46 Korean Chem. Eng. Res., 53(1), 46-52 (2015) http://dx.doi.org/10.9713/kcer.2015.53.1.46 PISSN 0304-128X, EISSN 2233-9558 Leaching Kinetics of Praseodymium in Sulfuric Acid of Rare Earth Elements (REE) Slag Concentrated by Pyrometallurgy from Magnetite Ore Chul-Joo Kim*, Ho-Sung Yoon*, Kyung Woo Chung*, Jin-Young Lee*, Sung-Don Kim*, Shun Myung Shin*, Hyung-Seop Kim**, Jong-Tae Cho**, Ji-Hye Kim**, Eun-Ji Lee**, Se-Il Lee** and Seung-Joon Yoo** ,† *Korea Institute of Geoscience and Mineral Resources, 124 Gwahang-no, Yuseong-gu, Daejeon 305-350, Korea **Department of Environmental and Chemical Engineering, Seonam University, 7-111 Pyeongchon-gil, Songak, Asan 336-922, Korea (Received 25 June 2014; Received in revised form 20 July 2014; accepted 23 July 2014) Abstract - A leaching kinetics was conducted for the purpose of recovery of praseodymium in sulfuric acid (H 2 SO 4 ) from REE slag concentrated by the smelting reduction process in an arc furnace as a reactant. The concentration of H 2 SO 4 was fixed at an excess ratio under the condition of slurry density of 1.500 g slag/L, 0.3 mol H 2 SO 4 , and the effect of tem- peratures was investigated under the condition of 30 to 80 o C. As a result, praseodymium oxide (Pr 6 O 11 ) existing in the slag was completely converted into praseodymium sulfate (Pr 2 (SO 4 ) 3 ·8H 2 O) after the leaching of 5 h. On the basis of the shrinking core model with a shape of sphere, the first leaching reaction was determined by chemical reaction mechanism. Gen- erally, the solubility of pure REEs decreases with the increase of leaching temperatures in sulfuric acid, but REE slag was oppositely increased with increasing temperatures. It occurs because the ash layer included in the slag is affected as a resistance against the leaching. By using the Arrhenius expression, the apparent activation energy of the first chemical reaction was determined to be 9.195 kJmol -1 . In the second stage, the leaching rate is determined by the ash layer dif- fusion mechanism. The apparent activation energy of the second ash layer diffusion was determined to be 19.106 kJmol -1 . These relative low activation energy values were obtained by the existence of unreacted ash layer in the REE slag. Key words: Leaching, REE Slag, Shrinking Core Model, Praseodymium Oxide, Praseodymium Sulfate, Sulfuric Acid 1. Introduction REEs (rare earth elements), according to the IUPAC definition, is a group of chemical elements with lanthanides plus scandium and yttrium. Based on their location in the periodic table and their atomic weights, it is possible to classify these elements into light REEs or LREEs (lanthanum, cerium, praseodymium, neodymium, prome- thium and samarium, with atomic numbers 57-62) and heavy REEs or HREEs (europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium atomic number 63-71) [1]. The lanthanides among the REEs are the filling of the 4f outer-shell electrons. The electronic structure of the lanthanide elements has [Xe]5d 1 6s 2 4f n with minor exceptions. These 4f orbitals are buried inside atom and are shielded from the atom’s environment by the 4d and 5p electrons. The 4f orbitals in the lanthanides are sufficiently low in energy that the electrons are seldom ionized or shared [2,3]. REEs are broadly used to the high-tech industry like high strength permanent magnets, lasers, automotive catalytic converters, fiber optics/superconductors, and electronic devices. Because of the ongo- ing development of new advanced technologies, an ever-increasing demand on REEs will persist in the international markets. China dominates the world market of REEs with over 95% recently [4]. The demand for REE metals has rapidly been increasing, but China has steadily increased export taxes on REEs and has nationally been restricting the export quotas of them. Therefore, REE resources- free countries, such as South Korea and Japan, have to develop the new raw material resources like low-grade REE sources. It is well- known that hydrometallurgy is the most effective method for the leaching of low-grade raw materials because of the selective leach- ing by solvent, low process cost and occurrence of relatively small pollutants [5-17]. This study was also conducted to recover REE metals from low- grade monazite-type REE raw material and selected praseodymium as a research objective among the components in REE slag because praseodymium cost increased as highest growth rate of price from 14 US$/kg to now 175 US$/kg recently [4]. The leaching mechanism of slag was hypothesized by a shrinking core model with a constant size and a two-stage model with a chem- ical reaction and ash layer diffusion because some part of the REE slag was partly oxidized by arc furnace even though it is reduced through the smelting reduction process. Finally, the REE slag remains in the ash layers after the completion of leaching as shown in Fig. 1. 1-1. Surface reaction control Assuming the first-order chemical reaction rate model based on the shrinking core model with the same particle size before and after † To whom correspondence should be addressed. E-mail: [email protected]‡ This article is dedicated to Prof. Kyun Young Park on the occasion of his retirement from Kongju National University. This is an Open-Access article distributed under the terms of the Creative Com- mons Attribution Non-Commercial License (http://creativecommons.org/licenses/by- nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduc- tion in any medium, provided the original work is properly cited.
