Hydrometallurgy 84 (2006) 239 – 246
www.elsevier.com/locate/hydromet
Dissolution kinetics of celestite (SrSO4) in
HCl solution with BaCl2
Salih Aydoğan a,⁎, Murat Erdemoğlu b , Ali Aras a , Gökhan Uçar a , Alper Özkan a
a
b
Department of Mining Engineering, Selçuk University, 42075 Konya, Turkey
Department of Mining Engineering, Id nönü University, 44280 Malatya, Turkey
Received 12 June 2006; received in revised form 28 June 2006; accepted 30 June 2006
Available online 9 August 2006
Abstract
Leaching of celestite (SrSO4) in hydrochloric acid solution with BaCl2 was investigated to produce SrCl2 in solution, which is
the main source for SrCO3. The effects of variables such as stirring speed, BaCl2 and HCl concentrations, and temperature and
particle size, and also the presence of NaCl in the leaching solution were studied. The leaching was modeled according to the
shrinking core model. The activation energy for the leaching process in 8.25 × 10− 3 M BaCl2 solution equilibrated with 0.5 M HCl
was found as 68.8 kJ mol− 1. This value reveals that the dissolution of celestite is a chemical reaction controlled process. In
agreement with the model, the reaction rate is inversely proportional to the particle size and increases as 0.73, 0.70 and 0.19 powers
of the H+, Cl− and Ba2+ concentrations, respectively.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Celestite; Hydrochloric acid; Barium chloride; Reaction kinetics
1. Introduction
Majority of the artificially produced strontium
carbonate (SrCO3) has been consumed as an additive
in the production of faceplate glass of colour television
picture tubes to block X-ray transmission and improve
the appearance of the glass. Other end uses of SrCO3 are
the production of ferrite magnets for small DC motors,
iridescent and special glasses, pyrotechnics, pigments,
paints, driers and the production of strontium metal and
all other strontium chemicals.
There are two different SrCO3 production methods:
the black ash process and the direct conversion process.
⁎ Corresponding author. Tel.: +90 332 223 20 60; fax: +90 332 241 06 35.
E-mail address: [email protected] (S. Aydoğan).
0304-386X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.hydromet.2006.06.001
In the black ash process, strontium sulphide (SrS) is
obtained by reduction roasting the high-grade celestite
(SrSO4) concentrate with metallurgical grade coke at
about 1100–1300 °C. The soluble SrS is then leached
with water at elevated temperatures. The loaded liquor
from leaching is then contacted with either CO2 gas or
Na2CO3 to precipitate the chemical grade SrCO3
(Erdemoğlu et al., 1998; Owusu and Litz, 2000). In
the direct conversion method, finely ground, washed
and thickened celestite concentrate is directly reacted
with soda ash and treated with steam at 95 °C for 1 to 3 h
to obtain crude strontium carbonate and sodium sulphate. Since the crude SrCO3 is impure and contains
undissolved solids, it is then decomposed using HCl
solutions to obtain aqueous SrCl2 to be reacted with CO2
or Na2CO3. Therefore, the process is also called as
double decomposition process. Iwai and Toguri (1989),
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S. Aydoğan et al. / Hydrometallurgy 84 (2006) 239–246
Carrillo et al. (1995) and Castillejos et al. (1996) have
extensively studied the thermodynamic conditions of
the direct conversion process to be able to enhance
process efficiency.
Because of the problems either originated from the
content and grade of celestite concentrate or the problems occurred during the conversion of celestite to SrS
in the black ash process or to SrCO3 in the direct conversion process, improvements for the relevant processes have been investigated by many of the researchers.
