Kinetics of the interaction of iron, copper, and nickel sulfides with a sodium nitrate-sodium carbonate mixture

Article abstract of DOI:10.1134/S0036023611060052

The interaction of FeS₂, Cu₂S, and Ni ₃S₂ with sodium nitrate and sodium carbonate between 573 and 973 K has been investigated by chemical analysis, X-ray diffraction, electron probe X-ray microanalysis, and thermal analysis. The kinetic limitations in these reactions are due to the formation of a passivating layer of reaction products on metal sulfide particles. The solid products of the reactions are sodium sulfate, Fe₂O₃, CuO, NiO, and copper metal. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S0036023611060052

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 6, pp. 831–834. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © E.V. Bogorodskii, S.G. Rybkin, V.G. Barankevich, 2011, published in Zhurnal Neorganicheskoi Khimii, 2011, Vol. 56, No. 6, pp. 883–887.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Kinetics of the Interaction of Iron, Copper, and Nickel Sulfides
with a Sodium Nitrate–Sodium Carbonate Mixture
E. V. Bogorodskii, S. G. Rybkin, and V. G. Barankevich
Irkutsk Research Institute of Noble and Rare Metals and Diamonds, bul’v. Gagarina 38, Irkutsk, 664025 Russia
Received September 4, 2009
Abstract—The interaction of FeS , Cu S, and Ni S with sodium nitrate and sodium carbonate between 573
2
2
3 2
and 973 K has been investigated by chemical analysis, Xꢀray diffraction, electron probe Xꢀray microanalysis,
and thermal analysis. The kinetic limitations in these reactions are due to the formation of a passivating layer
of reaction products on metal sulfide particles. The solid products of the reactions are sodium sulfate, Fe O ,
2
3
CuO, NiO, and copper metal.
DOI: 10.1134/S0036023611060052
Noble metals in ores of various mineralogical types per and nickel sulfides (Cu2S and Ni3S2) with a
and in the products of their processing are usually
determined by assaying. In this method, samples of the
material to be analyzed are melted with fluxes and a
[NaNO + Na CO3] mixture.
3 2
collector at 1000–1300
°
С. Upon melting, the rockꢀ
EXPERIMENTAL
The starting chemicals were sodium nitrate (anaꢀ
lytical grade), sodium carbonate (analytical grade),
and natural pyrite (monomineral FeS2 fraction).
forming oxides pass into slag and the noble metals
concentrate quantitatively in the collector. After coolꢀ
ing the melt, the collector is separated from the slag
and is then chemically processed to determine the
noble metal content.
The most common and most economical variant of
assaying includes assay smelting with a lead collector,
which yields a lead button, and subsequent cupellation
Nickel sulfide Ni3S and copper sulfide Cu2S were synꢀ
2
thesized by melting the respective metal sulfates
(
reagent grade) with a carbonaceous reductant under a
layer of anhydrous sodium tetraborate (Na B O7) in a
2
4
corundum crucible at 1000–1200 С. The composiꢀ
°
(
oxidizing melting) of the button in a magnesite cupel
tion of the metal sulfides was checked by chemical
analysis and Xꢀray diffraction. The reactants were used
as powders with a particle size of <0.3 mm.
to obtain the desired gold–silver of silver regulus [1].
In the analysis of sulfide ores and products by this
method, the initial material is pretreated to decomꢀ
pose the sulfides. This is usually done by oxidative firꢀ
ing of the sample at 500–800
chloric acid leaching [2, 3].
Stoichiometric amounts of a metal sulfide and
°
С
or by sulfuric or hydroꢀ sodium nitrate and carbonate were mixed in a porceꢀ
lain mortar. The resulting mixture was placed in a
stainless steel boat, which was covered with a lid. The
boat was placed in a resistance muffle furnace preꢀ
heated to the preset temperature. The duration of isoꢀ
thermal heat treatment was 1–60 min. Thereafter, the
boat was withdrawn from the furnace and was cooled.
