Preparation Of Praseodymium Neodymium Oxide With Large-Size And High-Purity By Precipitating Sodium Bicarbonate Method

Praseodymium neodymium oxide is widely used in rare earth permanent magnet materials,storage materials and refrigeration materials,and is also a key upstream raw material for the production and manufacture of electric motors,the core components of new energy vehicles.At present,the industrial preparation of praseodymium neodymium oxide mainly uses oxalic acid or ammonium bicarbonate as precipitant to prepare praseodymium neodymium oxalate or carbonate,and then through high temperature burning.The use of oxalic acid or ammonium bicarbonate as precipitator has the disadvantages of high production cost and unfriendly to the environment.It is a promising new method to use low-cost sodium carbonate or sodium bicarbonate as precipitant to reduce the production cost of praseodymium oxide.However,due to the small solubility product of rare earth carbonate,the precursor has a serious amorphous trend,which is easy to cause problems such as difficult crystallization of precursor,low particle size,long extraction and washing time and high impurity content.Using sodium bicarbonate as precipitator and praseodymium neodymium chloride as raw material,this paper carried out the research on precipitation process,burning process and orthogonal experiment process parameters optimization.The particle size,particle size distribution,impurity content,crystal shape and morphology of precursors and praseodymium oxide were characterized by ICP,particle size analyzer,X-ray diffraction and scanning electron microscope.The main conclusions are as follows:（1）In the precipitation process,the effects of precipitation terminal pH value,precipitation temperature,concentration ratio and aging time on the particle size distribution,crystallization properties,impurity content and morphology of praseodymium neodymium oxide precursor were investigated by single factor method.The results show that the increase of pH value and precipitation temperature at the end point is not conducive to the increase of particle size and crystallization of precursor,but is beneficial to the particle size distribution.The increase of concentration ratio and the extension of aging time are beneficial to the increase of particle size.Too high or too low precipitation terminal pH and precipitation temperature can make the content of chloride and sodium ions high,but the aging time has the opposite effect on the content of chloride and sodium ions.The content of chloride ion increases with the increase of the concentration of raw material,while the content of sodium ion decreases with the increase of the concentration of raw material.The prolongation of aging time is conducive to the conversion of amorphous precursor to crystalline form.The optimal precipitation process parameters determined by single factor experiment are:The precipitation terminal pH=5.10,precipitation temperature 50℃,concentration ratio 0.7:1.5,aging time 20 hours,the preparation of precursor powder performance is good,as Pr₂（CO₃）₃·8H₂O,Nd₂（CO₃）₃·8H₂O with 8 crystallizing water.PDF#31-1143,PDF#29-0918).（2）In the sintering process,the effects of sintering temperature,heating rate and holding time on the particle size and distribution,crystallization properties,impurity content and morphology of praseodymium neodymium oxide were investigated.The results show that too low sintering temperature will cause insufficient decomposition of precursor,too high sintering temperature will cause agglomeration phenomenon,and will also change the spatial configuration of praseodymium oxide.Too high or too low sintering temperature will cause large particle size of the products.The effect of heating rate and holding time on particle size distribution is small,while the effect of burning temperature on particle size distribution is large.The sintering temperature can reduce the impurity content of praseodymium and neodymium oxide powder,but the heating rate has little effect on the impurity content.The optimal burning process parameters determined by single factor experiment are:The sintering temperature was 900℃,the heating rate was9℃/min,and the holding time was 1 hour.The prepared praseodymium oxide was Pr₄O₇,Nd₂O₃（PDF#65-6027,PDF#74-2139）,which had the advantages of large particle size,low impurity content,no sintering agglomeration and high production efficiency.（3）In the optimization process study,single factor experiment parameters were optimized by orthogonal experiment.The optimal process after optimization was as follows:precipitation terminal pH=4.90,precipitation temperature 55℃,concentration ratio 0.9:1.5,aging time 16 hours,burning temperature 1000℃,heating rate 9℃/min,and holding time 1 hour.The median particle size of the precursor was D₅₀=38.855μm,ω_Cl-=0.029%,ω_Na+=0.018%.The middle particle size of praseodymium neodymium oxide is D₅₀=24.435μm,ω_Cl-=0.024%,ω_Na+=0.021%.The prepared precursor and praseodymium neodymium oxide powder have excellent performance.