Decomposition Kinetics And Flash Calcination Of Praseodymium Neodymium Carbonate

Precipitation method-kiln roasting method is commonly used in industry to prepare rare earth oxides.This process has problems such as high energy consumption,low heat utilization rate,long process flow,high production cost,and unstable calcined product quality.The preparation method of green,high-efficiency and low-carbon rare earth oxides has important theoretical and practical significance.Using praseodymium carbonate,neodymium carbonate and neodymium praseodymium carbonate as raw materials,the paper explores the preparation technology of praseodymium neodymium oxide by flash calcination on the basis of research on the thermal decomposition kinetics of praseodymium neodymium carbonate,and obtains better process parameters.（1）The thermal decomposition process of praseodymium carbonate,neodymium carbonate and neodymium praseodymium carbonate in air atmosphere was studied by thermogravimetric-differential thermal（TG-DTA）technique,and the thermal decomposition reaction was studied by Kissinger method,Crane method and Coats-Redfem integral method Kinetic parameters.The results show that the thermal decomposition reaction process of praseodymium carbonate,neodymium carbonate and neodymium praseodymium carbonate is roughly the same,which can be divided into three stages.The first stage is dehydration reaction;the second stage,praseodymium carbonate forms the precursor Pr₂CO₅,and neodymium carbonate forms the precursor.The bulk Nd₂O₂CO₃ and praseodymium neodymium carbonate form mixed precursors（Pr₂CO₅,Nd₂O₂CO₃）;the third stage is the decomposition of the precursors into rare earth oxides.（2）The apparent activation energies of the three stages of thermal decomposition of praseodymium carbonate are 36.32 k J·mol^-1,163.16 k J·mol^-1,129.66 k J·mol^-1.The reaction order n is 0.8,0.9,0.9.The pre-exponential factor 1.6×10⁴ S^-1,6.3×10¹⁰ S^-1,1.3×10⁷ S^-1.The second stage is controlled by nucleation growth（n=1）,the corresponding mechanism function is g（α）=-[ln（1-α）],αis the conversion rate,and the third stage is controlled by nucleation growth（n=2）control,the corresponding mechanism function is g（α）=-[ln（1-α）]^1/2,andαis the conversion rate.（3）The apparent activation energy of the three stages of the thermal decomposition reaction of neodymium carbonate is 36.32 k J·mol^-1,163.16 k J·mol^-1,129.66 k J·mol^-1.The reaction order n is 0.8,0.9,0.9.The pre-exponential factor 1.6×10⁴ S^-1,6.3×10¹⁰ S^-1,1.3×10⁷S^-1.The second stage is controlled by one-dimensional diffusion,and the corresponding mechanism function is g（α）=α²,whereαis the conversion rate.The third stage is controlled by nucleation growth（n=2）,and the corresponding mechanism function is g（α）=-[ln（1-α）]^1/2,αis the conversion rate.（4）The apparent activation energies of the three stages of thermal decomposition of neodymium praseodymium carbonate are 34.35 k J·mol^-1,262.83 k J·mol^-1,150.11 k J·mol^-1.The reaction order n is 0.9,1.2,1.The pre-exponential factor 4.5×10⁴ S^-1,2.7×10¹⁸ S^-1,3.42×10⁸ S^-1.The second stage is controlled by two-dimensional diffusion,and the reaction mechanism function is g（α）=α+（1+α）Ln（1-α）,whereαis the conversion rate;the third stage is controlled by three-dimensional diffusion.The reaction mechanism function is g（α）=[（1+α）^1/3-1]²,whereαis the conversion rate.（5）The flash calcination experiments of praseodymium carbonate,neodymium carbonate and neodymium praseodymium carbonate were carried out.influence of appearance.The results show that the higher the temperature,the smaller the particle size of the raw materials,the larger the negative pressure in the furnace,and the smaller the feeding speed,the better the thermal decomposition efficiency of praseodymium and neodymium carbonate can be,and the thermal decomposition reaction can be promoted forward.The optimal process conditions for flash calcination of praseodymium carbonate are as follows:temperature 800℃,negative pressure in the furnace 300 mm H₂O,air pressure at the feed inlet 0.025 Mpa,particle size of praseodymium carbonate 200 mesh;the optimal process conditions for flash calcination of neodymium carbonate are:calcination temperature 850℃,the negative pressure in the furnace is 300 mm H₂O,the air pressure at the feeding port is 0.025 Mpa,and the particle size of neodymium carbonate is 200 mesh;the optimal process conditions for flash calcination of praseodymium carbonate and neodymium carbonate are:calcination temperature 980℃,negative pressure in the furnace 300 mm H₂O,air pressure at the feeding port It is 0.025 Mpa,and the particle size of Nd praseodymium carbonate is 200 mesh.The Nd praseodymium oxide obtained under optimal process conditions has a complete crystal phase and a uniform particle size distribution.The research results provide new ideas and new methods for the green and low-carbon preparation of rare earth oxides.