The resulting cake was taken out of the boat, weighed,
The auxiliary operations involved in the decompoꢀ
sition of sulfide minerals in fire assaying with a lead
collector make the process more costly and lower the
analytical accuracy because of the possible entrainꢀ
ment of noble metals by acid leach solutions and oxiꢀ
dative firing gases. It is, therefore, of scientific and
practical interest to improve the process of sulfide ore
assay smelting with a lead collector. It is desired that
sulfide mineral decomposition and sample melting be
combined in one processing step and take place
through the physical and chemical interaction of samꢀ
ple components with the fluxes and additions making
up the assay stock.
crushed, and leached with water at 60 С for 40 min.
°
The pulp was filtered and the insoluble residue of the
cake was dried, weighed, and analyzed for sulfide sulꢀ
fur and oxidized sulfur by chemical methods.
The Xꢀray powder diffraction patterns of the metal
sulfides, cakes, and insoluble residues of the cakes
were obtained on a DRONꢀ2 diffractometer (Cu
K
α
Statistical analysis demonstrates that gold, silver, radiation). Phases were identified by comparing
and platinumꢀgroup metals in sulfide ores are typically experimental data with reference data from the
accompanied by iron, copper, and nickel sulfide minꢀ ICPDS database of 1997. The structure of the insoluꢀ
erals [4]. Here, we report the kinetics of the interacꢀ ble residues of the cakes was studied using a CAMEꢀ
tion of iron disulfide (FeS2) and thermally stable copꢀ BAX SX50 electron probe Xꢀray microanalyzer. The
831

832
BOGORODSKII et al.
1
20
00
1
300
°С
°С
°С
°С
°С
400
500
600
700
80
60
40
20
Fe O
2
3
0
10
20
30 40
Time, min
50
60
70
FeS2
Fig. 1. Kinetics of interaction in the FeS , NaNO ,
2
3
Na CO mixture.
(а)
100 μm
2
3
samples to be examined were fixed in epoxy blocks and
were then ground and polished.
100 мкм
Fe O
2
3
RESULTS AND DISCUSSION
Interaction between FeS and [NaNO + Na CO ]
2
3
2
3
According to Xꢀray diffraction and chemical analꢀ
ysis data, the solid products of the interaction between
FeS2 and the sodium nitrate–sodium carbonate mixꢀ
ture are sodium sulfate Na SO and iron(III) oxide
FeS2
2
4
Fe O3. Thermodynamic calculations show that the
2
°
G
(b)
100 μm
Gibbs energy (
Δ
) of reaction (1) at 300–700°C
t
under normal conditions is negative and increases
negatively from –6494.3 to –7080.1 kJ/mol as the
temperature is raised in this interval. Therefore, this
reaction is thermodynamically favorable under norꢀ
mal conditions.
Fig. 2. Iron oxide–covered pyrite grains in the mixture
heatꢀtreated T 300 for 60 min.
°С
kinetic limitations preventing complete iron disulfide
decomposition are caused by the fairly dense films of
reaction products on comparatively large pyrite grains.
These films block the access of sodium nitrate and carꢀ
bonate to iron disulfide.
6
FeS + 18NaNO + 3Na CO
2 3 2 3
(1)
=
3Fe O + 12Na SO + 9N + 3CO .
