Study On The Strength Leaching Process Of Wasted Rare Earth Phosphors

The Rare Earth fluorescent powder has been used in tricolor energy-saving lamps, plasmadisplays, CRT TV, LCD back light, etc. It played an important role in many application fieldsbecause of its high luminous efficacy, better color purity, droop characteristics, appropriateemission wavelength and harmlessness. As the "national semiconductor lighting project" started,the production and sales volume of rare earth phosphor powder used in lamp is increasing year byyear. It Predicts that the demand of rare earth fluorescent lamp will up to6billion to the year of2015.The consume of rare earth phosphor powder will be ten thousand tons, including nearly sixthousand tons (REO) and the large amounts of waste in producing the production. Therefore, thereaction mechanism in exploring and researching of recycling waste rare earth phosphor has beencarried in this paper. The main work and achievements are as follows:To deal with the waste rare earth phosphor which shows green light when exposed to theWavelengths, the first step is roasting it using Na2CO3to reconstruct the phase, then dissolved itin acid solution according to the XRD figure of leached residue and the figure of roasted productE-pH by acid leaching, it also shows that the material CeO2in roasting product is more difficultto be leached out. So dissolving it in acid solution with the cosolvent of H2O2.The reactionconditions are as follows: the temperature of calcination is900℃, the roasting time is2h, theadding of sodium carbonate is1.0,the volume fraction of hydrogen peroxide is5%,the leachingtemperature is75℃, the concentration of hydrochloric acid is2mol L-1, the leaching time is1h,the liquid-solid ratio (leaching liquid vs the quality of the solid before leached) is14.Afterleaching the waste rare earth phosphor in those conditions, the results show that the rare earthleaching rate reached93.4%.To deal with the waste rare earth phosphor which shows blue light when exposed to theWavelengths, the theory is the same. Firstly, using the roasting method with Na2CO3toreconstruct phase. Secondly, leaching it in acid solution. The reaction conditions are as follows:the calcination temperature is800℃, the roasting time is2h, the adding of sodium carbonate is1.0,the leaching temperature is85℃, the concentration of hydrochloric acid is4mol L-1,theliquid-solid ratio(leaching liquid vs the quality of the solid before leached)is14.After leachingreaction, the results show that rare earth leaching rate reaches98.56%.Through thethermodynamic calculation of product which is roasted then acid leached, the result shows thatrare earth Eu can exist in Eu3+stability in aqueous solution when controlling pH <3.79.To deal with the waste rare earth phosphor which shows red light when exposed to the Wavelengths, the direct acid leaching method is adopted. Controlling the reaction conditions, thedetails as follows: the leaching temperature is85℃, the leaching time is1.5h, the concentrationof hydrochloric acid is2mol L-1, the liquid-solid ratio(leaching liquid vs the quality of the solidbefore leached) is13.After leaching reaction, the result shows that the rare earth leaching rate is90.32%.To deal with the Waste mixed rare earth phosphor after roasting, directly and in sectionsleaching methods are compared, the results show that leaching the rare earth which is directlyroasted, the leaching rate can reaches96.23%, but the segmentation of leaching rare earth,theleaching rate is only92.17%.The production of the first method was rare earth mixture, but wecan get part of the rare earth separated by the segmented leaching method.Research results show that the waste rare earth phosphor can be leached very well in thisprocess, it provides a very good instruction function from the reaction mechanism, and lay a solidfoundation for the subsequent process of rare earth separation.