Study On Determination Of Solubility Of Rare Earth Oxide In Molten Salts

REF3-LiF-RE2O3 molten salt system is the basic electrolytes for production of rare earth RE and its alloys by electrolysis in modern industry.In the electrolysis process,RE2O3 is the raw electrolytic material and continuously consumed.So,RE2O3 needs to be continuously added to the electrolysis cell.However,due to the limited solubility of RE2O3 in the electrolyte,the continuous addition of electrolytic material might lead to the formation of sediment on the bottom of the electrolysis cell.In some serious circumstances,it will result in stratification and even slagging phenomenon,which can directly impact on the electrolytic rate and current efficiency and lead to the deterioration of the electrolysis process.Therefore,the rate and quantity of addition of RE2O3 play an important role in the production of rare earth RE by molten salt electrolysis with REF3-LiF-RE2O3 system.In this paper,the solubility of RE2O3 in REF3-LiF-RE2O3 system is measured.These studies will provide the experimental basis for the deep investigation of the theory of rare earth oxide electrolysis,and also be beneficial to research on rare earth oxide electrolysis technology.Thus,the results of this study will contribute to the early realization low trough voltage,high current efficiency of rare earth industry,and energy saving and environmental protection of preparation of rare earth materials,which can achieve huge economic and social benefits.In this paper,the solubility of RE2O3 in REF3-LiF-RE2O3 system was determined by thermal saturated EDTA titration and primary crystallization temperature method,respectively.The X-ray diffraction and DTA were used to analyze the chemical reaction of RE2O3 in REF3-LiF molten salt system,and then the course of dissolution of RE2O3 was confirmed.So as to establish the correct analysis formula,which is basis of chemical analysis.REOF was prepared by high temperature solid state method,which was used to verify the chemical reaction of RE2O3 in REF3-LiF molten salt system.The total rare earth content and changing law before and after RE2O3 and REOF added in system were analyzed,and the solubility and dissolution rate of RE2O3 were determined by thermal saturation EDTA method.The added RE2O3 impact on the liquidus temperature of the molten system.So,in this paper,it has studied the influence of RE2O3 on liquidus temperature.According to the step cooling curve of the molten system after different quantity of RE2O3 was added,the solubility of RE2O3 in LaF3(83wt%)-LiF(17wt%),NdF3(83wt%)-LiF(17wt%)system at 1100? was determined.Through comparison the thermal saturated EDTA titration method and liquidus temperature determination method,it can be found that the liquidus temperature determination method is reliable and convenient operation.It can be used in the spot electrolysis production for its simple,rapid and reliable determination of concentration of rare earth oxide.