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Non-isothermal leaching kinetics of braunite in water saturated with sulphur dioxide
Resources, Conservation and Recycling 26 (1999) 35–42
Non-isothermal leaching kinetics of braunite in water saturated with sulphur dioxide Ayhan Demirbas¸ Education Faculty, Karadeniz Technical Uni6ersity, 61335 Akc¸aabat, Trabzon, Turkey Accepted 6 October 1998
Abstract In the leaching of braunite in water, saturated with sulphur dioxide, it was observed that the leaching rate increases with increasing temperature, leaching time and stirring speed, and with decreasing solid-to-liquid ratio and particle size. The optimum conditions for leaching braunite using water, saturated with SO2, are temperature: 358 K, leaching time: 150 min, particle size: 80 mm, solid-to-liquid ratio: 0.01 g ml − 1, and stirring speed: 4500 min − 1. The leaching kinetic parameters were the activation energy 65.3 kJ mol − 1, the pre-exponential factor; 4.51 ×1012 min − 1, and rate constant 1.28 × 102 min − 2. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Leaching kinetics; Baunite; Manganese ore; Sulphur dioxide
1. Introduction The braunite mineral (3Mn2O3·MnSiO3) found in manganese ore has a tetragonal crystal system. Braunite departs only slightly from cubic symmetry and so the crystals appear octahedral, and as found in nature, are brownish black in colour. Braunite is soluble in hydrochloric acid [1]. The processing of manganese ore for the production of manganese compounds is very important commercially [2].
0921-3449/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 3 4 4 9 ( 9 8 ) 0 0 0 7 3 - 1
36
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
Manganese, a less available element in the earth, is an important substance used widely, especially in metallurgy and chemical industries. Approximately 95% of processed manganese ore is consumed by battery production, and in the chemical, glass and ceramic industries. MnSO4 is a manganese compound used in the largest amounts following ferrous-manganese alloys and used as a raw material in the production of some manganese compounds in the dye, pharmacy, textile industries. SO2 gas produced in the roasting of sulfide minerals can cause substantial air pollution. Increasingly such SO2 is being captured effectively for the production of H2SO4 [3]. Sulphur dioxide has potential for the treatment of ores and for the production of chemicals [4,5]. Sulphur dioxide, in aqueous solution, has been shown to be a very good leaching agent [2,6–10]. The use of SO2 as a leaching agent has the following advantages: (1) it is cheaper than mineral acids; (2) it is effective for the dissolution of manganese ores; and (3) the air pollution caused by SO2 can be reduced. Percolation leaching of manganese ore by aqueous sulphur dioxide has been carried out by Abruzzese who found that SO2 could be used as an effective leachant for manganese dissolution owing to fast dissolution kinetics and low temperature [11]. The purpose of this paper is to present new data on the leaching of manganese from the braunite with sulfur dioxide in aqueous solution and to study its leaching kinetics.
2. Experimental The manganese ore used in this study was supplied from the Erzurum region in Eastern Anatolia, Turkey. It has been reported that the ore consists mainly of braunite (3Mn2O3·MnSiO3) [2]. The ore was ground and sieved and then fractionated to obtain particles having average diameters of 80, 100, 120, and 140 mm. The ore was analyzed according to Furman [12]. The principle of the process depends upon the fact that under certain condition bivalent manganese can be quantitatively oxidized to permanganic acid by sodium bismuthate. The braunite sample analyzed 49.53% MnO, 22.16% MnO2, 0.11% Fe2O3, 0.03% MgO, 8.60% SiO2, 1.68% CaO, 1.35% heating loss, and 16.54% remainder. The leaching process was carried out in a 250-ml glass reactor at ambient pressure, using a mechanical stirrer. A thermostat was used to control the reaction temperature (9 2 K). The reactor was fitted with a cooler to prevent the reduction of the reaction volume by evaporation of the solution. During leaching, sulphur dioxide gas was bubbled continuously at a controlled rate to keep the solution saturated [8].
