1070-4272/02/7505-0849$27.00C2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 5, 2002, pp. 849!851. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 5,
2002, pp. 866!868.
Original Russian Text Copyright + 2002 by Natorkhin.
Effect of KBr Additions on NiS Anodic Dissolution
in Sulfate Electrolytes
M. I. Natorkhin
St. Petersburg State Technical University, St. Petersburg, Russia
Received October 21, 1999; in final form, July 2001
Abstract-Electrochemical behavior of nickel sulfide (NiS) in 0.5 M solutions of Na
at pH 2.032.2 and T =90oC was studied. A possibility was shown for depassivation and efficient dissolution
of nickel sulfides upon addition of KBr to the electrolyte.
Oxidative dissolution of sulfides of non-ferrous
metals is a promising hydrometallurgical process
. As found previously [4, 5], autoclave leaching
solution results in active dissolution of
nickel sulfides with H
S evolution. However, utiliza-
tion of the forming H
S is a serious problem, and
therefore efforts are made to develop alternative proce-
dures for leaching of nickel concentrates.
In this study we examined the effect of bromide
ions on the anodic dissolution of nickel sulfide in
acidic sulfate solutions.
According to , autoclave leaching of lower nick-
el sulfides (Ni
) results in stepwise for-
mation of sulfides with increasing sulfur content, up
to NiS. Therefore, for our study we chose b-NiS with
50% nickel content obtained by a direct synthesis
from cathodic nickel (N0 grade) and sulfur (analytical-
ly pure grade) . The working electrode was made
by soldering a piece of nickel sulfide to a copper
holder. The back side of the electrode was insulated
with nitrolacquer. The working surface of the elec-
trode (surface area 1 cm
) was smoothed out with
a flint-paper no. 0 and washed with alcohol and di-
stilled water. Electrolytes was prepared using Na
O (both analytically pure grade).
Solution pH 2.032.2 was adjusted with a solution of
(ultrapure grade). Potassium bromide was of
chemically pure grade.
The study was carried out by cyclic voltammetry
(CVA) on a PI-50-1.1 potentiostat and a PDP4-002
recorder in a YaES-1 standard electrochemical cell at
90+ 0.5oC (Fig. 1). The temperature was controlled
with a UTU-2/77 thermostat. We used the following
three-electrode scheme: nickel sulfide sample as
a working electrode, platinum auxiliary electrode, and
saturated silver chloride reference electrode (the po-
tentials are referenced to standard hydrogen electrode).
To carry out the experiments, we filled the cell
with 50 ml of 0.5 M solutions of CuSO
with a KBr addition. The nickel(II) content in the
anolyte was determined by the known photometric
procedures [8, 9].
The anodic dissolution of nickel sulfide in CuSO
solution is accompanied by electrode passivation
Fig. 1. Cyclic voltammograms of NiS (50%) in solutions
of (1) 0.5 M CuSO
and (2) 0.5 M CuSO
+ 100 g l
KBr at pH 2.1. Temperature 90+0.5oC, scanning rate
100 mV s
; the same for Fig. 3. (I) Anode current and
(E) potential; the same for Fig. 3.