000 program.
Measurements were made in a three-electrode cell,
relative to a silver chloride electrode (E0 = +0.203 V).
An auxiliary electrode was made of platinum. Voltam-
mograms were obtained mainly at potential sweep
rates of 50–250 mV/s. To clarify the mechanism
behind the processes that occur during polarization by
alternating current, the electrodes were subjected to
cyclic polarization; i.e., the curves were recorded in
both the cathodic–anodic and the anodic–cathodic
directions.
To study the electrochemical behavior of thallium
in a solution of hydrochloric acid, our main experi-
ments were performed in a 100 mL cell with no sepa-
ration of the electrode spaces. We used working elec-
trodes in the form of thallium plates with surface areas
In [7–11], we studied the electrochemical behavior
of different metals under polarization with alternating
current of industrial frequency. Analysis of the litera-
ture data showed there were very few works devoted to
the electrochemical behavior of thallium. Studying the of ~4.3 cm2. Before each experiment, the electrodes
ionization of thallium under the action of industrial were thoroughly cleaned, degreased, and washed with
1817

1818
SARBAEVA et al.
cathodic current maximum corresponding to the
ꢀ0.008
ꢀ0.006
ꢀ0.004
ꢀ0.002
0
reduction of the thallium(I) chloride film formed on
the electrode surface was recorded when the potential
of thallium electrode shifted to negative values, and
the hydrogen ions were reduced at a potential of
−1.4 V. When the electrode potential was shifted in the
positive direction, the anodic current maximum cor-
responding to thallium anodic oxidation was recorded
at potentials of −0.6 to −0.7 V. Up to a potential of
+1.0 V, the voltammetric curve did not show any max-
ima of the subsequent oxidation of thallium ions or the
oxidation of chloride ions.
0.002
0.004
0.4 0.2
0
ꢀ0.2 ꢀ0.4 ꢀ0.6 ꢀ0.8 ꢀ1.0 ꢀ1.2
The concentration of the solution affected the
reaction of thallium electrodissolution. We found that
when the concentration of hydrochloric acid was var-
ied within 0.5–4.0 M, the potential of the thallium
electrode was −0.6 to −0.7 V. When the thallium elec-
trode potential was shifted toward the positive poten-
tial values, the voltammetric curves show that anodic
current values grew with an increase in the concentra-
tion of hydrochloric acid. It was established that at
potentials higher than −0.2 V, the rate of thallium dis-
solution did not grow; from that moment on, a film of
thallium chloride formed on the surface of the metal
dissolving in the transpassive mode. The anodic
curves of thallium oxidation in an aqueous solution of
hydrochloric acid were measured at the potential
sweep rate in the range of 25–250 mV/s (Fig. 2). The
observed oxidation current grew along with the poten-
tial sweep rate.
We calculated two kinetic parameters to character-
ize the electrooxidation of thallium according to Galus
[12]: the diffusion coefficient (D = 8.4 × 10−5 cm2/s)
and the heterogeneous rate constant of the electrode
process (ks = 2.6 × 10−1 s−1). It was established that
thallium does not dissolve anodically in a solution of
hydrochloric acid. When polarized by an industrial
alternating current with a frequency of 50 Hz, it dis-
solves with a high current efficiency with formation of
thallium chloride. We established that under optimum
conditions, monovalent ions form on the surface of a
thallium electrode in the anodic half-period, and
hydrogen is released in the cathodic half-period.
Fig. 1. (Color online) Cathodic/anodic potentiodynamic
cyclic polarization curve in a hydrochloric acid solution;
C = 2.5 M; sweep rate, 250 mV/s; t = 25°С.
distilled water. Hydrochloric acid of analytical grade
and bidistilled water were used to prepare solutions.
Sinusoidal alternating current was supplied from
V-24 power block (basically a step-down transformer
that allowed smooth regulation of the current) with
AC terminals. The current in the circuit was measured
with an ABO-5MI multimeter. Changes in the shape
of the sinusoidal alternating current during electrolysis
were observed using an S1-77 oscilloscope. The oscil-
loscope also was used to observe the ratio of the ampli-
tudes of the anodic and cathodic half-cycles of the
alternating current. A GZM sound-frequency genera-
tor was connected to the setup to study the effect the
frequency of the alternating current had on the rate of
thallium dissolution in an electrochemical circuit.
This allowed electrolysis to be conducted at frequen-
cies from 20 to 20000 Hz. A special YaSE-2 electro-
lytic cell, mounted in an ITZh-0-03 thermostat, was
used for studies at a constant temperature.