2 3 2 4 2 2
The kinetic data obtained for reaction (1) are preꢀ
sented in Fig. 1. In the temperature range from 400 to
7
9
00°C, the reaction under isothermal conditions is
5–98% complete within 3–5 min. At 300 , the
Interaction between Cu S and [NaNO + Na CO ]
2
3
2
3
°
С
According to Xꢀray diffraction and chemical analꢀ
ysis data, the solid products of the interaction between
Cu2S and the sodium nitrate–sodium carbonate mixꢀ
reaction begins after a ~15ꢀminꢀlong delay, but it nevꢀ
ertheless reaches a 94–95% conversion level as the isoꢀ
thermal heat treatment is continued.
ture are Na SO4 and copper(II) oxide CuO. Thermoꢀ
An electron probe Xꢀray microanalysis of the insolꢀ
2
uble residues that resulted from the aqueous leaching dynamic calculations show that ΔG°t for reaction (2)
of the cakes revealed the cause of the kinetic limitaꢀ
at 300–700 С under normal conditions is negative and
°
tions responsible for the incomplete decomposition of
iron disulfide. Some coarse grains of iron disulfide
have a porous Fe O coating on their surface. These
increases negatively from –3186.6 to –3366.3 kJ/mol
as the temperature is raised in this interval. Therefore,
this reaction is thermodynamically favorable under
normal conditions.
2
3
oxide coatings have a layered structure. They nonuniꢀ
formly cover the sulfide grains and have a thickness of
5–50
μ
m. In most cases, the thick porous coating is on
5Cu
S + 8NaNO + Na CO
2 3 2 3
(2)
one side of the grain, while the rest of the grain is covꢀ
ered by an ordinary, thin oxide film (Fig. 2).
=
5Cu + 5CuO + 5Na SO + 4N + CO .
2
4
2
2
The fact that the Fe O coating has a porous strucꢀ
The kinetic data obtained for reaction (3) are preꢀ
, the reaction proceeds very
2
3
ture suggests that the pores are filled with Na SO4, the sented in Fig. 3. At 300 С
°
2
waterꢀsoluble product of the reaction. Thus, the slowly: copper sulfide decomposes to the extent of
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 6 2011

KINETICS OF THE INTERACTION
833
1
20
00
1
300
°С
°С
°С
°С
°С
400
500
600
700
80
60
40
20
CuO
Cu2S
0
10 20 30 40 50 60 70
Time, min
100 µm
Fig. 3. Kinetics of interaction in the Cu S, NaNO ,
Fig. 4. SEM image of a copper oxideꢀcovered copper sulꢀ
fide grain in the mixture heatꢀtreated at 400 for 60 min.
2
3
Na CO mixture.
°С
2
3
1
20
00
1
5
00
°
°
°
°
°
С
80
550
С
С
С
С
CuO
Cu
60
6
6
00
50
40
0
700
2
0
10 20 30 40 50 60 70
Time, min
50 µm
Fig. 5. SEM image of a copper oxide grain with copper
metal inclusions in the mixture heatꢀtreated at 600°C for
Fig. 6. Kinetics of interaction in the Ni S , NaNO ,
3 2 3
60 min.
Na CO3 mixture.
2
only 17% as a result of 60ꢀminꢀlong isothermal heat
treatment of the mixture. The reaction rate increases
Interaction between Ni S and [NaNO + Na CO ]
3 2 3 2 3
According to Xꢀray diffraction and chemical analꢀ
ysis data, the solid products of the interaction between
Ni3S2 and the sodium nitrate–sodium carbonate mixꢀ
as the temperature is raised, and, at 600
°
С, the extent
of decomposition of Cu2S is 98–99% in 10 min.
An electron probe Xꢀray microanalysis of the insolꢀ ture are Na
uble residues of the cakes obtained by isothermal heat
treatment of the initial stock at 400 demonstrated
SO
namic calculations show that ΔGt° for reaction (3) at
00–700 under normal conditions is negative and
and nickel(II) oxide NiO. Thermodyꢀ
2
4
°
C
5
°
С
that large copper sulfide grains up to several hundreds
of micrometers in size have a practically continuous,
increases negatively from –8212.9 to –8415.9 kJ/mol
as the temperature is raised in this interval. Therefore,
this reaction is thermodynamically favorable under
normal conditions.
dense copper oxide coating up to 20
Fig. 4).