3. Results and discussion When SO2 gas is in contact with water the following equilibria are established [13]:
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
SO2(g) +H2O(l) X H2SO3(aq)
(1)
H2SO3(aq) +H2O(l) X H3O (aq)+ HSO (aq) +
37
− 3
(2)
The solubility of SO2 depends upon temperature and pressure. pH measurements were made at the beginning of each experiment at room temperature and at 610 mmHg. The pH was 0.61. The dissolution reaction of the braunite mineral in water saturated with SO2 can be written as: MnO2(s) +SO2(g) +H2O(l) Mn + 2(aq)+ SO4− 2(aq)+ H2O(l)
(3)
MnO(s) + 2SO2(g) +H2O(l) Mn + 2(aq)+ 2HSO3− (aq)
(4)
Eqs. (3) and (4) assume that there is no solid product layer formed during the leaching reaction, hence the possibility of product layer diffusion being the ratecontrolling step can be ruled out. In recent years weight loss based methods have been widely used to study the kinetics of various solid-state decomposition reactions. Several computational methods have been presented in the literature which utilize non-isothermal weight loss resulted data to obtain kinetic information [14–16]. Generally the rate of mass loss for a decomposition reaction is described by the Eq. (5), (dX/dt) = kf(W)
Fig. 1. Arrhenius plot for temperature range 320 – 360 K.
(5)
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A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
Fig. 2. Effect of stirring speed on leaching of manganese from braunite. Particle size, 80 mm; solid-to-liquid ratio, 0.01 g ml − 1; leaching time, 150 min.
X =(W0 −W)/W0
(6)
k = A exp( − E/RT)
(7)
T = T0 +bt
or
t = (T −T0)/b
(8)
where X is the degree of leaching, W0 is the initial weight (g), W is the remaining weight (g), t is time (s), k is the reaction rate constant (s − 1), f(W) is a function depending on the reaction mechanism, A and E are the pre-exponential factor (s − 1) and activation energy (kJ mol − 1), respectively; R is the gas constant (kJ mol − 1 K − 1), T is the absolute temperature (K), b is the linear heating rate (K s − 1) and T0 is the initial reaction temperature (K). By combination the above expressions give the general non-isothermal kinetic Eq. (5), (dX)/(dT) =(A/b)exp( −E/RT)
(9)
where X is the fractional weight loss. The simple nth order kinetic equation, describing the rate of weight loss of the sample is assumed to be [17] ( − 1/W0)(dW/dT) = k exp( − E/RT)f(W)n
(10)
Assuming that f(W)n =[(W0 −W)/(W0)]n
(11)
The reaction rate constant (k) and the order of reaction (n) can be calculated from Eq. (9). If n = 1 the following equation must be used ln[( − 1/W0)(dW/dT)] = −(E/RT)+ln[(W0 − W)/(W0)]+ ln(A/b)
(12)
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
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Fig. 3. Effect of particle size on leaching of manganese from braunite. Solid-to-liquid ratio, 0.01 g ml − 1; stirring speed, 4500 min − 1; leaching time, 150 min.
Fig. 4. Effect of stirring time on leaching of manganese from braunite. Particle size, 80 mm; solid-to-liquid ratio, 0.01 g ml − 1; stirring speed, 4500 min − 1.
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
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Fig. 5. Effect of solid-to-liquid ratio on leaching of manganese from braunite. Stirring speed, 4500 min − 1; particle size, 80 mm; leaching time, 150 min. Table 1 Kinetic parameters for leaching of manganese from braunite samples at different leaching times (min) Parameter
15
30
60
90
150
DX a T1 (K)b T2 (K)c DT (K) −In(DX/DT)(K−l) A (min−1) k(min−1)
0.44 293 358 65 4.995 9.11×1012 162.16
0.47 293 358 65 4.929 3.74×1012 124.92
0.50 293 358 65 4.868 5.75×1012 142.60
0.53 293 358 65 4.809 2.64×1012 118.01
0.59 293 358 65 4.719 1.31×1012 91.96
Eav = 65.3 kJ mol−1
Aav =4.51×1012 min−1
kav =127.93 min−1
DX instead of (dW/W0) and DT instead of dT were used. T1, initial leaching temperature. c T2, final leaching temperature; particle size: 80 mm; solid-to-liquid ratio, 0.01 g ml−1; stirring speed: 4500 min−1. a
b
Thus, if drawing a plot of either In[(− l/W0)(dW/dT)] versus (1/T) should result in a straight line of slope − (E/R). An Arrhenius plot for temperature range 320–360 K is given in Fig. 1.
