Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 1, pp. 48−53.
Pleiades Publishing, Ltd., 2014.
Original Russian Text T.P. Petrova, E.E. Starodubets, A.M. Shapnik, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 1, pp. 52−57.
OF ELECTROCHEMICAL INDUSTRY
Kinetics of Electrode Processes on a Bismuth Electrode
in Acid Solutions Containing Thiourea
and Formamidine Disulphide
T. P. Petrova, E. E. Starodubets, and A. M. Shapnik
Kazan National Research Technological University, ul. Karla Marksa 68,
Kazan, Tatarstan, 420015 Russia
Received December 30, 2013
Abstract—A study of the mechanism by which bismuth is electrodissolved in an aqueous solution of thiourea on
the background of H
demonstrated that, in the thiourea concentration range 0.001 M < c < 0.5 M, a current
oscillation is observed in cyclic voltammograms at E ≈ 0.4–0.3 V when the potential is swept from the anodic to the
cathodic region. This oscillation is due to the loosening of the passivating ﬁ lm formed in the anodic process. It is
shown that thiourea is not oxidized to formamidine disulphide at the bismuth electrode. thiourea and formamidine
disulphide have mutually opposite effects on the height of the cathodic peak: the peak current falls with increasing
thiourea concentration and grows with increasing formamidine disulphide concentration. According to the results
of an X-ray ﬂ uorescence analysis, sulfur is formed on the bismuth electrode upon its prolonged polarization of in
a 0.5 M solution of thiourea. An explanation is provided for the experimental facts observed in the study.
In recent years, interest has been growing in electro-
chemical processes containing thiourea (Thio), which is
used as inhibitor of steel  and copper  destruction
in acid media and reagent in electrodeposition of metals
[3–5]. Thiourea solutions are regarded as an alternative
to toxic cyanide electrolytes in hydrometallurgy in re-
covery of gold and silver from minerals [6–10].
The purpose of our study was to determine the
mechanism by which bismuth is electrodissolved in
an aqueous solution of thiourea on the background of
sulfuric acid. To understand the processes occurring on
the surface of a bismuth electrode, we simultaneously
examined the redox reactions involving formamidine
disulphide (FDS), which is known to be the oxidation
product of Thio [11–13]. Previously, similar studies
have been carried out with a platinum electrode .
All the electrochemical measurements were made
with an IPC Pro MF potentiostat in a three-electrode cell
with separated cathode and anode spaces. A personal
computer served as recording device. As the bismuth
electrode served the edge of a Bi00 bismuth rod with an
apparent surface area of 0.28 cm
, embedded in Teﬂ on.
The electrode preparation procedure was described in
detail in . The solutions to be studied were prepared
with twice-distilled water and sulfuric acid of chemically
pure grade. Thiourea of chemically pure grade was twice
recrystallized from aqueous solutions. Formamidine
disulphide was synthesized by the method suggested
in . All the experiments were performed in freshly
prepared naturally aerated solutions at a temperature of
293 K. The potentials are given relative to a Ag/AgCl
(3 M KCl) reference electrode.
The X-ray ﬂ uorescence analysis was used to deter-
mine whether thiourea or products of its destruction can
be incorporated into the anodic ﬁ lm. The analysis was
made at the Collective Usage Center “Nanotechnologies
and nanomaterials” at Kazan National Research
Technological University on a SUR-02 RENOM-FV