Other carbon sources like petroleum coke were investigated to lower the energy consumption in the black
ash process. Contacting the liquor from SrS leaching
with CO2 gas together with atmospheric oxygen is
another attempt to enhance the SrCO3 precipitation efficiency in the same process (Erdemoğlu and Canbazoğlu,
1998). In the direct conversion process, ammonium carbonate and ammonium bicarbonate were examined by
Debuda (1987) and by Cheng and Jiang (1992), respectively, instead of soda ash. Erdemoğlu et al. (2006) studied
the leaching of celestite in sodium sulphide solution to
convert the sulphate to water-soluble sulphides at ambient
temperatures. They found that celestite can be converted
to strontium disulphide, but the reaction rate is too slow,
depending on reaction products deposited at the surface of
the unreacted mineral. Xu and Zhu (2005) developed a
new flow sheet for direct conversion process of continual
reaction between CO2 and SrCl2 by means of neutralizing
the produced HCl or removing it to another phase. They
found that coupling the reaction with solvent extraction is
a way to lower the acidity of the aqueous solution and to
allow the reaction to proceed continually. Suárez-Orduña
et al. (2004) have investigated the exchange of SO42− ions
with CO32− ions in natural celestite single crystals under
alkaline hydrothermal conditions. Recently, Obut et al. (in
press) have investigated the direct conversion of celestite
to strontium carbonate by mechanochemical processing in
sodium carbonate solution at ambient temperatures. It is
expected that investigations about the conversion of
celestite to strontium carbonate will not be stopped since
there are still certain drawbacks of the relevant methods,
such as high energy consumption in the black ash process
and high temperature leaching and acid costs in the double
decomposition process.
In this present study, an attempt was made to convert
the celestite directly to soluble SrCl2 by leaching the
celestite in acidic barium chloride (BaCl2) solutions. By
this way, crude strontium carbonate production stage in
the direct conversion method may be discarded from the
process flow sheet. During the dissolution investigation,
effects of such main leaching parameters as stirring
speed, HCl concentration, BaCl2 concentration, temper-
ature and particle size, and effect of NaCl addition to the
leaching medium were investigated. For modeling the
celestite dissolution, a kinetic analysis was also performed using shrinking core model.
2. Material and methods
2.1. Material
In this study, samples of the celestite concentrate
purchased from Barit Maden Türk A.Ş. Concentrator
(Sivas, Turkey) were used. The samples were wet sieved
to obtain 106 × 75, 75 × 45, and 45 × 38 μm particle size
ranges. According to mineralogical and XRD analysis
together with chemical analysis, celestite is the major
mineral in the sample with minor gypsum (CaSO4·2H2O)
and trace barite (BaSO4), while other minerals vary only
from 1.49 to 1.02%. Chemical analyses of different size
fractions of the sample are listed in Table 1.
2.2. Experimental procedure
A Pyrex beaker of 1 L was used as a leaching reactor
with a rubber cover. Temperature of the leach solution in
the reactor was provided by a thermostatically controlled water bath with ± 0.2 °C sensitivity. Stirring was
carried out by Heidolph Mark RZR 2021 model mechanical stirrer equipped with propeller. During the set
up of the experiments, solid content of the solution was
held constant at 0.4% (w/v). Stirring speed was altered
in the range of 100–600 rpm; temperature was varied in
the range of 40–80 °C; HCl concentration was in the
range of 0.05–0.75 M. BaCl2 concentrations were 10,
25, 50, 75 and 100% BaCl2 (1.1 × 10− 3, 2.75 × 10− 3,
5.5 × 10− 3, 8.25 × 10− 3 and 1.1 × 10− 2 M, respectively)
with respect to the stoichiometric amount required for
dissolution of 1 g of celestite. Particle size fractions
were as 106 × 75, 75 × 45 and 45 × 38 μm. For element
analysis, 1 mL of solution was withdrawn from the
reactor at various time intervals. The sample solution
was diluted with distilled water to 100 mL in a volumetric flask. Strontium and barium in the leach solution
Table 1
Chemical analysis of the different size fractions of the celestite sample
(wt.%)
Mineral
Particle size, μm
106 × 75
75 × 45
45 × 38
SrSO4
BaSO4
CaSO4.2H2O
Others
96.67
0.35
1.49
1.49
97.32
0.33
1.33
1.02
97.24
0.33
1.33
1.10
S. Aydoğan et al. / Hydrometallurgy 84 (2006) 239–246
241
samples were determined by ICP AES. In calculating the
fraction of strontium leached, a volume correction
formula was used — which includes in itself correction
factors to account for the volume losses due to sampling
(Georgiou and Papangelakis, 1998).
i−1
i−1
P
P
V− vi CM;i þ vi CM;i
i¼1
i¼1
XM;i ¼
ð1Þ
mðcM =100Þ
Ba 2+ ions from BaCl2 into the solution, BaSO4
immediately precipitates, leaving the Sr2+ in the solution
with chloride ions
where V is the initial volume (mL) of the solution, vi is
the volume (mL) of the sample i withdrawn each time,
CM,i is the concentration of M (Sr, Ba) in sample i (mg
L− 1), m is the initial mass of celestite in g (on a dried
basis) added into the reaction vessel and cM is the
concentration of M in celestite sample (wt.% dried
solids).
