ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 9, pp. 1487!1491. + Pleiades Publishing, Ltd., 2008.
Original Russian Text + T.I. Markovich, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 9, pp. 1413!1417.
AND INDUSTRIAL INORGANIC CHEMISTRY
Kinetics of Iron(II) Oxidation in Pyrrhotine Leaching with Acid
Sulfate Solutions in the Presence of Nitrous Acid
T. I. Markovich
Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Received September 10, 2008
Abstract-Variation of the ratio between the concentrations of Fe
ions in leaching of pyrrhotine
with acid sulfate solutions containing HNO
was studied for the example of the oxidation of iron(II) with
molecular oxygen, which widely occurs in the nature and is widely used in hydrometallurgy.
According to modern concepts, oxidative leaching
of iron sulfides in acid media is not limited to only a
topochemical reaction, but may also include multi-
step reaction between molecular oxygen and solu-
tions of iron(II) salts [1, 2].
One of methods for raising the rate of this proc-
ess is to use activating agents, nitrogen compounds
(oxides, nitrates, nitrites, etc.) . The mechanism
of catalysis is rather complex and has not been
elucidated so far. In the course of oxidation, quite
a number of species (NO, N
) with widely
different activating capacities can be formed in vari-
ous amounts and disappear. According to numerous
experimental studies, nitrous acid and products of its
dissociation are the most kinetically reactive species.
As shown in [4, 6], the activating effect of HNO
low concentrations (<1 M) exceeds severalfold the
catalytic activity of all other oxygen compounds of
Another way to accelerate the oxidation of Fe
is based on passing from the homogeneous mech-
anism of activation of molecular O
to a heterogene-
ous mechanism based on the capacity of a number
of solid substances to absorb dissolved oxygen on
active centers of their surface .
This study is concerned with the behavior of
iron(II) in the system Fe
in decomposition of the solid sulfide
phase that can chemisorb dissolved oxygen .
We studied the kinetics of Fe
sulfuric acid solutions containing nitrous acid in
parallel with an analysis of the process of pyrrhotine
breakdown. For this purpose, we used polydisperse
samples (53374-mm fraction) of the selective pyrrho-
tine concentrate from the Norilsk deposit, which
contained, according to the results of an X-ray
phase analysis, 93.2% Fe
S, 1.5% CuFeS
A weighed portion of the sulfide was leached
under temperature control and continuous agitation
with an upper drive in a closed reaction vessel
equipped with a sampler with a finely porous filter, a
batcher for an activating solution, and a system for
delivery and discharge of gases, which provided
oxygen supply to the reaction zone at a pressure of
1 atm. Nitrous acid was produced by the reaction
by batching a sodium nitrite solution directly into
the reaction pulp at prescribed intervals of time.
The catalyst supply mode was developed with ac-
count of the occurrence of concurrent processes in
the oxidizing system and made it possible to main-
tain the concentration of nitrous acid at a level as
close as possible to the prescribed value of 0.001 M.
The initial concentration of sulfuric acid in the
, was varied from 0.25 to 1.02 M,
and the temperature of the experiment, in the
range 2933333 K. The concentration of nitric acid
(0.001 M), angular velocity of stirrer rotation (w =
), and oxygen pressure (P
were maintained constant in all the experiments. The
s : l ratio was 1 : 100 (2 g of the sulfide per 200 ml
of the solution).