Research On Process And Mechanism Of Recovery Of Rare Earth From Waste Rare Earth Fluorescent Powders Using Alkaline Roasting-two Steps Of Acid Leaching Process

In China,the product of rare earth?RE?fluorescent powder is increasing,but rare earth ore reserves is decreasing rapidly.It is significant that recycling rare earth elements from the waste fluorescent powder.Based on problem existed on recycling RE from the waste fluorescent powder,such as low RE leaching rate,high content of aluminum,large consumption of acid and alkali,lack of thermodynamics and dynamics research about RE leaching process,we adopt process of alkali fusion-two steps of acid leaching to analyze the phase mechanism of roasting process and study the thermodynamics and kinetics of leaching process.Specific works are as follow:Firstly,the thermodynamic analysis was carried out on the acid leaching process.The influence factors of leaching were studied with thermodynamic analysis.When the hydrochloric acid concentration of 3 mol · L^-1,leaching temperature of 80 ?,extraction time of 60 min,stirring speed of 360 r·min-1,liquid-solid ratio of 4: 1,the acid leaching rate reaches the highest.The initial and final temperature of the two reactions were determined by analyzing DTA-TG diagrams of reactions of the green powder with sodium hydroxide,blue powder with sodium hydroxide.In sodium hydroxide and rare earth phosphor,when caustic ratio?Na₂O?: n?Al₂O₃?= 2: 1,roasting temperature 850?,roasting time2 h,the RE elements such as Ce,Eu,and Tb form a single oxide,namely Tb₄O₇,CeO₂,Eu₂O₃,non-rare RE elements Al become NaAl O₂,Mg form MgO,Ba transform into Ba CO₃.Under this conditions,rare earth alkali roasting the best.The optimum pH value of sodium aluminate hydrolysis is determined by plotting the Al-H₂ O potential-pH diagram.The effects of water leaching factors on the aluminum removal rate is investigated.when the caustic ratio?Na₂O?: n?Al₂O₃?=2: 1,the ratio of water immersion to liquid is 3: 1,leaching temperature is 25 ?,the leaching rate of sodium aluminate was the highest,reaching 98.56%.Thermodynamics analysis of the secondary acid leaching process and plotting the Ce-Tb-H₂ O potential-pH diagram are carried out.The results show that CeO₂ and TbO₂ can not be directly leached by hydrochloric acid,and additional reducing agent is needed.The effect of H₂O₂,as reducing agent,on leaching rate is better than that of NaNO₂,Na₂SO₃ and Na₂ S.The secondary acid leaching reaction is applied to the kinetic equation 1-?1-??1/3 = kt,and the leaching process is controlled by interface chemical reaction.The apparent activation energy Ea is 6.645kJ·mol-1,the apparentseries is 0.2035.