UCTEA Chamber of Metallurgical & Materials Engineers
The Conversion of Strontium Sulfate to Strontium
Carbonate by Using Hydrometallurgical Method
Abstract
SrCO3 produced from SrSO4, which is the main
compound in celestite concentrate, is used for the
production of strontium metal or its compounds. SrCO 3
can be produced from celestite ore by Direct Carbon
Reduction Method or by Conversion Method using
alkaline Na2CO3 solution. For the industrial use of
SrCO3 produced according to the methods mentioned
above, it is necessary to eliminate alkaline
contaminations.It is possible to obtain alkaline free
product by conversion SrSO4 to SrCO3 by
hydrometallurgical method using (NH4)2CO3 solution.
In this work, the effects of CO32- ion concentration,
particle size and temperature on the conversion
reaction rate were investigated using (NH4)2CO3
containing solutions.
The commercially available product (NH4)2CO3 is an
equimolar mixture of ammonium carbamate and
ammonium
bicarbonate.
This
mixture
is
dissolved/hydrolyzed in water to obtain CO32- ion
containing solution. SrSO4 is converted to porous
SrCO3 by reacting with CO32- ions in the solution
pseudomorphically and the produced SO42- ions pass to
the solution. The conversion reaction proceeds by
equimolar counter diffusion of SO 42- and CO32- ions
through the pores of SrCO3 layer. It was determined
that the rate determining step is the ion – exchange
reaction. XRD, SEM and simultaneous DTA-TG
analytical techniques were usedfor the phase
characterization of the celestite concentrate and the
solid reaction products.
1. Introduction
The black ash method and the double decomposition
method are used to produce SrCO3. In the first method
SrS is produced by calcination of SrSO4 with coke at
1273-1473 K and the SrS is dissolved in hot water.
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Mert Zorağa, Cem Kahruman, İbrahim Yusufoğlu
İstanbul University - Türkiye
The solution treated with solutions containing CO32ions [2]. In the second method, SrSO4 is reacted
directly with CO32- ions containing solutions to
produce SrCO3 [3-7].
In the recent years, mechanochemical processes [8-12]
and hydrothermal methods [13-15] have been used to
convert SrSO4 to SrCO3.
2. Experimental Procedure
Crushed, ground and enriched SrSO4 concentrate was
obtained from Barit Maden Turk A.S..The SrSO4
concentrate was wet sieved and the fraction of – 315 +
250, – 180 + 150 and – 125 + 90 ȝm particle sizes were
collected. The concentrate mineral consist of 95.74% (wt.)
SrSO4.
The commercially available product (NH4)2CO3 (AC)
(Merck) is an equimolar mixture of ammonium
carbamate and ammonium bicarbonate. HCO3-, CO32-,
NH4+ and NH3 containing solution with a pH value of
8.9 was obtained by solving chemically pure AC in
distilled water. Reactant solutions were prepared by
dissolving 0.1, 0.2, 0.3 and 0.5 moles of AC in 1 L
solution. The experiments were performed in water
heated jacketed hydrometallurgical reactor and the
details of experimental set up were given by Kalpakli
et al. [16]. 2 g of SrSO4 concentrate was added to the
reactor. The conversion reaction was carried out under
isothermal conditions for 3 h.The quantitative analyses
of SO42- ions passed in the solution taken during certain
time intervals were performed by ICP-OES. XRD and
DTA-TG techniques were used for characterization of
solid reactant and products.
3. Results and Discussion
Strontium occurs commonly in nature as two minerals
which are celestite (SrSO4) and strontianite (SrCO3)
and celestite is more common in economic deposits.
The strontium sulfate is converted to strontium
carbonate and other strontium compounds (strontium
chloride, chromate, nitrate, oxalate, oxide and peroxide
etc.). [1]
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Reaction 1 and 2 are valid in the solution.
+
+
'
'
+
(1)
+
(2)
Conversion of SrSO4 to SrCO3 in the presence of CO32ions is given by Reaction 3:
18 th International Metallurgy & Materials Congress
+
ĺ
+
(3)
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TMMOB Metalurji ve Malzeme Mühendisleri Odası
CO32- ions in the solution reacts with SrSO4 and it is
consumed. The consumption of CO32- forces the
Reaction 2 to proceed towards the left side. For the
formation of CO32-, HCO3- must react with NH3 that
needs to be present stoichiometrically in the solution.
Thus, the quantity of CO32- that can be formed depends
on the limit of the stoichiometrically available
reactants.
The fractional conversion of SrSO4 (X) at any reaction
time (t) was calculated according to Eq. 4, where Wo is
the initial weight of SrSO4 fed to the solution, Wt is the
weight of unreacted SrSO4 at any reaction time.
(4)
For the determination of particle size effect on the
reaction rate 1 L solution obtained by
dissolving/hydrolyzing of 0.3 mole AC, 323 K, 500
rpm and 2 g of – 315 + 250, – 180 + 150 and – 125 + 90
ȝm particle size fractions of concentrated celestite were
used. The fractional conversion (X) vs time (t)
diagrams were shown in Figure1.
