Study On Side Reactions And Crystallization Behavior Of Molten Salt Of Neodymium Oxide In Electrolysis Process

The use of graphite anodes in the electrolysis of neodymium oxide molten salts causes carbon impurities to contaminate product quality,which is the main problem that plagues actual production.Therefore,understanding the carbonization mechanism in metallic neodymium is very important to improve product quality.In this paper,the side reactions in the electrolyte and the physical and chemical properties such as the viscosity of the molten salt of the electrolyte and the crystallization of the electrolyte are studied in order to grasp the influence of the anode gas on the carbon content in the metal neodymium and investigate the crystallization behavior of the electrolyte.Through high-temperature simulation experiments,CO gas was blown into the electrolyte NdF₃-Li F and metal neodymium composition system,and the influence of CO gas injection position,reaction time,temperature of molten salt system,and electrolyte composition on the increase of carbon content in metal neodymium was investigated.The results of chemical composition analysis show that:when the distance from the CO blowing position to the liquid level of the neodymium metal increases from 35mm to 55mm,the carbon content in the neodymium metal increases from 0.048%to 0.093%;the reaction time is about 15min,and the carbon content increases in the neodymium metal.reach the peak.The temperature of the molten salt system was increased from 1050℃to 1100℃,and the carbon content in the metallic neodymium increased from 0.048%to 0.112%.The NdF3 content in the electrolyte composition increased from 85%to 91%,and the carbon content in the metal neodymium increased from 0.048%to 0.051%and then decreased to 0.002%,but the increase in the NdF₃content resulted in a significant increase in the viscosity of the molten salt.When the CO bubbles are in contact with the liquid metal neodymium interface,a chemical reaction will occur to generate carbon and Nd₂O₃,in which the carbon will undergo a carburizing reaction with the metal neodymium,thereby increasing the carbon content in the metal neodymium.Two side reactions,Nd₂O₃ and NdF₃ to form Nd OF and metal neodymium to NdF₃ to form NdF₂,will occur with the reaction of CO with NdF₃.At the same time,the results of XRD phase analysis show that the phase structure of the electrolyte molten salt after the reaction is NdF₃,LiF,NdOF,NdF₂.Combined with the research on the carbonization reaction in metallic neodymium,the influence of the composition change on the molten salt was further studied.The rotational viscosity method was used to measure the cooling viscosity curve of the electrolyte with different composition systems.Crystallization behavior of salts.When NdF₃:Li F=85:15 is the basic electrolyte system,in the NdF₃-Li F-Nd₂O₃ ternary system,as the Nd₂O₃ content increases from 1%to 4%,the constant temperature viscosity of molten salt at 1050℃decreases from0.040 Pa·s to 0.019Pa·s,the initial crystallization temperature increased from 925℃to 979℃;in the NdF₃-Li F-NdF₂ ternary molten salt system,with the NdF₂ content from 1%to 3%,the constant temperature viscosity of the molten salt at 1050℃increased from 0.019 Pa·s to0.032Pa·s,the initial crystallization temperature increased from 902℃to 936℃;while in the quaternary composite system（NdF₃-Li F-Nd₂O₃-NdF₂）,when the fixed Nd₂O₃ addition amount was 2～3%,as the NdF₂ addition amount increased from From 1%to 3%,the constant temperature viscosity of molten salt at 1050℃fluctuates between 0.023 Pa·s～0.039Pa·s,and the crystallization temperature increases from 986℃to 993℃.Under the joint influence of Nd₂O₃ and NdF₂,the crystallization behavior of molten salt exacerbated.