Distilled water and reagent grade chemicals were
used to make up all required solutions. Each experiment
was repeated at least three times and the arithmetic mean
of the results was used in the discussion of experimental
results.
SrSO4 ðsÞ þ BaCl2 ðaqÞ ¼ BaSO4 ðsÞ þ SrCl2 ðaqÞ
3. Results and discussion
3.1. Thermodynamic considerations
When celestite is introduced into an aqueous
solution, dissolution occurs with the formation of Sr2+,
SrOH+, SrSO4(aq), HSO4− and SO42− species depending
on the pH of the solution (López-Valdivieso et al.,
2000). The concentration of the chemical species in
solution is well represented in the pH-log solubility
diagram using the available thermodynamic data for
formation constant of the species and solubility of
strontium sulfate (Fig. 1). From this diagram, it is
possible to intend the following equilibrium reactions
together with the solubility products (log Ksp) of the
species, in the broad pH range of 2–14,
SrSO4 ðsÞ ¼ Sr2þ þ SO2−
4
log Ksp ¼ −6:62
ð2Þ
SrSO4 ðaqÞ ¼ Sr2þ þ SO2−
4
log K ¼ −2:29
ð3Þ
Ba2þ þ SO2−
4 ¼ BaSO4 ðsÞ
log Ksp ¼ −9:96
ð5Þ
According to these equilibrium reactions occurred in
SrSO4–BaCl2–H2O system, one can easily suggest the
following dissolution reaction,
ð6Þ
The driving force for this reaction is the relatively low
solubility of BaSO4 (log Ksp = − 9.96 at 20 °C) compared with SrSO4 (log Ksp = − 6.62).
Preliminary experiments showed that during the
leaching of celestite in barium chloride solution at high
acidic conditions (pH = ∼ 1), Sr2+ concentration increased
with respect to decreasing Ba2+ concentration with the
course of time (Fig. 2). Initial concentration of Ba2+ from
BaCl2 in 0.5 M HCl solution containing 2 g celestite
sample was 8.25× 10− 3 M. After 240 min of leaching,
final Ba2+ and Sr2+ concentrations were measured as
2.64× 10− 4 M and 8.17 × 10− 3 M, respectively, meaning
that almost all of the Ba2+ was consumed. Both the
chemical analysis performed by XRF and mineralogical
analysis performed by XRD method revealed the presence
of nearly 71% BaSO4 in the leaching residue.
These experiments also confirmed that the pH of the
solution kept constant at pH 0.7 throughout the leach as
expected. From this point of view, H+ ion acts as a catalyst
in order to increase the dissolution rate of celestite. Similar
Sr2+ extraction recoveries were obtained in repeated
experiments using other acid types like HNO3 and HClO4,
confirming the catalytic effect of H+ ion.
Additionally, in the pH range below 7, sulfate ion gains
one proton and bisulfate ion appears,
−
SO2−
4 þ H ¼ HSO4
log K ¼ 1:91
ð4Þ
As seen from Fig. 1, concentrations of SO42− and HSO4−
species at pH 2 are almost identical. During the
dissolution in acidic aqueous solutions, if one adds
Fig. 1. Solubility of celestite in aqueous solutions closed to the atmosphere at 25 °C (after López-Valdivieso et al., 2000).
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S. Aydoğan et al. / Hydrometallurgy 84 (2006) 239–246
Fig. 2. Variations of Ba2+ and Sr2+ concentrations during the leaching
of celestite (BaCl2: 8.25 × 10− 3 M; HCl: 0.5 M; S/L ratio: 1/250 w/v;
T: 60 °C; Particle size 45 × 38 μm; Stirring speed: 400 rpm).
3.2. Effect of stirring speed
The effect of stirring speed on the dissolution of
celestite was investigated at different stirring rates from
100 to 600 min− 1 in 8.25 × 10− 3 M BaCl2 (i.e. 75%
stoichiometric amount) equilibrated with 0.5 M HCl at
60 °C. It was found that at stirring rates of 400 rpm and
higher, the dissolution rate was independent of the stirring speed. Slow dissolution was evident at 100 rpm due
to the inability to keep the particles in suspension and
sustain a realistically homogeneous solution. A stirring
rate of 200 rpm may be considered as boundary between
insufficient and sufficient mixing. Therefore, the stirring
rate was kept constant at 400 rpm to investigate the
effect of other parameters on the dissolution.
