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Leaching Kinetics of Lanthanide in Sulfuric Acid from Low Grade Bauxite
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 18 (2019) 462–467
www.materialstoday.com/proceedings
AEM 2018
Leaching Kinetics of Lanthanide in Sulfuric Acid from Low Grade Bauxite Eny Kusrinia*, Anwar Usmanb, Nici Triskoa, Sri Harjantoc, Arif Rahmane a
Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Depok, 16424, Indonesia b Department of Chemistry, Faculty of Sciences, Universiti Brunei Darrusalam, Negara Brunei Darussalam c Department of Metallurgy and Material Engineering, Faculty of Engineering, Universitas Indonesia, Depok, 16424, Indonesia d Department of Chemistry, Faculty of Mathematics & Natural Sciences, Universitas Negeri Jakarta, Indonesia
Abstract
The utilization of low grade bauxite which was obtained from washing waste in bauxite mining from Madong, Indonesia, was investigated as a resource of the rare earth elements. In this study, the ores of low grade bauxite contained 39.6 ppm lanthanides, such as lanthanum (18.4 ppm), cerium (19.3 ppm), and yttrium (1.9 ppm) was leached by using 3 M sulfuric acid with the ratio of solid to liquid being 1 g/20 mL. The leaching process was measured at different temperatures and reaction time. The leaching kinetics was evaluated by shrinking core model where the leaching undergoes two stages; fast chemical reaction in early stage and slower leaching rate due to diffusion at later stage. The diffusion stage was found to be relatively more temperature-dependent the chemical reaction stage. The leaching results indicated that operating conditions at 60 °C and 3 M sulfuric acid would be efficiently leach and convert the lanthanides into their sulfuric salts with the fractional conversion as high as 0.67. The activation energy of the chemical reaction and diffusion stage was estimated to be 10.37 and 48.15 kJ/mol, respectively. This finding can potentially lead to the development of enhanced leaching processes of lanthanides from low grade bauxite. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Third International Conference on Advanced Energy Materials. Keywords: Chemical reaction; Diffusion Kinetics: Lanthanides: Leaching; Low grade bauxite
*
Corresponding author’s e-mail address: [email protected], [email protected], Tel.: +62-21-7863516 ext. 204, Fax: +62-21-7863515.
2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Third International Conference on Advanced Energy Materials.
E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
463
1. INTRODUCTION Lanthanides are the rare-earth elements found in a relatively small amounts scattered among other elements in crust of the earth [1]. Therefore, lanthanides are usually obtained as a small part of minerals in ores, such as monazite, baznazites, and xenotimes, instead of as free individual minerals [2]. For instance, monazites contain lanthanum, cerium, and samarium as much as 9, 21, and 1.3 ppm, respectively [3]. On the other hand, low grade bauxite have higher contents of lanthanum and yttrium oxide (La2O3 and Y2O3), i.e. 52 and 41 ppm, respectively [4,5]. This provides a perspective that it is possible and economical to extract the rare earth metals from low grade bauxite, enhancing the value added of the mineral ores. In this sense, efficient and low cost extraction methods of the rare-earth elements from low grade bauxite are pursued. Considering that lanthanides and other metal elements can be dissolved in sulfuric acid, the efficient method would be solid-liquid extraction (also known as leaching). In this case, the lanthanides and other metals will be deposited in the form of their sulfates [6]. In order to optimize dissolution of lanthanides from low grade bauxites by using sulfuric acid, the reaction kinetics between lanthanides and sulfuric acid has to be fully understood. In this sense, the kinetics of dissolution process of lanthanides from basnezite and monazite has been reported [7,8]. On the other hands, leaching kinetics of lanthanum from slag consisting of pyrometallurgy and hydrometallurgy in sulfuric acid has been reported by Kim [8], where the reaction is suggested to be: 3H2SO4 (aq) + Ln2O3 (s) → Ln2(SO4)3 (aq) + 3H2O (l)
(1)
The reaction of the slag has been analyzed using a shrinking core model with the shape of the particle was assumed to be spherical and the rate of the reaction is determined by the slowest stage in the process [7]. The reaction kinetics between slag and solvent can be approached evaluated by using two models; e.g. the control of chemical reactions and the control of diffusion. The concentration of sulfuric acid may be negligible during chemical reactions if the sulfuric acid or solvent added into the reactor exceeds the reaction of the stoichiometric ratio [7]. Despite the reaction kinetics of lanthanides from slag of ores with sulfuric acid have been discussed in detail in a number of literature, to the best of our knowledge, there has not been a thorough study to investigate the leaching kinetics of lanthanides from bauxite using acids as leachant. In this study, we systematically explored the leaching kinetics of lanthanides from low grade bauxite produced in Madong, Indonesia, using sulfuric acid as a leaching agent. The composition and distribution of lanthanides in the low grade bauxite were evaluated using inductively coupled plasma optical emission spectrometry (ICP-OES). Our findings provide fundamental understandings of leaching kinetics of lanthanides, offering a paved way for further development of their leaching processes from low grade bauxite at large scale.
