Reducing Greenhouse Gas Emission from the Neodymium Oxide Electrolysis. Part I: Analysis of the Anodic Gas Formation

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• 作者：Hanno Vogel ; Benedikt Flerus ; Felix Stoffner…
• 关键词：Rare earth ; Neodymium ; Electrolysis ; Greenhouse gas emission ; Off ; gas
• 刊名：Journal of Sustainable Metallurgy
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：3
• 期：1
• 页码：99-107
• 全文大小：2047KB
• 刊物类别：Metallic Materials; Sustainable Development; Industrial Chemistry/Chemical Engineering;
• 刊物主题：Sustainable Development; Metallic Materials;
• 出版者：Springer International Publishing
• ISSN：2199-3831
• 卷排序：3

文摘

Neodymium metal is produced nowadays only via Chinese technology, by the electrolysis of neodymium oxide in a NdF₃–LiF electrolyte at about 1050 °C. The process is not automated and is known to emit a large amount of perfluorocarbons (PFCs), with a tremendous greenhouse gas potential. The electrochemical system is analyzed by calculating the theoretical voltages of formation of the relevant anodic gas products. Linear voltammograms are conducted together with a simultaneous off-gas measurement to determine the dynamic behaviors of CO, CO₂, CF₄, and C₂F₆ in relation to the electrochemical behavior. The measurements show that the PFC emission starts with the occurrence of a partial anode effect, where the first CF₄ is detected, and the anode is passivated partially. The direct enabling of CF₄ formation activates the anode again, and at higher voltages, also C₂F₆ is formed. The critical current density and voltage of this partial anode effect are determined depending on the oxygen content of the electrolyte to be able to define a process window, with no PFC formation. An estimation of the off-gas emission continuously containing 7 % CF₄ and 0.7 % C₂F₆ leads to an emission of about 20 million t CO₂-eq. per year during the production of 30,000 t/a neodymium, which can explain a part of the gap between the amounts of atmospheric measured PFCs and the data from the aluminum and semiconductor industry. Minimizing the PFC emission must be the primary goal for the whole rare earth electrolysis.