Fig. 3. Rate curves for the dissolution of celestite for different BaCl2
concentrations with respect to 10, 25, 50, 75 and 100% stoichiometric
amount required to dissolve the celestite according to Eq. (6) (HCl: 0.5
M; S/L ratio: 1/250 w/v; 400 rpm; T: 60 °C; Particle size 45 × 38 μm).
these low concentrations. The change in the dissolution
rate to slow at high concentrations may be due to more
limited diffusion of H+ ions through a boundary layer of
BaSO4 which is precipitating at the shrinking celestite
particle surface. The strontium extraction after 240 min of
leaching in 1.1 × 10 − 3 and 1.1 × 10 − 2 M of Ba 2+
concentrations was 54.4% and 91.3%, respectively.
3.4. Effect of HCl concentration
The effect of HCl concentration on the celestite
dissolution was investigated by varying the HCl concentration in the 0.05–0.75 M range in 8.25 × 10− 3 M BaCl2
3.3. Effect of Ba2+ concentration
Fig. 3 shows the dissolution curves obtained when
celestite was reacted at 60 °C with different BaCl2 to
SrSO4 ratios. The BaCl2 concentrations were 10, 25, 50,
75 and 100% the stoichiometric amount required to
dissolve the entire celestite sample according to Eq. (6).
Excess amounts of BaCl2 were not tested to avoid
contamination of the SrCl2 in the leach solution with
unused BaCl2. As seen from Fig. 3, dissolution of celestite
is dependent on the Ba2+ concentration. It is interesting to
observe that when 1.1 × 10− 3 or 2.75 × 10− 3 M BaCl2
solution was tested, the initial dissolution rate was faster
than the other higher concentrations but then reached a
plateau and kept unchanged. This behavior may be
attributed to the fast dissolution of celestite with the aid of
acid, without the formation of solid BaSO4, since there are
not enough Ba2+ ions to exceed the solubility product at
Fig. 4. Rate curves for the dissolution of celestite for different HCl
concentrations (BaCl2: 8.25 × 10− 3 M; S/L ratio: 1/250 w/v; 400 rpm;
T: 60 °C; Particle size 45 × 38 μm).
S. Aydoğan et al. / Hydrometallurgy 84 (2006) 239–246
243
solution at 60 °C. As shown in Fig. 4, the strontium
extraction increases with increasing HCl concentration.
The strontium extractions after 240 min of leaching with
0.05 M and 0.75 M HCl are 22.3% and 88.3%,
respectively. These results reveal that HCl has significant effect on the celestite dissolution by forming HSO4−
ions, according to Eq. (4), and minimizing the equilibrium concentration of SO42− ions released from celestite that can back-react.
3.5. Effect of temperature
Experiments were conducted to determine the effect
of temperature on the dissolution of celestite in the
temperature range of 40–80 °C, using 0.5 M HCl and
8.25 × 10− 3 M BaCl2 solution. As seen in Fig. 5, as the
temperature is increased, the rate of dissolution of celestite increases. It is known that the solubility of celestite in pure water decreases with increasing temperature
(Reardon and Armstrong, 1987) — likewise barium
sulfate. The celestite solubility in pure water is small,
less than 6.6 × 10 − 4 M. Although the solubility of
celestite in water increases as the ionic strength or salt
concentration of solution increases, the increment with
concentration is limited (Risthaus et al., 2001).
The rapid decrease in the dissolution rates observed
during leaching at 70 and 80 °C after 60 min is not
surprising as only 75% of the required amount of Ba2+ ions
were initially present and were rapidly consumed leaving
unreacted celestite. As can be seen in Fig. 6, Ba2+ concentration decreased from 8.25 ×10− 3 to 5.75 ×10− 4 and
7.05× 10− 4 M within 120 and 90 min of leaching at 70 and
80 °C, respectively.
Fig. 5. Rate curves for the dissolution of celestite at different leaching
temperatures (BaCl2: 8.25 × 10− 3 M; HCl: 0.5 M; S/L ratio: 1/250 w/v:
400 rpm; Particle size 45 × 38 μm).
Fig. 6. Decrease in Ba2+ concentration during the leaching at various
temperatures.
