Effect of SO2 on chlorination of zinc ferrite ZnFe 2O4 and a mixture of ZnO and Fe2O3

Article abstract of DOI:10.1134/S1070427208030038

Results of thermodynamic calculations and kinetic studies of the reaction of zinc ferrite ZnFe₂O₄ and of a mixture of oxides, ZnO and Fe₂O₃, with chlorine and SO₂ are presented.

Full text of DOI:10.1134/S1070427208030038

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 3, pp. 370 374. Pleiades Publishing, Ltd., 2008.
Original Russian Text L.E. Derlyukova, M.V. Vinokurova, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 3, pp. 384 388.
INORGANIC SYNTHESIS
AND INDUSTRIAL INORGANIC CHEMISTRY
Effect of SO2 on Chlorination of Zinc Ferrite ZnFe2O4
and a Mixture of ZnO and Fe2O3
L. E. Derlyukova and M. V. Vinokurova
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka,
Moscow oblast, Russia
Received July 21, 2007
Abstract Results of thermodynamic calculations and kinetic studies of the reaction of zinc ferrite ZnFe2O4
and of a mixture of oxides, ZnO and Fe2O3, with chlorine and SO2 are presented.
DOI: 10.1134/S1070427208030038
Chloride sublimation processes are widely used to
produce anhydrous chlorides and oxychlorides in in-
organic synthesis, recover rare and nonferrous metals
from complex polymetallic raw materials in metal-
lurgy, purify compounds to remove impurities, and
separate metals [1 3]. In all these cases, the reacting
systems are multicomponent.
from that observed in chlorination of their individual
oxides, but this fact was not explained.
Most kinds of zinc raw materials contain a large
amount of iron. The basic form of zinc compounds in
oxidized materials is ferrite. It has been found in
a study of the reaction of ZnO with mixtures of chlor-
ine and sulfur dioxide that formation of a stable zinc
sulfate markedly diminishes the rate at which zinc
chloride is formed [12]. By contrast, formation of iron
sulfate in the reaction of Fe O with chlorine in
Introduction of a new reagent into a heterogeneous
system is, as a rule, accompanied by a change not
only in the equilibrium composition of the products
formed, but also in the rates of particular reactions
occurring in the system [4]. It has been shown previ-
ously that results obtained in chlorination of individ-
ual metal oxides cannot be used to make definite
conclusions about the chlorination kinetics of their
mixtures [5, 6]. A noticeable influence on the rate of
chloride sublimation is exerted by the composition of
the gas phase. For example, addition of sulfur dioxide
to chlorine accelerates the process even in those cases
when the sulfur oxide does not react with a metal
oxide in the absence of chlorine [7]. It has been found
that the recovery of tungsten dioxydichloride from
scheelite wolframite concentrates into the sublimate
increases in the presence of sulfur dioxide [8].
2
3
the presence of SO leads to an increase in the degree
2
of chloride sublimation of iron [13].
Here we report the results of thermodynamic calcu-
lations and kinetic studies of chlorination of zinc
ferrite ZnFe O and of an equimolar mixture of ZnO
2
4
and Fe O in the presence of SO .
2
3
2
EXPERIMENTAL
The equilibrium compositions of the gas and con-
densed phases of the system under study were calcu-
lated by the method of free energy minimization by
ASTRA software [14] in the temperature range 300
800 C. The chlorination kinetics was studied at 500
700 C by the gravimetric method under isothermal
conditions on an installation that automatically re-
corded the variation of mass with time. The sensitivity
of the installation was 0.001 g per 1 mm of the scale.
The weighed portion of a sample was 0.180 0.200 g.
Under the experimental conditions, the Cl : SO ratio
To find the optimal conditions of selective re-
covery of metals in the form of chlorides, it is highly
important to study the reaction of double oxides or
their mixtures with chlorine and the effect of the com-
position of the gas phase on this process.
However, published data on the behavior of double
oxides in the atmosphere of chlorine are scarce. It was
found in [9 11] that, in the reaction of cobalt and
nickel ferrites with chlorine, the degree of chlorination
of the elements contained in these compounds differs
2
2
1
was 1 : 1. The total gas flow rate was 200 ml min
1
at a linear flow velocity of 0.05 m s . Such a rate of
gas supply to the surface did not impose any limita-
tions on the chlorination process.
370

EFFECT OF SO2 ON CHLORINATION OF ZINC FERRITE ZnFe2O4
The reaction products formed were identified by
X-ray phase analysis (XPA) on an ADP-2-01 dif-
fractometer and by chemical analysis using standard
procedures.
