熔盐电解Nd用石墨阳极失效及浸渍硼酸盐防护  

Failure and Borate Impregnation Protection of Graphite Anode for Neodymium Electrodeposition in Molten Salt

作　　者：薛娟琴[1] 刘妮娜[1] 刘志飞[1] 唐长斌[1] 毕强[1] 

机构地区：[1]西安建筑科技大学冶金工程学院,陕西省黄金与资源重点实验室,陕西西安710055

出　　处：《稀有金属》2016年第8期806-815,共10页Chinese Journal of Rare Metals

基　　金：国家自然科学基金项目(51278407,51478379,51408468)资助

摘　　要：稀土氧化物熔盐电解过程中石墨阳极过早失效并引发碳杂质污染产品是困扰生产的现实紧迫问题。对稀土熔盐电解过程中石墨阳极的消耗情况进行现场调研以分析其失效机制并试验研究了浸渍硼酸盐的防护特性。结果表明,多孔结构的石墨与活性氧发生高温氧化及其与浸渗的氟盐发生化学侵蚀从而导致过早失效;其中高温氧化占据主导机制,高的温度促进氧化,熔盐"翻滚流动"造成冲刷及其附带的充足供氧协同使得熔盐液面处破损最严重;化学侵蚀作用影响不及氧化损伤,却能与氧化相互促进;两种损伤机制均存在孔洞内活性反应,引发石墨颗粒剥落,导致熔盐和稀土金属污染。硼酸盐浸渍可填充石墨孔隙和覆盖阳极表面,归因于在高温下形成的玻璃态B_2O_3附着性好,可起到隔绝氧化和熔盐化学侵蚀的作用而使石墨在1 h内得到保护;但随着时间延长,保护作用丧失,这与覆盖在石墨表面和孔隙中的硼酸盐浸渍物在高温下挥发和自身发生反应有关。In the neodymium production by electrolysis of rare earth neodymium oxide,the premature failure of graphite anode is an urgent problem which might lead to contamination of product by carbon impurities. In order to analyze graphite anode failure mechanism,the consumption of graphite anode in the molten salt electrolysis of neodymium was investigated both on the spot and in the laboratory,and the protection behavior of graphite by borate impregnation was systematically studied. Some results showed that early failure of graphite anode with porous structure resulted from oxidation reaction with reactive oxygen species and chemical erosion of fluoride at high temperature. High temperature oxidation played the dominant role in the process of graphite anode failure because high temperature promoted oxidation. The flowing and rolling erosion of molten salt and sufficient oxygen supplying interaction caused the most serious damages above the molten salt surface. Moreover,though the chemical erosion by fluoride was less significant compared to elevated temperature oxidation,it could promote oxidation and show synergistic effect. The graphite particles were probably peeled off as a result of active reaction in the graphite hole for the both above mentioned damage mechanism,and contaminated molten salt and rare earth metal. Since glassy state B_2O_3 with good adhesion formed at high temperature,utilizing borate impregnation to fill hole and cover surface could isolate the graphite from oxidation and chemical attack of molten salt,and it might effectively protect graphite anode within one hour. However,the protection effect of borate layer forfeited after 1 h because the borate impregnant inside or on the surface of pores gradually volatilized and reacted at high temperature.

关 键 词：熔盐电解钕 石墨阳极 氧化 浸渍 

分 类 号：TF845.6[冶金工程—有色金属冶金]