Abstract
Neodymium is produced commercially by the fused salt electrolysis of Nd2O3–NdF3–CaF2–LiF melt. The efficiency of the process is low due to the limited solubility of Nd2O3 in the fluoride melt. The suitability of making Nd directly from Nd2O3 by the FFC Cambridge process seems very attractive. The basic requirements for FFC Cambridge process are that (a) the oxide should not dissolve in the molten salt (usually CaCl2 or CaF2–LiF) and (b) the decomposition potential of oxide should be below the decomposition potential of salt. The present study was to understand the first requirement. It reports for the first time the in situ chemical interactions of Nd2O3 with molten CaCl2 and CaF2–LiF using confocal scanning laser microscope. In molten CaCl2, Nd2O3 reacts vigorously to form NdOCl. The product detaches from the parent Nd2O3 surface, exposing the oxide surface to further attack from molten CaCl2. The reaction rate becomes faster as the temperature increases. In a molten CaF2–LiF melt, Nd2O3 dissolves. Owing to the limited solubility of the oxide in CaF2–LiF melt, the direct electroreduction may still proceed in an oxide-saturated CaF2–LiF melt.
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References
Binnemans K, Jones PT, Blanpain B, Van Gerven T, Yang Y, Walton A, Buchert M (2013) Recycling of rare earths: a critical review. J Clean Prod 51:1–22. doi:10.1016/j.jclepro.2012.12.037
Humphries M (2012) Rare earth elements: the global supply chain. Congressional Research Service, 2011, 7-5700
Gupta CK, Krishnamurthy N (2004) Extractive metallurgy of rare earths. CRC, Boca Raton
Mukherjee A, Awasthi A, Krishnamurthy N (2016) Studies on calcium reduction of yttrium fluoride. Miner Process Extr Metall 125(1):p26–31
Dennison DH, Tschetter MJ, Gschneidner KA Jr (1966) The solubility of tantalum in eight liquid rare-earth metals. J Less Common Metals 10(2):108–115. doi:10.1016/0022-5088(66)90119-6
Dennison DH, Tschetter MJ, Gschneidner KA Jr (1966) The solubility of tantalum and tungsten in liquid rare-earth metals. J Less Common Metals 11(6):423–435. doi:10.1016/0022-5088(66)90089-0
Druding LF (1960) Interactions of praseodymium and neodymium metals with their molten chlorides and iodides. Iowa State University, Ames, pp 1–82
Novoselova A, Smolenski V (2013) Electrochemical behavior of neodymium compounds in molten chlorides. Electrochim Acta 87:657–662. doi:10.1016/j.electacta.2012.09.064
Hayashi H, Akabori M, Ogawa T, Minato K (2004) Spectrophotometric study of Nd2+ ions in LiCl–KCl eutectic melt. Zeitschrift Fur Naturforschung A 59(10):705–710
Chambers MF, Murphy JE (1991) Electrolytic production of neodymium metal from a molten chloride electrolyte. US Department of the Interior, Bureau of Mines, Reno, pp 1–7
Thudum R, Srivastava A, Nandi S, Nagaraj A, Shekhar R (2010) Molten salt electrolysis of neodymium: electrolyte selection and deposition mechanism. Miner Process Extr Metall 119(2):88–92
Stefanidaki E, Hasiotis C, Kontoyannis C (2001) Electrodeposition of neodymium from LiF–NdF3–Nd2O3 melts. Electrochem Acta 46(17):2665–2670. doi:10.1016/S0013-4686(01)00489-3
Chen GZ, Fray DJ, Farthing TW (2000) Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride. Nature 407(6802):361–364
Abdelkader AM, Kilby KT, Cox A, Fray DJ (2013) DC voltammetry of electro-deoxidation of solid oxides. Chem Rev 113(5):2863–2886. doi:10.1021/cr200305x
Gibilaro M, Pivato J, Cassayre L, Massot L, Chamelot P, Taxil P (2011) Direct electroreduction of oxides in molten fluoride salts. Electrochem Acta 56(15):5410–5415
Mohandas KS (2013) Direct electrochemical conversion of metal oxides to metal by molten salt electrolysis: a review. Miner Process Extr Metall 122(4):195–212. doi:10.1179/0371955313Z.00000000069
