Preparation Of Gadolinium Oxide And Neodymium Praseodymium Oxide By Ultrasonic Spray Pyrolysis

At present,the industrial method for preparing rare earth oxides is usually the precipitation-calcination method.The method has problems such as high precipitant cost,high energy consumption,by-products and difficult treatment of wastewater.Therefore,exploring a green and efficient method for preparing rare earth oxides is of great significance to the technological upgrading of the rare earth industry.In this paper,the theoretical and experimental research on the preparation of rare earth oxides by citric acid-assisted ultrasonic spray pyrolysis was carried out with rare earth chloride solution as the raw material.The rare earth oxide products with the content of chlorine root meeting the industrial demand were obtained.The brief work content and research results are as follows:（1）A thermodynamic calculation study on the possible related reactions during the pyrolysis of gadolinium chloride and neodymium praseodymium chloride.Based on the analysis of thermodynamic data,an experimental study of citric acid-assisted ultrasonic spray pyrolysis was carried out.Using pure gadolinium chloride as a raw material,the feasibility of preparing rare earth oxides by citric acid-assisted ultrasonic spray pyrolysis was explored,and the role of citric acid in ultrasonic spray pyrolysis was analyzed.The experimental results show that the precursor prepared by introducing citric acid was porous spherical shell or fragment with loose morphology,which was conducive to the entry of reaction gas and the escape of generated gas.The calcination temperature required for the conversion of the precursor to the gadolinium oxide product was significantly reduced,and the gadolinium oxide powder product can be obtained by calcination at about 700℃for 4 h.（2）Carried out the ultrasonic spray pyrolysis experiment of industrial raw material acid gadolinium chloride solution,and explored the applicability of citric acid-assisted ultrasonic spray pyrolysis for industrial raw materials.The main research was to study the influence of citric acid addition,precursor roasting temperature and other process parameters on the phase and chloride content of the final product.The optimal process conditions for preparing gadolinium oxide were obtained:the precursor was 2:1,the calcination temperature was950℃,and the calcination time was 4 h.Under these conditions,a gadolinium oxide product with a chloride content of 401 ppm can be prepared.（3）The ultrasonic spray pyrolysis experiment of the acidic mixed solution of industrial raw material praseodymium chloride and neodymium chloride was carried out to further study the universality of this type of ultrasonic spray pyrolysis process.The effects of citric acid addition,precursor roasting temperature and roasting time on the phase and chloride content of mixed oxide complex products were deeply studied.The optimal process conditions for preparing neodymium praseodymium oxide were as follows:the precursor was 4:1,the calcination temperature was 1050℃,and the calcination time was 4 h.Under these conditions,praseodymium and neodymium oxide products with a chloride content of 136ppm can be prepared.The phases of praseodymium and neodymium oxide were Pr₄O₇ and A-type Nd₂O₃.The research results of the experiment show that the citric acid-assisted ultrasonic spray pyrolysis process can effectively prepare rare earth oxides with low chloride content at lower temperatures.Compared with the traditional precipitation-roasting method,the production cost and waste water production were greatly reduced.The research results provide a certain theoretical and practice basis for promoting the widespread application of the ultrasonic spray pyrolysis process.