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46
Korean Chem. Eng. Res., 53(1), 46-52 (2015)
http://dx.doi.org/10.9713/kcer.2015.53.1.46
PISSN 0304-128X, EISSN 2233-9558
Leaching Kinetics of Praseodymium in Sulfuric Acid of Rare Earth Elements (REE)
Slag Concentrated by Pyrometallurgy from Magnetite Ore
optics/superconductors, and electronic devices. Because of the ongo-
ing development of new advanced technologies, an ever-increasing
demand on REEs will persist in the international markets. China
dominates the world market of REEs with over 95% recently [4].
The demand for REE metals has rapidly been increasing, but
China has steadily increased export taxes on REEs and has nationally
been restricting the export quotas of them. Therefore, REE resources-
free countries, such as South Korea and Japan, have to develop the
new raw material resources like low-grade REE sources. It is well-
known that hydrometallurgy is the most effective method for the
leaching of low-grade raw materials because of the selective leach-
ing by solvent, low process cost and occurrence of relatively small
pollutants [5-17].
This study was also conducted to recover REE metals from low-
grade monazite-type REE raw material and selected praseodymium
as a research objective among the components in REE slag because
praseodymium cost increased as highest growth rate of price from
14 US$/kg to now 175 US$/kg recently [4].
The leaching mechanism of slag was hypothesized by a shrinking
core model with a constant size and a two-stage model with a chem-
ical reaction and ash layer diffusion because some part of the REE
slag was partly oxidized by arc furnace even though it is reduced
through the smelting reduction process. Finally, the REE slag remains
in the ash layers after the completion of leaching as shown in Fig. 1.
1-1. Surface reaction control
Assuming the first-order chemical reaction rate model based on
the shrinking core model with the same particle size before and after
†To whom correspondence should be addressed.E-mail: [email protected]‡This article is dedicated to Prof. Kyun Young Park on the occasion of his retirement from Kongju National University.This is an Open-Access article distributed under the terms of the Creative Com-mons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduc-tion in any medium, provided the original work is properly cited.
Leaching Kinetics of Praseodymium in Sulfuric Acid of Rare Earth Elements (REE) Slag Concentrated by Pyrometallurgy from Magnetite Ore 47
Korean Chem. Eng. Res., Vol. 53, No. 1, February, 2015
the leaching [18,19] that has a shape of a spherical particle, the
chemical reaction may be expressed in the following Eq. (2).
(2)
However, the variation of CA can be neglected during the chem-
ical reaction because the H2SO4 is added into the reactor more
excessively than the stoichiometric ratio.
Since CA can be accepted as a constant in Eq. (2), this model is
modified as follows:
(3)
(4)
This can be written in terms of fractional conversion by noting that
Therefore
(5)
The variation of H2SO4 (XA) can be neglected because it is added
excessively.
kc,chem is the apparent rate constant for chemical reaction and
inverse of the time required for complete conversion is given when
rc = 0.
(6)
1-2. Ash layer diffusion control
During the chemical reaction, the praseodymium component on
the surface of REE slag is first leached out. Then the ash layers
remaining after the initial chemical reaction become thicker and act
as a resistance for H2SO4 solution to go inner from the surface.
Therefore, the ash layer diffusion can be considered as a second step
for the rate determining stage. In diffusion controlled reaction mod-
els, there are many kinetic equations [20,21]. The reaction rate can
be expressed in terms of the diffusion rate of H2SO4 through the ash
layers as follows:
(7)
where kc,ash is the apparent rate constant for ash layer diffusion
and inverse of the time required for complete conversion of a par-
ticle, rc = 0.
(8)
2. Materials and Methods
The raw material was mined from Hongcheongun in Korea and
concentrated by the smelting reduction process in an arc furnace.
The REE slag obtained after the smelting reduction process was
milled and washed with water to remove impurities on the REE
slag. Finally, particle size had a size range of 100 to 200 μm.
The concentrations of H2SO4 were added into reactor as the
excess ratios of 0.1 to 0.3 M over the stoichiometric ratio, but the
leaching rate was not significantly affected by the excess ratio of
H2SO4 concentration. Nevertheless, the H2SO4 concentration was
fixed at 0.3 M higher than the stoichiometric ratio in this experiment
for the concentration of H2SO4 to be constant during reaction.
Accordingly, the concentration of H2SO4 was assumed to be con-
stant. All the solutions indicated the scale of pH 1.0.
3. Analysis
Metal compositions included in the REE slag were analyzed
under the condition of 1,300 W RF Power, 27.12 MHz RF frequency,
13 L/min Coolant gas flow and 0.9 L/min Nebulizer gas flow by
2. Antolini, E. and Perez, J., “The Use of Rare Earth-based Mate-rials in Low-temperature Fuel Cells,” Int. J. Hydrog. Energy, 36,15752-15765(2011).