Figure 1. X vs t diagrams for different particle sizes
(AC: 0.3 mole , solution: 1 L, stirring speed: 500 rpm,
T: 323 K)
According to the Figure 1, decrease in the particle size
of the concentrated SrSO4 particles increases the
reaction rate.
The conversion experiments were carried out to
investigate the effects of temperature and mole
amounts of AC on the reaction rate using 2 g of
concentrated celestite, 1 L solution obtained by
dissolving/hydrolyzing of 0.1, 0.2, 0.3 and 0.5 mole
AC and 303, 313, 323 K.The effects of temperature on
the conversion rate at constant AC amount were shown
in Figure 2.
The diagrams given in Figure 2 were re-plotted at
constant temperature for various AC amounts in order
to assist in observing the effect of CO32- concentration
on the conversion reaction rate (Fig. 3)
Figure 2. X vs t diagrams obtained for different temperatures
and constant AC amounts dissolved in 1 L solution
(a) 0.1 (b) 0.2 (c) 0.3 (d) 0.5 mole AC
(Particle size: – 125 + 90 ȝm, stirring speed: 500 rpm).
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UCTEA Chamber of Metallurgical & Materials Engineers
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Figure 4. DTA-TG diagrams of the solid products.
(a)
Figure 3. X vs t diagrams obtained for different AC amount
dissolved in 1 L solution and constant temperatures
(Particle size: – 125 + 90 ȝm, stirring speed: 500 rpm).
According to the Figures 2 and 3, the conversion
reaction rate increases with increasing temperature
(chemical reaction control) and the concentration of
CO32- has no effect on the conversion reaction rate
in solution obtained by dissolving/hydrolyzing of 0.1,
0.2 and 0.3 mole AC (zero order reaction) and
decreases for 0.5 mole AC (negative order).
Simultaneous DTA-TG diagrams and SEM images of
the solid reaction products are shown in Figure 4 and 5,
respectively.
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(b)
Figure 5.SEM images of solid reaction products
(a) 323 K, (b) 303 K
(AC: 0.3 mole, solution: 1 L, particle size: – 125 + 90 ȝm,
stirring speed: 500 rpm).
It was determined that only SrCO3 in the solid mixture
was decomposed to SrO and CO2 during thermal
analysis. TG diagram of the solid mixture obtained by
uncompletedreaction showed less weight loss with
respect to the completed reaction solid product. DTA
diagrams showed the endothermic effect of the
decomposition of SrCO3 as a broad peak with a
minimum at 1278 K. The reversible allotropic change
of rhombohedral to hexagonal SrCO3 can be seen as
an endothermic peak at 1204 K. It was observed
from the DTA diagram that SrSO4 has a reversible
allotropic change at 1426 K. The SEM images showed
that the porous SrCO3 formed upwards over the
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surfaces of the SrSO4 particles. The grain morphology
of SrCO3 is not affected by temperature.
XRD diagram of the solid product is shown in Figure
6.
TMMOB Metalurji ve Malzeme Mühendisleri Odası
[11] D. Bingol, S.Aydogan, S.K.Bozbas,J. Ind. and
Eng. Chem., 18(2012), 834-838.
[12] E. Turianicova,A.Obut, A. Zorkovska, P. Balaz,
M. Matik,J.Briancin,Min. Eng., 49 (2013) 98-102.
[13] R. Suarez-Orduna, J. C. Rendon-Angeles, Z.
Matamaros-Veloza, K. Yanagisawa,Solid State Ions,
172 (2004) 293-296.
[14] J. C. Rendon-Angeles, M. I.Pech-Canul, J. LopezCuevas, Z. Matamaros-Veloza, K. Yanagisawa,J. Solid
State Chem., 179 (2006) 3645-3652.
[15] R. Suarez-Orduna, J. C. Rendon-Angeles, K.
Yanagisawa,Int. J. Min. Process., 83 (2007) 12-18.
[16] A. O. Kalpakli, S. Ilhan,C.Kahruman,I.Yusufoglu,
Hydrometallurgy, 121 (2012) 7-15.
Figure 6.XRD diagram of solid reaction product
(AC: 0.3 mole, solution: 1 L, particle size: – 125 + 90 ȝm,
stirring speed: 500 rpm, T: 323 K).
The solid product consists only of SrCO3 and this result
is in good accordance with the conversion given in
Figure 2.
4. Conclusion
During the hydrolysis and dissolving of AC in water
CO32-, HCO3-, NH4+ and NH3 are formed.The
conversion reaction rate of SrSO4 to SrCO3 increases
with increased temperature. The reaction rate is zero
order with respect to the CO32- ion concentration in
solutions obtained by dissolving/hydrolyzing 0.1, 0.2,
and 0.3 mole of AC in 1 L solution. The order is
changed to negative if 0.5 mole of AC was used. In
addition, the decrease of the particle size of the
concentrated celestite increases the reaction rate.
References
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[2] M. Erdemoglu, M.Canbazoglu, Hydrometallurgy,
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[4]F. De Buda, U.S. Patent. 4666688 (1987) 1-9.
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[6] A. H. Castillejos, B.De La Cruz Del, S. Uribe,
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