3.6. Effect of particle size
Effect of particle size was investigated by using the
particle size ranges of 106 × 75, 75 × 45 and 45 × 38 μm in
solution containing 1.1 × 10− 2 M Ba2+ equilibrated with
0.5 M HCl at 60 °C. The strontium extraction increased
with decreasing particle size, as shown in Fig. 7, reaching
to 55.1% and 91.4% after 240 min of leaching of 106 × 75
and 45 × 38 μm particle size fractions, respectively.
3.7. Effect of NaCl addition
There are many reports on the solubility of sulfate
minerals like gypsum, barite and celestite in NaCl
Fig. 7. Rate curves for the dissolution of celestite with various
particle size ranges (BaCl2: 1.1 × 10− 2 M; HCl: 0.5 M; 400 rpm; S/L
ratio: 1/250 w/v; T: 60 °C).
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S. Aydoğan et al. / Hydrometallurgy 84 (2006) 239–246
solutions. Nearly all of these studies have investigated
the thermodynamics of those scale forming minerals in
oil and gas production. The effects of temperature,
pressure and, ideal and non-ideal solutions have been
analyzed (Macdonald and North, 1974; Reardon and
Armstrong, 1987; Raju and Atkinson, 1989; Howell et
al., 1992; He et al., 1995; Atkinson and Mecik, 1997;
Krumgalz et al., 1999; Risthaus et al., 2001; Freyer and
Voigt, 2003). Solubility of celestite at the 25–50 °C
temperature range increases with NaCl concentration up
to 3 M and then slows down and decreases (Reardon and
Armstrong, 1987). The most possible chemical reaction
for celestite in NaCl solution can be written as,
−
SrSO4 þ 4Cl ¼ ½SrCl4 2−
þ
SO2−
4
ð7Þ
with the formation of strontium tetrachloride complex,
[SrCl4]2−. By introducing Ba2+ ions in acidic medium,
BaSO4 immediately precipitates from the solution,
according to
Hþ
SrSO4 þ 4Cl− þ Ba2þ Y½SrCl4 2− þ BaSO4
ð8Þ
The curves with solid lines in Fig. 8 represent the effect of
NaCl concentration on the dissolution of celestite in
solutions containing 8.25 × 10− 3 M BaCl2 equilibrated
with 0.5 M HCl at 60 °C. For a comparison, the result of
one separate leaching test performed with 1 M NaCl and
8.25 × 10− 3 M BaCl2 in the absence of HCl in the solution
(Fig. 8: dashed line). It is easily observed that celestite
dissolution is negligible in the absence of H+ ions. But it is
significantly enhanced by the presence of both NaCl and
HCl in the leach solution. This increase can be interpreted
Fig. 8. Rate curves for the dissolution of celestite for different NaCl
concentrations (BaCl2: 8.25 × 10− 3 M; 0.5 M; 400 rpm; S/L ratio:
1/250 w/v; T: 60 °C; Particle size: 45 × 38 μm).
as synergistic effect of H+ ions protonating the sulfate ion
and Cl− ions from HCl, BaCl2 and NaCl forming a
strontium chloro-complex and lowering strontium ion
activity for dissolution of celestite.
3.8. Kinetic analysis
The dissolution of celestite can be explained by a
shrinking core model. Hence, diffusion and surface
reaction control models were investigated. If reaction is
controlled by diffusion the following equation can be
used (Levenspiel, 1972):
2
2MB DCA
1− X −ð1−X Þ2=3 ¼
t ¼ kd t
3
qB ar02
ð9Þ
If reaction is controlled by surface reaction:
1−ð1−X Þ1=3 ¼
kc MB CA
t ¼ kr t
qB ar0
ð10Þ
Where X is the fraction reacted, kc is the kinetic
constant, MB is the molecular weight of the solid, CA is
the concentration of the dissolved lixiviant A in the bulk
of the solution, a is the stoichiometric coefficient of the
reagent in the leaching reaction, r0 is the initial radius of
the solid particle, t is the reaction time, D is the diffusion coefficient in the porous product layer, ρB density
of the solid and kd and kr are the rate constants, respectively, which are calculated from Eqs. (9) and (10)
respectively.
Eq. (9) reveals that if the diffusion through the product layer controls the leaching rate, there must be a
linear relation between the left side of equation and time.
The slope of the line is the rate constant kd, it must be
directly proportional to 1/r02. If the surface reaction
controls the rate, the relation between the left side of Eq.