Jiang K, Hu X, Ma M, Wang D, Qiu G, Jin X, Chen GZ (2006) “Perovskitization”-assisted electrochemical reduction of solid TiO2 in molten CaCl2. Angew Chem Int Ed 45(3):428–432. doi:10.1002/anie.200502318
Liu J, Guo M, Jones PT, Verhaeghe F, Blanpain B, Wollants P (2007) In situ observation of the direct and indirect dissolution of MgO particles in CaO–Al2O3–SiO2-based slags. J Eur Ceram Soc 27(4):1961–1972. doi:10.1016/j.jeurceramsoc.2006.05.107
Michelic S, Goriupp J, Feichtinger S, Kang Y-B, Bernhard C, Schenk J (2016) Study on oxide inclusion dissolution in secondary steelmaking slags using high temperature confocal scanning laser microscopy. Steel Res Int 87:57–67. doi:10.1002/srin.201500102
Liu J, Zhu L, Guo M, Verhaeghe F, Blanpain B, Wollants P (2008) In-situ observation of the dissolution of ZrO2 oxide particles in mould fluxes. Metall Res Technol 105(05):255–262. doi:10.1051/metal:2008039
Hagemann R, Pettsold L, Sheller P (2010) The process of oxide non-metallic inclusion dissolution in slag. Steelmaking 2(4):262–266
Monaghan BJ, Chen L, Sorbe J (2005) Comparative study of oxide inclusion dissolution in CaO–SiO2–Al2O3 slag. Ironmak Steelmak 32(3):258–264
Orrling C, Fang Y, Phinichka N, Sridhar S, Cramb A (1999) Observing and measuring solidification phenomena at high temperatures. JOM-e 51(7)
Orrling C, Sridhar S, Cramb A (2000) In situ observation of the role of alumina particles on the crystallization behavior of slags. ISIJ Int 40(9):877–885
Yuki N, Shibata H, Emi T (1998) Solubility of MnS in Fe–Ni alloys as determined by in-situ observation of precipitation of MnS with a confocal scanning laser microscope. ISIJ Int 38(4):317–323. doi:10.2355/isijinternational.38.317
Mohandas K, Fray D (2004) FFC cambridge process and removal of oxygen from metal-oxygen systems by molten salt electrolysis: an overview. Trans Indian Inst Metals 57(6):579–592
Blanchard TP (1992) Electrochemical studies of calcium chloride-based molten salt systems (LA-SUB-94-165). University of Tennessee, Knoxville, p 1992
Wang S, Zhang F, Liu X, Zhang L (2008) CaO solubility and activity coefficient in molten salts CaCl2–x (x=0, NaCl, KCl, SrCl2, BaCl2 and LiCl). Thermochim Acta 470(1–2):105–107. doi:10.1016/j.tca.2008.02.007
Xu C, Gao W (2000) Pilling–Bedworth ratio for oxidation of alloys. Mat Res Innovat 3(4):231–235. doi:10.1007/s100190050008
Sharma RA, Seefurth RN (1988) Metallothermic reduction of Nd2O3 with Ca in CaCl2–NaCl melts. J Electrochem Soc 135(1):66–71
Guo X, Sun Z, Van Dyck J, Guo M, Blanpain B (2014) In Situ observation on lime dissolution in molten metallurgical slags-kinetic aspects. Ind Eng Chem Res 53(15):6325–6333
Guo X, Sietsma J, Yang Y (2014) Solubility of rare earth oxides in molten fluorides. In: 1st European rare earth resources conference, Milos, Greece, pp 149–155
Stefanidaki E, Photiadis GM, Kontoyannis CG, Vik AF, Østvold T (2002) Oxide solubility and raman spectra of NdF3–LiF–KF–MgF2–Nd2O3 melts. J Chem Soc Dalton Trans 11:2302–2307
Dysinger D, Murphy JE (1994) Electrowinning of neodymium from a molten oxide-fluoride electrolyte. U.S. Department of the Interior, Bureau of Mines, Reno, pp 1–8
Acknowledgements
The authors thank KU Leuven for financial support (IOF-KP Rare3 Project). The authors thank Paul Crabbe and Joop Van Deursen for their technical assistance.
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Mukherjee, A., Van Dyck, J., Blanpain, B. et al. CSLM study on the interaction of Nd2O3 with CaCl2 and CaF2–LiF molten melts. J Mater Sci 52, 1717–1726 (2017). https://doi.org/10.1007/s10853-016-0463-x
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DOI: https://doi.org/10.1007/s10853-016-0463-x