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
41
There are various models developed to obtain some kinetic parameters using thermogravimetric data [18]. In this study to determine the kinetic parameters for the leaching of manganese the first order (n = 1) percent of weight loss based model proposed in earlier studies [14,19] was used. This method, which requires the fractional weight loss or conversion and temperature differences DX and DT between approximate initial and final conversion levels, the average temperature was used to calculate the pre-exponential factor, A. Finally, the rate of reaction constant, k, was calculated using A and E values in the Arrhenius equation − k =Ae − E/RT
(13)
The effect of the stirring speed on the leaching rate was studied at the different stirring speeds of 1500, 2000, 3000, and 4500 min − 1 at temperature of 358 K, the solid-to-liquid ratio of 0.01, and the particle size 80 mm. The experimental results are exhibited in Fig. 2. The effect of particle size on the leaching rate was investigated using four particle size fractions of 80, 100, 120, and 140 mm at temperature of 358 K, a solid-to-liquid ratio of 0.01 and a stirring speed of 4500 min − 1. The results obtained from these experiments are given in Fig. 3. As seen from Fig. 3, the conversion rate, in other words the fractional leaching weight, increases with decreasing particle size. The effect of temperature on the leaching rate was studied at 293, 308, 318, 328, 338, and 358 K, a solid-to-liquid ratio of 0.01, particle size 80 mm and a stirring speed of 4500 min − 1. As expected, the leaching rate increases with the increase in the reaction temperature (Fig. 4). The effect of the solid-to-liquid ratio on the leaching rate was investigated for the ratios 0.01, 0.02, 0.04, and 0.06 g ml − 1 at 358 K, a stirring speed of 4500 min − 1, and a particle size of 80 mm. As can be seen from Fig. 5, the leaching rate decreases with increasing solid-to-liquid ratio. The other important kinetic parameters for the leaching of manganese from braunite samples at different leaching times (min) are given in Table 1. The apparent activation energy (E) is 65.3 kJ mol − 1, the pre-exponential factor (A) is 4.51× 1012 min − 1, and leaching rate constant (k) is 1.28× 102 min − 1.
4. Conclusions The dissolution of braunite was investigated in a semi-batch reactor, and it was observed that sulphur dioxide-saturated water can dissolve the ore efficiency. The leaching rate increases with increasing temperature, leaching time and stirring speed, and decreasing solid-to-liquid ratio and particle size. In this study, the leaching time (t) is given as a function of the temperature (T) and the linear heating rate (b). The activation energy of leaching process is 65.3 kJ mol − 1. The effective parameters on the leaching can be given the temperature, the stirring speed, the particle size, the solid-to-liquid ratio and leaching time, respectively.
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A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
References [1] Hamilton WR, Wooley AR, Bishop AR. Minerals, rocks and fossils. In: Country life books, 4th. Middlesex, England: Twickenham, 1987:86. [2] Yartas¸i A, C ¸ opur M, Kocakerim MM. Dissolution kinetics of manganese ore in water saturated with sulphur dioxide. Chim Acta Turc 1997;25:53. [3] Yartas¸i A, Kocakerim MM, O8 zmetin C, Abali Y. Dissolution of braunite in sulphuric acid. J Miner Eng 1996;9:1269. [4] Habashi F. Sulphur dioxide in metallurgy. Sulphur Inst J 1976;12:3. [5] Hanf NW. Leaching of cobalt and/or nickel values from ores by (NH4)2SO3, NH4+ , SO3− 2, or both. S Afr Pat. 7302, 1974;448. [6] Abali Y, C ¸ olak S, Ekmekyapar A. Dissolution kinetics of magnesite mineral in water saturated by sulfur dioxide. Dog˘a-Tr J Eng Environ Sci 1991;16:319. [7] McCullough J, Philips JF, Tate LR. Preparation of dicalcium phosphate rock by the use of sulphur dioxide, water, and carbonyl compounds. 