The sizes and shapes of the particles of the resulting
thallium(I) chloride were determined on a JSM 6490
LA scanning electron microscope with a magnifica-
tion of ×10000. An LS 13320 laser analyzer with a liq-
uid water module was used to study the size distribu-
tion of thallium(I) chloride particles. The range of
particle size measurement was 0.020 to 200 μm. Laser
light with a wavelength of 750 nm, formed in an ultra-
sonic emitter combined with an LS 13320 unit, was
used to measure the particles via diffraction. X-ray dif-
fraction analysis was performed on a DRON-3.0 dif-
fractometer. The counter rotated at a rate of
2 deg/min.
We studied the effect the density current on a thal-
lium electrode in the formation of thallium(I) ions in
the range of 6000–16000 A/m2 (Table 1). It was found
that thallium does not dissolve at low current densi-
ties. When polarized with an alternating current in a
solution of hydrochloric acid, the rate of thallium dis-
solution with the formation of TlCl increases. For
example, the rate of thallium dissolution at 6000 A/m2
is 83.11 g/(cm2 h). With a current density of
16000 A/m2, it is 198.2 g/(cm2 h). Upon an increase in
the density of alternating current in its anodic half-
period, the rate of oxide film formation slows, and
thallium(I) chloride forms as a result. At high densities
The laws of the dissolution of a thallium electrode
in a solution of hydrochloric acid were preliminarily
established by recording the cathodic, anodic, and
cyclic potentiodynamic polarization curves. The effect
the concentration of hydrochloric acid and the poten-
tial sweep rate had on the reduction of the thallium
electrode was studied. Figure 1 shows the cyclic
cathodic–anodic polarization curve measured on the (above 16000 A/m2), the electrode overheats, and
thallium electrode in hydrochloric acid solution. The electrolysis becomes difficult. Current densities of
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KINETICS OF THALLIUM DISSOLUTION
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6
5
Imax, A
−0.008
−0.006
−0.004
−0.002
0
4
0.008
0.006
0.004
3
0 50100150200250
v, mV/s
2
1
−0.7
−0.8
−0.9
−1.0
−1.1
−1.2
−1.3
−1.4
Fig. 2. (Color online) Cathodic potentiodynamic polarization curves of thallium at different potential sweep rates V: (1) 25,
(2) 50, (3) 100, (4) 150, (5) 200, (6) 250 mV/s; t = 25°С; C
= 2.5 M. The insert shows the dependence of the cathodic current’s
HCl
maximum on the potential sweep rate.
14 000–16000 A/m2 are thus considered optimal. It
should be noted that the rate of thallium dissolution
during anodic polarization (i.e., when the metal was
polarized with alternating current) did not exceed
0.01 g/(cm2 h). When polarized with industrial alter-
nating current, the rate of thallium dissolution grew by
more than 104 times. The rate of the metal’s dissolu-
tion was determined using the formula
tion of thallium was determined using the results from
our experiment:
n[xy − xy
2
b =
n
x2 −
x
(
 
)
5 × 4.4877 − (3.322 × 6.274)
5 × 2.5207 − (3.322)2
=
= 1.01.
The effect the temperature of the electrolyte has on
the rate of thallium dissolution during the polarization
of thallium electrodes by an unsteady current in an
acidic medium was considered in the range of 20–
80°C at a current density of 6000 A/m2 (Table 3). At an
alternating current density of 6000 A/m2, an increase
in the rate of thallium electrode dissolution was
observed when the temperature of the solution was
raised from 20 to 80°C: It grew from 34.63 to
583 g/(cm2 h). The activity of the acid apparently
increased along with the temperature of the electro-
lyte, so the rate of interaction and the mobility of ions
in the solution grew as well. The activation energy
(Eeff) of the process was calculated from the depen-
dence of the current efficiency on the temperature of
the electrolyte: 6.214 kJ/mol. It was established that
mpract
sτ
ϑdiss
=
= g/(сm2 h).
The effect the concentration of hydrochloric acid
had on the formation of thallium(I) ions was studied in
the range of 2.0–10.0 M. High concentrations of
hydrochloric acid had a strong effect on the formation
of thallium(I) chloride. At an initial concentration of
2.0 M, the rate of thallium dissolution was
58.86 g/(cm2 h); at 10.0 M, it was 198.2 g/(cm2 h)
(Table 2). The increase in the thallium electrode dis-
solution rate at high concentrations was apparently
associated with an increase in the activity of chloride
and hydrogen ions, when chloride ions aggressively
attacked the metal crystal lattice. Interaction of Cl−
ions with Tl+ formed in the anodic half-cycle of alter-
nating current results in formation of TlCl. The
increase in the acid concentration also prevented the
formation of an oxide film on the surface of the elec-
trode. Being a metal with a negative potential, capable
to reduce hydrogen ions, it dissolves with the forma-
tion of its own ions. The reaction order of the oxida-
Table 1. Effect of alternating current density (i) on the rate
of thallium dissolution ( diss) with the formation of thal-
v
lium(І) ions at СHCl = 10 M, τ = 0.5 h, and t = 20°С
і × 10–3, А/m2
diss, g/(cm2 h) 83.11
6
8
10
14
16
95.6 125.84 154.5 198.2
v
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 93 No. 9 2019

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SARBAEVA et al.
solution from 34.63 to 1.22 g/(cm2 h). This change was
due to a reduction in the average current amplitude as
the AC frequency rose, weakening the polarization of
the electrodes. At high frequencies, the duration of the
anodic half-period required for the dissolution reac-
tion to proceed was also not ensured.