371
c, wt %
An equimolar mixture of oxides was produced by
mechanical mixing of ZnO and -Fe O of ultrapure
2
3
grade, and zinc ferrite, by joint decomposition of zinc
and iron carbonates at 800 C [15]. According to the
results of chemical and X-ray phase analyses, the
sample produced by decomposition of the carbonates
was composed of a single phase, ZnFe O , stable
2
4
in air below 1590 C [16].
The specific surface area was found by the BET
method from the low-temperature adsorption of kryp-
ton. The specific surface areas of ZnO, Fe O , and
T, C
2
3
Fig. 1. Equilibrium composition c of the condensed phase
of the system ZnO Fe O Cl SO vs. temperature T.
2
1
ZnFe O were 3.4, 10.0, and 40.0 m g , respec-
2
4
2
3
2
2
4 3
tively.
(1) ZnCl , (2) ZnSO , (3) Fe (SO ) , and (4) Fe O .
2
4
2
2 3
The equilibrium compositions of the condensed
and gas phases of the system ZnO Fe O Cl SO
2
2
3
2
are shown in Figs. 1 and 2. In contrast to the system
with individual zinc oxide, there is no ZnSO in
4
the condensed phase at 300 500 C (Fig. 1). Zinc
is represented by the chloride. Iron is in the form of
Fe (SO ) and Fe O . Noticeable amounts of ZnSO
2
4 3
2
3
4
4 3
appear above 550 C, when the content of Fe (SO )
2
and ZnCl substantially decreases.
2
The main components of the gas phase (Fig. 2) are
zinc and iron chlorides, SO , SO , O , and Cl . Even
2
3
2
2
at 300 550 C, when the main part of ZnCl is in
2
the condensed phase, the partial pressure of zinc di-
chloride exceeds the partial pressures of iron chlorides
by two orders of magnitude. At higher temperatures,
the difference between the equilibrium pressures of
zinc and iron becomes as large as four orders of mag-
nitude. The partial pressures of ZnCl , SO , and SO
T, C
Fig. 2. Equilibrium composition of the gas phase of the
system ZnO Fe O Cl SO vs. temperature T. (p ) Partial
2
2
3
2
2
i
pressure. (1) Cl , (2) SO , (3) O , (4) SO , (5) ZnCl ,
2
2
3
2
(6) FeCl , (7) Fe Cl , and (8) FeCl .
3
2
6
2
2
2
3
steadily increase with temperature, the maximum con-
tent of iron chlorides is reached at 550 600 C, when
zinc is partly present in the form of a sulfate. The
overall process at 300 550 C can be described by
the equation
An increase in the content of chlorine in the start-
ing system leads to a substantial rise in the content of
iron chlorides in the gas phase and, accordingly, to
a decrease in the selectivity of the process.
The pronounced difference between the partial
pressures of zinc and iron chlorides in the system
ZnO Fe O Cl led the authors of [6] to conclude
3ZnO + Fe2O3 + 3Cl2 + 3SO2 = 3ZnCl2 + Fe2(SO4)3.
2
3
2
that selective transfer of ZnCl to the gas phase is
At 550 650 C, part of chlorine is consumed for
chlorination of Fe O because of the parallel forma-
2
possible in joint chlorination of ZnO and Fe O .
2
3
2
3
The thermodynamic calculations performed demon-
tion of zinc dichloride and zinc sulfate. At 650
800 C, the main part of iron is in the condensed phase
in the form of an oxide. The gas phase contains con-
siderable amounts of sulfur oxides, i.e., processes of
parallel formation of ZnCl and SO may occur in
strated that addition of SO to the system under con-
2
sideration must lead to a decrease in the selectivity of
the process because of the increase in the concentra-
tion of iron chlorides in the gas phase.
2
3
the system.