1978; U.S. Patent 4, 113, 842. [8] Yartas¸i A, Kocakerim MM, Yapici S, O8 zmetin C. Dissolution kinetics of phosphate ore in SO2-saturated water. Ind Eng Chem Res 1994;33:2220. [9] Kocakerim MM, Alkan M. Dissolution kinetics of colemanite in SO2-saturated water. Hydrometallurgy 1988;19:385. [10] Yang RT, Cunningham PT, Wilson WI, Johnson JA. Kinetics of the reaction of half-calcined dolomite with SO2. Chem Eng Div 1975;139:57. [11] Abbruzzese C. Percolation leaching of manganese ore aqueous sulphur dioxide. Hydrometallurgy 1993;25:85. [12] Furman NH. Standard methods of chemical analysis, 6th. Princeton, NJ: D. Van Nostrand Company, 1963. [13] Prausnitz JM. Molecular thermodynamics of fluid phase equilibria. Englewood Cliffs, NJ: PrenticeHall, 1969:380. [14] Ersoy-Meric¸boyu A, Ku¨c¸u¨kbayrak S. Kinetic analysis of non-isothermal calcination TG curves of natural Turkish dolomites. Thermochim Acta 1994;232:225 – 32. [15] Demirbas¸ A. Kinetics for non-isothermal flash pyrolysis of hazelnut shell. Bioresour Technol 1998;66:247. [16] Demirbas¸ A. Recycling of lithium from borogypsum by leaching with water and leaching kinetics. Res. Convers. Recycl. (in press). [17] Tran DQ, Rai C. A kinetic model for pyrolysis of Douglas fir bark. Fuel 1978;57:293. [18] Ersoy-Meric¸boyu A, Ku¨c¸u¨kbayrak S, Yavuz R. Thermal decomposition kinetics of natural Turkish limestone under non-isothermal conditions. Thermochim Acta 1993;223:121. [19] Ersoy-Meric¸boyu A, Ku¨c¸u¨kbayrak S, Du¨ru¨s B. Evaluation of the kinetic parameters for the thermal decomposition of natural Turkish limestones from their thermogravimetric curves using a computer programme. J Thermal Anal 1993;39:707.
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Non-isothermal leaching kinetics of braunite in water saturated with sulphur dioxide Ayhan Demirbas¸ Education Faculty, Karadeniz Technical Uni6ersity, 61335 Akc¸aabat, Trabzon, Turkey Accepted 6 October 1998
Abstract In the leaching of braunite in water, saturated with sulphur dioxide, it was observed that the leaching rate increases with increasing temperature, leaching time and stirring speed, and with decreasing solid-to-liquid ratio and particle size. The optimum conditions for leaching braunite using water, saturated with SO2, are temperature: 358 K, leaching time: 150 min, particle size: 80 mm, solid-to-liquid ratio: 0.01 g ml − 1, and stirring speed: 4500 min − 1. The leaching kinetic parameters were the activation energy 65.3 kJ mol − 1, the pre-exponential factor; 4.51 ×1012 min − 1, and rate constant 1.28 × 102 min − 2. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Leaching kinetics; Baunite; Manganese ore; Sulphur dioxide
1. Introduction The braunite mineral (3Mn2O3·MnSiO3) found in manganese ore has a tetragonal crystal system. Braunite departs only slightly from cubic symmetry and so the crystals appear octahedral, and as found in nature, are brownish black in colour. Braunite is soluble in hydrochloric acid [1]. The processing of manganese ore for the production of manganese compounds is very important commercially [2].
0921-3449/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 3 4 4 9 ( 9 8 ) 0 0 0 7 3 - 1
36
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
Manganese, a less available element in the earth, is an important substance used widely, especially in metallurgy and chemical industries. Approximately 95% of processed manganese ore is consumed by battery production, and in the chemical, glass and ceramic industries. MnSO4 is a manganese compound used in the largest amounts following ferrous-manganese alloys and used as a raw material in the production of some manganese compounds in the dye, pharmacy, textile industries. SO2 gas produced in the roasting of sulfide minerals can cause substantial air pollution. Increasingly such SO2 is being captured effectively for the production of H2SO4 [3]. Sulphur dioxide has potential for the treatment of ores and for the production of chemicals [4,5]. Sulphur dioxide, in aqueous solution, has been shown to be a very good leaching agent [2,6–10]. The use of SO2 as a leaching agent has the following advantages: (1) it is cheaper than mineral acids; (2) it is effective for the dissolution of manganese ores; and (3) the air pollution caused by SO2 can be reduced. Percolation leaching of manganese ore by aqueous sulphur dioxide has been carried out by Abruzzese who found that SO2 could be used as an effective leachant for manganese dissolution owing to fast dissolution kinetics and low temperature [11]. The purpose of this paper is to present new data on the leaching of manganese from the braunite with sulfur dioxide in aqueous solution and to study its leaching kinetics.
