NH4 HCO 3 Liquid Phase Precipitation To Prepare Low Bismuth Oxychloride

Rare earth is an important resource in China.As one of Rare Earth element,lanthanum oxide（La₂O₃）possesses excellent performance and is widely used in optical glass,ceramic capacitors,catalysts,and preparation alloys.With the high requirements of the society for materials,the lanthanum oxide produced by the existing processes cannot meet the requirements of high purity,low chlorine,and good morphology,thereby limiting the application of lanthanum oxide materials.Therefore,the production of lanthanum oxide with low chloride content,good dispersibility,and regular appearance is an important task at present.In order to prepare low-chlorine lanthanum oxide and reduce production costs,this study studied the preparation of rare earth oxides using liquid-phase precipitation method using LaCl₃stripped from rare earth production lines and using NH₄HCO₃ as a precipitant under the assistance of multiple microwave,ultrasonic and airwave fields.The following results were obtained through experiments:（1）In the microwave field to investigate the influence of various factors on the morphology and chlorine content of lanthanum oxide precursors,the concentration of LaCl₃ solution was0.1 mol·L^-1,the molar ratio was 1:3.5,the reaction temperature was 50°C,the feed rate was1.15 ml·min^-1,and the solution pH was 5.The reaction was started by cocurrent feeding.At the end of the reaction,the lanthanum oxide precursor with a chloride ion content of less than 0.01%can be obtained by washing and filtering three times with aging for 2 hours.The use of co-current addition of the prepared lanthanum oxide precursor is superior to the positive and negative addition methods in terms of chlorine content and morphology;the addition of the external field has a significant promoting effect on the morphology and low chlorine in comparison with the ordinary water bath heating.At the same time,the content of chloride ion in the precursor is closely related to the morphology.The more regular the precursor is,the higher the surface smoothness is,and the lower the chloride ion content is.（2）In the preparation of low-chlorine lanthanum oxide precursors by microwave and magnetic stirring,microwave and air agitation,and microwave and ultrasonic synergies in three fields,the ultrasound and microwave synergies are more effective in preparing lanthanum oxide precursors with good regularity,good dispersibility and low chloride ion content.Ultrasound power 500 W,mode 2:1,microwave power 500 W,can produce lanthanum oxide precursor with chloride content of about 0.005%.（3）The precursor was roasted to obtain La₂O₃,and the decomposition of the precursor during roasting was studied.The lanthanum oxide precursor was basic lanthanum carbonate,which was characterized by TG-DTA,FI-IR and XRD.In the process of the preparation of lanthanum oxide by thermal decomposition of the lanthanum oxide precursor,the content of chloride ion does not change much,indicating that the preparation of the precursor is the most critical step influencing the chloride ion content.The thermal decomposition process of the precursor has little change in the profile,and numerous fine pores appear on the surface of the crystal.Throughout the process,there is both genetic and variation.