3. Yu, Z. and Chen, M., Rare Earth Elements and Their Applica-
tions, Metallurgical Industry Press(1995). 4. Massari, S. and Ruberti, M., “Rare Earth Elements as Critical
Raw Materials: Focus on International Markets and Future Strat-egies,” Resources Policy, 38, 36-43(2013).
5. Aarabi-Karasgani, M., Rashchi, F., Mostoufi, N. and Vahidi, E.,“Leaching of Vanadium from LD Converter Slag Using SulfuricAcid,” Hydrometallurgy, 102, 14-21(2010).
6. Dehghan, R., Noaparast, M. and Kolahdoozan, M., “Leaching andKinetic Modelling of Low-grade Calcareous Sphalerite in AcidicFerric Chloride Solution,” Hydrometallurgy, 96, 275-282(2009).
7. El-Nadi, Y. A., “Lanthanum and Neodymium from EgyptianMonazite: Synergistic Extractive Separation Using Organophos-phorus Reagents,” Hydrometallurgy, 119-120, 23-29(2012).
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. and Kim,S.-H., “Leaching Kinetics of Lanthanum in Sulfuric Acid fromRare Earth Element (REE) Slag,” Hydrometallurgy, 146, 133-137(2014).
9. Kim C.-J., Yoon H,-S,, Chung K.W., Lee J.-Y., Kim S.-D., ShinS. M., Lee S.-J., Joe A.-R., Lee S.-I., Yoo S.-J. and Kim J.-G.,“Leaching Kinetics of Neodymium in Sulfuric Acid from E-scrapof NdFeB Permanent Magnet,” Korean J. Chem. Eng., 31, 706-711(2014).
10. Kostova, I., “Lanthanides as Anticancer Agents,” Curr. Med. Chem.,5, 591-602(2005).
11. Kul, M., Topkaya, Y. and Karakaya, I., “Rare Earth Double Sulfatesfrom Pre-concentrated Bastnasite,” Hydrometallurgy, 93, 129-135(2008).
12. Liu, K., Chen, Q., Yin, Z., Hu, H. and Ding, Z., “Kinetics ofLeaching of a Chinese Laterite Containing Maghemite and Magne-tite in Sulfuric Acid Solutions,” Hydrometallurgy, 125-126, 125-136(2012).
13. Manhique, A. J., Focke, W. W. and Carvalho, M., “Titania Recoveryfrom Low-grage Titanoferrous Minerals,” Hydrometallurgy, 109,230-236(2011).
14. Minting, L., Chang, W., Shuang, Q., Xuejiao, Z., Cunxiong, L.and Zhigan, D., “Kinetics of Vanadium Dissolution from Black Shalein Pressure Acid Leaching,” Hydrometallurgy, 104, 193-200(2010).
15. Moldoveanu, G. A. and Papangelakis, V. G., “Recovery of RareEarth Elements Adsorbed on Clay Minerals: I. Desorption Mecha-nism,” Hydrometallurgy, 117-118, 71-78(2012).
16. Yoo, S.-J., Yoon, H.-S., Jang, H. D., Lee, M.-J., Lee, S.-I., Park,S.-T. and Hong, H. S., “Dissolution Kinetics of Aluminum Canin Isopropyl Alcohol for Aluminum Isopropoxide,” Chem. Eng.
“Kinetics of Aluminum Can Dissolution in Sec-butyl Alcohol forAluminum Sec-butoxide,” Hydrometallurgy, 96, 223-229(2009).
18. Levenspiel, O., Chemical Reaction Engineering, 3rd ed., Wiley,New York(1999).
19. Schmidt, L.D., The Engineering of Chemical Reactions, 2nd ed.,Oxford University Press(2005).
20. Dickinson, C. F. and Heal, G. R., “Solid-liquid Diffusion ControlledRate Equations,” Thermochim. Acta, 340-341, 89-103(1999).
21. Órfão, J. J. M. and Martins, F. G., “Kinetic Analysis of Thermo-gravimetric Data Obtained Under Linear Temperature Program-ming-a Method Based on Calculations of the Temperature Integralby Interpolation,” Thermochim. Acta, 390, 195-211(2002).
22. Akinlua, T. N. and Ajayi, T. R., “Determination of Rare EarthElements in Niger Delta Crude Oils by Imductively CoupledPlasma-mass Spectrometry,” Fuel, 87, 1469-1477(2008).
23. Lichtfouse, E. (ed.), Organic Farming, Pest Control and Reme-
diation of Soil Pollutants, Sustainable Agriculture Review 1, SpringerScience+Business Media B.V(2009).
24. Clavier, N., Podor, R. and Dacheux, N., “Crystal Chemistry of theMonazite Structure,” J. European Ceram. Soc., 31, 941-976(2011).
25. HSC Chemistry 5.0 Chemical Reaction and Equilibrium Softwarewith Extensive Thermochemical Database. Ver 5.11, OutokumpuResearch, Finland.