2. Experimental The manganese ore used in this study was supplied from the Erzurum region in Eastern Anatolia, Turkey. It has been reported that the ore consists mainly of braunite (3Mn2O3·MnSiO3) [2]. The ore was ground and sieved and then fractionated to obtain particles having average diameters of 80, 100, 120, and 140 mm. The ore was analyzed according to Furman [12]. The principle of the process depends upon the fact that under certain condition bivalent manganese can be quantitatively oxidized to permanganic acid by sodium bismuthate. The braunite sample analyzed 49.53% MnO, 22.16% MnO2, 0.11% Fe2O3, 0.03% MgO, 8.60% SiO2, 1.68% CaO, 1.35% heating loss, and 16.54% remainder. The leaching process was carried out in a 250-ml glass reactor at ambient pressure, using a mechanical stirrer. A thermostat was used to control the reaction temperature (9 2 K). The reactor was fitted with a cooler to prevent the reduction of the reaction volume by evaporation of the solution. During leaching, sulphur dioxide gas was bubbled continuously at a controlled rate to keep the solution saturated [8].
3. Results and discussion When SO2 gas is in contact with water the following equilibria are established [13]:
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
SO2(g) +H2O(l) X H2SO3(aq)
(1)
H2SO3(aq) +H2O(l) X H3O (aq)+ HSO (aq) +
37
− 3
(2)
The solubility of SO2 depends upon temperature and pressure. pH measurements were made at the beginning of each experiment at room temperature and at 610 mmHg. The pH was 0.61. The dissolution reaction of the braunite mineral in water saturated with SO2 can be written as: MnO2(s) +SO2(g) +H2O(l) Mn + 2(aq)+ SO4− 2(aq)+ H2O(l)
(3)
MnO(s) + 2SO2(g) +H2O(l) Mn + 2(aq)+ 2HSO3− (aq)
(4)
Eqs. (3) and (4) assume that there is no solid product layer formed during the leaching reaction, hence the possibility of product layer diffusion being the ratecontrolling step can be ruled out. In recent years weight loss based methods have been widely used to study the kinetics of various solid-state decomposition reactions. Several computational methods have been presented in the literature which utilize non-isothermal weight loss resulted data to obtain kinetic information [14–16]. Generally the rate of mass loss for a decomposition reaction is described by the Eq. (5), (dX/dt) = kf(W)
Fig. 1. Arrhenius plot for temperature range 320 – 360 K.
(5)
38
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
Fig. 2. Effect of stirring speed on leaching of manganese from braunite. Particle size, 80 mm; solid-to-liquid ratio, 0.01 g ml − 1; leaching time, 150 min.
X =(W0 −W)/W0
(6)
k = A exp( − E/RT)
(7)
T = T0 +bt
or
t = (T −T0)/b
(8)
where X is the degree of leaching, W0 is the initial weight (g), W is the remaining weight (g), t is time (s), k is the reaction rate constant (s − 1), f(W) is a function depending on the reaction mechanism, A and E are the pre-exponential factor (s − 1) and activation energy (kJ mol − 1), respectively; R is the gas constant (kJ mol − 1 K − 1), T is the absolute temperature (K), b is the linear heating rate (K s − 1) and T0 is the initial reaction temperature (K). By combination the above expressions give the general non-isothermal kinetic Eq. (5), (dX)/(dT) =(A/b)exp( −E/RT)
(9)
where X is the fractional weight loss. The simple nth order kinetic equation, describing the rate of weight loss of the sample is assumed to be [17] ( − 1/W0)(dW/dT) = k exp( − E/RT)f(W)n
(10)
Assuming that f(W)n =[(W0 −W)/(W0)]n
(11)
The reaction rate constant (k) and the order of reaction (n) can be calculated from Eq. (9). If n = 1 the following equation must be used ln[( − 1/W0)(dW/dT)] = −(E/RT)+ln[(W0 − W)/(W0)]+ ln(A/b)
(12)
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
39
Fig. 3. Effect of particle size on leaching of manganese from braunite. Solid-to-liquid ratio, 0.01 g ml − 1; stirring speed, 4500 min − 1; leaching time, 150 min.