2. EXPERIMENTAL 2.1 Materials The lanthanides used in this study were derived from low grade bauxites (Madong, Bintan Island, Indonesia) which have undergone magnetic test prior to the leaching process. The bauxites possessed lanthanum (La) cerium (Ce), and yttrium (Y) is 18.4, 19.3, 1.9 ppm, respectively, while it contained silica (Si) 49%, aluminum (Al) 34%, and iron (Fe) 11%. The low grade bauxites size were ground using pestle mortar and were sieved using 200 mesh screen. 2.2 Procedure Leaching experiments were carried out by mixing 5 g low grade bauxite microparticles with 100 mL sulfuric acid (H2SO4, 3M) in 200 mL conical flasks, thus the ratio between weight of bauxite and the volume of acid is 1 g : 20 mL. The mixture was stirred using a magnetic stirrer for the determined amount of time. After thorough stirring, the mixture was filtered off by vacuum filtration method, using filter paper (Whatman No. 1) to separate the microparticles from the filtrate. The filtrate was then diluted accordingly with distilled water, and the concentrations of lanthanides in the filtrate were analyzed using an ICP-OES. To evaluate the effects of leaching parameters, different leaching conditions were carried out. For the reaction time, the mixtures of bauxite and H2SO4 were stirred
464
E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
at different time (5, 10, 15, 20, 30, and 60 min) at room temperature. For thermodynamic study, the mixtures were stirred at different temperatures (25, 40, and 60ºC). 3. RESULT AND DISCUSSION 3.1 Chemical Reaction Stage Figure 1 presents the fractional conversion (XB) of lanthanides during the leaching as a function stirring time at different temperatures. It is clearly seen that the fractional conversion of lanthanides increases non-linearly with the stirring time, where the conversion undergoes rapidly at early stirring time, followed by slower kinetics at later stirring time. The rapid conversion is faster when the temperature is increased. In particular, at high temperature (60°C) the conversion shows no significant change after reaction time longer than 30 min up to 60 min, indicating that the leaching process reaches an equilibrium. On the other hand, slower kinetics shows faster rates at lower temperature. This suggests that at low temperature, the slower kinetics is predominant before the leaching process reaches an equilibrium. Irrespective of the reaction kinetics, the fractional conversion of lanthanides from the low grade bauxites is more efficient due to effective dissolution of lanthanides at higher temperature.