The chlorination kinetics in the reaction of both
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 3 2008

372
DERLYUKOVA, VINOKUROVA
Table 1. Distribution of zinc and iron in the products formed in the reaction of a mixture of ZnO and Fe2O3 with
an equimolar mixture of Cl2 and SO2
Reaction conditions
Content in the solid phase, % relative to initial value
Sublimation, % relative to
initial content
Zn
Fe
,
m/m0,
%
T, C
min
ZnCl2
ZnSO4
FeCl3
Fe2(SO4)3
Fe2O3
Zn
Fe
400
15
60
120
30
45
15
45
15
30
10
15
20
45
37.4
60.4
60.5
53.8
35.5
43.8
36.7
20.8
10.8
13.3
13.2
1.8
73.2
100
100
22.8
0
0
0
0
13.8
0
5.6
0
0
0
0
0
13.5
44.4
44.0
32.8
43.3
37.6
48.0
43.4
51.4
49.4
47.9
46.9
42.9
75.7
43.7
44.7
60.8
39.4
44.0
26.9
40.0
19.3
26.8
29.6
19.1
17.8
0
0
0
4.4
12.6
9.3
39.3
62.9
78.7
78.1
78.0
87.2
94.2
10.6
11.2
8.6
2.6
5.2
3.3
0
4.7
0
0
0
0
0
450
500
550
600
95.6
87.4
76.9
60.7
31.5
21.3
21.9
22.0
12.8
5.8
1.2
13.9
18.3
20.4
16.5
29.4
23.8
21.7
33.4
39.5
0
0
12.5
0
the equimolar mixture ZnO + Fe O and ZnFe O
2 4
2
3
m/m0, %
(a)
with chlorine in the presence of SO was studied
2
in the temperature range 500 650 C. Isotherms of
chlorination of a mixture of ZnO with Fe O are
, min
2
3
shown in Fig. 3a. At 500 600 C, the isotherms show
a slight initial increase in the sample mass, which is
due, according to chemical analysis data, to the forma-
tion of Fe (SO ) . Making the experiment longer
2
4 3
results in that the mass decreases because of the trans-
fer of ZnCl and FeCl to the gas phase. At 500 C,
2
3
the process rate markedly decreases in the course
of time.
The activation energy of the process was estimated
1
for a 15% decrease in mass. A value of 62.8 kJ mol
m/m0, %
(b)
was obtained, which coincides with that calculated for
chlorination of Fe O in the presence of SO at tem-
peratures of 600 750 C [13].
2
3
2
, min
For a more detailed examination of the composi-
tion of the chlorination products and solid-phase resi-
due, a number of special-purpose experiments were
carried out with an increased sample weight (0.600
1.000 g). The solid-phase residue was analyzed for
2
the content of zinc, iron, and Cl and SO ions.
4
The distribution of zinc and iron in the chlorination
products is presented in Table 1. The results obtained
demonstrated that nearly the whole amount of zinc is
in the form of chloride in the entire temperature range
Fig. 3. Isotherms of interaction of (a) mixture of ZnO and
Fe O and (b) ZnFe O with an equimolar mixture of Cl
2
3
2
4
2
studied (400 600 C). At 400 C, ZnCl is contained
2
and SO at different temperatures. T, C: (1) 500, (2) 550,
2
in the solid phase. As temperature is raised, the chlor-
ide sublimes. The formation of minor amounts of
(3) 600, (4) 650, and (5) 700. ( m/m ) Relative change in
0
mass and ( ) time.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 3 2008

EFFECT OF SO2 ON CHLORINATION OF ZINC FERRITE ZnFe2O4
373
Table 2. Conditions and parameters of the reaction of a mixture of ZnO and Fe2O3 with chlorine and an equimolar
mixture of Cl2 and SO2. Solid phase: ZnO + Fe2O3
Reaction conditions
Conversion parameters
content in residue, % sublimation, % relative to initial content
gas phase
T,
C
, min
m/m0, %
Zn
Fe
Zn
Fe
Cl2
Cl2 + SO2
500
500
32
31
33.5
33.9
0.9
1.0
67.4
64.8
97.4
97.2
0
4.0
Cl2
Cl2 + SO2
550
550
25
25
35.1
43.8
0.9
1.1
67.9
47.3
97.4
97.3
1.3
44.6
Cl2
Cl2 + SO2
600
600
17
13
36.1
41.7
1.9
1.0
67.1
46.2
94.6
98.3
3.9
43.7
ZnSO is observed only in the initial stage of chlori-
nation at comparatively low temperatures. In contrast
mass decreases because of the sublimation of both
ZnCl and FeCl . The rates of chemical sublimation
4
2
3
to ZnSO , the presence of a considerable amount of
of the chlorides are close for ZnFe O and a mixture
4
2
4
Fe (SO ) is recorded in the entire temperature range
of oxides. As in the case of the mixture of oxides,
2
4 3
studied. As the experimental temperature increases,
the content of Fe (SO ) in the solid phase grows, so
the rate at which FeCl passes into the gas phase from
3
the ferrite in the presence of SO exceeds that in
2
4 3
2
that the fraction of iron in the form of sulfate ap-
proaches 50% at 500 600 C. In parallel with the
accumulation of Fe (SO ) , FeCl is formed. Iron
the atmosphere of individual chlorine.