Fig. 4. Effect of stirring time on leaching of manganese from braunite. Particle size, 80 mm; solid-to-liquid ratio, 0.01 g ml − 1; stirring speed, 4500 min − 1.
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
40
Fig. 5. Effect of solid-to-liquid ratio on leaching of manganese from braunite. Stirring speed, 4500 min − 1; particle size, 80 mm; leaching time, 150 min. Table 1 Kinetic parameters for leaching of manganese from braunite samples at different leaching times (min) Parameter
15
30
60
90
150
DX a T1 (K)b T2 (K)c DT (K) −In(DX/DT)(K−l) A (min−1) k(min−1)
0.44 293 358 65 4.995 9.11×1012 162.16
0.47 293 358 65 4.929 3.74×1012 124.92
0.50 293 358 65 4.868 5.75×1012 142.60
0.53 293 358 65 4.809 2.64×1012 118.01
0.59 293 358 65 4.719 1.31×1012 91.96
Eav = 65.3 kJ mol−1
Aav =4.51×1012 min−1
kav =127.93 min−1
DX instead of (dW/W0) and DT instead of dT were used. T1, initial leaching temperature. c T2, final leaching temperature; particle size: 80 mm; solid-to-liquid ratio, 0.01 g ml−1; stirring speed: 4500 min−1. a
b
Thus, if drawing a plot of either In[(− l/W0)(dW/dT)] versus (1/T) should result in a straight line of slope − (E/R). An Arrhenius plot for temperature range 320–360 K is given in Fig. 1.
A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
41
There are various models developed to obtain some kinetic parameters using thermogravimetric data [18]. In this study to determine the kinetic parameters for the leaching of manganese the first order (n = 1) percent of weight loss based model proposed in earlier studies [14,19] was used. This method, which requires the fractional weight loss or conversion and temperature differences DX and DT between approximate initial and final conversion levels, the average temperature was used to calculate the pre-exponential factor, A. Finally, the rate of reaction constant, k, was calculated using A and E values in the Arrhenius equation − k =Ae − E/RT
(13)
The effect of the stirring speed on the leaching rate was studied at the different stirring speeds of 1500, 2000, 3000, and 4500 min − 1 at temperature of 358 K, the solid-to-liquid ratio of 0.01, and the particle size 80 mm. The experimental results are exhibited in Fig. 2. The effect of particle size on the leaching rate was investigated using four particle size fractions of 80, 100, 120, and 140 mm at temperature of 358 K, a solid-to-liquid ratio of 0.01 and a stirring speed of 4500 min − 1. The results obtained from these experiments are given in Fig. 3. As seen from Fig. 3, the conversion rate, in other words the fractional leaching weight, increases with decreasing particle size. The effect of temperature on the leaching rate was studied at 293, 308, 318, 328, 338, and 358 K, a solid-to-liquid ratio of 0.01, particle size 80 mm and a stirring speed of 4500 min − 1. As expected, the leaching rate increases with the increase in the reaction temperature (Fig. 4). The effect of the solid-to-liquid ratio on the leaching rate was investigated for the ratios 0.01, 0.02, 0.04, and 0.06 g ml − 1 at 358 K, a stirring speed of 4500 min − 1, and a particle size of 80 mm. As can be seen from Fig. 5, the leaching rate decreases with increasing solid-to-liquid ratio. The other important kinetic parameters for the leaching of manganese from braunite samples at different leaching times (min) are given in Table 1. The apparent activation energy (E) is 65.3 kJ mol − 1, the pre-exponential factor (A) is 4.51× 1012 min − 1, and leaching rate constant (k) is 1.28× 102 min − 1.
4. Conclusions The dissolution of braunite was investigated in a semi-batch reactor, and it was observed that sulphur dioxide-saturated water can dissolve the ore efficiency. The leaching rate increases with increasing temperature, leaching time and stirring speed, and decreasing solid-to-liquid ratio and particle size. In this study, the leaching time (t) is given as a function of the temperature (T) and the linear heating rate (b). The activation energy of leaching process is 65.3 kJ mol − 1. The effective parameters on the leaching can be given the temperature, the stirring speed, the particle size, the solid-to-liquid ratio and leaching time, respectively.
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A. Demirbas¸ / Resources, Conser6ation and Recycling 26 (1999) 35–42
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