The Study Of Direct Preparation Of CeO₂ With Large Specific Surface Area By CeCl₃ Solution

As a new type of energy material with practical significance and development prospect,rare earth has been paid more and more attention by various countries and regions.The largest mineral deposit in China and even in the world is the baotou bayan obo iron-niobb-rare earth deposit,which is dominated by light rare earth resources.Its rare earth reserves account for about 96%of the country's total,among which 98%are lanthanum,cerium,praseodymium and neodymium.Cerium,which accounts for 50%of light rare earth resources,which is the most widely used functional material in China.The traditional preparation methods of cerium oxide are mainly liquid phase method,including precipitation method,hydrolysis method,sol-gel method and alcohol-saline method,among which the most widely used are precipitation method and sol-gel method.The operation process of preparing cerium oxide by liquid phase method is complex,the reaction conditions and process are harsh,and it is easy to introduce new impurities,cause ion loss,consume a lot of water resources and other disadvantages in the washing process.Using cerium chloride as raw material,a new green short process?spray pyrolysis and roasting?was used to prepare cerium oxide products with large specific surface area,which can effectively avoid the above disadvantages.Based on the theoretical analysis of thermodynamics,cerium oxide products with large specific surface area were prepared by spray pyrolysis.First of all,the effect of spray pyrolysis temperature on cerium oxide specific surface area was studied under the condition that the molar ratio of cerium chloride to citric acid was 1:1.5,the carrier gas pressure was 0.3MPa,the second roasting temperature was 700?and the time was 2h.The furnace temperature variables were set as 500?,650?,750?and 850?for the study.When the furnace temperature was 650?,the cerium oxide prepared had the largest specific surface area and the smallest grain size,which were 40.21m²/g and 19.19nm respectively.Therefore,the temperature was the best furnace temperature.Based on the determination of spray pyrolysis temperature,the effect of the molar ratio of cerium chloride to citric acid on the specific surface area of cerium oxide was studied to determine the optimal molar ratio of cerium chloride to citric acid.Under the condition that the furnace temperature is 650?,the gas pressure is 0.3MPa,the secondary calcination temperature is 700?and the calcination time is instantaneous?3 min?,the molar ratio of cerium-citric acid is set as 1:0,1:0.5,1:1,1:1.5,1:2 and 1:2.5,respectively.when n?CeCl₃?:n?C₆H₈O₇?=1:1.5 for the preparation of large specific surface area the best mole ratio of cerium oxide preparation cerium oxide with specific surface area of the largest and the smallest grain size,respectively is 87.02 m²/g and 11.84nm,Therefore,the molar ratio is the optimal ratio of cerium chloride to citric acid.The influence of secondary roasting temperature on cerium oxide specific surface area was studied based on the parameters of spray pyrolysis temperature and the molar ratio of cerium chloride to citric acid.Parameter in determining the conditions under which the temperature is 650?,carrier gas pressure is 0.3MPa,and the molar ratio of cerium chloride to citric acid is 1:1.5,the second roasting for instantaneous roasting,the second roasting temperature variables respectively is 500?,600?,700?and 800?were studied,when the secondary calcination temperature is 500?,the preparation of cerium oxide with specific surface area of the largest and the smallest grain size,respectively is106.49 m²/g and 14.27nm,secondary calcination temperature and temperature is the best.In addition,the study also found that the precursor of the preparation of citric acid solution of the cerium oxide prepared by spray pyrolysis method through second product of chloride ion content significantly decreased after roasting,chlorine ion with SEM and EDS analysis product without detection to 0.43%between the highest?individual?,of which 700?calcination under sample of chloride ion content is only 0.024%?using the chemical method of chlorine ion content in the product?,below the rare earth factories carbonate roasting generated cerium oxide chloride ion content in the products.Therefore,in summary,the optimal experimental conditions for cerium oxide preparation using a new green short-process of spray pyrolysis and roasting using cerium chloride as the raw material and citric acid as the additive are as follows:the furnace temperature is 650?,the cerium-citric acid molar ratio is 1:1.5,the carrier gas pressure is0.3MPa,and the secondary roasting temperature is 500?.The content of chlorine ions in cerium oxide with large specific surface area prepared by this method is lower than the standard required for the production of chlorine ions in cerium oxide by roasting in carbonate.