Rare earth is known as the vitamin of modern industry. Due to its high luminous efficiency and energy saving, rare earth fluorescent lamps have gradually replaced traditional incandescent lamps. The service life of rare earth fluorescent lamps is generally only 3 to 5 years. Once scrapped, a large number of waste fluorescent lamps will be produced. At present, many countries are facing the risk of rare earth supply. The recovery of strategic rare earth elements Y, Eu, Tb, Ce, etc. 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. This article described the research progress in the recovery of rare earth elements from waste fluorescent lamps in recent years. The advantages and disadvantages of the direct acid leaching method, pretreatment-acid leaching method, comprehensive recovery method, and emerging recovery methods were compared and analyzed, focusing on the summary of the related research of wet acid leaching. At last, some issues worthy of special attention for future recycling of waste phosphor were pointed out. The direct separation and recovery method was to separate halophosphate phosphors from waste phosphors, or to directly separate monochromatic phosphors. The usual methods included flotation, extraction, heavy medium centrifugation, wind separation, and magnetic separation. However, due to the various types of recovered monochromatic phosphors and structural damage, it was difficult to meet the purity requirements of commercial phosphors, making it difficult to achieve industrial application. Y and Eu in the red powder existed in the form of oxides, which were easily leached by acid; while green powder and blue powder were magnesia-aluminum spinel structures, in which Tb, Ce and Eu were difficult to be leached directly with acid. Therefore, how to improve the leaching performance of green powder and blue powder had become a key issue for increasing the total leaching rate of rare earths in waste phosphors. For this reason, most researchers focused on pretreatment of waste phosphors. There were two commonly used pretreatment methods: mechanical activation and alkali melting. The total leaching rate of rare earths could be significantly increased after pretreatment. However, few researchers paid attention to issues such as energy consumption and equipment selection in the mechanical activation process, which were crucial to industrialization. The alkali fusion pretreatment method needed to further strengthen the reaction kinetics to reduce the reaction temperature or shorten the time, thereby reducing energy consumption, and the total recovery rate of rare earths also needed to be further improved. Stepwise leaching method was used to selectively leach rare earth elements and separate impurities, and finally, rare earth oxide products were obtained by extraction, oxalic acid precipitation and roasting. Some unconventional emerging recovery methods had also been reported in recent years: such as microwave pretreatment, ionic liquid leaching, chelating agent leaching, sub-molten salt leaching, biological leaching, and pressure leaching and supercritical extraction method. In order to further realize the green and efficient resource utilization of waste phosphors, the following aspects needed to be focused on in the future: (1) It was worthy of further increasing the recovery rate of rare earth Ce, Tb, La and Eu in green powder and blue powder, comprehensively considering the processes of leaching, purification and separation of rare earth elements. The behaviors of rare earths and impurities should be considered comprehensively, achieving zero waste discharge. It was necessary to develop new methods that could selectively separate and recover different rare earth elements, to develop new high-efficiency rare earth ion extractants. The separation, extraction and material preparation should be integrated to obtain high-value rare earth products. (2) It was especially worthwhile to explore the mechanism of the pretreatment process in depth and develop new pretreatment processes that were more efficient, energy-saving and environmentally friendly. It was necessary to explore new methods that were more environmentally friendly and more efficient in rare earth extraction. (3) It deserved more attention on the research on real waste phosphors, starting from the dismantling of waste fluorescent lamps and enrichment of rare earth phosphors, comprehensively considering the pre-removal methods of mercury, silicon oxide and aluminum oxide in phosphors and its impact on the extraction of rare earths. Finally, more targeted comprehensive recovery methods should be designed. Expanded experiments should be carried out to comprehensively evaluate the economics, environmental protection and feasibility of the recycling process, and further promoting the industrialized operation process of the recycling of rare earths in waste phosphors. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.
