废弃荧光灯中稀土元素回收方法研究进展

Recovery of Rare Earth Elements in Waste Fluorescent Lamps:A Review

随着稀土荧光灯的广泛使用以及全球可持续发展战略的实施,废弃荧光灯中稀土元素的回收已成为全球关注的热点问题之一。从废弃荧光灯中回收战略性稀土元素Y,Eu,Tb,Ce等,可以缓解稀土供应风险,避免稀土矿过度开采,减少环境污染,具有显著的环保效益和经济效益。本文阐述了近年来从废弃荧光灯中富集荧光粉并回收稀土元素的研究进展,废弃荧光灯经拆解分离出玻璃、汞、氧化铝等杂质以富集荧光粉,废弃荧光粉的富集包括干法工艺和湿法工艺。废弃荧光粉的回收方法主要分为直接分选回收法、湿法酸浸法(直接酸浸法、预处理-酸浸法)和新兴回收法,评述了各种方法的优缺点,重点对研究较多的湿法酸浸法的相关研究进行了总结。预处理是提高绿粉和蓝粉中稀土元素浸出率的关键手段,主要有机械活化预处理和碱熔预处理,其机理主要是破坏晶体结构以提高稀土元素的浸出性能。以高值化稀土产品的获取为目标的酸浸法具有绿色环保、资源综合回收率高的优点,是未来发展的一个重点方向,采用非常规技术的新兴回收法也值得进一步探索。

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.