Reducing Greenhouse Gas Emission from the Neodymium Oxide Electrolysis. Part I: Analysis of the Anodic Gas Formation
Reducing Greenhouse Gas Emission from the Neodymium Oxide Electrolysis. Part I: Analysis of the Anodic Gas Formation
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DOI：
10.1007/s40831-016-0086-0
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发表时间：
2017-03
影响因子：
2.4
通讯作者：
H. Vogel;Benedikt Flerus;Felix Stoffner;B. Friedrich
中科院分区：
文献类型：
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作者：
H. Vogel;Benedikt Flerus;Felix Stoffner;B. Friedrich
钕金属目前仅通过中国技术生产，通过在NdF 3-LiF电解质中在约1050 °C下电解氧化钕。该过程不是自动化的，并且已知会排放大量的全氟化碳（PFC），具有巨大的温室气体潜力。通过计算相关阳极气体产物形成的理论电压来分析电化学系统。线性伏安图进行了一起，同时废气测量，以确定CO，CO2，CF 4，和C2 F6的动态行为的电化学行为。测量结果表明，PFC排放开始与部分阳极效应的发生，在第一CF 4被检测到，和阳极部分钝化。CF 4形成的直接启动再次激活阳极，并且在更高的电压下，也形成C2 F6。该部分阳极效应的临界电流密度和电压取决于电解质的氧含量来确定，以能够限定工艺窗口，而不形成PFC。废气排放量连续含有7%CF4和0.7%C2F6的估计导致约2000万吨CO2当量的排放。在3万t/a钕的生产过程中，大气中PFCs的排放量与铝工业和半导体工业的数据存在一定的差距。减少PFC排放是整个稀土电解过程的首要目标。
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 C2F6in relation to the electrochemical behavior. The measurements show that the PFC emission starts with the occurrence of a partial anode effect, where the first CF4is detected, and the anode is passivated partially. The direct enabling of CF4formation activates the anode again, and at higher voltages, also C2F6is 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 % CF4and 0.7 % C2F6leads 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.