0.7 0.6 0.5
XB
0.4 0.3 0.2 0.1 0.0 0
10
20
30
40
50
60
Time [min] Figure 1. The fractional conversion (XB) of lanthanides as a function of reaction time at different temperatures; 25 ºC (□), 40 ºC (●), and at 60 ºC (∆). The leaching kinetics was analyzed using a shrinking core model at the chemical reaction stage. In this sense, the outer particles layer is considered to react first with the solvent when the chemical reaction reaches its stage. The chemical reaction then eventually will reach the optimum point when the particle size is equal to zero. The rate of reaction is determined from the rate-determining step of chemical reaction, which can be modelled by eq. (1) [7,9]. = 1 − (1 − ) / (1) The value of the reaction rate constant ( ) at the chemical reaction stage which is the early stage of the leaching process is deduced from the least square method using the linear relation between 1 − (1 − ) / and time ( ), as shown in Figure 2. It is clearly seen that is temperature-dependent, where it tends to increase with temperature, indicating that the reaction rate to form lanthanide sulfate from lanthanide oxide mineral in the bauxite is faster at higher temperature. Basically, activation energy ( ) of the leaching of the lanthanides can be obtained by using the
E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
465
⁄ Arrhenius equation ( = ; where is a pre-exponential factor, is the universal gas constant, and to be 10.37 kJ/mol. the operating temperature of leaching. From the linear plot ln versus 1/ , we found
is
1.0
1-(1-XB)
1/3
0.8
0.6
0.4
0.2
0.0 0
10
20
Time [min] Figure 2. The linear plot of 1 − (1 −
)
/
as a function of time at different temperatures; 25 ºC (□), 40 ºC (●), and at 60 ºC (∆).
3.2 Diffusion Stage The shrinking core model also allows chemical reaction at the diffusion reaction stage which is the later stage of the leaching process. This second exponential term is mathematically modelled by eq. (2) [7,9]. = 1 − 3(1 −
) + 2(1 −
)
(2)
The rate constant at the diffusion stage ( ) was determined from the linear relation between 1 − 3(1 − ) + 2(1 − ) and time ( ), as shown in Figure 3. The value of are 0.0010, 0.0035, 0.0069 /min for 25, 40 and 60 ºC. The activation energy of the leaching process at the diffusion stage was estimated to be 48.15 kJ/mol, and this is slightly higher than that of the leaching kinetics of lanthanides from slag in sulfuric acid (24.8 kJ/mol) (Kim et al. (2014). From the kinetics data of the leaching at both the chemical reaction and diffusion stage, we found that rate constant of the reaction stage is much higher than that of the diffusion stage. As the reaction rate should be controlled by the slowest stage, the data suggest that the dissolution of lanthanides is the sulfuric acid solution is mainly controlled by the diffusion. This indicates that during the chemical reaction process, the lanthanides presents on the surface of the bauxite particles will undergo leaching process. The unreacted surface layer will be a barrier for sulfuric acid to react with subsequent layers inside the particles so that the diffusion takes place at the later stage.
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E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
2/3
1-3(1-XB) +2(1-XB)
1/3
0.2
0.1
0.0 0
10
20
30
40
50
60
Time [min] Figure 3. The linear plot of 1 − 3(1 −
) + 2(1 − ) as a function of time at different temperatures; 25 ºC (□), 40 ºC (●), and at 60 ºC (∆).
4. CONCLUSION Low grade bauxite which contains relatively high lanthanides among mineral ores can be utilized as a resource of the rare earth elements. We have demonstrated that the lanthanides can be extracted from the low grade bauxite by leaching process with sulfuric acid as leachant, enhancing the value added of the mineral ores. The leaching process can be performed without any pre-treatment. The leaching results indicated that operating conditions at 60 °C and 3 M sulfuric acid would be efficiently leach and convert the lanthanides into their sulfuric salts with the fractional conversion as high as 0.67. The leaching rate is very fast and leaching efficiencies increase rapidly with time during the first 15 min, followed by gradual slower process, before its saturation, indicating that the leaching of lanthanides from low grade bauxite undergoes in two stages, which are chemical reaction and diffusion, according to shrinking core model. The activation energy of the chemical reaction and diffusion stage was estimated to be 10.37 and 48.15 kJ/mol, respectively. The diffusion stage was found to be relatively more temperature-dependent the chemical reaction stage. This finding can potentially lead to the development of enhanced leaching processes of lanthanides from low grade bauxite. Acknowledgments This research was funded by PTUPT grant No. 2740/UN2.R3.1/HKP05.00/2017 and No. 492/UN2.R3.1/HKP05.00/2018 from RISTEKDIKTI, Indonesia.