An X-ray phase analysis made after chemical sub-
limation of zinc chloride from the ferrite demonstrated
that the solid-phase residue contains exclusively
-Fe O . The data obtained and the fact that the
2
4 3
3
trichloride virtually completely passes into the gas
phase. At 550 600 C, more than 30% of iron is in
2
3
the form of FeCl .
3
processes of chemical sublimation of the chlorides
from the ferrite and the mixture of oxides are virtually
completely identical suggest that, in the course of
chlorination, the ferrite stable in air in the temperature
range under consideration decomposes into ZnO and
-Fe O . The specific structural features of ZnFe O ,
Table 2 compares the rates at which zinc and iron
chlorides pass into the gas phase under kinetic condi-
tions in the atmosphere of chlorine or a mixture of Cl
2
with SO . The results obtained demonstrate that the
2
rate at which the mass of the mixture of ZnO and
Fe O changes in the presence of SO exceeds that
2
3
2 4
2
3
2
which is a normal spinel, suggest that ZnFe O will
2
4
in the atmosphere of chlorine. This is particularly
noticeable at temperatures higher than 500 C. The
chlorination rate of zinc is virtually unaffected by
decompose to -Fe O . However, no -phase was
2
3
found in the temperature range studied. Thus, the
chlorination of ZnFe O occurs simultaneously with
2
4
SO , whereas chlorination of iron occurs at a higher
2
its decomposition to ZnO and -Fe O . The same
2
3
rate. In the atmosphere of chlorine, the appearance of
iron chlorides in the gas phase was observed only
upon complete chemical sublimation of zinc, whereas
conclusion was made by the authors of [9 11], who
considered the chlorination of cobalt and nickel
ferrites.
in the presence of SO , iron and zinc chlorides pass
2
into the gas phase virtually simultaneously. As also in
the atmosphere of chlorine, the rate of chemical sub-
limation of zinc dichloride exceeds that of iron chlor-
ides, but the difference between the rates is not so
significant.
The fundamental aspects of the chemical sublima-
tion of iron from a mixture of ZnO and Fe O in
2
3
the presence of SO are similar to those observed in
2
the chlorination of Fe O [13]: at comparatively low
2
3
temperatures (300 500 C) it predominantly occurs via
the reaction of simultaneous formation of Fe (SO )
Figure 3b shows isotherms of interaction of zinc
ferrite ZnFe O with an equimolar mixture of Cl and
2
4 3
and FeCl . The accumulation of Fe (SO ) , stable
3
2
4 3
2
4
2
in the atmosphere of chlorine, in the solid phase
decelerates the process. At 600 750 C, the chemical
sublimation of iron is due to the parallel formation of
FeCl and SO .
SO . They virtually coincide with the isotherms of
2
chlorination of a mixture of oxides. The stage of the
initial increase in mass, caused by the formation of
Fe (SO ) , is followed by that in which the sample
2
4 3
3
3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 3 2008

374
DERLYUKOVA, VINOKUROVA
The kinetics of the chemical sublimation of zinc
from the mixture of oxides in the presence of SO
strongly differs from that observed in chlorination of
complex by introduction of an additional component,
SO , into the gas phase does not change fundamental-
2
2
ly the pathway of the process.
ZnO under the same conditions [12], when ZnCl is
formed as a result of successive occurrence of the
2
(3) Presence in the reaction mixture of a solid
component, Fe O , whose reaction with chlorine
changes the composition of the gas phase, affects
the fundamental aspects of chlorination to a consider-
ably greater extent.
2
3
reactions of formation and chlorination of ZnSO ,
4
whose considerable amounts were recorded in a wide
temperature range.
In the reaction of a mixture of oxides with Cl and
2
REFERENCES
SO , the amount of ZnSO in the solid phase is
2
4
extremely low. This cannot be due to the thermal in-
1. Kanari, N., Gaballah, I., and Allain, E., Thermochim.
Acta, 2000, vol. 351, nos. 1 2, pp. 109 117.
2. Kanari, N., Gaballah, I., and Allain, E., Thermochim.
Acta, 2001, vol. 371, nos. 1 2, pp. 75 86.
3. Murase, K., Nishikawa, K., Ozaki, T., et al., J. Alloys
Comp., 1998, vol. 264, nos. 1 2, pp. 151 156.