Table 2. Effect of hydrochloric acid concentration on the
rate of thallium dissolution with the formation of thal-
lium(І) ions at і = 16000 A/m2, τ = 0.5 h, and t = 20°С
СHCl, М
2.0
4.0
6.0
8.0
10.0
diss, g/(cm2 h) 58.86 94.1 147.36 168.5 198.2
v
Electrochemically obtained thallium(I) chloride
was studied via X-ray phase analysis on DRON-3 dif-
fractometer in the 10°–50° range of angles. The pres-
ence in the XRD pattern of thallium(I) chloride sam-
ple of diffraction lines with interplanar distances of
6.5, 3.6, 3.45, 3.34, 3.17, 2.86, 2.78, and 2.3 Å corre-
sponds to the values in the ASTM card file. These dif-
fraction peaks are characteristic of the crystal lattice of
thallium(I) chloride. The XRD pattern of electro-
chemically synthesized thallium(I) chloride is shown
in Fig. 3.
The sizes and shapes of the particles of the resulting
compound were determined from micrographs
obtained using a JSM 6490 LA scanning electron
microscope. Several microphotographs were taken for
each sample of thallium chloride obtained after elec-
trolysis, allowing us to determine the dispersed com-
position of the powder. Micrographs of thallium(I)
chloride are shown in Fig. 4.
Table 3. Effect of solution temperature (t) on the rate of
thallium dissolution with the formation of thallium(І) ions
at і = 6000 А/m2, τ = 0.5 h, and СНСl = 10 М
t, °C
20
40
60
80
diss, g/(cm2 h)
34.63
40.2
49.5
58.3
v
Table 4. Effect of alternating current frequency (ν) on the
rate of thallium dissolution with the formation of thal-
lium(I) ions at і = 6000 А/m2, τ = 0.5 h, and СНСl = 10 М
ν, Hz
50
100 200 300 400 500
5.0 3.8 2.45 1.22
diss, g/(cm2 h) 34.63 7.3
v
the electrochemical dissolution of thallium proceeds
in the diffusion mode.
One of our main electrochemical parameters was
the frequency of the alternating current. We therefore
studied the effect the frequency the alternating current
had on the rate of thallium dissolution with the forma-
tion of thallium(I) ions in hydrochloric acid solution
(Table 4). Our study was conducted in the frequency
range of 50–500 Hz. An increase in the frequency of
CONCLUSIONS
From the measured cyclic potentiodynamic polar-
ization curves, it was established that fairly complex
electrochemical reactions occur in a solution of
hydrochloric acid on a thallium electrode. Patterns of
the kinetics of thallium oxidation in an acidic medium
the alternating current slowed the rate of thallium dis- were identified. Under normal conditions, a protective
3.34
6.5
2.78
3.45
3.17
2.86
2.3
3.6
22
50
46
42
38
34
30
26
18
14
10
Fig. 3. XRD pattern of thallium(I) chloride, obtained electrochemically.
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KINETICS OF THALLIUM DISSOLUTION
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1.481 μm
1.444 μm
1.444 μm
1.710 μm
1.710 μm
1.279 μm
1.279 μm
(а)
(b)
Fig. 4. (Color online) Micrographs of thallium chloride: (a) ×1000, (b) ×10 000.
5. G. A. Seilkhanova, E. Zh. Usipbekova, A. Berezovskii,
and A. P. Kurbatov, Izv. NAN RK, No. 1 (403), 104
(2014).
film forms on a surface of thallium, making it difficult
to dissolve. When polarized with an alternating current
in an acidic medium, thallium dissolves to form corre-
sponding compounds. Fine precipitate of thallium(I)
chloride were obtained via electrochemical synthesis.
These and other data we obtained in earlier studies can
serve as theoretical bases for creating new ways of syn-
thesizing a number of compounds that are widely used
in various industries.
6. O. A. Petrii, G. A. Tsirlina, and Z. V. Kuzminova, Elek-
trokhimiya 31, 999 (1995).
7. E. Zh. Tuleshova and A. Bayeshov, Russ. J. Appl.
Chem. 88, 1142 (2015).
8. G. T. Sarbaeva, A. B. Baeshov, U. A. Abdualieva, and
E. Zh. Tuleshova, Vestn. NAN RK, No. 2, 73 (2017).
9. E. Zh. Tuleshova, A. Bayeshov, and A. Tukibayeva,
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Translated by M. Aladina
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 93 No. 9 2019