REFERENCES [1] F. Sadri, A. M. Nazari, A. Ghahreman, Journal of Rare Earths 35 (2017) 739-752. [2] C.K. Gupta, N. Krishnamurthy, N. (2005). Extractive metallurgy of rare earths, CRC Press, pp. 20-250. [3] I. Lesmana. (2012). Pembuatan unsur tanah jarang dari mineral monasit menggunakan asam nitrat. Skripsi, Program Sarjana, Jurusan Kimia, Fakultas MIPA, Universitas Padjadjaran. [4] E. Kusrini, A. Rahman, A.A. Bumi, C.S. Utami, E.A. Prasetyanto, 2018. IOP Conf. Ser.: Earth Environ. Sci. 105, 012006. [5] E. Kusrini, Z. J. Bahari, A. Usman, A. Rahman, E. A. Prasetyanto, Materials Science Forum Vol. 929 (2018) 171-176.
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467
[6] R.C. Borra J. Mermans, B. Blanpain, Y. Pontikes, K. Binnemans, T.V. Gerven. Minerals Engineering, 92 (2016), pp 151-159. [7] J.K. Chul, S.Y. Ho, W.C. Kyung, Y.L. Jin, D.K. Sung, M.Y., Shun, J.L. Su, J. Ram, I.L. Se, J.L. Seung, H.K. Seung. Hydrometallurgy, 146 (2014)133-137. [8] Kim, C.J., Yoon, H.S., Chung, K.W., Lee, J.Y., Kim, S.D., Shin, S.M., Lee, S.J., Joe, A.R., Lee, S.I., Yoo, S.J., Kim, S.H., Hydrometallurgy 146 (2014) 133-137 [9] Levenspiel, O..Chemical reaction engineering, 3rd ed. John Willey & Sons Inc., New York, (1999) pp. 358-371.
ScienceDirect Materials Today: Proceedings 18 (2019) 462–467
www.materialstoday.com/proceedings
AEM 2018
Leaching Kinetics of Lanthanide in Sulfuric Acid from Low Grade Bauxite Eny Kusrinia*, Anwar Usmanb, Nici Triskoa, Sri Harjantoc, Arif Rahmane a
Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Depok, 16424, Indonesia b Department of Chemistry, Faculty of Sciences, Universiti Brunei Darrusalam, Negara Brunei Darussalam c Department of Metallurgy and Material Engineering, Faculty of Engineering, Universitas Indonesia, Depok, 16424, Indonesia d Department of Chemistry, Faculty of Mathematics & Natural Sciences, Universitas Negeri Jakarta, Indonesia
Abstract
The utilization of low grade bauxite which was obtained from washing waste in bauxite mining from Madong, Indonesia, was investigated as a resource of the rare earth elements. In this study, the ores of low grade bauxite contained 39.6 ppm lanthanides, such as lanthanum (18.4 ppm), cerium (19.3 ppm), and yttrium (1.9 ppm) was leached by using 3 M sulfuric acid with the ratio of solid to liquid being 1 g/20 mL. The leaching process was measured at different temperatures and reaction time. The leaching kinetics was evaluated by shrinking core model where the leaching undergoes two stages; fast chemical reaction in early stage and slower leaching rate due to diffusion at later stage. The diffusion stage was found to be relatively more temperature-dependent the chemical reaction stage. The leaching results indicated that operating conditions at 60 °C and 3 M sulfuric acid would be efficiently leach and convert the lanthanides into their sulfuric salts with the fractional conversion as high as 0.67. The activation energy of the chemical reaction and diffusion stage was estimated to be 10.37 and 48.15 kJ/mol, respectively. This finding can potentially lead to the development of enhanced leaching processes of lanthanides from low grade bauxite. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Third International Conference on Advanced Energy Materials. Keywords: Chemical reaction; Diffusion Kinetics: Lanthanides: Leaching; Low grade bauxite
*
Corresponding author’s e-mail address: [email protected], [email protected], Tel.: +62-21-7863516 ext. 204, Fax: +62-21-7863515.
