Study On The New Technology Of Extracting Rare Earth In Phosphors By Microwave Alkali Fusion-acid Leaching

With the widespread use of rare earth fluorescent lamps and the implementation of the global sustainable development strategy,the recovery of rare earth elements in waste fluorescent lamps has become one of the hot issues of global concern.The recovery of strategic rare earth elements Y,Eu,Ce,Tb from waste fluorescent lamps can alleviate the risk of rare earth supply,avoid over-exploitation of rare earth mines,reduce environmental pollution,and have significant environmental and economic benefits.Ai ming at the problem that the rare earth elements Eu,Ce and Tb in the blue phosphor and the green phosphor of alu minate phosphor are difficult to efficiently extract,blue phosphor（BAM）,green phosphor（CMAT）and mixed phosphor are used as research object.A new idea of microwave alkali fusion pretreatment to strengthen the acid leaching recovery of rare earth elements in phosphors is proposed.The influence of microwave pretreatment conditions and acid leaching conditions on the leaching rate of rare earth elements was systematically studied,and optimized process parameters were obtained.This paper analyzes the reaction process of phosphors during microwave alkali fusion,calculates the microwave alkali fusion kinetics and acid leaching kinetics of rare earth elements Eu,Ce,Tb,and reveals the mechanism of microwave alkali fusion pretreatment to strengthen the leaching of rare earth elements.The main conclusions obtained are as follows:（1）The optimized extraction process conditions of the rare earth element Eu in the blue phosphor are:the roasting temperature is 400℃,the holding time is 30 min,the Na OH/BAM mass ratio is 2:1,the HCl concentration is 4 mol/L,and the liquid-solid ratio is 10 m L/g,acid leaching temperature is 60℃,stirring speed is 200 rpm,acid leaching time is 2 h.Eu leaching rate is 97.81%,which is higher than the conventional alkaline fusion pretreatment-acid leaching process.The microwave roasting alkali melting kinetics of Eu in the blue phosphor conforms to the mixed control model,and the alkali melting activation energy is 28.9 k J/mol.The acid leaching process of Eu in the alkaline molten slag washing product conforms to the product layer diffusion control model,and the acid leaching activation energy of Eu is 5.74k J/mol.（2）The optimized extraction process conditions for the rare earth elements Ce and Tb in the green phosphor are:the roasting temperature is 800°C,the holding time is 30 minutes,the Na OH/CMAT mass ratio is 2:1,the HCl concentration is 4 mol/L,and the liquid-solid ratio is 10 m L/g,the acid leaching temperature is 60℃,the stirring speed is 200 rpm,and the acid leaching time is 2 h.The Ce and Tb leaching rates are 97.86%and 95.75%,respectively,which are higher than the conventional alkaline fusion pretreatment-acid leaching process.The microwave roasting alkali fusion process of Ce and Tb in the green phosphor and the acid leaching process of the alkali fusion washing product conform to the mixed control model.The alkali fusion activation energy and acid leaching activation energy of Ce are 35.1k J/mol and 36.3 k J/mol,respectively,and the alkali fusion activation energy and acid leaching activation energy of Tb are 32.0 k J/mol and 32.4 k J/mol,respectively.（3）The microscopic morphology and phase composition of blue phosphor and green phosphor after microwave alkali fusion pretreatment have changed significantly.The higher the alkali melting temperature,the more fully the dissociation of the phosphor,and the smaller the new substance produced.The phosphor will produce Eu₂O₃,CeO₂,Tb₂O₃,Na Al O₂,Mg O,Ba CO₃,etc.after alkali fusion.（4）The optimized extraction process conditions of the rare earth elements Ce and Tb in the mixed phosphor are:the alkali melting temperature is 800℃,the holding time is 30 min,the mass ratio of Na OH/mixed phosphor is 2:1,the concentration of HCl is 4 mol/L,liquid-solid ratio is 10 m L/g,the acid leaching temperature is 60℃,the stirring speed is 200rpm,and the acid leaching time is 120 min,the leaching rates of Eu,Ce and Tb are 94.80%,94.94%and 94.65%,respectively.（5）Compared with conventional alkali fusion pretreatment,microwave alkali fusion can lower the reaction temperature and shorten the reaction time,thereby strengthening the leaching of rare earth elements.This has positive significance for the extraction of rare earth elements in phosphors by the microwave alkali fusion pretreatment-acid leaching process.