| Fluorescent lamp(FL)has been widely used for the facilities in houses,public buildings and places instead of incandescent lamp,due to the better performance of FL on energy-saving and long lifespan.Because of the potential environmental and human health challenges caused by mercury in FL,the expanding use of FL and its relevant obsolete have caused increasing concern from the public.At the same time,a considerable amounts of rare earth elements(REEs)resources in waste FL makes it one of the focuses of the field of resources recycling from wastes.The study work of this thesis aims to promote the environmentally sound management of waste FLs and the effective recycling of REEs resources in waste phosphors from waste FLs.The Generation and regional distribution of waste FLs in China till year 2020 were predicted and estimated through models established in this study,then the environmental impacts and resources potential from FLs obsolescence was analyzed in detail as well.The generation of waste FL in China is increasing annually due to the popularization of FL.The amount of waste FL generated in 2020 is expected to reach 5.84 billion units,which represent approximately 937,400 tonnes of solid waste be generated.This waste contains about 4,440 tonnes of yttrium(Y),2,160 tonnes of lanthanum(La),970 tonnes of cerium(Ce),520 tonnes of terbium(Tb)and 320 tonnes of europium(Eu)(all the REEs are counted as metal).The potential mercury emission from waste FL is about 5.37-7.59 tonnes for the same year.Net environmental benefits can be achieved and the life cycle environmental performance of FL can be improved when professional facilities and processes are employed properly to the treatment of waste FLs and other resources,such as glass,aluminum,mercury and so on,in waste FLs are recycled properly.As for the recovery of REEs resources in waste phosphors from waste FLs,an innovated approach-enhanced leaching of REEs in waste phosphors with the assistance of mechanical activation was proposed in this study;the effects of mechanical activation on the physico-chemical properties of waste phosphors,leaching rates of REEs and leaching kinetics were investigated systematically.Mechanical activation can significantly enhance the leaching performance of REEs that can hardly be leached out from waste phosphors.The leaching rates of Tb,Ce and La can be dramatically increased to more than 90% from the leaching rates of less than 1% of the inacticated sapmles.Meanwhile,leaching performance of Eu and Y also can be improved with the increase from around 80% and 85% to more than 90% and 95%,respectively.The apparent activation energy of REEs leaching from waste phosphors decrease significantly after the mechanical activation.For terbium as example,the apparent activation energy of leaching is 52.82 ± 3.95 kJ/mol for inactivated waste phosphors,while it decreases to 10.96 ± 2.79 kJ/mol after mechanically activted at the condition of 600 rpm and 60 min.Mechanical activation can not only reduce the particle size of waste phosphors significantly,but also increase specific surface area of particles because the generation of new surface during activation.In addition,mechanical activation can also cause defects in the crystal structure of compounds in waste phosphors,the structure will be destroyed gradually and structural disorder will increase with the progress of activation;the activation can cause the increase in internal stress of crystal lattice.Changes in physico-chemical properties of waste phosphors caused by the mechanical activation can lead to enhance of waste phosphors' leaching activity,decrease of apparent activation energy for REEs leaching reaction and increase in apparent reaction rate of leaching.The achievements obtained from this present thesis provide basic data for the environmentally sound management of waste FLs in China;besides,they can be helpful to provide the technological and theoretical basis for recovery of REEs from waste phosphors. |
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