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Competitive Coordination of Chloride and Fluoride Anions Towards Trivalent Lanthanide Cations (La3+ and Nd3+) in Molten Salts |
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| Authors: | Shilin Jiang Dr. Jianhui Lan Dr. Lin Wang Dr. Yalan Liu Yuke Zhong Yichuan Liu Dr. Liyong L.-Y. Yuan Dr. Lirong Zheng Prof. Zhifang Chai Prof. Weiqun Shi |
| Affiliation: | 1. Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049 China University of Chinese Academy of Sciences, Beijing, 100049 China These authors contributed equally to this work.;2. Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049 China These authors contributed equally to this work.;3. Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049 China;4. Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049 China University of Chinese Academy of Sciences, Beijing, 100049 China;5. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049 China;6. Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049 China Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Industrial Technology, Chinese Academy of Sciences, Ningbo, 315201 China |
| Abstract: | Molten salt electrolysis is a vital technique to produce high-purity lanthanide metals and alloys. However, the coordination environments of lanthanides in molten salts, which heavily affect the related redox potential and electrochemical properties, have not been well elucidated. Here, the competitive coordination of chloride and fluoride anions towards lanthanide cations (La3+ and Nd3+) is explored in molten LiCl-KCl-LiF-LnCl3 salts using electrochemical, spectroscopic, and computational approaches. Electrochemical analyses show that significant negative shifts in the reduction potential of Ln3+ occur when F− concentration increases, indicating that the F− anions interact with Ln3+ via substituting the coordinated Cl− anions, and confirm [LnClxFy]3−x−y (ymax=3) complexes are prevailing in molten salts. Spectroscopic and computational results on solution structures further reveal the competition between Cl− and F− anions, which leads to the formation of four distinct Ln(III) species: [LnCl6]3−, [LnCl5F]3−, [LnCl4F2]3− and [LnCl4F3]4−. Among them, the seven-coordinated [LnCl4F3]4− complex possesses a low-symmetry structure evidenced by the pattern change of Raman spectra. After comparing the polarizing power (Z/r) among different metal cations, it was concluded that Ln−F interaction is weaker than that between transition metal and F− ions. |
| Keywords: | coordination electrochemistry lanthanides molecular dynamics simulations X-ray absorption spectroscopy |