2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Third International Conference on Advanced Energy Materials.
E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
463
1. INTRODUCTION Lanthanides are the rare-earth elements found in a relatively small amounts scattered among other elements in crust of the earth [1]. Therefore, lanthanides are usually obtained as a small part of minerals in ores, such as monazite, baznazites, and xenotimes, instead of as free individual minerals [2]. For instance, monazites contain lanthanum, cerium, and samarium as much as 9, 21, and 1.3 ppm, respectively [3]. On the other hand, low grade bauxite have higher contents of lanthanum and yttrium oxide (La2O3 and Y2O3), i.e. 52 and 41 ppm, respectively [4,5]. This provides a perspective that it is possible and economical to extract the rare earth metals from low grade bauxite, enhancing the value added of the mineral ores. In this sense, efficient and low cost extraction methods of the rare-earth elements from low grade bauxite are pursued. Considering that lanthanides and other metal elements can be dissolved in sulfuric acid, the efficient method would be solid-liquid extraction (also known as leaching). In this case, the lanthanides and other metals will be deposited in the form of their sulfates [6]. In order to optimize dissolution of lanthanides from low grade bauxites by using sulfuric acid, the reaction kinetics between lanthanides and sulfuric acid has to be fully understood. In this sense, the kinetics of dissolution process of lanthanides from basnezite and monazite has been reported [7,8]. On the other hands, leaching kinetics of lanthanum from slag consisting of pyrometallurgy and hydrometallurgy in sulfuric acid has been reported by Kim [8], where the reaction is suggested to be: 3H2SO4 (aq) + Ln2O3 (s) → Ln2(SO4)3 (aq) + 3H2O (l)
(1)
The reaction of the slag has been analyzed using a shrinking core model with the shape of the particle was assumed to be spherical and the rate of the reaction is determined by the slowest stage in the process [7]. The reaction kinetics between slag and solvent can be approached evaluated by using two models; e.g. the control of chemical reactions and the control of diffusion. The concentration of sulfuric acid may be negligible during chemical reactions if the sulfuric acid or solvent added into the reactor exceeds the reaction of the stoichiometric ratio [7]. Despite the reaction kinetics of lanthanides from slag of ores with sulfuric acid have been discussed in detail in a number of literature, to the best of our knowledge, there has not been a thorough study to investigate the leaching kinetics of lanthanides from bauxite using acids as leachant. In this study, we systematically explored the leaching kinetics of lanthanides from low grade bauxite produced in Madong, Indonesia, using sulfuric acid as a leaching agent. The composition and distribution of lanthanides in the low grade bauxite were evaluated using inductively coupled plasma optical emission spectrometry (ICP-OES). Our findings provide fundamental understandings of leaching kinetics of lanthanides, offering a paved way for further development of their leaching processes from low grade bauxite at large scale.
