Study On The Evolution And Mechanism Of High-temperature Roasting Mixed Rare Earth Concentrates

Bayan Obo ore is low grade,fine disseminated particle size,and the occurrence states of rare earth are dispersive,which make it impossible be beneficiated by the conventional ore dressing methods and obtain high-grade rare earth concentrates.As for the existing techniques to extract rare earth from Bayan Obo mixed rare earth ore,such as roasting with concentrated sulfuric acid,caustic soda method and chlorination process etc,all of them have problems of low recovery of rare earth,high energy consuming,seriously polluting and difficult recovery of associated elements.However,with the rapid development of science and technology,the output of rare earth and the purity of single rare earth are gradually increasing.Therefore,the research on the green and efficient separation process of rare earth elements needs to be developed urgently.In order to solve the above mentioned problems,an innovative process was proposed in the present study to pre-concentrate,after changes the occurrence state of rare earths in rare earth ores by roasting,enriching rare earth phases in mixed rare earth ores,analyzes the element migration law and reaction mechanism.The research of roasting mixed rare earth ore by sodium carbonate and analysis of the mineral evolution law in the high temperature system.By XRD,FT-IR,SEM-EDS and other analytical techniques,the results show that during this process,the rare earth phase is first converted into rare earth oxide and rare earth oxyfluoride.At 1100℃,Ca,P,and F phases begin to fuse.After 1300℃,La and Ce elements are layered and enriched.When the temperature rises to 1400℃,phases P and F begin to separate.When it reaches 1500℃,lanthanum ferrite is produced.According to the phase diagram analysis,the production of Ca5(PO4)3F is due to the reaction between monazite and fluorite,and the formation of phase CeF2 and CeF3.The decomposition behavior and selective leaching behavior of roasted products in Na2CO3 roasting system of 65%mixed rare earth concentrate of Bayan Obo were studied.The experimental results show that the calcination loss rate is 17.94%and the monazite decomposition rate is 95.62%under the experimental conditions of roasting temperature of 660℃,roasting time of 1.5h,sodium carbonate addition amount of 24%,and sodium carbonate particle size of 60-90μm.When other roasting conditions remain unchanged,when the roasting time is prolonged to 2h,the fluorine fixation rate can reach 87.91%.At the same time,when the amount of sodium carbonate is increased to 28%,the Ce leaching rate and non-Ce rare earth leaching rate are also both reached the 9.14%and 89.21%,respectivelyThen,the ore phase transition and reaction law of sodium carbonate roasting of rare earth at high temperature were studied,and the roasting temperature was set according to the measurement results of TG-DSC.Studies have shown that during the high-temperature roasting of sodium carbonate,Na2CO3 can significantly reduce the melting temperature and promote the melt flow.As the temperature increases,the crystal lattice gradually decreases,and the crystallinity of the crystals gradually increases,and Ce and Th elements migrate and enrich with F and Ca elements.When the temperature reaches 1428℃,the rare earths La and Ce react with iron oxide and alumina to form perovskite structures La(AlO3),LaFeO3,and CeAlO3.