(10) and time must be linear. The slope of this line is
called the apparent rate constant kr and must be directly
proportional to 1/r0.
Eqs. (9) and (10) were applied from obtained results
from each temperature value. The plot of Eq. (10) gave a
straight line (Fig. 9). It must be noted here that the data
points after 90 and 60 min of leaching time were excluded
from the curves plotted for 70 and 80 °C, respectively.
This part of the data does not represent the actual dissolution behavior of celestite since the required amount of
BaCl2 (i.e., 1.1 × 10− 2 M) was not used in these tests. The
apparent rate constants (kr) were calculated as slopes of
the straight lines. Using the apparent rate constants obtained by application of Eq. (10), the Arrhenius plot was
obtained (Fig. 10).
S. Aydoğan et al. / Hydrometallurgy 84 (2006) 239–246
Fig. 9. Plot of 1 − (1 − χ)1/3 versus time for different temperatures
(BaCl2: 8.25 × 10− 3 M; HCl: 0.5 M; S/L ratio: 1/250 w/v; 400 rpm;
Particle size: 45 × 38 μm).
The activation energy was calculated as 68.8 kJ
mol− 1. This value clearly confirms that this process is
controlled by chemical reaction at the celestite surface,
which is the rate-determining step in the dissolution of
celestite by Ba2+ in HCl (Habashi, 1999). In addition, the
kinetic curves for particle size results were linearized by
means of Eq. (10) and the apparent rate constant (kr) were
drawn as a function of the inverse of the particle radius.
Direct relationship between kr versus 1/r0, which can be
formulized as kr = 0.09/r0 with a correlation coefficient of
1.00, confirms the chemical reaction on the celestite
surface as the rate-controlling step.
In order to decide the specific effect of H+ and Cl−
ions, the results on the effect of HCl and NaCl concentrations were applied to this kinetic model. Total Cl−
ion concentrations of the test solutions with NaCl were
calculated and found as 0.617, 1.017 and 1.517 M with
respect to 0.1, 0.5 and 1 M NaCl concentrations. The kr
values for each H+ and Cl− concentration were deter-
Fig. 10. Arrhenius plot of reaction rate against reciprocal temperature.
245
Fig. 11. Plots representing the order of reaction with H+, Ba2+ and
Cl−concentrations.
mined. From the corresponding kr and H+ and Cl−
concentration values, plots of ln kr versus ln [H+] and ln
[Cl−] were obtained. As seen from Fig. 11, the order of
reaction with respect to H+ and Cl− is proportional to
0.73 power of H+ concentration ([H+]0.73) and 0.70
power of Cl− concentration ([Cl−]0.70) with a correlation
coefficient of 1.00, respectively. It was also computed
by the same way that the order of the reaction with
respect to Ba2+ concentration is proportional to 0.19
power of Ba2+ concentration ([Ba2+]0.19) with a correlation coefficient of 0.99.
4. Conclusions
Leaching of celestite in hydrochloric acid solution in
the presence of BaCl2 was investigated to produce SrCl2
in the solution, over a broad range of experimental conditions. The effects of variables such as stirring speed,
HCl and BaCl2 concentrations, temperature, particle size
and also the presence of NaCl in the leaching solution
were studied. According to the thermodynamical considerations, celestite solubility increases in BaCl2 solutions with H+ ion which acts as a catalyst to enhance the
formation of bisulfate ion (HSO4−) and with Cl− ion
which reacts with Sr2+ ion to produce strontium tetrachloride complex, [SrCl4]2−. The reaction of celestite
obeys the shrinking core model, incorporating chemical
reaction of Sr2+ and SO42− ions with Cl− and H+, respectively, as the rate determining step. As presented by the
model, the reaction rate is inversely proportional to the
particle size and increases as 0.73, 0.70 and 0.19 powers
of the H+, Cl− and Ba2+ concentrations, respectively. The
leaching rate of celestite increases with temperature, the
apparent activation energy being 68.8 kJ mol− 1. Under
well-mixed conditions, in the solution of 0.5 M HCl,
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S. Aydoğan et al. / Hydrometallurgy 84 (2006) 239–246
8.25 × 10− 3 M BaCl2 (75% stoichiometric amount) and
1 M NaCl at 60 °C, celestite was entirely dissolved within
180 min at a solid/liquid ratio of 1/250.
Acknowledgement
This study was supported by The Research Foundation
of Selçuk University under Project No. BAP-2004/098.
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