Nature of the Cathode Polarization during Reduction
of Chromate Ions in Alkaline Solutions
Z. G. Gasanly and M. N. Mamedov
Institute of Chemical Problems, National Academy of Sciences of Azerbaijan, Baku, Azerbaijan
Received May 12, 2009
Abstract—The effect of potential scanning rate and temperature on the kinetics of the reduction of chromate
ions in alkaline solutions was studied, and the nature of polarization in separate stages of the cathode process
ISSN 1070-4272, Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 12, pp. 2217–2219. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © Z.G. Gasanly, M.N. Mamedov, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 12, pp. 2072–2074.
The main raw materials for obtaining alumina are
bauxites which contain 0.01–0.045% of chromium .
When this raw material is processed into alumina by
Bayer’s method, resulting aluminate solutions contain
0.004–0.005 M of chromium.
The effect of certain admixtures (V, Si, Ti, Fe, etc.),
which present in industrial aluminate solutions, on
gallium electrowinning was studied in [2–4], however
we have not found any data on the influence of
chromium on the kinetics of gallium electrowinning. In
this connection the study of the kinetics of the
reduction of chromate anions in alkaline solutions was
The solution was prepared by dissolving 0.005 mol
in a 6 M NaOH solution. Concentrations of
chromium and alkali in this solution corresponded to
the concentrations of industrial aluminate solutions at
alumina plants operating by Bayer’s method .
The experiments were carried out in a 100 ml cell.
Polarization curves (PC) were obtained under potentio-
dynamic conditions on a P-5827 M potentiostat and
recorded on an N 301/1 flat-bed two-coordinate
recorder. A wire Pt-electrode with an area of 0.22 cm
was used as a working electrode, an anode was a
platinum plate with a working surface area of 10 cm
The cathode potential was measured relative to a
saturated silver chloride electrode. Results of the
experiments are shown in Figs. 1–5.
It is seen from Fig. 1 (curves 1–4) that the cathode
polarization curves contain two sections corresponding
to the reduction of chromate anions. It points to the
fact that the reduction of chromate anions proceeds in
two stages (I, II). In section I of the polarization curves
in the range of potentials from –0.18 to –0.52 V
chromate-ions are reduced in an alkaline solution up to
ions. Therewith the color of the solution changes
from yellow up to virescent. In section II of the
Fig. 1. Potentiometric polarization curves of the chromate
ions reduction at various potential scanning rates (T = 25°C).
Solution: 6 M NaOH + 0.005 M CrO
; the same for Fig. 3.
) current density, A dm
, (E) potential (V); the same for
Fig. 3. Scanning rate (mV s
): (1) 20, (2) 40, (3) 60, (4) 80.
, A dm