4. Boldyrev, V.V., Delmon, B., and Bulens, M.,
The Control of the Reactivity of Solids, Amsterdam:
Elsevier, 1979.
5. Vinokurova, M.V., Derlyukova, L.E., Babiev-
skaya, I.Z., et al., Zh. Neorg. Khim., 1989, vol. 34,
no. 12, pp. 2998 3003.
6. Derlyukova, L.E., Vinokurova, M.V., and Evdoki-
mov, V.I., Zh. Neorg. Khim., 1991, vol. 36, no. 5,
pp. 1135 1140.
7. Vinokurova, M.V. and Derlyukova, L.E., Zh. Neorg.
Khim., 2004, vol. 49, no. 9, pp. 1432 1435.
8. Menendez, C.J., Tavani, E.L., and Nolasco, E.J., Ther-
mochim. Acta, 1999, vol. 338, nos. 1 2, pp. 103 112.
stability of the sulfate, because ZnSO decomposes
4
at temperatures higher than 700 C [12]. In the system
under consideration, ZnCl is formed by direct chlori-
2
nation of ZnO. SO is bound because of the occur-
2
rence of the most thermodynamically favorable proc-
esses of formation of Fe (SO ) , which is more stable
2
4 3
in the atmosphere of chlorine than ZnSO , and also
4
via the reaction of simultaneous formation of FeCl
3
and SO . As a result, the rate of transfer to the gas
3
phase changes for only a single component, iron. The
rate of the chemical sublimation of ZnCl is indepen-
2
dent of whether SO is present in the gas phase.
2
This process is affected by Fe O to a considerably
2
3
greater extent. As shown previously [6], the rate of
the chemical sublimation of ZnCl both from a mix-
2
ture of oxides and from zinc ferrite in the atmosphere
of chlorine increases nearly 10-fold in the presence
of Fe O . This is due to specific features of the inter-
2
3
9. Piskunov, I.N., Orlov, A.K., Smirnov, Yu.N., and Te-
lyakov, N.M., Izv. Vyssh. Uchebn. Zaved., Tsvetn.
Met., 1976, no. 3, pp. 46 49.
action of chlorine with the inhomogeneous surface of
Fe O . Although the chlorination rate of Fe O is
2
3
2 3
lower than that of ZnO, microscopic amounts of FeCl
3
3
10. Fruehan, R.J. and Martonic, I.J., Metallurg. Trans.,
are formed on the most active areas of the Fe O
surface even at 350 C. The multiple involvement of
2
1973, vol. 4, pp. 2793 2799.
11. Telyakov, N.M., Orlov, A.K., and Piskunov, I.N., Izv.
Vyssh. Uchebn. Zaved., Tsvetn. Met., 1977, no. 4,
pp. 45 48.
12. Derlyukova, L.E., Vinokurova, M.V., and Evdoki-
mov, V.I., Zh. Neorg. Khim., 1986, vol. 31, no. 4,
pp. 846 851.
13. Derlyukova, L.E., Eliseeva, N.A., and Evdoki-
mov, V.I., Zh. Neorg. Khim., 1987, vol. 32, no. 9,
pp. 2096 2100.
14. Sinyarev, G.B., Vatolin, N.A., Trusov, B.G., and
Moiseev, G.K., Primenenie EVM dlya termodinami-
cheskikh raschetov metallurgicheskikh protsessov (Use
of Computers for Thermodynamic Calculations of
Metallurgical Processes), Moscow: Nauka, 1982.
FeCl in events of reaction with ZnO results in that
3
the concentration of chlorine near the surface of the
substance being chlorinated increases and the chemical
sublimation of zinc is intensified. The chemical sub-
limation of iron occurs only after ZnCl completely
2
passes into the sublimate. The presence of SO in
2
the gas phase markedly facilitates the formation of
FeCl and thereby impairs the selectivity of the
3
chemical sublimation.
CONCLUSIONS
(1) The fundamental aspects of chlorination in the
presence of SO are the same for zinc ferrite ZnFe O
2 4
2
15. Brauer, G., Handbuch der Praparativen anorgani-
schen Chemie, Stuttgart: Ferdinand Enke, 1954.
16. Goronovskii, I.T., Nazarenko, Yu.P., and Nek-
ryach, E.F., Spravochnik po khimii (Handbook of
Chemistry), Kiev: Naukova Dumka, 1987.
and an equimolar mixture of ZnO and Fe O , just as
2
3
in the case of chlorination in the atmosphere of pure
chlorine.
(2) Making the system ZnO Fe O Cl more
2
2
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 3 2008