2. EXPERIMENTAL 2.1 Materials The lanthanides used in this study were derived from low grade bauxites (Madong, Bintan Island, Indonesia) which have undergone magnetic test prior to the leaching process. The bauxites possessed lanthanum (La) cerium (Ce), and yttrium (Y) is 18.4, 19.3, 1.9 ppm, respectively, while it contained silica (Si) 49%, aluminum (Al) 34%, and iron (Fe) 11%. The low grade bauxites size were ground using pestle mortar and were sieved using 200 mesh screen. 2.2 Procedure Leaching experiments were carried out by mixing 5 g low grade bauxite microparticles with 100 mL sulfuric acid (H2SO4, 3M) in 200 mL conical flasks, thus the ratio between weight of bauxite and the volume of acid is 1 g : 20 mL. The mixture was stirred using a magnetic stirrer for the determined amount of time. After thorough stirring, the mixture was filtered off by vacuum filtration method, using filter paper (Whatman No. 1) to separate the microparticles from the filtrate. The filtrate was then diluted accordingly with distilled water, and the concentrations of lanthanides in the filtrate were analyzed using an ICP-OES. To evaluate the effects of leaching parameters, different leaching conditions were carried out. For the reaction time, the mixtures of bauxite and H2SO4 were stirred
464
E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
at different time (5, 10, 15, 20, 30, and 60 min) at room temperature. For thermodynamic study, the mixtures were stirred at different temperatures (25, 40, and 60ºC). 3. RESULT AND DISCUSSION 3.1 Chemical Reaction Stage Figure 1 presents the fractional conversion (XB) of lanthanides during the leaching as a function stirring time at different temperatures. It is clearly seen that the fractional conversion of lanthanides increases non-linearly with the stirring time, where the conversion undergoes rapidly at early stirring time, followed by slower kinetics at later stirring time. The rapid conversion is faster when the temperature is increased. In particular, at high temperature (60°C) the conversion shows no significant change after reaction time longer than 30 min up to 60 min, indicating that the leaching process reaches an equilibrium. On the other hand, slower kinetics shows faster rates at lower temperature. This suggests that at low temperature, the slower kinetics is predominant before the leaching process reaches an equilibrium. Irrespective of the reaction kinetics, the fractional conversion of lanthanides from the low grade bauxites is more efficient due to effective dissolution of lanthanides at higher temperature.
0.7 0.6 0.5
XB
0.4 0.3 0.2 0.1 0.0 0
10
20
30
40
50
60
Time [min] Figure 1. The fractional conversion (XB) of lanthanides as a function of reaction time at different temperatures; 25 ºC (□), 40 ºC (●), and at 60 ºC (∆). The leaching kinetics was analyzed using a shrinking core model at the chemical reaction stage. In this sense, the outer particles layer is considered to react first with the solvent when the chemical reaction reaches its stage. The chemical reaction then eventually will reach the optimum point when the particle size is equal to zero. The rate of reaction is determined from the rate-determining step of chemical reaction, which can be modelled by eq. (1) [7,9]. = 1 − (1 − ) / (1) The value of the reaction rate constant ( ) at the chemical reaction stage which is the early stage of the leaching process is deduced from the least square method using the linear relation between 1 − (1 − ) / and time ( ), as shown in Figure 2. It is clearly seen that is temperature-dependent, where it tends to increase with temperature, indicating that the reaction rate to form lanthanide sulfate from lanthanide oxide mineral in the bauxite is faster at higher temperature. Basically, activation energy ( ) of the leaching of the lanthanides can be obtained by using the
E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
465
⁄ Arrhenius equation ( = ; where is a pre-exponential factor, is the universal gas constant, and to be 10.37 kJ/mol. the operating temperature of leaching. From the linear plot ln versus 1/ , we found
is
1.0
1-(1-XB)
1/3
0.8
0.6
0.4
0.2
0.0 0
10
20
Time [min] Figure 2. The linear plot of 1 − (1 −
)
/
as a function of time at different temperatures; 25 ºC (□), 40 ºC (●), and at 60 ºC (∆).
3.2 Diffusion Stage The shrinking core model also allows chemical reaction at the diffusion reaction stage which is the later stage of the leaching process. This second exponential term is mathematically modelled by eq. (2) [7,9]. = 1 − 3(1 −
) + 2(1 −
)
(2)
The rate constant at the diffusion stage ( ) was determined from the linear relation between 1 − 3(1 − ) + 2(1 − ) and time ( ), as shown in Figure 3. The value of are 0.0010, 0.0035, 0.0069 /min for 25, 40 and 60 ºC. The activation energy of the leaching process at the diffusion stage was estimated to be 48.15 kJ/mol, and this is slightly higher than that of the leaching kinetics of lanthanides from slag in sulfuric acid (24.8 kJ/mol) (Kim et al. (2014). From the kinetics data of the leaching at both the chemical reaction and diffusion stage, we found that rate constant of the reaction stage is much higher than that of the diffusion stage. As the reaction rate should be controlled by the slowest stage, the data suggest that the dissolution of lanthanides is the sulfuric acid solution is mainly controlled by the diffusion. This indicates that during the chemical reaction process, the lanthanides presents on the surface of the bauxite particles will undergo leaching process. The unreacted surface layer will be a barrier for sulfuric acid to react with subsequent layers inside the particles so that the diffusion takes place at the later stage.