μ
m in thickness
(
Figure 5 shows a micrograph of a large grain of
copper oxide with copper metal inclusions, a product
resulting from the heat treatment of the reaction mixꢀ
5
Ni S + 18NaNO + Na CO
3 2 3 2 3
(3)
= 15NiO + 10Na SO + 9N + CO .
2
4
2
2
ture at 600°С for 60 min.
The kinetic data obtained for reaction (3) are preꢀ
Thus, the kinetic limitations preventing complete sented in Fig. 6. Clearly, the reaction between nickel
copper sulfide decomposition are caused by the forꢀ sulfide and the sodium nitrate–sodium carbonate
mation of the fairly dense CuO film on the Cu2S mixture proceeds rapidly at 650–700
grains, which blocks the access of sodium nitrate and decomposition of the sulfide as a result of isothermal
carbonate to copper sulfide. heat treatment is 95–99% in 10 min.
°
С. the degree of
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 6 2011

834
BOGORODSKII et al.
Ni3S2
Ni3S2
NiO
Ni3S2
NiO
20
µ
m
20 µm
Fig. 7. SEM image of a nickel oxideꢀcovered nickel sulfide
grain in the mixture heatꢀtreated at 650 for 60 min.
Fig. 8. Group of nickel sulfide and nickel oxide grain in the
mixture heatꢀtreated at 600 for 60 min.
°С
°С
An electron probe Xꢀray microanalysis of the insolꢀ metal–containing sulfide ores, which includes the
uble residues obtained between 600 and 700°C demꢀ introduction of an extra amount of sodium nitrate into
onstrated the presence of nickel oxide coatings on the stock and lowꢀtemperature treatment of this stock.
Ni3S2 grains. The coatings are discontinuous and cover This technology is now being subjected to field tests. It
only a negligible part of the grain surface (Fig. 7). allows the accuracy of the analytical procedure to be
Some nickel oxide grains are mixed with sulfide grains enhanced. Furthermore, it makes the process less
and have an irregular shape, and their size does not costly by obviating the need for sample pretreatment
exceed 20
μm (Fig. 8).
by acidic decomposition or oxidative firing.
Thus, the kinetic study of the interaction of FeS2
,
Cu2S, and Ni3S2 with the sodium nitrate–sodium carꢀ
bonate mixture demonstrated that rapid reactions take
place in the stoichiometric mixtures of the reactants at
REFERENCES
1. Sampling and Analysis of Precious Metals, Ed. by I. F. Baryꢀ
shnikov (Metallurgiya, Moscow, 1968), pp. 121, 154 [in
Russian].
4
00–700 С, yielding sodium sulfate, Fe O3, CuO,
°
2
NiO, and copper metal in the solid phase. The extent
of the reactions under isothermal conditions in this
temperature range is 95–99% at a reaction time of
2
3
4
5
. V. V. Nedler, T. E. Zolotukhin, and K. L. Pomytoe,
Analysis of the Platinum Group Metals, Gold, and Silver
(Metallurgizdat, Moscow, 1960) [in Russian].
1
0 min. The kinetic limitations in these reactions are
due to the formation of a passivating layer of reaction
products on the surface of relatively large (>100ꢀ m)
.
Analysis of the Platinum Group Metals, Gold, and Silver.
Collected Works (Metallurgiya, Moscow, 1960) [in Rusꢀ
sian].
μ
metal sulfide particles. These kinetic limitations are
eliminated by holding the reaction mixture at a higher
temperature within the range examined to disrupt the
passivating film.
The thermochemical decomposition data for iron,
copper, and nickel sulfides provided a basis for an
improved technology for the assay smelting of noble
. S. M. Anisimov, et al., Analysis of the Platinum Group
Metals, Gold, and Silver (Metallurgizdat, Moscow,
1960) [in Russian].
.
Phase Diagrams of Silicate Systems. Handbook, Ed. by
N. A. Toropov (Nauka, Leningrad, 1965), Issue 1 [in
Russian].
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 6 2011