466
E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
2/3
1-3(1-XB) +2(1-XB)
1/3
0.2
0.1
0.0 0
10
20
30
40
50
60
Time [min] Figure 3. The linear plot of 1 − 3(1 −
) + 2(1 − ) as a function of time at different temperatures; 25 ºC (□), 40 ºC (●), and at 60 ºC (∆).
4. CONCLUSION Low grade bauxite which contains relatively high lanthanides among mineral ores can be utilized as a resource of the rare earth elements. We have demonstrated that the lanthanides can be extracted from the low grade bauxite by leaching process with sulfuric acid as leachant, enhancing the value added of the mineral ores. The leaching process can be performed without any pre-treatment. The leaching results indicated that operating conditions at 60 °C and 3 M sulfuric acid would be efficiently leach and convert the lanthanides into their sulfuric salts with the fractional conversion as high as 0.67. The leaching rate is very fast and leaching efficiencies increase rapidly with time during the first 15 min, followed by gradual slower process, before its saturation, indicating that the leaching of lanthanides from low grade bauxite undergoes in two stages, which are chemical reaction and diffusion, according to shrinking core model. The activation energy of the chemical reaction and diffusion stage was estimated to be 10.37 and 48.15 kJ/mol, respectively. The diffusion stage was found to be relatively more temperature-dependent the chemical reaction stage. This finding can potentially lead to the development of enhanced leaching processes of lanthanides from low grade bauxite. Acknowledgments This research was funded by PTUPT grant No. 2740/UN2.R3.1/HKP05.00/2017 and No. 492/UN2.R3.1/HKP05.00/2018 from RISTEKDIKTI, Indonesia.
REFERENCES [1] F. Sadri, A. M. Nazari, A. Ghahreman, Journal of Rare Earths 35 (2017) 739-752. [2] C.K. Gupta, N. Krishnamurthy, N. (2005). Extractive metallurgy of rare earths, CRC Press, pp. 20-250. [3] I. Lesmana. (2012). Pembuatan unsur tanah jarang dari mineral monasit menggunakan asam nitrat. Skripsi, Program Sarjana, Jurusan Kimia, Fakultas MIPA, Universitas Padjadjaran. [4] E. Kusrini, A. Rahman, A.A. Bumi, C.S. Utami, E.A. Prasetyanto, 2018. IOP Conf. Ser.: Earth Environ. Sci. 105, 012006. [5] E. Kusrini, Z. J. Bahari, A. Usman, A. Rahman, E. A. Prasetyanto, Materials Science Forum Vol. 929 (2018) 171-176.
E. Kusrini et al. / Materials Today: Proceedings 18 (2019) 462–467
467
[6] R.C. Borra J. Mermans, B. Blanpain, Y. Pontikes, K. Binnemans, T.V. Gerven. Minerals Engineering, 92 (2016), pp 151-159. [7] J.K. Chul, S.Y. Ho, W.C. Kyung, Y.L. Jin, D.K. Sung, M.Y., Shun, J.L. Su, J. Ram, I.L. Se, J.L. Seung, H.K. Seung. Hydrometallurgy, 146 (2014)133-137. [8] Kim, C.J., Yoon, H.S., Chung, K.W., Lee, J.Y., Kim, S.D., Shin, S.M., Lee, S.J., Joe, A.R., Lee, S.I., Yoo, S.J., Kim, S.H., Hydrometallurgy 146 (2014) 133-137 [9] Levenspiel, O..Chemical reaction engineering, 3rd ed. John Willey & Sons Inc., New York, (1999) pp. 358-371.